ACETYLENE THE PRINCIPLES OF ITS GENERATION AND USE A PRACTICAL HANDBOOK ON THE PRODUCTION, PURIFICATION, AND SUBSEQUENTTREATMENT OF ACETYLENE FOR THE DEVELOPMENT OF LIGHT, HEAT, AND POWER Second Edition REVISED AND ENLARGED BY F. H. LEEDS, F. I. C. FOR SOME YEARS TECHNICAL EDITOR OF THE JOURNAL "ACETYLENE" AND W. J. ATKINSON BUTTERFIELD, M. A. AUTHOR OF "THE CHEMISTRY OF GAS MANUFACTURE" PREFATORY NOTE TO THE FIRST EDITION In compiling this work on the uses and application of acetylene, thespecial aim of the authors has been to explain the various physical andchemical phenomena: (1) Accompanying the generation of acetylene from calcium carbide andwater. (2) Accompanying the combustion of the gas in luminous or incandescentburners, and (3) Its employment for any purpose--(a) neat, (b) compressed intocylinders, (c) diluted, and (d) as an enriching material. They have essayed a comparison between the value of acetylene and otherilluminants on the basis of "illuminating effect" instead of on themisleading basis of pure "illuminating power, " a distinction which theyhope and believe will do much to clear up the misconceptions existing onthe subject. Tables are included, for the first time (it is believed) inEnglish publications, of the proper sizes of mains and service-pipes fordelivering acetylene at different effective pressures, which, it ishoped, will prove of use to those concerned in the installation ofacetylene lighting systems. _June_ 1903 NOTE TO THE SECOND EDITION The revision of this work for a new edition was already far advanced whenit was interrupted by the sudden death on April 30, 1908, of Mr. F. H. Leeds. The revision was thereafter continued single-handed, with the helpof very full notes which Mr. Leeds had prepared, by the undersigned. Ithad been agreed prior to Mr. Leeds' death that it would add to theutility of the work if descriptions of a number of representativeacetylene generators were given in an Appendix, such as that which nowappears at the conclusion of this volume. Thanks are due to the numerousfirms and individuals who have assisted by supplying information for usein this Appendix. W. J. ATKINSON BUTTERFIELD WESTMINSTER _August 1909_ CONTENTS CHAPTER I INTRODUCTORY--THE COST AND ADVANTAGES OF ACETYLENE LIGHTING Intrinsic advantagesHygienic advantagesAcetylene and paraffin oilBlackened ceilingsCost of acetylene lightingCost of acetylene and coal-gasCost of acetylene and electric lightingCost of acetylene and paraffin oilCost of acetylene and air-gasCost of acetylene and candlesTabular statement of costs (_to face_)Illuminating power and effect CHAPTER II THE PHYSICS AND CHEMISTRY OF THE REACTION BETWEEN CARBIDE AND WATER Nature of calcium carbideStorage of calcium carbideFire risks of acetylene lightingPurchase of carbideQuality and sizes of carbideTreated and scented carbideReaction between carbide and water chemical nature heat evolved difference between heat and temperature amount of heat evolved effect of heat on process of generationReaction: effects of heat effect of heat on the chemical reaction effects of heat on the acetylene effects of heat on the carbideColour of spent carbideMaximum attainable temperaturesSoft solder in generatorsReactions at low temperaturesReactions at high temperaturesPressure in generators CHAPTER III THE GENERAL PRINCIPLES OF ACETYLENE GENERATION ACETYLENE GENERATINGAPPARATUS Automatic and non-automatic generatorsControl of the chemical reactionNon-automatic carbide-to-water generatorsNon-automatic water-to-carbide generatorsAutomatic devicesDisplacement gasholdersAction of water-to-carbide generatorsAction of carbide-to-water generatorsUse of oil in generatorRising gasholderDeterioration of acetylene on storageFreezing and its avoidanceCorrosion in apparatusIsolation of holder from generatorWater-sealsVent pipes and safety valveFrothing in generatorDry process of generationArtificial lighting of generator sheds CHAPTER IV THE SELECTION OF AN ACETYLENE GENERATOR Points to be observedRecommendations of Home Office CommitteeBritish and Foreign regulations for the construction and installation of acetylene generating plant CHAPTER V THE TREATMENT OF ACETYLENE AFTER GENERATION Impurities in calcium carbideImpurities of acetyleneRemoval of moistureGenerator impurities in acetyleneFiltersCarbide impurities in acetyleneWashersReasons for purificationNecessary extent of purificationQuantity of impurities in acetylenePurifying materialsBleaching powderHeratol, frankoline, acagine, and puratyleneEfficiency of purifying materialMinor reagentMethod of a gas purifierMethods of determining exhaustion of purifying materialRegulations for purificationDryingPosition of purifierFiltrationGeneral arrangement of plansGenerator residuesDisposal of residue CHAPTER VI THE CHEMICAL AND PHYSICAL PROPERTIES OF ACETYLENE Physical propertiesLeakageHeat of combustionExplosive limitsRange of explosibilitySolubility in liquidsToxicityEndothermic naturePolymerisationHeats of formation and combustionColour of flameRadiant efficiencyChemical propertiesReactions with copper CHAPTER VII MAINS AND SERVICE-PIPES--SUBSIDIARY APPARATUS MetersGovernorsGasholder pressurePressure-gaugesDimensions of mains and pipesVelocity of flow in pipesService-pipes and mainsLeakagePipes and fittingsLaying mainsExpelling air from pipesTables of pipes and mains CHAPTER VIII COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS--THEIR DISPOSITION Nature of luminous flamesIlluminating powerEarly burnersInjector and twin-flame burnersIlluminating power of self-luminous burnersGlassware for burners CHAPTER IX INCANDESCENT BURNERS--HEATING APPARATUS--MOTORS--AUTOGENOUS SOLDERING Merits of incandescent lightingConditions for incandescent lightingIlluminating power of incandescent burnersDurability of mantlesTypical incandescent burnersAcetylene for heating and cookingAcetylene motorsBlowpipesAutogenous soldering and welding CHAPTER X CARBURETTED ACETYLENE Carburetted acetyleneIlluminating power of carburetted acetyleneCarburetted acetylene for "power" CHAPTER XI COMPRESSED AND DISSOLVED ACETYLENE--MIXTURES WITH OTHER GASES CompressionDissolved acetyleneSolution in acetoneLiquefied acetyleneDilution with carbon dioxideDilution with airMixed carbidesDilution with, methane and hydrogenSelf-inflammable acetyleneEnrichment with acetylenePartial pressureAcetylene-oil-gas CHAPTER XII SUNDRY USES Destruction of noxious mothsDestruction of phylloxera and mildewManufacture of lampblackProduction of tetrachlorethaneUtilisation of residuesSundry uses for the gas CHAPTER XIII PORTABLE ACETYLENE LAMPS AND PLANT Table and vehicular lampsFlare lampsCartridges of carbideCycle-lamp burnersRailway lighting CHAPTER XIV VALUATION AND ANALYSIS OF CARBIDE Regulations of British Acetylene AssociationRegulations o£ German Acetylene AssociationRegulations of Austrian Acetylene AssociationSampling carbideYield of gas from small carbideCorrection of volumes for temperature and pressureEstimation of impuritiesTabular numbers APPENDIX DESCRIPTIONS OP GENERATORS America: CanadaAmerica: United StatesAustria-HungaryBelgiumFranceGermanyGreat Britain and Ireland INDEX INDEX TO APPENDIX ACETYLENE CHAPTER I INTRODUCTORY--THE COST AND ADVANTAGES OF ACETYLENE LIGHTING Acetylene is a gas [Footnote: For this reason the expression, "acetylenegas, " which is frequently met with, would be objectionable on the groundof tautology, even if it were not grammatically and technicallyincorrect. "Acetylene-gas" is perhaps somewhat more permissible, but itis equally redundant and unnecessary. ] of which the most importantapplication at the present time is for illuminating purposes, for whichits properties render it specially well adapted. No other gas which canbe produced on a commercial scale is capable of giving, volume forvolume, so great a yield of light as acetylene. Hence, apart from theadvantages accruing to it from its mode of production and the nature ofthe raw material from which it is produced, it possesses an inherentadvantage over other illuminating gases in the smaller storageaccommodation and smaller mains and service-pipes requisite for themaintenance of a given supply of artificial light. For instance, if agasholder is required to contain sufficient gas for the lighting of anestablishment or district for twenty-four hours, its capacity need not benearly so great if acetylene is employed as if oil-gas, coal-gas, orother illuminating gas is used. Consequently, for an acetylene supply thegasholder can be erected on a smaller area and for considerably lessoutlay than for other gas supplies. In this respect acetylene has anunquestionable economical advantage as a competitor with other varietiesof illuminating gas for supplies which have generally been regarded aslying peculiarly within their preserves. The extent of this advantagewill be referred to later. The advantages that accrue to acetylene from its mode of production, andthe nature of the raw material from which it is obtained, are in realityof more importance. Acetylene is readily and quickly produced from a rawmaterial--calcium carbide--which, relatively to the yield of light of thegaseous product, is less bulky than the raw materials of other gases. Incomparison also with oils and candles, calcium carbide is capable ofyielding, through the acetylene obtainable from it, more light per unitof space occupied by it. This higher light-yielding capacity of calciumcarbide, ready to be developed through acetylene, gives the latter gas agreat advantage over all other illuminants in respect of compactness fortransport or storage. Hence, where facilities for transport or storageare bad or costly, acetylene may be the most convenient or cheapestilluminant, notwithstanding its relatively high cost in many other cases. For example, in a district to which coal and oil must be brought greatdistances, the freight on them may be so heavy that--regarding thequestion as simply one of obtaining light in the cheapest manner--it maybe more economical to bring calcium carbide an equal or even greaterdistance and generate acetylene from it on the spot, than to use oil ormake coal-gas for lighting purposes, notwithstanding that acetylene maynot be able to compete on equal terms with oil--or coal-gas at the placefrom which the carbide is brought. Likewise where storage accommodationis limited, as in vehicles or in ships or lighthouses, calcium carbidemay be preferable to oil or other illuminants as a source of light. Disregarding for the moment intrinsic advantages which the lightobtainable from acetylene has over other lights, there are many caseswhere, owing to saving in cost of carriage, acetylene is the mosteconomical illuminant; and many other cases where, owing to limited spacefor storage, acetylene far surpasses other illuminants in convenience, and is practically indispensable. The light of the acetylene flame has, however, some intrinsic advantagesover the light of other artificial illuminants. In the first place, thelight more closely resembles sunlight in composition or "colour. " It ismore nearly a pure "white" light than is any other flame or incandescentbody in general use for illuminating purposes. The nature or compositionof the light of the acetylene flame will be dealt with more exhaustivelylater, and compared with that afforded by other illuminants; but, speaking generally, it may be said that the self-luminous acetylene lightis superior in tint, to all other artificial lights, for which reason itis invaluable for colour-judging and shade-matching. In the secondplace, when the gas issues from a suitable self-luminous burner underproper pressure, the acetylene flame is perfectly steady; and in thisrespect it in preferable to most types of electric light, to all self-luminous coal-gas flames and candles, and to many varieties of oil-lamp. In steadiness and freedom from flicker it is fully equal to incandescentcoal-gas light, but it in distinctly superior to the latter by virtue ofits complete freedom from noise. The incandescent acetylene flame emits aslight roaring, but usually not more than that coming from anatmospheric coal-gas burner. With the exception of the electric arc, self-luminous acetylene yields a flame of unsurpassed intensity, and yetits light is agreeably soft. In the third place, where electricity isabsent, a brilliancy of illumination which can readily be obtained fromself-luminous acetylene can otherwise only be procured by the employmentof the incandescent system applied either to coal-gas or to oil; andthere are numerous situations, such as factories, workshops, and thelike, where the vibration of the machinery or the prevalence of dustrenders the use of mantles troublesome if not impossible. Anticipatingwhat will be said later, in cases like these, the cost of lighting byself-luminous acetylene may fairly be compared with self-luminous coal-gas or oil only; although in other positions the economy of the Welsbachmantle must be borne in mind. Acetylene lighting presents also certain important hygienic advantagesover other forms of flame lighting, in that it exhausts, vitiates, andheats the air of a room to a less degree, for a given yield of light, than do either coal-gas, oils, or candles. This point in favour ofacetylene is referred to here only in general terms; the evidence onwhich the foregoing statement is based will be recorded in a tabularcomparison of the cost and qualities of different illuminants. Exhaustionof the air means, in this connexion, depletion of the oxygen normallypresent in it. One volume of acetylene requires 2-1/2 volumes of oxygenfor its complete combustion, and since 21 volumes of oxygen areassociated in atmospheric air with 79 volumes of inert gases--chieflynitrogen--which do not actively participate in combustion, it followsthat about 11. 90 volumes of air are wholly exhausted, or deprived ofoxygen, in the course of the combustion of one volume of acetylene. Ifthe light which may be developed by the acetylene is brought intoconsideration, it will be found that, relatively to other illuminants, acetylene causes less exhaustion of the air than any other illuminatingagent except electricity. For instance, coal-gas exhausts only about 6-1/2 times its volume of air when it is burnt; but since, volume forvolume, acetylene ordinarily yields from three to fifteen times as muchlight as coal-gas, it follows that the same illuminative value isobtainable from acetylene by considerably less exhaustion of the air thanfrom coal-gas. The exact ratio depends on the degree of efficiency of theburners, or of the methods by which light is obtained from the gases, aswill be realised by reference to the table which follows. Broadlyspeaking, however, no illuminant which evolves light by combustion(oxidation), and which therefore requires a supply of oxygen or air forits maintenance, affords light with so little exhaustion of the air asacetylene. Hence in confined, ill-ventilated, or crowded rooms, the airwill suffer less exhaustion, and accordingly be better for breathing, ifacetylene is chosen rather than any other illuminant, except electricity. Next, in regard to vitiation of the air, by which is meant the alterationin its composition resulting from the admixture of products of combustionwith it. Electric lighting is as superior to other modes of lighting inrespect of direct vitiation as of exhaustion of the air, because it doesnot depend on combustion. Putting it aside, however, light is obtainableby means of acetylene with less attendant vitiation of the air than bymeans of any other gas or of oil or candles. The principal vitiatingfactor in all cases is the carbonic acid produced by the combustion. Nowone volume of acetylene on combustion yields two volumes of carbonicacid, whereas one volume of coal-gas yields about 0. 6 volume of carbonicacid. But even assuming that the incandescent system of lighting isapplied in the case of coal-gas and not of acetylene, the ratio of theconsumption of the two gases for the development of a given illuminativeeffect will be such that no more carbonic acid will be produced by theacetylene; and if the incandescent system is applied either in both casesor in neither, the ratio will be greatly in favour of acetylene. Theother factors which determine the vitiation of the air of a room in whichthe gas is burning are likewise under ordinary conditions more in favourof acetylene. They are not, however, constant, since the so-called"impurities, " which on combustion cause vitiation of the air, varygreatly in amount according to the extent to which the gases have beenpurified. London coal-gas, which was formerly purified to the highestdegree practically attainable, used to contain on the average only 10 to12 grains of sulphur per 100 cubic feet, and virtually no other impurity. But now coal-gas, in London and most provincial towns, contains 40 to 50grains of sulphur per 100 cubic foot. At least 5 grains of ammonia per100 cubic foot in also present in coal-gas in some towns. Crude acetylenealso contains sulphur and ammonia, that coming from good quality calciumcarbide at the present day including about 31 grains of the former and25 grains of the latter per 100 cubic feet. But crude acetylene is alsoaccompanied by a third impurity, viz. , phosphoretted hydrogen orphosphine, which in unknown in coal-gas, and which is considerably moreobjectionable than either ammonia or sulphur. The formation, behaviour, and removal of those various impurities will be discussed in Chapter V. ;but here it may be said that there is no reason why, if calcium carbideof a fair degree of purity has been used, and if the gas has beengenerated from it in a properly designed and smoothly working apparatus--this being quite as important as, or even more important than, the purityof the original carbide--the gas should not be freed from phosphorus, sulphur, and ammonia to the utmost necessary or desirable extent, byprocesses which are neither complicated nor expensive. And if this isdone, as it always should be whenever the acetylene is required fordomestic lighting, the vitiation of the air of a room due to the"impurities" in the gas will become much less in the case of acetylenethan in that of even well-purified coal-gas; taking equal illuminatingeffect as the basis for comparison. Acetylene is similarly superior, speaking generally, to petroleum inrespect of impurities, though the sulphur present in petroleum oils, suchas are sold in this country for household use, though very variable, isoften quite small in amount, and seldom is responsible for seriousvitiation of the atmosphere. Regarding somewhat more closely the relative convenience and safety ofacetylene and paraffin for the illumination of country residences, it maybe remarked that an extraordinarily great amount of care must he bestowedupon each separate lamp if the whole house is to be kept free from anodour which is very offensive to the nostrils; and the time occupied inthis process, which of itself is a disagreeable one, reaches severalhours every day. Habit has taught the country dweller to accept asinevitable this waste of time, and largely to ignore the odour ofpetroleum in his abode; but the use of acetylene entirely does away withthe daily cleaning of lamps, and, if the pipe-fitting work has been doneproperly, yields light absolutely unaccompanied by smell. Again, unlessmost carefully managed, the lamp-room of a large house, with its store ofcombustible oil, and its collection of greasy rags, must unavoidablyprove a sensible addition to the risk of fire. The analogue of the lamp-room when acetylene is employed is the generator-house, and this is aseparate building at some distance from the residence proper. There needbe no appreciable odour in the generator-house, except during the timesof charging the apparatus; but if there is, it passes into the open airinstead of percolating into the occupied apartments. The amount of heat developed by the combustion of acetylene also is lessfor a given yield of light than that developed by most other illuminants. The gas, indeed, is a powerful heating gas, but owing to the amountconsumed being so small in proportion to the light developed, the heatarising from acetylene lighting in a room is less than that from mostother illuminating agents, if the latter are employed to the extentrequired to afford equally good illumination. The ratio of the heatdeveloped in acetylene lighting to that developed in, _e. G. _, lighting by ordinary coal-gas, varies considerably according to thedegree of efficiency of the burners, or, in other words, of the methodsby which light is obtained from the gases. Volume for volume, acetyleneyields on combustion about three and a half times as much heat as coal-gas, yet, owing to its superior efficiency as an illuminant, any requiredlight may be obtained through it with no greater evolution of heat thanthe best practicable (incandescent) burners for coal-gas produce. Theheat evolved by acetylene burners adequate to yield a certain light isvery much less than that evolved by ordinary flat-flame coal-gas burnersor by oil-lamps giving the same light, and is not more than about threetimes as much as that from ordinary electric lamps used in numberssufficient to give the same light. More exact figures for the ratiobetween the heat developed in acetylene lighting and that in other modesof lighting are given in the table already referred to. In connexion with the smaller amount of heat developed per unit of lightwhen acetylene is the illuminant, the frequently exaggerated claim thatacetylene does not blacken ceilings at all may be studied. Except it be acarelessly manipulated petroleum-lamp, no form of artificial illuminantemployed nowadays ever emits black smoke, soot, or carbon, in spite ofthe fact that all luminous flames commercially capable of utilisation docontain free carbon in the elemental state. The black mark on a ceilingover a source of light is caused by a rising current of hot air andcombustion products set up by the heat accompanying the light, whichcurrent of hot gas carries with it the dust and dirt always present inthe atmosphere of an inhabited room. As this current of air and burnt gastravels in a fairly concentrated vertical stream, and as the ceiling iscomparatively cool and exhibits a rough surface, that dust and dirt aredeposited on the ceiling above the flame, but the stain is seldom ornever composed of soot from the illuminant itself. Proof of thisstatement may be found in the circumstance that a black mark iseventually produced over an electric glow-lamp and above a pipedelivering hot water. Clearly, therefore, the depth and extent of themark will depend on the volume and temperature of the hot gaseouscurrent; and since per unit of light acetylene emits a far smallerquantity of combustion products and a far smaller amount of heat than anyother flame illuminant except incandescent coal-gas, the inevitable blackmark over its flame takes very much longer to appear. Quite roughlyspeaking, as may be deduced from what has already been said on thissubject, the luminous flame of acetylene "blackens" a ceiling at aboutthe same rate as a coal-gas burner of the best Welsbach type. There is one respect in which acetylene and other flame illuminants aresuperior to electric lighting, viz. , that they sterilise a larger volumeof air. All the air which is needed to support combustion, as well as theexcess of air which actually passes through the burner tube and flame inincandescent burners, is obviously sterilised; but so also is the muchlarger volume of air which, by virtue of the up-current due to the heatof the flame, is brought into anything like close proximity with thelight. The electric glow-lamp, and the most popular and economical modernenclosed electric arc-lamp, sterilise only the much smaller volume of airwhich is brought into direct contact with their glass bulbs. Moreover, when large numbers of persons are congregated in insufficientlyventilated buildings--and many public rooms are insufficientlyventilated--the air becomes nauseous to inspire and positivelydetrimental to the health of delicate people, by reason of the humaneffluvia which arise from soiled raiment and uncleansed or unhealthybodies, long before the proportion of carbonic acid by itself is highenough to be objectionable. Thus a certain proportion of carbonic acidcoming from human lungs and skin is more harmful than the same proportionof carbonic acid derived from the combustion of gas or oil. Henceacetylene and flame illuminants generally have the valuable hygienicadvantages over electric lighting, not only of killing a far largernumber of the micro-organisms that may be present in the air, but, byvirtue of their naked flames, of burning up and destroying a considerablequantity of the aforesaid odoriferous matter, thus relieving the nose andmaterially assisting in the prevention of that lassitude and anæmiaoccasionally follow the constant inspiration of air rendered foul byhuman exhalations. The more important advantages of acetylene as an illuminant have now beenindicated, and it remains to discuss the cost of acetylene lighting incomparison with other modes of procuring artificial light. At the outsetit may be stated that a very much greater reduction in the price ofcalcium carbide--from which acetylene is produced--than is likely toensue under the present methods and conditions of manufacture will berequired to make acetylene lighting as cheap as ordinary gas lighting intowns in this country, provided incandescent burners are used for thegas. On the score of cheapness (and of convenience, unless the acetylenewere delivered to the premises from some central generating station)acetylene cannot compete as an illuminant with coal-gas where the lattercosts, say, not more than 5s. Per 1000 cubic feet, if onlyreasonable attention is given to the gas-burners, and at least a quarterof them are on the incandescent system. If, on the other hand, coal-gasis misused and wasted through the employment only of interior or worn-outflat-flame burners, while the best types of burner are used foracetylene, the latter gas may prove as cheap for lighting as coal-gas at, say, 2s. 6d. Per 1000 cubic feet (and be far better hygienically);whereas, contrariwise, if coal-gas is used only with good and properlymaintained incandescent burners, it may cost over 10s. Per 1000 cubicfeet, and be cheaper than acetylene burned in good burners (and as goodfrom the hygienic standpoint). More precise figures on the relative costsof coal-gas lighting and acetylene lighting are given in the tabularstatement at the close of this chapter. With regard to electric lighting it is somewhat difficult to lay down afair basis of comparison, owing to the wide variations in the cost ofcurrent, and in the efficiency of lamps, and to the undoubted hygienicand aesthetic claims of electric lighting to precedence. But in towns inthis country where there is a public electricity supply, electriclighting will be used rather than acetylene for the same reasons that itis preferred to coal-gas. Cost is only a secondary consideration in suchcases, and where coal-gas is reasonably cheap, and nevertheless givesplace to electric lighting, acetylene clearly cannot hope to supplant thelatter. [Footnote: Where, however, as is frequently the case with smallpublic electricity-supply works, the voltage of the supply variesgreatly, the fluctuations in the light of the lamps, and the frequentdestruction of fuses and lamps, are such manifest inconveniences thatacetylene is in fact now being generally preferred to electric lightingin such circumstances. ] But where current cannot be had from anelectricity-supply undertaking, and it is a question, in the event ofelectric lighting being adopted, of generating current by driving adynamo, either by means of a gas-engine supplied from public gas-mains, by means of a special boiler installation, or by means of an oil-engineor of a power gas-plant and gas-engine, the claims of acetylene topreference are very strong. An important factor in the estimation of therelative advantages of electricity and acetylene in such cases is thecost of labour in looking after the generating plant. Where a gas-enginesupplied from public gas-mains is used for driving the dynamo, electriclighting can be had at a relatively small expenditure for attendance onthe generating plant. But the cost of the gas consumed will be high, andactually light could be obtained directly from the gas by means ofincandescent mantles at far loss cost than by consuming the gas in amotor for the indirect production of light by means of electric current. Therefore electric lighting, if adopted under these conditions, must bepreferred to gas lighting from considerations which are deemed tooutweigh those of a much higher cost, and acetylene does not present sogreat advantages over coal-gas as to affect the choice of electriclighting. But in the cases where there is no public gas-supply, andcurrent must be generated from coal or coke or oil consumed on the spot, the cost of the skilled labour required to look after either a boiler, steam-engine and dynamo, or a power gas-plant and gas-engine or oil-engine and dynamo, will be so heavy that unless the capacity of theinstallation is very great, acetylene will almost certainly prove acheaper and more convenient method of obtaining light. The attentionrequired by an acetylene installation, such as a country house of upwardsof thirty rooms would want, is limited to one or two hours' labour perdiem at any convenient time during daylight. Moreover, the attendant neednot be highly paid, as he will not have required an engineman's training, as will the attendant on an electric lighting plant. The latter, too, must be present throughout the hours when light is wanted unless a heavyexpenditure has been incurred on accumulators. Furthermore, the capitaloutlay on generating plant will be very much less for acetylene than forelectric lighting. General considerations such as these lead to theconclusion that in almost all country districts in this country a houseor institution could be lighted more cheaply by means of acetylene thanby electricity. In the tabular statement of comparative costs ofdifferent modes of lighting, electric lighting has been included only onthe basis of a fixed cost per unit, as owing to the very varied cost ofgenerating current by small installations in different parts of thecountry it would be futile to attempt to give the cost of electriclighting on any other basis, such as the prime cost of coal or coke in aparticular district. Where current is supplied by a public electricity-supply undertaking, the cost per unit is known, and the comparative costsof electric light and acetylene can be arrived at with tolerableprecision. It has not been thought necessary to include in the tabularstatement electric arc-lamps, as they are only suitable for the lightingof large spaces, where the steadiness and uniformity of the illuminationare of secondary importance. Under such conditions, it may be statedparenthetically, the electric arc-light is much less costly thanacetylene lighting would be, but it is now in many places beingsuperseded by high-pressure gas or oil incandescent lights, which aresteady and generally more economical than the arc light. The illuminant which acetylene is best fitted to supersede on the scoreof convenience, cleanliness, and hygienic advantages is oil. By oil ismeant, in this connection, the ordinary burning petroleum, kerosene, orparaffin oil, obtained by distilling and refining various natural oilsand shales, found in many countries, of which the United States(principally Pennsylvania), Russia (the Caucasus chiefly), and Scotlandare practically the only ones which supply considerable quantities foruse in Great Britain. Attempts are often made to claim superiority forparticular grades of these oils, but it may be at once stated that so foras actual yield of light is concerned, the same weight of any of thecommercial oils will give practically the same result. Hence in thecomparative statement of the cost of different methods of lighting, oilwill be taken at the cheapest rate at which it could ordinarily beobtained, including delivery charges, at a country house, when bought bythe barrel. This rate at the present time is about ninepence per gallon. A higher price may be paid for grades of mineral oil reputed to be saferor to give a "brighter" or "clearer" light; but as the quantity of lightdepends mainly upon the care and attention bestowed on the burner andglass fittings of the lamp, and partly upon the employment of a suitablewick, while the safety of each lamp depends at least as much upon thedesign of that lamp, and the accuracy with which the wick fits the burnertube, as upon the temperature at which the oil "flashes, " the extraexpense involved in burning fancy-priced oils will not be consideredhere. The efficiency (_i. E. _, the light yielded per pint or other unitvolume consumed) of oil-lamps varies greatly, and, speaking broadly, increases with the power of the lamp. But as large or high-power lampsare not needed throughout a house, it is fairer to assume that the lightobtainable from oil in ordinary household use is the mean of thatafforded by large and that afforded by small lamps. A large oil-lamp ascommonly used in country houses will give a light of about 20 candle-power, while a convenient small lamp will give a light of not more thanabout 5 candle-power. The large lamp will burn about 55 hours for everygallon of oil consumed, or give an illuminating duty of about 1100candle-hours (_i. E. _, the product of candle-power by burning-hours)per gallon. The small lamp, on the other hand, will burn about 140 hoursfor every gallon of oil consumed, or give an illuminating duty of about700 candle-hours per gallon. Actually large lamps would in most countryhouses be used only in the entrance hall, living-rooms, and kitchen, while passages and minor rooms on the lower floors would be lighted bysmall lamps. Hence, making due allowance for the lower rate ofconsumption of the small lamps, it will be seen that, given equal numbersof large and small lamps in use, the mean illuminating duty of a gallonof oil as burnt in country houses will be 987, or, in round figures, 990candle-hours. Usually candles are used in the bedrooms of country houseswhere the lower floors are lighted by means of petroleum lamps; but whenacetylene is installed in such a house it will frequently be adopted inthe principal bed- and dressing-rooms as well as in the living-rooms, as, unless candles are employed very lavishly, they are really totallyinadequate to meet the reasonable demands for light of, _e. G. _, alady dressing for dinner. Where acetylene displaces candles as well aslamps in a country house, it is necessary, in comparing the cost of thenew illuminant with that of the candles and oil, to bear in mind thesuperior degree of illumination which is secured in all rooms, at leastwhere candles were formerly used. In regard to exhaustion and vitiation of the air, and to heat evolved, self-luminous petroleum lamps stand on much the same footing as coal-gaswhen the latter is burned in flat-flame burners, if the comparison isbased on a given yield of light. A large lamp, owing to its higherilluminating efficiency, is better in this respect than a small one--light for light, it is more hygienic than ordinary flat-flame coal-gasburners, while a small lamp is less hygienic. It will therefore beunderstood at once, from what has already been said about the superiorityon hygienic grounds of acetylene to flat-flame coal-gas lighting, thatacetylene is in this respect far superior to petroleum lamps. The degreeof its superiority is indicated more precisely by the figures quoted inthe tabular statement which concludes this chapter. Before giving the tabular statement, however, it is necessary to say afew words in regard to one method of lighting which, may possibly developinto a more serious competitor with acetylene for the lighting of thebetter class of country house than any of the illuminating agents andmodes of lighting so far referred to. The method in question is lightingby so-called air-gas used for raising mantles to incandescence inupturned or inverted burners of the Welsbach-Kern type. "Air-gas" isordinary atmospheric air, more or less completely saturated with thevapour of some highly volatile hydrocarbon. The hydrocarbons practicallyapplied have so far been only "petroleum spirit" or "carburine, " and"benzol. " "Petroleum spirit" or "carburine" consists of the more highlyvolatile portion of petroleum, which is removed by distillation beforethe kerosene or burning oil is recovered from the crude oil. Severalgrades of this highly volatile petroleum distillate are distinguished incommerce; they differ in the temperature at which they begin to distiland the range of temperature covered by their distillation, and, speakingmore generally, in their degree of volatility, uniformity, and density. If the petroleum distillate is sufficiently volatile and fairly uniformin character, good air-gas may be produced merely by allowing air to passover an extended surface of the liquid. The vapour of the petroleumspirit is of greater density than air, and hence, if the course of theair-gas is downward from the apparatus at which it is produced, the flowof air into the apparatus and over the surface of the spirit will beautomatically maintained by the "pull" of the descending air-gas whenonce the flow has been started until the outlet for the air-gas isstopped or the spirit in the apparatus is exhausted. Hence, if theapparatus for saturating air with the vapour of the light petroleum isplaced well above all the points at which the air-gas is to be burnt--_e. G. _, on the roof of the house--the production of the air-gas mayby simple devices become automatic, and the only attention the apparatuswill require will be the replenishing of its reservoir from time to timewith light petroleum. But a number of precautions are required to makethis simple process operate without interruption or difficulty. Forinstance, the evaporation of the spirit must not be so rapid relativelyto its total bulk as to lower its temperature, and thereby that of theoverflowing air, too much; the reservoir must be protected from extremecold and extreme heat; and the risk of fire from the presence of a highlyvolatile and highly inflammable liquid on or near the roof of the housemust be met. This risk is one to which fire insurance companies takeexception. More commonly, however, air-gas is made non-automatically, or more orless automatically by the employment of some mechanical means. The lightpetroleum, benzol, or other suitable volatile hydrocarbon is volatilised, where necessary, by the application of gentle heat, while air is drivenover or through it by means of a small motor, which in some cases is ahot-air engine operated by heat supplied by a flame of the air-gasproduced. These air-gas producers, or at least the reservoir of volatilehydrocarbon, may be placed in an outbuilding, so that the risk of fire inthe house itself is minimised. They require, however, as much attentionas an acetylene generator, usually more. It is difficult to give reliabledata as to the cost of air-gas, inclusive of the expenses of production. It varies considerably with the description of hydrocarbon employed, andits market price. Air-gas is only slightly inferior hygienically toacetylene, and the colour of its light is that of the incandescent lightas produced by coal-gas or acetylene. Air-gas of a certain grade may beused for lighting by flat-flame burners, but it has been available thusfor very many years, and has failed to achieve even moderate success. Butthe advent of the incandescent burner has completely changed its positionrelatively to most other illuminants, and under certain conditions itseems likely to be the most formidable competitor with acetylene. Sinceair-gas, and the numerous chemically identical products offered underdifferent proprietary names, is simply atmospheric air more or lessloaded with the vapour of a volatile hydrocarbon which is normallyliquid, it possesses no definite chemical constitution, but varies incomposition according to the design of the generating plant, theatmospheric temperature at the time of preparation, the original degreeof volatility of the hydrocarbon, the remaining degree of volatilityafter the more volatile portions have been vaporised, and the speed atwhich the air is passed through the carburettor. The illuminating powerand the calorific value of air-gas, unless the manufacture is veryprecisely controlled, are apt to be variable, and the amount of light, emitted, either in self-luminous or in incandescent burners, is somewhatindeterminate. The generating plant must be so constructed that the aircannot at any time be mixed with as much hydrocarbon vapour asconstitutes an explosive mixture with it, otherwise the pipes andapparatus will contain a gas which will forthwith explode if it isignited, _i. E. _, if an attempt is made to consume it otherwise thanin burners with specially small orifices. The safely permissible mixturesare (1) air with less hydrocarbon vapour than constitutes an explosivemixture, and (2) air with more hydrocarbon vapour than constitutes anexplosive mixture. The first of these two mixtures is available forilluminating purposes only with incandescent mantles, and to ensure areasonable margin of safety the mixing apparatus must be so devised thatthe proportion of hydrocarbon vapour in the air-gas can never exceed 2per cent. From Chapter VI. It will be evident that a little more than 2per cent. Of benzene, pentane or benzoline vapour in air forms anexplosive mixture. What is the lowest proportion of such vapours inadmixture with air which will serve on combustion to maintain a mantle ina state of incandescence, or even to afford a flame at all, does notappear to have been precisely determined, but it cannot be much below 1-1/2 per cent. Hence the apparatus for producing air-gas of this firstclass must be provided with controlling or governing devices of suchnicety that the proportion of hydrocarbon vapour in the air-gas ismaintained between about 1-1/2 and 2 per cent. It is fair to say that innormal working conditions a number of devices appear to fulfil thisrequirement satisfactorily. The second of the two mixtures referred toabove, viz. , air with more hydrocarbon vapour than constitutes anexplosive mixture, is primarily suitable for combustion in self-luminousburners, but may also be consumed in properly designed incandescentburners. But the generating apparatus for such air-gas must be equippedwith some governing or controlling device which will ensure theproportion of hydrocarbon vapour in the mixture never falling below, say, 7 per cent. On the other hand, if saturation of the air with the vapouris practically attained, should the temperature of the gas fall before itarrives at the point of combustion, part of the spirit will condense out, and the product will thus lose part of its illuminating or calorificintensity, besides partially filling the pipes with liquid products ofcondensation. The loss of intensity in the gas during cold weather may ormay not be inconvenient according to circumstances; but the removal ofpart of the combustible material brings the residual air-gas nearer toits limit of explosibility--for it is simply a mixture of combustiblevapour with air, which, normally, is not explosive because the proportionof spirit is too high--and thus, when led into an atmospheric burner, theextra amount of air introduced at the injector jets may cause the mixtureto be an explosive mixture of air and spirit, so that it will take firewithin the burner tube instead of burning quietly at the proper orifice. This matter will be made clearer on studying what is said about explosivelimits in Chapter VI. , and what is stated about incandescent acetylene(carburetted or not) in Chapters IX. And X. Clearly, however, high-gradeair-gas is only suitable for preparation at the immediate spot where itis to be consumed; it cannot be supplied to a complete district unless itis intentionally made of such lower intensity that the proportion ofspirit is too small ever to allow of partial deposition in the mainsduring the winter. It is perhaps necessary to refer to the more extended use of candles forlighting in some few houses in which lamps are disliked on aesthetic, or, in some cases, ostensibly on hygienic grounds. Candle lighting, speakingbroadly, is either very inadequate so far as ordinary living-rooms areconcerned, or, if adequate, is very costly. Tests specially carried outby one of the authors to determine some of the figures required in theensuing table show that ordinary paraffin or "wax" candles usually emitabout 20 per cent. More light than that given by the standard spermaceticandle, whose luminosity is the unit by which the intensity of otherlights is reckoned in Great Britain; and also that the light so emittedby domestic candles is practically unaffected by the sizes--"sixes, ""eights, " or "twelves"--burnt. In the sizes examined the light evolvedhas varied between 1. 145 and 1. 298 "candles, " perhaps tending to increaseslightly with the diameter of the candle tested. Hence, to obtainillumination in a room equal on the average to that afforded by 100standard candles, or some other light or lights aggregating 100 candle-power, would require the use of only 80 to 85 ordinary paraffin, ozokerite, or wax candles. But actually the essential objects in a roomcould be equally well illuminated by, say, 30 candles well distributed, as by two or three incandescent gas-burners, or four or five large oil-lamps. Lights of high intensity, such as powerful gas-burners or oil-lamps, must give a higher degree of illumination in their immediatevicinity than is really necessary, if they are to illuminate adequatelythe more distant objects. The dissemination and diffusion of their lightcan be greatly aided by suitable colouring of ceilings, walls anddrapings; but unless the illumination by means of lights of relativelyhigh intensity is made almost wholly indirect, candles or other lights oflow intensity, such as small electric glow-lamps, can, by properdistribution, be made to give more uniform or more suitably apportionedillumination. In this respect candles have an economical and, in somemeasure, a material advantage over acetylene also. (But when the methodof lighting is by flames--candle or other--the multiplication of thenumber of units which is involved when they are of low intensity, seriously increases the risk of fire through accidental contact ofinflammable material with any one of the flames. This risk is muchgreater with naked flames, such as candles, than with, say, invertedincandescent gas flames, which are to all intents and purposes fullyprotected by a closed glass globe. ) Hence, in the tabular statement whichfollows of the comparative cost, &c. , of different illuminants, it willbe assumed that 30 good candles would in practice be equally efficient inregard to the illumination of a room as large oil-lamps, acetyleneflames, or incandescent gas-burners aggregating 100 candle-power. For the same reason it will be assumed that electric glow-lamps of lowintensity (nominally of 8 candle-power or less), aggregating 70-80candle-power, will practically serve, if suitably distributed, equally aswell as 100 candle-power obtained from more powerful sources of light. Electric glow-lamps of a nominal intensity of 16 candles or thereabouts, and good flat-flame gas-burners, aggregating 90-95 candle-power, willsimilarly be taken as equivalent, if suitably distributed, to 100 candle-power from more powerful sources of light. Of the latter it will beassumed that each source has an intensity between 20 and 30 candle-power, such as is afforded by a large oil-lamp, a No. 1 Welsbach-Kern upturned, or a "Bijou" inverted incandescent gas-burner, or a 0. 70-cubic-foot-per-hour acetylene burner. Either of these sources of light, when used insufficient numbers, so that with proper distribution they light a roomadequately, will be taken in the tabular statement which follows asaffording, per candle-power evolved, the standard illuminating effectrequired in that room. The same illuminating effect will be regarded asattainable by means of candles aggregating only 35 per cent. , or smallelectric glow-lamps aggregating 77 per cent. , or large electric glow-lamps and flat-flame gas-burners aggregating 90 to 95 per cent. Of thiscandle-power; while if sources of light of higher intensity are used, such as Osram or Tantalum electric lamps, or the larger incandescent gas-burners (the Welsbach "C" or "York, " or the Nos. 3 or 4 Welsbach-Kernupturned, or the No. 1 or larger size inverted burners) or incandescentacetylene burners, it will be assumed that their aggregate candle-powermust be in excess by about 15 per cent. , in order to compensate for theimpossibility of obtaining equally well distributed illumination. Theseassumptions are based on general considerations and data as to the effectof sources of light of different intensities in giving practically thesame degree of illumination in a room; it would occupy too much spacehere to discuss more fully the grounds on which they have been made. Itmust suffice to say that they have been adopted with the object of beingperfectly fair to each means of illumination. COST PER HOUR AND HYGIENIC EFFECT OF LIGHTING BY DIFFERENT MEANS The data (except in the column headed "cost per 100 candle-hours") referto the illumination afforded by medium-sized (0. 5 to 0. 7 cubic foot perhour) acetylene burners yielding together a light of about 100 candle-power, and to the approximately equivalent illumination as afforded byother means of illumination, when the lighting-units or sources of lightare rationally distributed. Interest and depreciation charges on the outlay on piping or wiring ahouse, on brackets, fittings, lamps, candelabra, and storageaccommodation (for carbide and oil) have been taken as equivalent for allmodes of lighting, and omitted in computing the total cost. The cost oflabour for attendance on acetylene plant, oil lamps, and candles is anuncertain and variable item--approximately equal for all these modes oflighting, but saved in coal-gas and electric lighting from public supplymains. ______________________________________________________________________| | | | | | || | |Candle- | Number |Aggregate| Cost || | |Power of| of | Candle- | per || | Description of | each |Lighting | Power | 100 ||Illuminant. | Burner or Lamp. |Lighting| Units |Afforded. |Candle-|| | | Unit. |Required. |(About. ) |Hours. || | |(About. )| | |Pence. ||____________|____________________|________|_________|_________|_______|| | | | | | || |Self-luminous; 0. 5 | | | | || | cubic foot per hour| 18 | 5 | 90 | 1. 11 || |Self-luminous; 0. 7 | | | | || Acetylene | cubic foot per hour| 27 | 4 | 108 | 1. 02 || |Self-luminous; 1. 0 | | | | || | cubic foot per hour| 45. 5 | 3 | 136 | 0. 85 || |Incandescent; 0. 5 | | | | || | cubic foot per hour| 50 | 3 | 150 | 0. 49 ||____________|____________________|________|_________|_________|_______|| | | | | | || Petroleum | Large lamp . . . . | 20 | 5 | 100 | 0. 84 || (paraffin | | | | | || oil) | Small lamp . . . . | 5 | 14 | 70 | 1. 31 ||____________|____________________|________|_________|_________|_______|| | | | | | || |Flat flame (bad) 5 | | | | || | cubic feet per hour| 8 | 10 | 80 | 3. 75 || |Flat flame (good) 6 | | | | || Coal Gas | cubic feet per hour| 16 | 6 | 96 | 2. 25 || |Incandescent (No. 1 | | | | || | Kern or Bijou In- | 25 | 4 | 100 | 0. 38 || | verted); 1-1/2 | | | | || | cubic feet per hour| | | | ||____________|____________________|________|_________|_________|_______|| | | | | | || Candles |"Wax" (so-called) . | 1. 2 | 30 | 35 | 6. 14 ||____________|____________________|________|_________|_________|_______|| | | | | | || | Small glow . . . . | 7 | 11 | 77 | 2. 81 || | Large glow . . . . | 13 | 7 | 91 | 2. 90 || Electricity| | | | | || | Tantalum . . . . . | 19 | 5 | 95 | 1. 52 || | Osram . . . . . . | 14 | 7 | 98 | 1. 00 ||____________|____________________|________|_________|_________|_______| ___________________________________________________________________| | | | || | | | || | | | Equivalent || | Description of | Assumed Cost | Illumin- ||Illuminant. | Burner or Lamp. | of Illuminant. | ation. || | | | Pence. || | | | ||____________|____________________|____________________|____________|| | | | || |Self-luminous; 0. 5 | Calcium carbide | || | cubic foot per hour| (yielding 5 | 1. 00 || |Self-luminous; 0. 7 | cubic feet of | || Acetylene | cubic foot per hour| acetylene per | 1. 10 || |Self-luminous; 1. 0 | lb. ) at 15s. | || | cubic foot per hour| per cwt. , inclu- | 1. 16 || |Incandescent; 0. 5 | ding delivery | || | cubic foot per hour| charges. | 0. 74 ||____________|____________________|____________________|____________|| | | | || Petroleum | Large lamp . . . . | Oil, 9d. Per gal- | 0. 84 || (paraffin | | lon, including | || oil) | Small lamp . . . . | delivery charges. | 0. 92 ||____________|____________________|____________________|____________|| | | | || |Flat flame (bad) 5 | | || | cubic feet per hour| Public supply | 3. 00 || |Flat flame (good) 6 | from small | || Coal Gas | cubic feet per hour| country works, | 2. 16 || |Incandescent (No. 1 | at 5s. Per 1000 | || | Kern or Bijou In- | cubic feet. | 0. 38 || | verted); 1-1/2 | | || | cubic feet per hour| | ||____________|____________________|____________________|____________|| | | | || Candles |"Wax" (so-called) . | 5d. Per lb. | 2. 60 ||____________|____________________|____________________|____________|| | | | || | Small glow . . . . | Public supply | 2. 16 || | Large glow . . . . | from small | 2. 64 || Electricity| | town works | || | Tantalum . . . . . | at 6d. Per | 1. 45 || | Osram . . . . . . | B. O. T. Unit. | 0. 98 ||____________|____________________|____________________|____________| _______________________________________________________________________| | | | | | || | |Inci- | Exhaus- |Vitiation | Heat || | | den- | tion of | of Air. |Produced. || | Description of | tal |Air. Cubic|Cubic Feet|Number of||Illuminant. | Burner or Lamp. |Expen-|Feet Dep-| of Car- |Units of || | | ces. |rived of |bonic Acid| Heat. || | | | Oxygen. | Formed. |Calories. ||____________|____________________|______|_________|__________|_________|| | | | | | || |Self-luminous; 0. 5 | | | | || | cubic foot per hour| [1] | 29. 8 | 5. 0 | 900 || |Self-luminous; 0. 7 | | | | || Acetylene | cubic foot per hour| | 33. 3 | 5. 6 | 1010 || |Self-luminous; 1. 0 | | | | || | cubic foot per hour| | 35. 7 | 6. 0 | 1000 || |Incandescent; 0. 5 | | | | || | cubic foot per hour| [2] | 17. 9 | 3. 0 | 545 ||____________|____________________|______|_________|__________|_________|| | | | | | || Petroleum | Large lamp . . . . | | 140. 0 | 19. 6 | 3630 || (paraffin | | [3] | | | || oil) | Small lamp . . . . | | 154. 0 | 21. 6 | 4000 ||____________|____________________|______|_________|__________|_________|| | | | | | || |Flat flame (bad) 5 | | | | || | cubic feet per hour| Nil | 270. 0 | 27. 0 | 7750 || |Flat flame (good) 6 | | | | || Coal Gas | cubic feet per hour| Nil | 195. 0 | 19. 5 | 5580 || |Incandescent (No. 1 | | | | || | Kern or Bijou In- | [4] | 27. 0 | 2. 7 | 775 || | verted); 1-1/2 | | | | || | cubic feet per hour| | | | ||____________|____________________|______|_________|__________|_________|| | | | | | || Candles |"Wax" (so-called) . | Nil | 100. 5 | 13. 7 | 2700 ||____________|____________________|______|_________|__________|_________|| | | | | | || | Small glow . . . . |2s. 6d. | Nil | Nil | 285 || | Large glow . . . . |2s. 6d. | " | " | 360 || Electricity| | [5] | | | || | Tantalum . . . . . |7s. 6d. | " | " | 172 || | Osram . . . . . . | 6s. | " | " | 96 ||____________|____________________|______|_________|__________|_________| [Footnote 1: Interest and depreciation charges on generating andpurifying plant = 0. 15 penny. Purifying material and burner renewals =0. 05 penny. ] [Footnote 2: Mantle renewals as for coal-gas. ] [Footnote 3: Renewals of wicks and chimneys = 0. 02 penny. ] [Footnote 4: Renewals and mantles (and chimneys) at contract rate of 3s. Per burner per annum. ] [Footnote 5: Renewals of lamps and fuses, at price indicated per lamp perannum. ] The conventional method of making pecuniary comparisons between differentsources of artificial light consists in simply calculating the cost ofdeveloping a certain number of candle-hours of light--_i. E. _, acertain amount of standard candle-power for a given number of hours--onthe assumption that as many separate sources of light are employed as maybe required to bring the combined illuminating power up to the totalamount wanted. In view of the facts as to dissemination and diffusion, orthe difference between sheer illuminating power and useful illuminatingeffect, which have just been elaborated, and in view of the differentintensities of the different unit sources of light (which range from thesingle candle to a powerful large incandescent gas-burner or a metallicfilament electric lamp), such a method of calculation is wholly illusory. The plan adopted in the following table may also appear unnecessarilycomplicated; but it is not so to the reader if he remembers that theapparently various amount of illumination is corrected by the differentnumbers of illuminating units until the amount of simple candle-powerdeveloped, whatever illuminant be employed, suffices to light a roomhaving an area of about 300 square feet (_i. E. _, a room, 17-1/2 feetsquare, or one 20 feet long by 15 feet wide), so that ordinary print maybe read comfortably in any part of the room, and the titles of books, engravings, &c. , in any position on the walls up to a height of 8 feetfrom the ground may be distinguished with ease. The difference in cost, &c. , of a greater or less degree of illumination, or of lighting a largeror smaller room by acetylene or any other of the illuminants named, willbe almost directly proportional to the cost given for the statedconditions. Nevertheless, it should be recollected that when theconventional system is retained--useful illuminating effect beingsacrificed to absolute illuminating power--acetylene is made to appearcheaper in comparison with all weaker unit sources of light, and dearerin comparison with all stronger unit sources of light than theaccompanying table indicates it to be. In using the comparative figuresgiven in the table, it should be borne in mind that they refer to moregeneral and more brilliant illumination of a room than is commonly invogue where the lighting is by means of electric light, candles, or oil-lamps. The standard of illumination adopted for the table is one which isonly gaining general recognition where incandescent gas or acetylenelighting is available, though in exceptional cases it has doubtless beenattained by means of oil-lamps or flat-flame gas-burners, but very rarelyif ever by means of carbon-filament electric glow-lamps, or candles. Itassumes that the occupants of a room do not wish to be troubled to bringwork or book "to the light, " but wish to be able to work or readwheresoever in the room they will, without consideration of thewhereabouts of the light or lights. It should, perhaps, be added that so high a price as 5s. Per 1000cubic feet for coal-gas rarely prevails in Great Britain, except in smalloutlying towns, whereas the price of 6d. Per Board of Trade unitfor electricity is not uncommonly exceeded in the few similar countryplaces in which there is a public electricity supply. CHAPTER II THE PHYSICS AND CHEMISTRY OF THE REACTION BETWEEN CARBIDE AND WATER THE NATURE OF CALCIUM CARBIDE. --The raw material from which, byinteraction with water, acetylene is obtained, is a solid body calledcalcium carbide or carbide of calcium. Inasmuch as this substance can atpresent only be made on a commercial scale in the electric furnace--andso far as may be foreseen will never be made on a large scale except bymeans of electricity--inasmuch as an electric furnace can only be workedremuneratively in large factories supplied with cheap coal or waterpower; and inasmuch as there is no possibility of the ordinary consumerof acetylene ever being able to prepare his own carbide, all descriptionsof this latter substance, all methods of winning it, and all itsproperties except those which concern the acetylene-generator builder orthe gas consumer have been omitted from the present book. Hithertocalcium carbide has found but few applications beyond that of evolvingacetylene on treatment with water or some aqueous liquid, hygroscopicsolid, or salt containing water of crystallisation; but it haspossibilities of further employment, should its price become suitable, and a few words will be devoted to this branch of the subject in ChapterXII. Setting these minor uses aside, calcium carbide has no intrinsicvalue except as a producer of acetylene, and therefore all itscharacteristics which interest the consumer of acetylene are developedincidentally throughout this volume as the necessity for dealing withthem arises. It is desirable, however, now to discuss one point connected with solidcarbide about which some misconception prevails. Calcium carbide is abody which evolves an inflammable, or on occasion an explosive, gas whentreated with water; and therefore its presence in a building has beensaid to cause a sensible increase in the fire risk because attempts toextinguish a fire in the ordinary manner with water may cause evolutionof acetylene which should determine a further production of flame andheat. In the absence of water, calcium carbide is absolutely inert asregards fire; and on several occasions drums of it have been recovereduninjured from the basement of a house which has been totally destroyedby fire. With the exception of small 1-lb. Tins of carbide, used only bycyclists, &c. , the material is always put into drums of stout sheet-ironwith riveted or folded seams. Provided the original lid has not beenremoved, the drums are air- and water-tight, so that the fireman's hosemay be directed upon them with impunity. When a drum has once beenopened, and not all of its contents have been put into the generator, ordinary caution--not merely as regards fire, but as regards thedeterioration of carbide when exposed to the atmosphere--suggests eitherthat the lid must be made air-tight again (not by soldering it), [Footnote: Carbide drums are not uncommonly fitted with self-sealing orlever-top lids, which are readily replaced hermetically tight afteropening and partial removal of the contents of the drum. ] or preferablythat the rest of the carbide shall be transferred to some convenientreceptacle which can be perfectly closed. [Footnote: It would be arefinement of caution, though hardly necessary in practice, to fit such areceptacle with a safety-valve. If then the vessel were subjected tosudden or severe heating, the expansion of the air and acetylene in itcould not possibly exert a disruptive effect upon the walls of thereceptacle, which, in the absence of the safety-valve, is imaginable. ]Now, assuming this done, the drums are not dependent upon soft solder tokeep them sound, and so they cannot open with heat. Fire and water, accordingly, cannot affect them, and only two risks remain: if stored inthe basement of a tall building, falling girders, beams or brickwork mayburst them; or if stored on an upper floor, they may fall into thebasement and be burst with the shock--in either event water then havingfree access to the contents. But drums of carbide would never be storedin such positions: a single one would be kept in the generator-house;several would be stored in a separate room therein, or in some similarisolated shed. The generator-house or shed would be of one story only;the drums could neither fall nor have heavy weights fall on them during afire; and therefore there is no reason why, if a fire should occur, thefiremen should not be permitted to use their hose in the ordinaryfashion. Very similar remarks apply to an active acetylene generator. Well built, such plant will stand much heat and fire without failure; ifit is non-automatic, and of combustible materials contains nothing butgas in the holder, the worst that could happen in times of fire would bethe unsealing of the bell or its fracture, and this would be followed, not at all by any explosion, but by a fairly quiet burning of theescaping gas, which would be over in a very short time, and would not addto the severity of the conflagration unless the generator-house were soclose to the residence that the large flame of burning gas could ignitepart of the main building. Even if the heat were so great near the holderthat the gas dissociated, it is scarcely conceivable that a dangerousexplosion should arise. But it is well to remember, that if thegenerator-house is properly isolated from the residence, if it isconstructed of non-inflammable materials, if the attendant obeysinstructions and refrains from taking a naked light into theneighbourhood of the plant, and if the plant itself is properly designedand constructed, a fire at or near an acetylene generator is extremelyunlikely to occur. At the same time, before the erection of plant tosupply any insured premises is undertaken, the policy or the companyshould be consulted to ascertain whether the adoption of acetylenelighting is possibly still regarded by the insurers as adding an extrarisk or even as vitiating the whole insurance. REGULATIONS FOR THE STORAGE OF CARBIDE: BRITISH. --There are also certainregulations imposed by many local authorities respecting the storage ofcarbide, and usually a licence for storage has to be obtained if morethan 5 lb. Is kept at a time. The idea of the rule is perfectlyjustifiable, and it is generally enforced in a sensible spirit. As therules may vary in different localities, the intending consumer ofacetylene must make the necessary inquiries, for failure to comply withthe regulations may obviously be followed by unpleasantness. Having regard to the fact that, in virtue of an Order in Council datedJuly 7, 1897, carbide may be stored without a licence only in separatesubstantial hermetically closed metal vessels containing not more than 1lb. Apiece and in quantities not exceeding 5 lb. In the aggregate, andhaving regard also to the fact that regulations are issued by localauthorities, the Fire Offices' Committee of the United Kingdom has not upto the present deemed it necessary to issue special rules with referenceto the storage of carbide of calcium. The following is a copy of the rules issued by the National Board of FireUnderwriters of the UNITED STATES OF AMERICA for the storage of calciumcarbide on insured premises: RULES FOR THE STORAGE OF CALCIUM CARBIDE. (_a_) Calcium carbide in quantities not to exceed six hundred (600)pounds may be stored, when contained in approved metal packages not toexceed one hundred (100) pounds each, inside insured property, providedthat the place of storage be dry, waterproof and well ventilated, andalso provided that all but one of the packages in any one building shallbe sealed and the seals shall not be broken so long as there is carbidein excess of one (1) pound in any other unsealed package in the building. (_b_) Calcium carbide in quantities in excess of six hundred (600)pounds must be stored above ground in detached buildings, usedexclusively for the storage of calcium carbide, in approved metalpackages, and such buildings shall be constructed to be dry, waterproofand well ventilated. (_c_) Packages to be approved must be made of metal of sufficientstrength to insure handling the package without rupture, and be providedwith a screwed top or its equivalent. They must be constructed so as to be water- and air-tight without the useof solder, and conspicuously marked "CALCIUM CARBIDE--DANGEROUS IF NOTKEPT DRY. " The following is a summary of the AUSTRIAN GOVERNMENT rules relating tothe storage and handling of carbide: (1) It must be sold and stored only in closed water-tight vessels, which, if the contents exceed 10 kilos. , must be marked in plain letters"CALCIUM CARBIDE--TO BE KEPT CLOSED AND DRY. " They must not be of copperand if soldered must be opened by mechanical means and not byunsoldering. They must be stored out of the reach of water. (2) Quantities not exceeding 300 kilos. May be stored in occupied houses, provided the single drums do not exceed 100 kilos. Nominal capacity. Thestorage-place must be dry and not underground. (3) The limits specified in Rule 2 apply also to generator-rooms, withthe proviso also that in general the amount stored shall not exceed fivedays' consumption. (4) Quantities ranging from 300 to 1000 kilos. Must be stored in specialwell-ventilated uninhabited non-basement rooms in which lights andsmoking are not allowed. (5) Quantities exceeding 1000 kilos. Must be stored in isolated fireproofmagazines with light water-tight roofs. The floors must be at least 8inches above ground-level. (6) Carbide in water-tight drums may be stored in the open in a fencedenclosure at least 30 feet from buildings, adjoining property, orinflammable materials. The drums must be protected from wet by a lightroof. (7) The breaking of carbide must be done by men provided with respiratorsand goggles, and care taken to avoid the formation of dust. (8) Local or other authorities will issue from time to time specialregulations in regard to carbide trade premises. The ITALIAN GOVERNMENT rules relating to the storage and transport ofcarbide follow in the main those of the Austrian Government, but forquantities between 300 and 2000 kilos sanction is required from the localauthorities, and for larger quantities from superior authorities. Thestorage of quantities ranging from 300 to 2000 kilos is forbidden indwelling-houses and above the latter quantity the storage-place must beisolated and specially selected. No special permit is required for thestorage of quantities not exceeding 300 kilos. Workmen exposed to carbidedust arising from the breaking of carbide or otherwise must have theireyes and respiratory organs suitably protected. THE PURCHASE OF CARBIDE. --Since calcium carbide is only useful as a meansof preparing acetylene, it should be bought under a guarantee (1) that itcontains less impurities than suffice to render the crude gas dangerousin respect of spontaneous inflammability, or objectionable in a manner tobe explained later on, when consumed; and (2) that it is capable ofevolving a fixed minimum quantity of acetylene when decomposed by water. Such determination, however, cannot be carried out by the ordinaryconsumer for himself. A generator which is perfectly satisfactory ingeneral behaviour, and which evolves a sufficient proportion of thepossible total make of gas to be economical, does not of necessitydecompose the carbide quantitatively; nor is it constructed in a fashionto render an exact measurement of the gas liberated at standardtemperature and pressure easy to obtain. For obvious reasons the carefulconsumer of acetylene will keep a record of the carbide decomposed and ofthe acetylene generated--the latter perhaps only in terms of burner-hours, or the like; but in the event of serious dispute as to the gas-making capacity of his raw material, he must have a proper analysis madeby a qualified chemist. Calcium carbide is crushed by the makers into several different sizes, ineach of which all the lumps exceed a certain size and are smaller thananother size. It is necessary to find out by experiment, or from themaker, what particular size suits the generator best, for different typesof apparatus require different sizes of carbide. Carbide cannot well becrushed by the consumer of acetylene. It is a difficult operation, andfraught with the production of dust which is harmful to the eyes andthroat, and if done in open vessels the carbide deteriorates in gas-making power by its exposure to the moisture of the atmosphere. True dustin carbide is objectionable, and practically useless for the generationof acetylene in any form of apparatus, but carbide exceeding 1 inch inmesh is usually sold to satisfy the suggestions of the British AcetyleneAssociation, which prescribes 5 per cent, of dust as the maximum. Somegrades of carbide are softer than others, and therefore tend to yieldmore dust if exposed to a long journey with frequent unloadings. There are certain varieties of ordinary carbide known as "treatedcarbide, " the value of which is more particularly discussed in ChapterIII. The treatment is of two kinds, or of a combination of both. In oneprocess the lumps are coated with a strong solution of glucose, with theobject of assisting in the removal of spent lime from their surface whenthe carbide is immersed in water. Lime is comparatively much more solublein solutions of sugar (to which class of substances glucose belongs) thanin plain water; so that carbide treated with glucose is not so likely tobe covered with a closely adherent skin of spent lime when decomposed bythe addition of water to it. In the other process, the carbide is coatedwith or immersed in some oil or grease to protect it from prematuredecomposition. The latter idea, at least, fulfils its promises, and doeskeep the carbide to a large extent unchanged if the lumps are exposed todamp air, while solving certain troubles otherwise met with in somegenerators (cf. Chapter III. ); but both operations involve additionalexpense, and since ordinary carbide can be used satisfactorily in a goodfixed generator, and can be preserved without serious deterioration bythe exercise of reasonable care, treated carbide is only to berecommended for employment in holderless generators, of which table-lampsare the most conspicuous forms. A third variant of plain carbide isoccasionally heard of, which is termed "scented" carbide. It is difficultto regard this material seriously. In all probability calcium carbide isodourless, but as it begins to evolve traces of gas immediatelyatmospheric moisture reaches it, a lump of carbide has always theunpleasant smell of crude acetylene. As the material is not to be storedin occupied rooms, and as all odour is lost to the senses directly thecarbide is put into the generator, scented carbide may be said to bedevoid of all utility. THE REACTION BETWEEN CARBIDE AND WATER. --The reaction which occurs whencalcium carbide and water are brought into contact belongs to the classthat chemists usually term double decompositions. Calcium carbide is achemical compound of the metal calcium with carbon, containing onechemical "part, " or atomic weight, of the former united to two chemicalparts, or atomic weights, of the latter; its composition expressed insymbols being CaC_2. Similarly, water is a compound of two chemical partsof hydrogen with one of oxygen, its formula being H_2O. When those twosubstances are mixed together the hydrogen of the water leaves itsoriginal partner, oxygen, and the carbon of the calcium carbide leavesthe calcium, uniting together to form that particular compound ofhydrogen and carbon, or hydrocarbon, which is known as acetylene, whoseformula is C_2H_2; while the residual calcium and oxygen join together toproduce calcium oxide or lime, CaO. Put into the usual form of anequation, the reaction proceeds thus-- (1) CaC_2 + H_2O = C_2H_2 + CaO. This equation not only means that calcium carbide and water combine toyield acetylene and lime, it also means that one chemical part of carbidereacts with one chemical part of water to produce one chemical part ofacetylene and one of lime. But these four chemical parts, or molecules, which are all equal chemically, are not equal in weight; although, according to a common law of chemistry, they each bear a fixed proportionto one another. Reference to the table of "Atomic Weights" contained inany text-book of chemistry will show that while the symbol Ca is used, for convenience, as a contraction or sign for the element calcium simply, it bears a more important quantitative significance, for to it will befound assigned the number 40. Against carbon will be seen the number 12;against oxygen, 16; and against hydrogen, 1. These numbers indicate thatif the smallest weight of hydrogen ever found in a chemical compound iscalled 1 as a unit of comparison, the smallest weights of calcium, carbon, and oxygen, similarly taking part in chemical reactions are 40, 12, and 16 respectively. Thus the symbol CaC_2, comes to convoy threeseparate ideas: (_a_) that the substance referred to is a compoundof calcium and carbon only, and that it is therefore a carbide ofcalcium; (_b_) that it is composed of one chemical part or atom ofcalcium and two atoms of carbon; and (_c_) that it contains 40 partsby weight of calcium combined with twice twelve, or 24, parts of carbon. It follows from (_c_) that the weight of one chemical part, nowtermed a molecule as the substance is a compound, of calcium carbide is(40 + 2 x 12) = 64. By identical methods of calculation it will be foundthat the weight of one molecule of water is 18; that of acetylene, 26;and that of lime, 56. The general equation (1) given above, therefore, states in chemical shorthand that 64 parts by weight of calcium carbidereact with 18 parts of water to give 26 parts by weight of acetylene and56 parts of lime; and it is very important to observe that just as thereare the same number of chemical parts, viz. , 2, on each side, so thereare the same number of parts by weight, for 64 + 18 = 56 + 26 = 82. Putinto other words equation (1) shows that if 64 grammes, lb. , or cwts. Ofcalcium carbide are treated with 18 grammes, lb. , or cwts. Of water, thewhole mass will be converted into acetylene and lime, and the residuewill not contain any unaltered calcium carbide or any water; whence itmay be inferred, as is the fact, that if the weights of carbide and wateroriginally taken do not stand to one another in the ratio 64 : 18, bothsubstances cannot be entirely decomposed, but a certain quantity of theone which was in excess will be left unattacked, and that quantity willbe in exact accordance with the amount of the said excess--indifferentlywhether the superabundant substance be carbide or water. Hitherto, for the sake of simplicity, the by-product in the preparationof acetylene has been described as calcium oxide or quicklime. It is, however, one of the leading characteristics of this body to behygroscopic, or greedy of moisture; so that if it is brought into thepresence of water, either in the form of liquid or as vapour, itimmediately combines therewith to yield calcium hydroxide, or slakedlime, whose chemical formula is Ca(OH)_2. Accordingly, in actualpractice, when calcium carbide is mixed with an excess of water, asecondary reaction takes place over and above that indicated by equation(1), the quicklime produced combining with one chemical part or moleculeof water, thus-- CaO + H_2O = Ca(OH)_2. As these two actions occur simultaneously, it is more usual, and more inagreement with the phenomena of an acetylene generator, to represent thedecomposition of calcium carbide by the combined equation-- (2) CaC_2 + 2H_2O = C_2H_2 + Ca(OH)_2. By the aid of calculations analogous to those employed in the precedingparagraph, it will be noticed that equation (2) states that 1 molecule ofcalcium carbide, or 64 parts by weight, combines with 2 molecules ofwater, or 36 parts by weight, to yield 1 molecule, or 26 parts by weightof acetylene, and 1 molecule, or 74 parts by weight of calcium hydroxide(slaked lime). Here again, if more than 36 parts of water are taken forevery 64 parts of calcium carbide, the excess of water over those 36parts is left undecomposed; and in the same fashion, if less than 36parts of water are taken for every 64 parts of calcium carbide, some ofthe latter must remain unattacked, whilst, obviously, the amount ofacetylene liberated cannot exceed that which corresponds with thequantity of substance suffering complete decomposition. If, for example, the quantity of water present in a generator is more than chemicallysufficient to attack all the carbide added, however largo or small thatexcess may be, no more, and, theoretically speaking, no less, acetylenecan ever be evolved than 26 parts by weight of gas for every 64 parts byweight of calcium carbide consumed. It is, however, not correct to invertthe proposition, and to say that if the carbide is in excess of the wateradded, no more, and, theoretically speaking, no less, acetylene can everbe evolved than 26 parts by weight of gas for every 36 parts of waterconsumed, as might be gathered from equation (2); because equation (1)shows that 26 parts of acetylene may, on occasion, be produced by thedecomposition of 18 parts by weight of water. From the purely chemicalpoint of view this apparent anomaly is explained by the circumstance thatof the 36 parts of water present on the left-hand aide of equation (2), only one-half, _i. E. _, 18 parts by weight, are actually decomposedinto hydrogen and oxygen, the other 18 parts remaining unattacked, andmerely attaching themselves as "water of hydration" to the 56 parts ofcalcium oxide in equation (1) so as to produce the 74 parts of calciumhydroxide appearing on the right-hand side of equation (2). The matter isperhaps rendered more intelligible by employing the old name for calciumhydroxide or slaked lime, viz. , hydrated oxide of calcium, and by writingits formula in the corresponding form, when equation (2) becomes CaC_2 + 2H_2O = C_2H_2 + CaO. H_2O. It is, therefore, absolutely correct to state that if the amount ofcalcium carbide present in an acetylene generator is more than chemicallysufficient to decompose all the water introduced, no more, andtheoretically speaking no less, acetylene can ever be liberated than 26parts by weight of gas for every 18 parts by weight of water attacked. This, it must be distinctly understood, is the condition of affairsobtaining in the ideal acetylene generator only; since, for reasons whichwill be immediately explained, when the output of gas is measured interms of the water decomposed, in no commercial apparatus, and indeed inno generator which can be imagined fit for actual employment, does thatoutput of gas ever approach the quantitative amount; but the volume ofwater used, if not actually disappearing, is always vastly in excess ofthe requirements of equation (2). On the contrary, when the make of gasis measured in terms of the calcium carbide consumed, the said make may, and frequently does, reach 80, 90, or even 99 per cent. Of what istheoretically possible. Inasmuch as calcium carbide is the one costlyingredient in the manufacture of acetylene, so long as it is not wasted--so long, that is to say, as nearly the theoretical yield of gas isobtained from it--an acetylene generator is satisfactory or efficient inthis particular; and except for the matter of solubility discussed in thefollowing chapter, the quantity of water consumed is of no importancewhatever. HEAT EVOLVED IN THE REACTION. --The chemical reaction between calciumcarbide and water is accompanied by a large evolution of heat, which, unless due precautions are taken to prevent it, raises the temperature ofthe substances employed, and of the apparatus containing them, to aserious and often inconvenient extent. This phenomenon is the mostimportant of all in connexion with acetylene manufacture; for upon aproper recognition of it, and upon the character of the precautions takento avoid its numerous evil effects, depend the actual value and capacityfor smooth working of any acetylene generator. Just as, by an immutablelaw of chemistry, a given weight of calcium carbide yields a given weightof acetylene, and by no amount of ingenuity can be made to produce eithermore or less; so, by an equally immutable law of physics, thedecomposition of a given weight of calcium carbide by water, or thedecomposition of a given weight of water by calcium carbide, yields aperfectly definite quantity of heat--a quantity of heat which cannot bereduced or increased by any artifice whatever. The result of a productionof heat is usually to raise the temperature of the material in which itis produced; but this is not always the case, and indeed there is nonecessary connexion or ratio between the quantity of heat liberated inany form of chemical reaction--of which ordinary combustion is thecommonest type--and the temperature attained by the substances concerned. This matter has so weighty a bearing upon acetylene generation, andappears to be so frequently misunderstood, that a couple of illustrationsmay with advantage be studied. If a vessel full of cold water, andcontaining also a thermometer, is placed over a lighted gas-burner, atfirst the temperature of the liquid rises steadily, and there is clearlya ratio between the size of the flame and the speed at which the mercurymounts up the scale. Finally, however, the thermometer indicates acertain point, viz. , 100° C, and the water begins to boil; yet althoughthe burner is untouched, and consequently, although heat must be passinginto the vessel at the same rate as before, the mercury refuses to moveas long as any liquid water is left. By the use of a gas meter it mightbe shown that the same volume of gas is always consumed (_a_) inraising the temperature of a given quantity of cold water to the boiling-point, and another equally constant volume of gas is always consumed(_b_) in causing the boiling water to disappear as steam. Hence, ascoal-gas is assumed for the present purpose to possess invariably thesame heating power, it appears that the same quantity of heat is alwaysneeded to convert a given amount of cold water at a certain temperatureinto steam; but inasmuch as reference to the meter would show that about5 times the volume of gas is consumed in changing the boiling water intosteam as is used in heating the cold water to the boiling-point, it willbe evident that the temperature of the mass is raised as high by the heatevolved during the combustion of one part of gas as it is by thatliberated on the combustion of 6 times that amount. A further example of the difference between quantity of heat and sensibletemperature may be seen in the combustion of coal, for (say) onehundredweight of that fuel might be consumed in a very few minutes in afurnace fitted with a powerful blast of air, the operation might bespread over a considerable number of hours in a domestic grate, or thecoal might be allowed to oxidise by exposure to warm air for a year ormore. In the last case the temperature might not attain that of boilingwater, in the second it would be about that of dull redness, and in thefirst it would be that of dazzling whiteness; but in all three cases thetotal quantity of heat produced by the time the coal was entirelyconsumed would be absolutely identical. The former experiment with waterand a gas-burner, too, might easily be modified to throw light uponanother problem in acetylene generation, for it would be found that ifalmost any other liquid than water were taken, less gas (_i. E. _, asmaller quantity of heat) would be required to raise a given weight of itfrom a certain low to a certain high temperature than in the case ofwater itself; while if it were possible similarly to treat the sameweight of iron (of which acetylene generators are constructed), or ofcalcium carbide, the quantity of heat used to raise it through a givennumber of thermometric degrees would hardly exceed one-tenth or one-quarter of that needed by water itself. In technical language thisdifference is due to the different specific heats of the substancesmentioned; the specific heat of a body being the relative quantity ofheat consumed in raising a certain weight of it a certain number ofdegrees when the quantity of heat needed to produce the same effect onthe same weight of water is called unity. Thus, the specific heat ofwater being termed 1. 0, that of iron or steel is 0. 1138, and that ofcalcium carbide 0. 247, [Footnote: This is Carlson's figure. Morel hastaken the value 0. 103 in certain calculations. ] both measured attemperatures where water is a liquid. Putting the foregoing facts inanother shape, for a given rise in temperature that substance will absorbthe most heat which has the highest specific heat, and therefore, in thisrespect, 1 part by weight of water will do the work of roughly 9 parts byweight of iron, and of about 4 parts by weight of calcium carbide. From the practical aspect what has been said amounts to this: During theoperation of an acetylene generator a large amount of heat is produced, the quantity of which is beyond human control. It is desirable, forvarious reasons, that the temperature shall be kept as low as possible. There are three substances present to which the heat may be compelled totransfer itself until it has opportunity to pass into the surroundingatmosphere: the material of which the apparatus is constructed, the gaswhich is in process of evolution, and whichever of the two bodies--calcium carbide or water--is in excess in the generator. Of these, thespecific heat at constant pressure of acetylene has unfortunately not yetbeen determined, but its relative capacity for absorbing heat isundoubtedly small; moreover the gas could not be permitted to becomesufficiently hot to carry off the heat without grave disadvantages. Thespecific heat of calcium carbide is also comparatively small, and thereare similar disadvantages in allowing it to become hot; moreover it isdeficient in heat-conducting power, so that heat communicated to oneportion of the mass does not extend rapidly throughout, but remainsconcentrated in one spot, causing the temperature to rise objectionably. Steel has a sufficient amount of heat-conducting power to prevent undueconcentration in one place; but, as has been stated, its specific heat isonly one-ninth that of water. Water is clearly, therefore, the propersubstance to employ for the dissipation of the heat generated, althoughit is strictly speaking almost devoid of heat-conducting power; for notonly is the specific heat of water much greater than that of any othermaterial present, but it possesses in a high degree the faculty ofabsorbing heat throughout its mass, by virtue of the action known asconvection, provided that heat is communicated to it at or near thebottom, and not too near its upper surface. Moreover, water is a muchmore valuable substance for dissipating heat than appears from theforegoing explanation; for reference to the experiment with the gas-burner will show that six and a quarter times as much heat can beabsorbed by a given weight of water if it is permitted to change intosteam, as if it is merely raised to the boiling-point; and since by nourging of the gas-burner can the temperature be raised above 100° C. Aslong as any liquid water remains unevaporated, if an excess of water isemployed in an acetylene generator, the temperature inside can never--except quite locally--exceed 100° C. , however fast the carbide bedecomposed. An indefinitely large consumption of water by evaporation ina generator matters nothing, for the liquid may be considered of nopecuniary value, and it can all be recovered by condensation in asubsequent portion of the plant. It has been said that the quantity of heat liberated when a certainamount of carbide suffers decomposition is fixed; it remains now toconsider what that quantity is. Quantities of heat are always measured interms of the amount needed to raise a certain weight of water a certainnumber of degrees on the thermometric scale. There are several units inuse, but the one which will be employed throughout this book is the"Large Calorie"; a large calorie being the amount of heat absorbed inraising 1 kilogramme of water 1° C. Referring for a moment to what hasbeen said about specific heats, it will be apparent that if 1 largecalorie is sufficient to heat 1 kilo, of water through 1° C. The samequantity will heat 1 kilo. Of steel, whose specific heat is roughly 0. 11, through (10/011) = 9° C. , or, which comes to the same thing, will heat 9kilos, of steel through 1° C. ; and similarly, 1 large calorie will raise4 kilos. Of calcium carbide 1° C. In temperature, or 1 kilo. 4° C. Thefact that a definite quantity of heat is manifested when a known weightof calcium carbide is decomposed by water is only typical; for in everychemical process some disturbance of heat, though not necessarily ofsensible (or thermometric) character, occurs, heat being either absorbedor set free. Moreover, if when given weights of two or more substancesunite to form a given weight of another substance, a certain quantity ofheat is set free, precisely the same amount of heat is absorbed, ordisappears, when the latter substance is decomposed to form the samequantities of the original substances; and, _per contra_, if thecombination is attended by a disappearance of heat, exactly the sameamount is liberated when the compound is broken up into its firstconstituents. Compounds are therefore of two kinds: those which absorbheat during their preparation, and consequently liberate heat when theyare decomposed--such being termed endothermic; and those which evolveheat during their preparation, and consequently absorb heat when they aredecomposed--such being called exothermic. If a substance absorbs heatduring its formation, it cannot be produced unless that heat is suppliedto it; and since heat, being a form of motion, is equally a form ofenergy, energy must be supplied, or work must be done, before thatsubstance can be obtained. Conversely, if a substance evolves heat duringits formation, its component parts evolve energy when the said substanceis being produced; and therefore the mere act of combination isaccompanied by a facility for doing work, which work may be applied inassisting some other reaction that requires heat, or may be usefullyemployed in any other fashion, or wasted if necessary. Seeing that thereis a tendency in nature for the steady dissipation of energy, it followsthat an exothermic substance is stable, for it tends to remain as it isunless heat is supplied to it, or work is done upon it; whereas, according to its degree of endothermicity, an endothermic substance ismore or less unstable, for it is always ready to emit heat, or to dowork, as soon as an opportunity is given to it to decompose. Thetheoretical and practical results of this circumstance will be elaboratedin Chapter VI. , when the endothermic nature of acetylene is more fullydiscussed. A very simple experiment will show that a notable quantity of heat is setfree when calcium carbide is brought into contact with water, and byarranging the details of the apparatus in a suitable manner, the quantityof heat manifested may be measured with considerable accuracy. A lengthydescription of the method of performing this operation, however, scarcelycomes within the province of the present book, and it must be sufficientto say that the heat is estimated by decomposing a known weight ofcarbide by means of water in a small vessel surrounded on all sides by acarefully jacketed receptacle full of water and provided with a sensitivethermometer. The quantity of water contained in the outer vessel beingknown, and its temperature having been noted before the reactioncommences, an observation of the thermometer after the decomposition isfinished, and when the mercury has reached its highest point, gives datawhich show that the reaction between water and a known weight of calciumcarbide produces heat sufficient in amount to raise a known weight ofwater through a known thermometric distance; and from these figures thecorresponding number of large calories may easily be calculated. Adetermination of this quantity of heat has been made experimentally byseveral investigators, including Lewes, who has found that the heatevolved on decomposing 1 gramme of ordinary commercial carbide with wateris 0. 406 large calorie. [Footnote: Lewes returns his result as 406calories, because he employs the "small calorie. " The small calorie isthe quantity of heat needed to raise 1 gramme of water 1° C. ; but asthere are 1000 grammes in 1 kilogramme, the large calorie is equal to1000 small calories. In many respects the former unit is to bepreferred. ] As the material operated upon contained only 91. 3 per cent. Of true calcium carbide, he estimates the heat corresponding with thedecomposition of 1 gramme of pure carbide to be 0. 4446 large calorie. As, however, it is better, and more in accordance with modern practice, toquote such data in terms of the atomic or molecular weight of thesubstance concerned, and as the molecular weight of calcium carbide is64, it is preferable to multiply these figures by 64, stating that, according to Lewes' researches, the heat of decomposition of "1 gramme-molecule" (_i. E. _, 64 grammes) of a calcium carbide having a purityof 91. 3 per cent. Is just under 26 calories, or that of 1 gramme-moleculeof pure carbide 28. 454 calories. It is customary now to omit the phrase"one gramme-molecule" in giving similar figures, physicists saying simplythat the heat of decomposition of calcium carbide by water when calciumhydroxide is the by-product, is 28. 454 large calories. Assuming all the necessary data known, as happens to be the case in thepresent instance, it is also possible to calculate theoretically the heatwhich should be evolved on decomposing calcium carbide by means of water. Equation (2), given on page 24, shows that of the substances taking partin the reaction 1 molecular weight of calcium carbide is decomposed, and1 molecular weight of acetylene is formed. Of the two molecules of water, only one is decomposed, the other passing to the calcium hydroxideunchanged; and the 1 molecule of calcium hydroxide is formed by thecombination of 1 atom of free calcium, 1 atom of free oxygen, and 1molecule of water already existing as such. Calcium hydroxide and waterare both exothermic substances, absorbing heat when they are decomposed, liberating it when they are formed. Acetylene is endothermic, liberatingheat when it is decomposed, absorbing it when it is produced. Unfortunately there is still some doubt about the heat of formation ofcalcium carbide, De Forcrand returning it as -0. 65 calorie, and Gin as+3. 9 calories. De Forcrand's figure means, as before explained, that 64grammes of carbide should absorb 0. 65 large calorie when they areproduced by the combination of 40 grammes of calcium with 24 grammes ofcarbon; the minus sign calling attention to the belief that calciumcarbide is endothermic, heat being liberated when it suffersdecomposition. On the contrary, Gin's figure expresses the idea thatcalcium carbide is exothermic, liberating 3. 9 calories when it isproduced, and absorbing them when it is decomposed. In the absence ofcorroborative evidence one way or the other, Gin's determination will beaccepted for the ensuing calculation. In equation (2), therefore, calciumcarbide is decomposed and absorbs heat; water is decomposed and absorbsheat; acetylene is produced and absorbs heat; and calcium hydroxide isproduced liberating heat. On consulting the tables of thermo-chemicaldata given in the various text-books on physical chemistry, all the otherconstants needed for the present purpose will be found; and it willappear that the heat of formation of water is +69 calories, that ofacetylene -58. 1 calories, and that of calcium hydroxide, when 1 atom ofcalcium, 1 atom of oxygen, and 1 molecule of water unite together, is+160. 1 calories. [Footnote: When 1 atom of calcium, 2 atoms of oxygen, and 2 atoms of hydrogen unite to form solid calcium hydroxide, the heatof formation of the latter is 229. 1 (cf. _infra_). This value issimply 160. 1 + 69. 0 = 229. 1; 69. 0 being the heat of formation of water. ]Collecting the results into the form of a balance-sheet, the effect ofdecomposing calcium carbide with water is this: _Heat liberated. _ | _Heat absorbed. _ |Formation of Ca(OH)_2 16O. 1 | Formation of acetylene 58. 1| Decomposition of water 69. 0 | Decomposition of carbide 3. 9 | Balance 29. 1 _____ | _____ | Total 160. 1 | Total 160. 1 Therefore when 64 grammes of calcium carbide are decomposed by water, orwhen 18 grammes of water are decomposed by calcium carbide (the by-product in each case being calcium hydroxide or slaked lime, for theformation of which a further 18 grammes of water must be present in thesecond instance), 29. 1 large calories are set free. It is not possibleyet to determine thermo-chemical data with extreme accuracy, especiallyon such a material as calcium carbide, which is hardly to be procured ina state of chemical purity; and so the value 28. 454 caloriesexperimentally found by Lewes agrees very satisfactorily, considering allthings, with the calculated value 29. 1 calories. It is to be noticed, however, that the above calculated value has been deduced on theassumption that the calcium hydroxide is obtained as a dry powder; but asslaked lime is somewhat soluble in water, and as it evolves 3 calories inso dissolving, if sufficient water is present to take up the calciumhydroxide entirely into the liquid form (_i. E. _, that of asolution), the amount of heat set free will be greater by those 3calories, _i. E. _, 32. 1 large calories altogether. THE PROCESS OF GENERATION. --Taking 28 as the number of large caloriesdeveloped when 64 grammes of ordinary commercial calcium carbide aredecomposed with sufficient water to leave dry solid calcium hydroxide asthe by-product in acetylene generation, this quantity of heat is capableof exerting any of the following effects. It is sufficient (1) to raise1000 grammes of water through 28° C. , say from 10° C. (50° F. , which isroughly the temperature of ordinary cold water) to 38° C. It issufficient (2) to raise 64 grammes of water (a weight equal to that ofthe carbide decomposed) through 438° C. , if that were possible. It wouldraise (3) 311 grammes of water through 90° C. , _i. E. _, from 10° C. To the boiling-point. If, however, instead of remaining in the liquidstate, the water were converted into vapour, the same quantity of heatwould suffice (4) to change 44. 7 grammes of water at 10° C. Into steam at100° C. ; or (5) to change 46. 7 grammes of water at 10° C. Into vapour atthe same temperature. It is an action of the last character which takesplace in acetylene generators of the most modern and usual pattern, someof the surplus water being evaporated and carried away as vapour at acomparatively low temperature with the escaping gas; for it must beremembered that although steam, as such, condenses into liquid waterimmediately the surrounding temperature falls below 100° C. , the vapourof water remains uncondensed, even at temperatures below the freezing-point, when that vapour is distributed among some permanent gas--theprecise quantity of vapour so remaining being a function of thetemperature and barometric height. Thus it appears that if the heatevolved during the decomposition of calcium carbide is not otherwiseconsumed, it is sufficient in amount to vaporise almost exactly 3 partsby weight of water for every 4 parts of carbide attacked; but if it wereexpended upon some substance such as acetylene, calcium carbide, orsteel, which, unlike water, could not absorb an extra amount by changingits physical state (from solid to liquid, or from liquid to gas), theheat generated during the decomposition of a given weight of carbidewould suffice to raise an equal weight of the particular substance underconsideration to a temperature vastly exceeding 438° C. The temperatureattained, indeed, measured in Centigrade degrees, would be 438 multipliedby the quotient obtained on dividing the specific heat of water by thespecific heat of the substance considered: which quotient, obviously, isthe "reciprocal" of the specific heat of the said substance. The analogy to the combustion of coal mentioned on a previous page showsthat although the quantity of heat evolved during a certain chemicalreaction is strictly fixed, the temperature attained is dependent on thetime over which the reaction is spread, being higher as the process ismore rapid. This is due to the fact that throughout the whole period ofreaction heat is escaping from the mass, and passing into the atmosphereat a fairly constant speed; so that, clearly, the more slowly heat isproduced, the better opportunity has it to pass away, and the less of itis left to collect in the material under consideration. During the actionof an acetylene generator, there is a current of gas constantlytravelling away from the carbide, there is vapour of water constantlyescaping with the gas, there are the walls of the generator itselfconstantly exposed to the cooling action of the atmosphere, and there iseither a mass of calcium carbide or of water within the generator. It isessential for good working that the temperature of both the acetylene andthe carbide shall be prevented from rising to any noteworthy extent;while the amount of heat capable of being dissipated into the air throughthe walls of the apparatus in a given time is narrowly limited, dependingupon the size and shape of the generator, and the temperature of thesurrounding air. If, then, a small, suitably designed generator isworking quite slowly, the loss of heat through the external walls of theapparatus may easily be rapid enough to prevent the internal temperaturefrom rising objectionably high; but the larger the generator, and themore rapidly it is evolving gas, the less does this become possible. Since of the substances in or about a generator water is the one whichhas by far the largest capacity for absorbing heat, and since it is theonly substance to which any necessary quantity of heat can be safely orconveniently transmitted, it follows that the larger in size an acetylenegenerator is, or the more rapidly that generator is made to deliver gas, the more desirable is it to use water as the means for dissipating thesurplus heat, and the more necessary is it to employ an apparatus inwhich water is in large chemical excess at the actual place ofdecomposition. The argument is sometimes advanced that an acetylene generator containingcarbide in excess will work satisfactorily without exhibiting anundesirable rise in internal temperature, if the vessel holding thecarbide is merely surrounded by a large quantity of cold water. The ideais that the heat evolved in that particular portion of the charge whichis suffering decomposition will be communicated with sufficient speedthroughout the whole mass of calcium carbide present, whence it will passthrough the walls of the containing vessel into the water all round. Provided the generator is quite small, provided the carbide container isso constructed as to possess the maximum of superficial area with theminimum of cubical capacity (a geometrical form to which the sphere, andin one direction the cylinder, are diametrically opposed), and providedthe walls of the container do not become coated internally or externallywith a coating of lime or water scale so as to diminish in heat-transmitting power, an apparatus designed in the manner indicated isundoubtedly free from grave objection; but immediately any of thoseprovisions is neglected, trouble is likely to ensue, for the heat willnot disappear from the place of actual reaction at the necessary speed. Apparent proof that heat is not accumulating unduly in a water-jacketedcarbide container even when the generator is evolving gas at a fair speedis easy to obtain; for if, as usually happens, the end of the containerthrough which the carbide is inserted is exposed to the air, the hand maybe placed upon it, and it will be found to be only slightly warm to thetouch. Such a test, however, is inconclusive, and frequently misleading, because if more than a pound or two of carbide is present as an undividedmass, and if water is allowed to attack one portion of it, thatparticular portion may attain a high temperature while the rest iscomparatively cool: and if the bulk of the carbide is comparatively cool, naturally the walls of the containing vessel themselves remainpractically unheated. Three causes work together to prevent this heatbeing dissipated through the walls of the carbide vessel with sufficientrapidity. In the first place, calcium carbide itself is a very badconductor of heat. So deficient in heat-conducting power is it that alump a few inches in diameter may be raised to redness in a gas flame atone spot, and kept hot for some minutes, while the rest of the massremains sufficiently cool to be held comfortably in the fingers. In thesecond place, commercial carbide exists in masses of highly irregularshape, so that when they are packed into any vessel they only touch attheir angles and edges; and accordingly, even if the material were afairly good heat conductor of itself, the air or gas present between eachlump would act as an insulator, protecting the second piece from the heatgenerated in the first. In the third place, the calcium hydroxideproduced as the by-product when calcium carbide is decomposed by wateroccupies considerably more space than the original carbide--usually twoor three times as much space, the exact figures depending upon theconditions in which it is formed--and therefore a carbide containercannot advisedly be charged with more than one-third the quantity ofsolid which it is apparently capable of holding. The remaining two-thirdsof the space is naturally full of air when the container is first putinto the generator, but the air is displaced by acetylene as soon as gasproduction begins. Whether that space, however, is occupied by air, byacetylene, or by a gradually growing loose mass of slaked lime, eachseparate lump of hot carbide is isolated from its neighbours by amaterial which is also a very bad heat conductor; and the heat has butlittle opportunity of distributing itself evenly. Moreover, although ironor steel is a notably better conductor of heat than any of the othersubstances present in the carbide vessel, it is, as a metal, only a poorconductor, being considerably inferior in this respect to copper. If heatdissipation were the only point to be studied in the construction of anacetylene apparatus, far better results might be obtained by theemployment of copper for the walls of the carbide container; and possiblyin that case a generator of considerable size, fitted with a water-jacketed decomposing vessel, might be free from the trouble ofoverheating. Nevertheless it will be seen in Chapter VI. That the use ofcopper is not permissible for such purposes, its advantages as a goodconductor of heat being neutralised by its more important defects. When suitable precautions are not taken to remove the heat liberated inan acetylene apparatus, the temperature of the calcium carbideoccasionally rises to a remarkable degree. Investigating this point, Carohas studied the phenomena of heat production in a "dipping" generator--_i. E. _, an apparatus in which a cage of carbide is alternatelyimmersed in and lifted out of a vessel containing water. Using agenerator designed to supply five burners, he has found a maximumrecording thermometer placed in the gas space of the apparatus to givereadings generally between 60° and 100° C. ; but in two tests out of tenhe obtained temperatures of about 160° C. To determine the actualtemperature of the calcium carbide itself, he scattered amongst thecarbide charge fragments of different fusible metallic alloys which wereknown to melt or soften at certain different temperatures. In all his tentests the alloys melting at 120° C. Were fused completely; in two testsother alloys melting at 216° and 240° C. Showed signs of fusion; and inone test an alloy melting at 280° C. Began to soften. Working with anexperimental apparatus constructed on the "dripping" principle--_i. E. _, a generator in which water is allowed to fall in singledrops or as a fine stream upon a mass of carbide--with the deliberateobject of ascertaining the highest temperatures capable of productionwhen calcium carbide is decomposed in this particular fashion, andemploying for the measurement of the heat a Le Chatelier thermo-couple, with its sensitive wires lying among the carbide lumps, Lewes hasobserved a maximum temperature of 674° C. To be reached in 19 minuteswhen water was dripped upon 227 grammes of carbide at a speed of about 8grammes per minute. In other experiments he used a laboratory apparatusdesigned upon the "dipping" principle, and found maximum temperatures, infour different trials, of 703°, 734°, 754°, and 807° C. , which werereached in periods of time ranging from 12 to 17 minutes. Even allowingfor the greater delicacy of the instrument adopted by Lewes for measuringthe temperature in comparison with the device employed by Caro, therestill remains an astonishing difference between Caro's maximum of 280°and Lewes' maximum of 807° C. The explanation of this discrepancy is tobe inferred from what has just been said. The generator used by Caro wasproperly made of metal, was quite small in size, was properly designedwith some skill to prevent overheating as much as possible, and wasworked at the speed for which it was intended--in a word, it was as goodan apparatus as could be made of this particular type. Lewes' generatorwas simply a piece of glass and metal, in which provisions to avoidoverheating were absent; and therefore the wide difference between thetemperatures noted does not suggest any inaccuracy of observation orexperiment, but shows what can be done to assist in the dissipation ofheat by careful arrangement of parts. The difference in temperaturebetween the acetylene and the carbide in Caro's test accentuates thedifficulty of gauging the heat in a carbide vessel by mere externaltouch, and supplies experimental proof of the previous assertions as tothe low heat-conducting power of calcium carbide and of the gases of thedecomposing vessel. It must not be supposed that temperatures such asLewes has found ever occur in any commercial generator of reasonably gooddesign and careful construction; they must be regarded rather asindications of what may happen in an acetylene apparatus when thephenomena accompanying the evolution of gas are not understood by themaker, and when all the precautions which can easily be taken to avoidexcessive heating have been omitted, either by building a generator withcarbide in excess too large in size, or by working it too rapidly, ormore generally by adopting a system of construction unsuited to the endsin view. The fact, however, that Lewes has noted the production of atemperature of 807° C. Is important; because this figure is appreciablyabove the point 780° C. , at which acetylene decomposes into its elementsin the absence of air. Nevertheless the production of a temperature somewhat exceeding 100° C. Among the lumps of carbide actually undergoing decomposition can hardlybe avoided in any practical generator. Based on a suggestion in the"Report of the Committee on Acetylene Generators" which was issued by theBritish Home Office in 1902, Fouché has proposed that 130° C. , asmeasured with the aid of fusible metallic rods, [Footnote: An alloy madeby melting together 55 parts by weight of commercial bismuth and 45 partsof lead fuses at 127° C. , and should be useful in performing the tests. ]should be considered the maximum permissible temperature in any part of agenerator working at full speed for a prolonged period of time. Fouchéadopts this figure on the ground that 130° C. Sensibly corresponds withthe temperature at which a yellow substance is formed in a generator by aprocess of polymerisation; and, referring to French conditions, statesthat few actual apparatus permit the development of so high atemperature. As a matter of fact, however, a fairly high temperatureamong the carbide is less important than in the gas, and perhaps it wouldbe better to say that the temperature in any part of a generator occupiedby acetylene should not exceed 100° C. Fraenkel has carried out someexperiments upon the temperature of the acetylene immediately afterevolution in a water-to-carbide apparatus containing the carbide in asubdivided receptacle, using an apparatus now frequently described asbelonging to the "drawer" system of construction. When a quantity ofabout 7 lb. Of carbide was distributed between 7 different cells of thereceptacle, each cell of which had a capacity of 25 fluid oz. , and theapparatus was caused to develop acetylene at the rate of 7 cubic feet perhour, maximum thermometers placed immediately over the carbide in thedifferent cells gave readings of from 70° to 90° C. , the average maximumtemperature being about 80° C. Hence the Austrian code of rules issued in1905 governing the construction of acetylene apparatus contains a clauseto the effect that the temperature in the gas space of a generator mustnever exceed 80° C. ; whereas the corresponding Italian code contains asimilar stipulation, but quotes the maximum temperature as 100° C. (_vide_ Chapter IV. ). It is now necessary to see why the production of an excessively hightemperature in an acetylene generator has to be avoided. It must beavoided, because whenever the temperature in the immediate neighbourhoodof a mass of calcium carbide which is evolving acetylene under the attackof water rises materially above the boiling-point of water, one or moreof three several objectionable effects is produced--(_a_) upon thegas generated, (_b_) upon the carbide decomposed, and (_c_)upon the general chemical reaction taking place. It has been stated above that in moat generators when the action betweenthe carbide and the water is proceeding smoothly, it occurs according toequation (2)-- (2) CaC_2 + 2H_2O = C_2H_2 + Ca(OH)_2 rather than in accordance with equation (1)-- (1) CaC_2 + H_2O = C_2H_2 + CaO. This is because calcium oxide, or quicklime, the by-product in (1), hasconsiderable affinity for water, evolving a noteworthy quantity of heatwhen it combines with one molecule of water to form one molecule ofcalcium hydroxide, or slaked lime, the by-product in (2). If, then, asmall amount of water is added to a large amount of calcium carbide, thecorresponding quantity of acetylene may be liberated on the lines ofequation (1), and there will remain behind a mixture of unaltered calciumcarbide, together with a certain amount of calcium oxide. Inasmuch asboth these substances possess an affinity for water (setting heat freewhen they combine with it), when a further limited amount of water isintroduced into the mixture some of it will probably be attracted to theoxide instead of to the carbide present. It is well known that atordinary temperatures quicklime absorbs moisture, or combines with water, to produce slaked lime; but it is equally well known that in a furnace, at about a red heat, slaked lime gives up water and changes intoquicklime. The reaction, in fact, between calcium oxide and water isreversible, and whether those substances combine or dissociate is simplya question of temperature. In other words, as the temperature rises, theheat of hydration of calcium oxide diminishes, and calcium hydroxidebecomes constantly a less stable material. If now it should happen thatthe affinity between calcium carbide and water should not diminish, orshould diminish in a lower ratio than the affinity between calcium oxideand water as the temperature of the mass rises from one cause or other, it is conceivable that at a certain temperature calcium carbide might becapable of withdrawing the water of hydration from the molecule of slakedlime, converting the latter into quicklime, and liberating one moleculeof acetylene, thus-- (3) CaC_2 + Ca_2(OH) = C_2H_2 + 2CaO. It has been proved that a reaction of this character does occur, thetemperature necessary to determine it being given by Lewes as from 420°to 430° C. , which is not much more than half that which he found in agenerator having carbide in excess, albeit one of extremely bad design. Treating this reaction in the manner previously adopted, the thermo-chemical phenomena of equation (3) are: _Heat liberated. _ | _Heat liberated. _ |Formation of 2CaO 290. 0 | Formation of acetylene 58. 1 | Decomposition of Ca(OH)_2 [1] 229. 1 | Decomposition of carbide 3. 9 Balance 1. 1 | ______ | _____ | 291. 1 | 291. 1 [1 Footnote: Into its elements, Ca, O_2, and H_2; _cf. _ footnote, p: 31. ] Or, since the calcium hydroxide is only dehydrated without beingentirely decomposed, and only one molecule of water is broken up, it maybe written: Formation of CaO 145. 0 | Formation of acetylene 58. 1 | Decomposition of Ca(OH)_2 15. 1 | Decomposition of water 69. 0 Balance 1. 1 | Decomposition of carbide 3. 9 _____ | _____ | 146. 1 | 146. 1 which comes to the same thing. Putting the matter in another shape, itmay be said that the reaction between calcium carbide and water isexothermic, evolving either 14. 0 or 29. 1 calories according as thebyproduct is calcium oxide or solid calcium hydroxide; and thereforeeither reaction proceeds without external assistance in the cold. Thereaction between carbide and slaked lime, however, is endothermic, absorbing 1. 1 calories; and therefore it requires external assistance(presence of an elevated temperature) to start it, or continuousintroduction of heat (as from the reaction between the rest of thecarbide present and the water) to cause it to proceed. Of itself, andwere it not for the disadvantages attending the production of atemperature remotely approaching 400° C. In an acetylene generator, whichdisadvantages will be explained in the following paragraphs, there is noparticular reason why reaction (3) should not be permitted to occur, forit involves (theoretically) no loss of acetylene, and no waste of calciumcarbide. Only one specific feature of the reaction has to be remembered, and due practical allowance made for it. The reaction represented byequation (2) proceeds almost instantaneously when the calcium carbide isof ordinarily good quality, and the acetylene resulting therefrom iswholly generated within a very few minutes. Equation (3), on thecontrary, consumes much time for its completion, and the gascorresponding with it is evolved at a gradually diminishing speed whichmay cause the reaction to continue for hours--a circumstance that may behighly inconvenient or quite immaterial according to the design of theapparatus. When, however, it is desired to construct an automaticacetylene generator, _i. E. _, an apparatus in which the quantity ofgas liberated has to be controlled to suit the requirements of anyindefinite number of burners in use on different occasions, equation (3)becomes a very important factor in the case. To determine the normalreaction (No. 2) of an acetylene generator, 64 parts by weight of calciumcarbide must react with 36 parts of water to yield 26 parts by weight ofacetylene, and apparently both carbide and water are entirely consumed;but if opportunity is given for the occurrence of reaction (3), another64 parts by weight of carbide may be attacked, without the addition ofany more water, producing, inevitably, another 26 parts of acetylene. If, then, water is in chemical excess in the generator, all the calciumcarbide present will be decomposed according to equation (2), and theaction will take place without delay; after a few minutes' interval thewhole of the acetylene capable of liberation will have been evolved, andnothing further can possibly happen until another charge of carbide isinserted in the apparatus. If, on the other hand, calcium carbide is inchemical excess in the generator, all the water run in will be consumedaccording to equation (2), and this action will again take place withoutdelay; but unless the temperature of the residual carbide has been keptwell below 400° C. , a further evolution of gas will occur which will notcease for an indeterminate period of time, and which, by strict theory, given the necessary conditions, might continue until a second volume ofacetylene equal to that liberated at first had been set free. In practicethis phenomenon of a secondary production of gas, which is known as"after-generation, " is regularly met with in all generators where thecarbide is in excess of the water added; but the amount of acetylene soevolved rarely exceeds one-quarter or one-third of the main make. Theactual amount evolved and the rate of evolution depend, not merely uponthe quantity of undecomposed carbide still remaining in contact with thedamp lime, but also upon the rapidity with which carbide naturallydecomposes in presence of liquid water, and the size of the lumps. Where"after-generation" is caused by the ascent of water vapour round lumps ofcarbide, the volume of gas produced in a given interval of time islargely governed by the temperature prevailing and the shape of theapparatus. It is evident that even copious "after-generation" is a matterof no consequence in any generator provided with a holder to store thegas, assuming that by some trustworthy device the addition of water isstopped by the time that the holder is two-thirds or three-quarters full. In the absence of a holder, or if the holder fitted is too small to serveits proper purpose, "aftergeneration" is extremely troublesome andsometimes dangerous, but a full discussion of this subject must bepostponed to the next chapter. EFFECT OF HEAT ON ACETYLENE. --The effect of excessive retention of heatin an acetylene generator upon the gas itself is very marked, asacetylene begins spontaneously to suffer change, and to be converted intoother compounds at elevated temperatures. Being a purely chemicalphenomenon, the behaviour of acetylene when exposed to heat will be fullydiscussed in Chapter VI. When the properties of the gas are beingsystematically dealt with. Here it will be sufficient to assume that thecharacter of the changes taking place is understood, and only thepractical results of those changes as affecting the various components ofan acetylene installation have to be studied. According to Lewes, acetylene commences to "polymerise" at a temperature of about 600° C. , when it is converted into other hydrocarbons having the same percentagecomposition, but containing more atoms of carbon and hydrogen in theirmolecules. The formula of acetylene is C_2H_2 which means that 2 atoms ofcarbon and 2 atoms of hydrogen unite to form 1 molecule of acetylene, abody evidently containing roughly 92. 3 per cent. By weight of carbon and7. 7 per cent. By weight of hydrogen. One of the most noteworthysubstances produced by the polymerisation of acetylene is benzene, theformula of which is C_6H_6, and this is formed in the manner indicated bythe equation-- (4) 3C_2H_2 = C_6H_6. Now benzene also contains 92. 3 per cent. Of carbon and 7. 7 per cent. Byweight of hydrogen in its composition, but its molecule contains 6 atomsof each element. When the chemical formula representing a compound bodyindicates a substance which is, or can be obtained as, a gas or vapour, it convoys another idea over and above those mentioned on a previouspage. The formula "C_2H_2, " for example, means 1 molecule, or 26 parts byweight of acetylene, just as "H_2" means 1 molecule, or 2 parts by weightof hydrogen; but both formulæ also mean equal parts by volume of therespective substances, and since H_2 must mean 2 volumes, being twice H, which is manifestly 1, C_2H_2 must mean 2 volumes of acetylene as well. Thus equation (4) states that 6 volumes of acetylene, or 3 x 26 parts byweight, unite to form 2 volumes of benzene, or 78 parts by weight. Ifthese hydrocarbons are burnt in air, both are indifferently convertedinto carbon dioxide (carbonic acid gas) and water vapour; and, neglectingfor the sake of simplicity the nitrogen of the atmosphere, the processesmay be shown thus: (5) 2C_2H_2 + 5O_2 = 4CO_2 + 2H_2O. (6) 2C_6H_6 + 15O_2 = 12CO_2 + 6H_2O. Equation (5) shows that 4 volumes of acetylene combine with 10 volumes ofoxygen to produce 8 volumes of carbon dioxide and 4 of water vapour;while equation (6) indicates that 4 volumes of benzene combine with 30volumes of oxygen to yield 24 volumes of carbon dioxide and 12 of watervapour. Two parts by volume of acetylene therefore require 5 parts byvolume of oxygen for perfect combustion, whereas two parts by volume ofbenzene need 15--_i. E. _, exactly three times as much. In order towork satisfactorily, and to develop the maximum of illuminating powerfrom any kind of gas consumed, a gas-burner has to be designed withconsiderable skill so as to attract to the base of the flame preciselythat volume of air which contains the quantity of oxygen necessary toinsure complete combustion, for an excess of air in a flame is only lessobjectionable than a deficiency thereof. If, then, an acetylene burner isproperly constructed, as most modern ones are, it draws into the flameair corresponding with two and a half volumes of oxygen for every onevolume of acetylene passing from the jets; whereas if it were intendedfor the combustion of benzene vapour it would have to attract three timesthat quantity. Since any flame supplied with too little air tends to emitfree carbon or soot, it follows that any well-made acetylene burnerdelivering a gas containing benzene vapour will yield a more or lenssmoky flame according to the proportion of benzene in the acetylene. Moreover, at ordinary temperatures benzene is a liquid, for it boils at81° C. , and although, as was explained above in the case of water, it iscapable of remaining in the state of vapour far below its boiling-pointso long as it is suspended in a sufficiency of some permanent gas likeacetylene, if the proportion of vapour in the gas at any giventemperature exceeds a certain amount the excess will be precipitated inthe liquid form; while as the temperature falls the proportion of vapourwhich can be retained in a given volume of gas also diminishes to anoteworthy extent. Should any liquid, be it water or benzene, or anyother substance, separate from the acetylene under the influence of coldwhile the gas is passing through pipes, the liquid will run downwards tothe lowest points in those pipes; and unless due precautions are taken, by the insertion of draw-off cocks, collecting wells, or the like, towithdraw the deposited water or other liquid, it will accumulate in allbends, angles, and dips till the pipes are partly or completely sealedagainst the passage of gas, and the lights will either "jump" or beextinguished altogether. In the specific case of an acetylene generatorthis trouble is very likely to arise, even when the gas is not heatedsufficiently during evolution for polymerisation to occur and benzene orother liquid hydrocarbons to be formed, because any excess of waterpresent in the decomposing vessel is liable to be vaporised by the heatof the reaction--as already stated it is desirable that water shall be sovaporised--and will remain safely vaporised as long as the pipes are keptwarm inside or near the generator; but directly the pipes pass away fromthe hot generator the cooling action of the air begins, and some liquidwater will be immediately produced. Like the phenomenon of after-generation, this equally inevitable phenomenon of water condensation willbe either an inconvenience or source of positive danger, or will be amatter of no consequence whatever, simply as the whole acetyleneinstallation, including the service-pipes, is ignorantly or intelligentlybuilt. As long as nothing but pure polymerisation happens to the acetylene, aslong, that is to say, as it is merely converted into other hydrocarbonsalso having the general formula C_(2n)H_(2n), no harm will be done to thegas as regards illuminating power, for benzene burns with a still moreluminous flame than acetylene itself; nor will any injury result to thegas if it is required for combustion in heating or cooking stoves beyondthe fact that the burners, luminous or atmospheric, will be delivering amaterial for the consumption of which they are not properly designed. Butif the temperature should rise much above the point at which benzene isthe most conspicuous product of polymerisation, other far morecomplicated changes occur, and harmful effects may be produced in twoseparate ways. Some of the new hydrocarbons formed may interact to yielda mixture of one or more other hydrocarbons containing a higherproportion of carbon than that which is present in acetylene and benzene, together with a corresponding proportion of free hydrogen; the formerwill probably be either liquids or solids, while the latter burns with aperfectly non-luminous flame. Thus the quantity of gas evolved from thecarbide and passed into the holder is less than it should be, owing tothe condensation of its non-gaseous constituents. To quote an instance ofthis, Haber has found 15 litres of acetylene to be reduced in volume to10 litres when the gas was heated to 638° C. By other changes, some"saturated hydrocarbons, " _i. E. _, bodies having the general formulaC_nH_(2n+2), of which methane or marsh-gas, CH_4 is the best known, maybe produced; and those all possess lower illuminating powers thanacetylene. In two of those experiments already described, where Lewesobserved maximum temperatures ranging from 703° to 807° C. , samples ofthe gas which issued when the heat was greatest were submitted tochemical analysis, and their illuminating powers were determined. Thefigures he gives are as follows: I. II. Per Cent. Per Cent. Acetylene 70. 0 69. 7 Saturated hydrocarbons 11. 3 11. 4 Hydrogen 18. 7 18. 9 _____ _____ 100. 0 100. 0 The average illuminating power of these mixed gases is about 126 candlesper 5 cubic feet, whereas that of pure acetylene burnt under goodlaboratory conditions is 240 candles per 5 cubic feet. The product, itwill be seen, had lost almost exactly 50 per cent. Of its value as anilluminant, owing to the excessive heating to which it had been, exposed. Some of the liquid hydrocarbons formed at the same time are not limpidfluids like benzene, which is less viscous than water, but are thick oilysubstances, or even tars. They therefore tend to block the tubes of theapparatus with great persistence, while the tar adheres to the calciumcarbide and causes its further attack by water to be very irregular, oreven altogether impossible. In some of the very badly designed generatorsof a few years back this tarry matter was distinctly visible when theapparatus was disconnected for recharging, for the spent carbide wasexceptionally yellow, brown, or blackish in colour, [Footnote: As will bepointed out later, the colour of the spent lime cannot always be employedas a means for judging whether overheating has occurred in a generator. ]and the odour of tar was as noticeable as that of crude acetylene. There is another effect of heat upon acetylene, more calculated to bedangerous than any of those just mentioned, which must not be lost sightof. Being an endothermic substance, acetylene is prone to decompose intoits elements-- (7) C_2H_2 -> C_2 + H_2 whenever it has the opportunity; and the opportunity arrives if thetemperature of the gas risen to 780° C. , or if the pressure under whichthe gas is stored exceeds two atmospheres absolute (roughly 30 lb. Persquare inch). It decomposes, be it carefully understood, in the completeabsence of air, directly the smallest spark of red-hot material or ofelectricity, or directly a gentle shock, such as that of a fall or blowon the vessel holding it, is applied to any volume of acetylene existingat a temperature exceeding 780° or at a gross pressure of 30 lb. Persquare inch; and however large that volume may be, unless it is containedin tubes of very small diameter, as will appear hereafter, thedecomposition or dissociation into its elements will extend throughoutthe whole of the gas. Equation (7) states that 2 volumes of acetyleneyield 2 volumes of hydrogen and a quantity of carbon which would measure2 volumes were it obtained in the state of gas, but which, being a solid, occupies a space that may be neglected. Apparently, therefore, thedissociation of acetylene involves no alteration in volume, and shouldnot exhibit explosive effects. This is erroneous, because 2 volumes ofacetylene only yield exactly 2 volumes of hydrogen when both gases aremeasured at the same temperature, and all gases increase in volume astheir temperature rises. As acetylene is endothermic and evolves muchheat on decomposition, and as that heat must primarily be communicated tothe hydrogen, it follows that the latter must be much hotter than theoriginal acetylene; the hydrogen accordingly strives to fill a muchlarger space than that occupied by the undecomposed gas, and if that gasis contained in a closed vessel, considerable internal pressure will beset up, which may or may not cause the vessel to burst. What has been said in the preceding paragraph about the temperature atwhich acetylene decomposes is only true when the gas is free from anynotable quantity of air. In presence of air, acetylene inflames at a muchlower temperature, viz. , 480° C. In a manner precisely similar to that ofall other combustible gases, if a stream of acetylene issues into theatmosphere, as from the orifices of a burner, the gas catches fire andburns quietly directly any substance having a temperature of 480° C. Orupwards is brought near it; but if acetylene in bulk is mixed with thenecessary quantity of air to support combustion, and any object exceeding480° C. In temperature comes in contact with it, the oxidation of thehydrocarbon proceeds at such a high rate of speed as to be termed anexplosion. The proportion of air needed to support combustion varies withevery combustible material within known limits (_cf. _ Chapter VI. ), and according to Eitner the smallest quantity of air required to makeacetylene burn or explode, as the case may be, is 25 per cent. If, byignorant design or by careless manipulation, the first batches ofacetylene evolved from a freshly charged generator should contain morethan 25 per cent. Of air; or if in the inauguration of a new installationthe air should not be swept out of the pipes, and the first makes of gasshould become diluted with 25 to 50 per cent. Of air, any glowing bodywhose temperature exceeds 480° C. Will fire the gas; and, as in theformer instance, the flame will extend all through the mass of acetylenewith disastrous violence and at enormous speed unless the gas is storedin narrow pipes of extremely small diameter. Three practical lessons areto be learnt from this circumstance: first, tobacco-smoking must never bepermitted in any building where an escape of raw acetylene is possible, because the temperature of a lighted cigar, &c. , exceeds 480° C. ;secondly, a light must never be applied to a pipe delivering acetyleneuntil a proper acetylene burner has been screwed into the aperture;thirdly, if any appreciable amount of acetylene is present in the air, nooperation should be performed upon any portion of an acetylene plantwhich involves such processes as scraping or chipping with the aid of asteel tool or shovel. If, for example, the iron or stoneware sludge-pipeis choked, or the interior of the dismantled generator is blocked, andattempts are made to remove the obstruction with a hard steel tool, aspark is very likely to be formed which, granting the existence ofsufficient acetylene in the air, is perfectly able to fire the gas. Forall such purposes wooden implements only are best employed; but theremark does not apply to the hand-charging of a carbide-to-watergenerator through its proper shoot. Before passing to another subject, itmay be remarked that a quantity of air far less than that which causesacetylene to become dangerous is objectionable, as its presence is apt toreduce the illuminating power of the gas unduly. EFFECT OF HEAT ON CARBIDE. --Chemically speaking, no amount of heatpossible of attainment in the worst acetylene generator can affectcalcium carbide in the slightest degree, because that substance may beraised to almost any temperature short of those distinguishing theelectric furnace, without suffering any change or deterioration. In theabsence of water, calcium carbide is as inert a substance as can well beimagined: it cannot be made to catch fire, for it is absolutelyincombustible, and it can be heated in any ordinary flame for reasonableperiods of time, or thrown into any non-electrical furnace withoutsuffering in the least. But in presence of water, or of any liquidcontaining water, matters are different. If the temperature of anacetylene generator rises to such an extent that part of the gas ispolymerised into tar, that tar naturally tends to coat the residualcarbide lumps, and, being greasy in character, more or less completelyprotects the interior from further attack. Action of this nature not onlymeans that the acetylene is diminished in quantity and quality by partialdecomposition, but it also means that the make is smaller owing toimperfect decomposition of the carbide: while over and above this is theliability to nuisance or danger when a mass of solid residue containingsome unaltered calcium carbide is removed from the apparatus and thrownaway. In fact, whenever the residue of a generator is not so saturatedwith excess of water as to be of a creamy consistency, it should be putinto an uncovered vessel in the open air, and treated with some ten timesits volume of water before being run into any drain or closed pipe wherean accumulation of acetylene may occur. Even at temperatures far belowthose needed to determine a production of tar or an oily coating on thecarbide, if water attacks an excess of calcium carbide somewhat rapidly, there is a marked tendency for the carbide to be "baked" by the heatproduced; the slaked lime adhering to the lumps as a hard skin whichgreatly retards the penetration of more water to the interior. COLOUR OF SPENT CARBIDE. --In the early days of the industry, it wasfrequently taken for granted that any degradation in the colour of thespent lime left in an acetylene generator was proof that overheating hadtaken place during the decomposition of the carbide. Since both calciumoxide and hydroxide are white substances, it was thought that a brownish, greyish, or blackish residue must necessarily point to incipientpolymerisation of the gas. This view would be correct if calcium carbidewere prepared in a state of chemical purity, for it also is a white body. Commercial carbide, however, is not pure; it usually contains someforeign matter which tints the residue remaining after gasification. Whena manufacturer strives to give his carbide the highest gas-making powerpossible he frequently increases the proportion of carbon in the chargesubmitted to electric smelting, until a small excess is reached, whichremains in the free state amongst the finished carbide. Afterdecomposition the fine particles of carbon stain the moist lime a bluishgrey tint, the depth of shade manifestly depending upon the amountpresent. If such a sludge is copiously diluted with water, particles ofcarbon having the appearance and gritty or flaky nature of coke oftenrise to the surface or fall to the bottom of the liquid; whence they caneasily be picked out and identified as pure or impure carbon by simpletests. Similarly the lime or carbon put into the electric furnace maycontain small quantities of compounds which are naturally coloured; andwhich, reappearing in the sludge either in their original or in adifferent state of combination, confer upon the sludge theircharacteristic tinge. Spent lime of a yellowish brown colour isfrequently to be met with in circumstances that are clearly no reproachto the generator. Doubtless the tint is due to the presence of somecoloured metallic oxide or other compound which has escaped reduction inthe electric furnace. The colour which the residual lime afterwardsassumes may not be noticeable in the dry carbide before decomposition, either because some change in the colour-giving impurity takes placeduring the chemical reactions in the generator or because the tint issimply masked by the greyish white of the carbide and its free carbon. Hence it follows that a bad colour in the waste lime removed from agenerator only points to overheating and polymerisation of the acetylenewhen corroborative evidence is obtained--such as a distinct tarry smell, the actual discovery of oily or tarry matters elsewhere, or a gravereduction in the illuminating power of the gas. MAXIMUM ATTAINABLE TEMPERATURES. --In order to discover the maximumtemperature which can be reached in or about an acetylene generator whenan apparatus belonging to one of the best types is fed at a proper ratewith calcium carbide in lumps of the most suitable size, the followingcalculation may be made. In the first place, it will be assumed that noloss of heat by radiation occurs from the walls of the generator;secondly, the small quantity of heat taken up by the calcium hydroxideproduced will be ignored; and, thirdly, the specific heat of acetylenewill be assumed to be 0. 25, which is about its most probable value. Now, a hand-fed carbide-to-water generator will work with half a gallon ofwater for every 1 lb. Of carbide decomposed, quantities which correspondwith 320 grammes of water per 64 grammes (1 molecular weight) of carbide. Of those 320 grammes of water, 18 are chemically destroyed, leaving 302. The decomposition of 64 grammes of commercial carbide evolves 28 largecalories of heat. Assuming all the heat to be absorbed by the water, 28calories would raise 302 grammes through (28 X 1000 / 302) = 93° C. , _i. E. _, from 44. 6° F. To the boiling-point. Assuming all the heat tobe communicated to the acetylene, those 28 calories would raise the 26grammes of gas liberated through (28 X 1000 / 26 / 0. 25) = 4308° C. , ifthat were possible. But if, as would actually be the case, the heat weredistributed uniformly amongst the 302 grammes of water and the 20 grammesof acetylene, both gas and water would be raised through the same numberof degrees, viz. , 90. 8° C. [Footnote: Let x = the number of largecalories absorbed by the water; then 28 - x = those taken up by the gas. Then-- 1000x / 302 = 1000 (28 - x) / (26 X 0. 25) whence x = 27. 41; and 28 - x = 0. 59. Therefore, for water, the rise in temperature is-- 27. 41 X 1000 / 302 = 90. 8° C. ; and for acetylene the rise is-- 0. 59 X 1000 / 26 / 0. 25 = 90. 8° C. ] If the generator were designed on lines to satisfy the United States FireUnderwriters, it would contain 8. 33 lb. Of water to every 1 lb. Ofcarbide attacked; identical calculations then showing that the originaltemperature of the water and gas would be raised through 53. 7° C. Provided the carbide is not charged into such an apparatus in lumps oftoo large a size, nor at too high a rate, there will be no appreciableamount of local overheating developed; and nowhere, therefore, will therise in temperature exceed 91° in the first instance, or 54° C. In thesecond. Indeed it will be considerably smaller than this, because a largeproportion of the heat evolved will be lost by radiation through thegenerator walls, while another portion will be converted from sensibleinto latent heat by causing part of the water to pass off as vapour withthe acetylene. EFFECT OF HIGH TEMPERATURES ON GENERATORS. --As the temperature amongstthe carbide in any generator in which water is not present in largeexcess may easily reach 200° C. Or upwards, no material ought to beemployed in the construction of such generators which is not competent towithstand a considerable amount of heat in perfect safety. The ordinaryvarieties of soft solder applied with the bitt in all kinds of lightmetal-work usually melt, according to their composition, at about 180°C. ; and therefore this method of making joints is only suitable forobjects that are never raised appreciably in temperature above theboiling-point of water. No joint in an acetylene generator, the partialor complete failure of which would radically affect the behaviour of theapparatus, by permitting the charges of carbide and of water to come intocontact at an abnormal rate of speed, by allowing the acetylene to escapedirectly through the crack into the atmosphere, or by enabling the waterto run out of the seal of any vessel containing gas so as to set up afree communication between that vessel and the air, ought ever to be madeof soft solder--every joint of this character should be constructedeither by riveting, by bolting, or by doubly folding the metal sheets. Apparently, a joint constantly immersed in water on one side cannot risein temperature above the boiling-point of the liquid, even when its otherside is heated strongly; but since, even if a generator is not chargedwith naturally hard water, its fluid contents soon become "hard" bydissolution of lime, there is always a liability to the deposition ofwater scale over the joint. Such water scale is a very bad heatconductor, as is seen in steam boilers, so that a seam coated with anexceedingly thin layer of scale, and heated sharply on one side, willrise above the boiling-point of water even if the liquid on its oppositeside is ice-cold. For a while the film of scale may be quite water-tight, but after it has been heated by contact with the hot metal several timesit becomes brittle and cracks without warning. But there is a moreimportant reason for avoiding the use of plumbers' solder. It might seemthat as the natural hard, protective skin of the metal is liable to beinjured or removed by the bending or by the drilling or punching whichprecedes the insertion of the rivets or studs, an application of softsolder to such a joint should be advantageous. This is not true becauseof the influence of galvanic action. As all soft solders consist largelyof lead, if a joint is soldered, a "galvanic couple" of lead and iron, orof lead and zinc (when the apparatus is built of galvanised steel), isexposed to the liquid bathing it; and since in both cases the lead ishighly electro-negative to the iron or zinc, it is the iron or zinc whichsuffers attack, assuming the liquid to possess any corrosive propertieswhatever. Galvanised iron which has been injured during the joint-makingpresents a zinc-iron couple to the water, but the zinc protects the iron;if a lead solder is present, the iron will begin to corrode immediatelythe zinc has disappeared. In the absence of lead it is the less importantmetal, but in the presence of lead it is the more important (thefoundation) metal which is the soluble element of the couple. Wherepracticable, joints in an acetylene generator may safely be made bywelding or by autogenous soldering ("burning"), because no other metal isintroduced into the system; any other process, except that of riveting orfolding, only hastens destruction of the plant. The ideal method ofmaking joints about an acetylene generator is manifestly that ofautogenous soldering, because, as will appear in Chapter IX. Of thisbook, the most convenient and efficient apparatus for performing theoperation is the oxy-acetylene blow-pipe, which can be employed so as toconvert two separate pieces of similar metal into one homogeneous whole. In less critical situations in an acetylene plant, such as the partitionsof a carbide container, &c. , where the collapse of the seam or jointwould not be followed by any of the effects previously suggested, thereis less cause for prohibiting the use of unfortified solder; but evenhere, two or three rivets, just sufficient to hold the metal in positionif the solder should give way, are advisedly put into all apparatus. Inother portions of an acetylene installation where a merely soldered jointis exposed to warm damp gas which is in process of cooling, instead ofbeing bathed in hard water, an equal, though totally dissimilar, dangeris courted. The main constituent of such solders that are capable ofbeing applied with the bitt is lead; lead is distinctly soluble in softor pure water; and the water which separates by condensation out of awarm damp gas is absolutely soft, for it has been distilled. Ifcondensation takes place at or near a soldered joint in such a way thatwater trickles over the solder, by slow degrees the metallic lead will bedissolved and removed, and eventually a time will come when the joint isno longer tight to gas. In fact, if an acetylene installation is of morethan very small dimensions, _e. G. _, when it is intended to supplyany building as large as, or larger than, the average country residence, if it is to give satisfaction to both constructor and purchaser by beingquite trustworthy and, possessed of a due lease of life, say ten orfifteen years, it must be built of stouter materials than the lightsheets which alone are suitable for manipulation with the soldering-ironor for bending in the ordinary type of metal press. Sound cast-iron, heavy sheet-metal, or light boiler-plate is the proper substance of whichto construct all the important parts of a generator, and the joints inwrought metal must be riveted and caulked or soldered autogeneously asmentioned above. So built, the installation becomes much more costly tolay down than an apparatus composed of tinplate, zinc, or thin galvanisediron, but it will prove more economical in the long run. It is not toomuch to say that if ignorant and short-sighted makers in the earliestdays of the acetylene industry had not recommended and supplied to theircustomers lightly built apparatus which has in many instances alreadybegun to give trouble, to need repairs, and to fail by thoroughcorrosion--apparatus which frequently had nothing but cheapness in itsfavour--the use of the gas would have spread more rapidly than it hasdone, and the public would not now be hearing of partial or completefailures of acetylene installations. Each of these failures, whetheraccompanied by explosions and injury to persons or not, acts morepowerfully to restrain a possible new customer from adopting theacetylene light, than several wholly successful plants urge him to takeit up; for the average member of the public is not in a position todistinguish properly between the collapse of a certain generator owing todefective design or construction (which reflects no discredit upon thegas itself), and the failure of acetylene to show in practice thoseadvantages that have been ascribed to it. One peculiar and noteworthyfeature of acetylene, often overlooked, is that the apparatus isconstructed by men who may have been accustomed to gas-making plant alltheir lives, and who may understand by mere habit how to superintend achemical operation; but the same apparatus is used by persons whogenerally have no special acquaintance with such subjects, and who, verypossibly, have not even burnt coal-gas at any period of their lives. Hence it happens that when some thoughtless action on the part of thecountry attendant of an acetylene apparatus is followed by an escape ofgas from the generator, and by an accumulation of that gas in the housewhere the plant is situated, or when, in disregard of rules, he takes anaked light into the house and an explosion follows, the builderdismisses the episode as a piece of stupidity or wilful misbehaviour forwhich he can in nowise be held morally responsible; whereas the builderhimself is to blame for designing an apparatus from which an escape ofgas can be accompanied by sensible risks to property or life. Howeverunpalatable this assertion may be, its truth cannot be controverted;because, short of criminal intention or insanity on the part of theattendant, it is in the first place a mere matter of knowledge and skillso to construct an acetylene plant that an escape of gas is extremelyunlikely, even when the apparatus is opened for recharging, or when it ismanipulated wrongly; and in the second place, it is easy so to arrangethe plant that any disturbance of its functions which may occur shall befollowed by an immediate removal of the surplus gas into a place ofcomplete safety outside and above the generator-house. GENERATION AT LOW TEMPERATURES. --In all that has been said hitherto aboutthe reaction between calcium carbide and water being instantaneous, ithas been assumed that the two substances are brought together at or aboutthe usual temperature of an occupied room, _i. E. _, 15 degrees C. If, however, the temperature is materially lower than this, the speed of thereaction falls off, until at -5 degrees C. , supposing the water still toremain liquid, evolution of acetylene practically ceases. Even at thefreezing-point of pure water gas is produced but slowly; and if a lump ofcarbide is thrown on to a block of ice, decomposition proceeds so gentlythat the liberated acetylene may be ignited to form a kind of torch, while heat is generated with insufficient rapidity to cause the carbideto sink into the block. This fact has very important bearings upon themanipulation of an acetylene generator in winter time. It is evident thatunless precautions are taken those portions of an apparatus which containwater are liable to freeze on a cold night; because, even if thegenerator has been at work producing gas (and consequently evolving heat)till late in the evening, the surplus heat stored in the plant may escapeinto the atmosphere long before more acetylene has to be made, andobviously while frost is still reigning in the neighbourhood. If thewater freezes in the water store, in the pipes leading therefrom, in theholder seal, or in the actual decomposing chamber, a fresh batch of gasis either totally incapable of production, because the water cannot bebrought into contact with the calcium carbide in the apparatus, or it canonly be generated with excessive slowness because the carbide introducedfalls on to solid ice. Theoretically, too, there is a possibility thatsome portion of the apparatus--a pipe in particular--may be burst by thefreezing, owing to the irresistible force with which water expands whenit changes into the solid condition. Probably this last contingency, clearly accompanied as it would be by grave risk, is somewhat remote, allthe plant being constructed of elastic material; but in practice even asimple interference with the functions of a generator by freezing, ideally of no special moment, is highly dangerous, because of the greatlikelihood that hurried and wholly improper attempts to thaw it will bemade by the attendant. As it has been well known for many years that thesolidifying point of water can be lowered to almost any degree belownormal freezing by dissolving in it certain salts in definiteproportions, one of the first methods suggested for preventing theformation of ice in an acetylene generator was to employ such a salt, using, in fact, for the decomposition of the carbide some saline solutionwhich remains liquid below the minimum night temperature of the winterseason. Such a process, however, has proved unsuitable for the purpose inview; and the explanation of that fact is found in what has just beenstated: the "water" of the generator may admittedly be safely maintainedin the fluid state, but from so cold a liquid acetylene will not begenerated smoothly, if at all. Moreover, were it not so, a process ofthis character is unnecessarily expensive, although suitable salts arevery cheap, for the water of the generator is constantly being consumed, [Footnote: It has already been said that most generators "consume" a muchlarger volume of water than the amount corresponding with the chemicalreaction involved: the excess of water passing into the sludge or by-product. Thus a considerable quantity of any anti-freezing agent must bethrown aside each time the apparatus is cleaned out or its fluid contentsare run off. ] and as constantly needs renewal; which means that a freshbatch of salt would be required every time the apparatus was recharged, so long as frost existed or might be expected. A somewhat differentcondition obtains in the holder of an acetylene installation. Here, whenever the holder is a separate item in the plant, not constituting aportion of the generating apparatus, the water which forms the seal of arising holder, or which fills half the space of a displacement holder, lasts indefinitely; and it behaves equally well, whatever its temperaturemay be, so long as it retains a fluid state. This matter will bediscussed with greater detail at the end of Chapter III. At present thepoint to be insisted on is that the temperature in any constituent of anacetylene installation which contains water must not be permitted to fallto the freezing-point; while the water actually used for decompositionmust be kept well above that temperature. GENERATION AT HIGH TEMPERATURES. --At temperatures largely exceeding thoseof the atmosphere, the reaction between calcium carbide and water tendsto become irregular; while at a red heat steam acts very slowly uponcarbide, evolving a mixture of acetylene and hydrogen in place of pureacetylene. But since at pressures which do not materially exceed that ofthe atmosphere, water changes into vapour at 100° C. , above thattemperature there can be no question of a reaction between carbide andliquid water. Moreover, as has been pointed out, steam or water vapourwill continue to exist as such at temperatures even as low as thefreezing-point so long as the vapour is suspended among the particles ofa permanent gas. Between calcium carbide and water vapour a doubledecomposition occurs chemically identical with that between carbide andliquid water; but the physical effect of the reaction and its practicalbearings are considerably modified. The quantity of heat liberated when30 parts by weight of steam react with 64 parts of calcium carbide shouldbe essentially unaltered from that evolved when the reagent is in theliquid state; but the temperature likely to be attained when the speed ofreaction remains the same as before will be considerably higher for twoconspicuous reasons. In the first place, the specific heat of steam in isonly 0. 48, while that of liquid water is 1. 0. Hence, the quantity of heatwhich is sufficient to raise the temperature of a given weight of liquidwater through _n_ thermometric degrees, will raise the temperatureof the same weight of water vapour through rather more than 2 _n_degrees. In the second place, that relatively large quantity of heatwhich in the case of liquid water merely changes the liquid into avapour, becoming "latent" or otherwise unrecognisable, and which, asalready shown, forms roughly five-sixths of the total heat needed toconvert cold water into steam, has no analogue if the water haspreviously been vaporised by other means; and therefore the whole of theheat supplied to water vapour raises its sensible temperature, asindicated by the thermometer. Thus it appears that, except for thesufficient amount of cooling that can be applied to a large vesselcontaining carbide by surrounding it with a water jacket, there is no wayof governing its temperature satisfactorily if water vapour is allowed toact upon a mass of carbide--assuming, of course, that the reactionproceeds at any moderate speed, _e. G. _, at a rate much above thatrequired to supply one or two burners with gas. The decomposition which with perfect chemical accuracy has been stated tooccur quantitatively between 36 parts by weight, of water and 64 parts ofcalcium carbide scarcely ever takes place in so simple a fashion in anactual generator. Owing to the heat developed when carbide is in excess, about half the water is converted into vapour; and so the reactionproceeds in two stages: half the water added reacting with the carbide asa liquid, the other half, in a state of vapour, afterwards reactingsimilarly, [Footnote: This secondary reaction is manifestly only anothervariety of the phenomenon known as "after-generation" (cf. _ante_). After-generation is possible between calcium carbide and mechanicallydamp slaked lime, between carbide and damp gas, or between carbide andcalcium hydroxide, as opportunity shall serve. In all cases the carbidemust be in excess. ] or hardly reacting at all, as the case may be. Suppose a vessel, A B, somewhat cylindrical in shape, is charged withcarbide, and that water is admitted at the end called A. Suppose now (1)that the exit for gas is at the opposite end, B. As the lumps near A areattacked by half the liquid introduced, while the other half is changedinto steam, a current, of acetylene and water vapour travels over thecharge lying between the decomposing spot and the end B. During itspassage the second half of the water, as vapour, reacts with the excessof carbide, the first make of acetylene being dried, and more gas beingproduced. Thus a second quantity of heat is developed, equal by theory tothat previously evolved; but a second elevation in temperature, far moreserious, and far less under control, than the former also occurs; andthis is easily sufficient to determine some of those undesirable effectsalready described. Digressing for a moment, it may be admitted that thedesiccation of the acetylene produced in this manner is beneficial, evennecessary; but the advantages of drying the gas at this period of itstreatment are outweighed by the concomitant disadvantages and by thelater inevitable remoistening thereof. Suppose now (2) that both thewater inlet and the gas exit of the carbide cylinder are at the same end, A. Again half the added water, as liquid, reacts with the carbide itfirst encounters, but the hot stream of damp gas is not permitted totravel over the rest of the lumps extending towards B: it is forced toreturn upon its steps, leaving B practically untouched. The gasaccordingly escapes from the cylinder at A still loaded with watervapour, and for a given weight of water introduced much less acetylene isevolved than in the former case. The gas, too, needs drying somewhereelse in the plant; but these defects are preferable to the apparentsuperiority of the first process because overheating is, or can be, morethoroughly guarded against. PRESSURE IN GENERATORS. --Inasmuch as acetylene is prone to dissociate ordecompose into its elements spontaneously whenever its pressure reaches 2atmospheres or 30 lb. Per square inch, as well as when its temperature atatmospheric pressure attains 780° C. , no pressure approaching that of 2atmospheres is permissible in the generator. A due observance of thisrule, however, unlike a proper maintenance of a low temperature in anacetylene apparatus, is perfectly easy to arrange for. The only reasonfor having an appreciable positive pressure in any form of generatingplant is that the gas may be compelled to travel through the pipes and toescape from the burner orifices; and since the plant is only installed toserve the burners, that pressure which best suits the burners must bethrown by the generator or its holder. Therefore the highest pressure itis ever requisite to employ in a generator is a pressure sufficient(_a_) to lift the gasholder bell, or to raise the water in adisplacement holder, (_b_) to drive the gas through the varioussubsidiary items in the plant, such as washers and purifiers, (_c_)to overcome the friction in the service-pipes, [Footnote: This frictionmanifestly causes a loss of pressure, _i. E. _, a fall in pressure, asa gas travels along a pipe; and, as will be shown in Chapter VII. , it isthe fall in pressure in a pipe rather than the initial pressure at whicha gas enters a pipe that governs the volume of gas passing through thatpipe. The proper behaviour and economic working of a burner (acetylene orother, luminous or incandescent) naturally depend upon the pressure inthe pipe to which the burner is immediately attached being exactly suitedto the design of that burner, and have nothing to do with the fall inpressure occurring in the delivery pipes. It is therefore necessary tokeep entirely separate the ideas of proper burner pressure and of maximumdesirable fall in pressure within the service due to friction. ] and(d) to give at the points of combustion a pressure which isrequired by the particular burners adopted. In all except village ordistrict installations, (_c_) may be virtually neglected. When theholder has a rising bell, (_a_) represents only an inch or so ofwater; but if a displacement holder is employed the pressure needed towork it is entirely indeterminate, being governed by the size and shapeof the said holder. It will be argued in Chapter III. That a risingholder is always preferable to one constructed on the displacementprinciple. The pressure (d) at the burners may be taken at 4inches of water as a maximum, the precise figure being dependent upon thekind of burners--luminous, incandescent, boiling, &c. --attached to themain. The pressure (_b_) also varies according to circumstances, butaverages 2 or 3 inches. Thus a pressure in the generator exceeding thatof the atmosphere by some 12 inches of water--_i. E. _, by about 7oz. , or less than half a pound per square inch--is amply sufficient forevery kind of installation, the less meritorious generators withdisplacement holders only excepted. This pressure, it should be noted, isthe net or effective pressure, the pressure with which the gas raises theliquid in a water-gauge glass out of the level while the opposite end ofthe water column is exposed to the atmosphere. The absolute pressure in avessel containing gas at an effective pressure of 12 inches of water is 7oz. Plus the normal, insensible pressure of the atmosphere itself--say15-1/4 lb. Per square inch. The liquid in a barometer which measures thepressure of the atmosphere stands at a height of 30 inches only, becausethat liquid is mercury, 13. 6 times as heavy as water. Were it filled withwater the barometer would stand at (30 X 13. 6) = 408 inches, or 34 feet, approximately. Gas pressures are always measured in inches of watercolumn, because expressed either as pounds per square inch or as inchesof mercury, the figures would be so small as to give decimals of unwieldylength. It would of course be perfectly safe so to arrange an acetylene plantthat the pressure in the generating chamber should reach the 100 inchesof water first laid down by the Home Office authorities as the maximumallowable. There is, however, no appreciable advantage to be gained by sodoing, or by exceeding that pressure which feeds the burners best. Anyhigher original pressure involves the use of a governor at the exit ofthe plant, and a governor is a costly and somewhat troublesome piece ofapparatus that can be dispensed with in most single installations by aproper employment of a well-balanced rising holder. CHAPTER III THE GENERAL PRINCIPLES OF ACETYLENE GENERATION--ACETYLENE GENERATINGAPPARATUS Inasmuch as acetylene is produced by the mere interaction of calciumcarbide and water, that is to say, by simply bringing those twosubstances in the cold into mutual contact within a suitable closedspace, and inasmuch as calcium carbide can always be purchased by theconsumer in a condition perfectly fit for immediate decomposition, thepreparation of the gas, at least from the theoretical aspect, ischaracterised by extreme simplicity. A cylinder of glass or metal, closedat one end and open at the other, filled with water, and inverted in alarger vessel containing the same liquid, may be charged almostinstantaneously with acetylene by dropping into the basin a lump ofcarbide, which sinks to the bottom, begins to decompose, and evolves arapid current of gas, displacing the water originally held in theinverted cylinder or "bell. " If a very minute hole is drilled in the topof the floating bell, acetylene at once escapes in a steady stream, beingdriven out by the pressure of the cylinder, the surplus weight of whichcauses it to descend into the water of the basin as rapidly as gas issuesfrom the orifice. As a laboratory experiment, and provided the bell hasbeen most carefully freed from atmospheric air in the first instance, this escaping gas may be set light to with a match, and will burn with amore or loss satisfactory flame of high illuminating power. Such is anacetylene generator stripped of all desirable or undesirable adjuncts, and reduced to its most elementary form; but it is needless to say thatso simple an apparatus would not in any way fulfil the requirements ofeveryday practice. Owing to the inequality of the seasons, and to the irregular nature ofthe demand for artificial light and heat in all households, the capacityof the plant installed for the service of any institution or districtmust be amply sufficient to meet the consumption of the longest winterevening--for, as will be shown in the proper place, attempts to make anacetylene generator evolve gas more quickly than it is designed to do arefraught with many objections--while the operation of the plant, must beunder such thorough control that not only can a sudden and unexpecteddemand for gas be met without delay, but also that a sudden andunexpected interruption or cessation of the demand shall not be followedby any disturbance in the working of the apparatus. Since, on the onehand, acetylene is produced in large volumes immediately calcium carbideis wetted with water, so that the gas may be burnt within a minute or twoof its first evolution; and, on the other, that acetylene once preparedcan be stored without trouble or appreciable waste for reasonable periodsof time in a water-sealed gasholder closely resembling, in everything butsize, the holders employed on coal-gas works; it follows that there aretwo ways of bringing the output of the plant into accord with theconsumption of the burners. It is possible to make the gas only as andwhen it is required, or it is possible in the space of an hour or so, during the most convenient part of the day, to prepare sufficient to lastan entire evening, storing it in a gasholder till the moment arrives forits combustion. It is clear that an apparatus needing human attentionthroughout the whole period of activity would be intolerable in the caseof small installations, and would only be permissible in the case oflarger ones if the district supplied with gas was populous enough tojustify the regular employment of two men at least in or about thegenerating station. But with the conditions obtaining in such a countryas Great Britain, and in other lands where coal is equally cheap andaccessible, if a neighbourhood was as thickly populated as has beensuggested, it would be preferable on various grounds to lay down a coal-gas or electricity works; for, as has been shown in the first chapter, unless a very material fall in the price of calcium carbide should takeplace--a fall which at present is not to be expected--acetylene can onlybe considered a suitable and economical illuminant and heating agent forsuch places as cannot be provided cheaply with coal-gas or electriccurrent. To meet this objection, acetylene generators have been inventedin which, broadly speaking, gas is only produced when it is required, control of the chemical reaction devolving upon some mechanicalarrangement. There are, therefore, two radically different types ofacetylene apparatus to be met with, known respectively as "automatic" and"non-automatic" generators. In a non-automatic generator the whole of thecalcium carbide put into the apparatus is more or less rapidlydecomposed, and the entire volume of gas evolved from it is collected ina holder, there to await the moment of consumption. In an automaticapparatus, by means of certain devices which will be discussed in theirproper place, the act of turning on a burner-tap causes some acetylene tobe produced, and the act of turning it off brings the reaction to an end, thus obviating the necessity for storage. That, at any rate, is thelogical definition of the two fundamentally different kinds of generator:in automatic apparatus the decomposition of the carbide is periodicallyinterrupted in such fashion as more or less accurately to synchronisewith the consumption of gas; in the non-automatic variety decompositionproceeds without a break until the carbide vessels are empty. Unfortunately a somewhat different interpretation of these two words hasfound frequent acceptance, a generator being denominated non-automatic orautomatic according as the holder attached to it is or is not largeenough to store the whole of the acetylene which the charge of carbide iscapable of producing if it is decomposed all at once. Apart from the factthat a holder, though desirable, is not an absolutely indispensable partof an acetylene plant, the definition just quoted was sufficiently freefrom objection in the earliest days of the industry; but now efficientcommercial generators are to be met with which become either automatic ornon-automatic according to the manner of working them, while some wouldbe termed non-automatic which comprise mechanism of a conspicuously self-acting kind. AUTOMATIC AND NON-AUTOMATIC GENERATORS. --Before proceeding to a detaileddescription of the various devices which may be adopted to render anacetylene generator automatic in action, the relative advantages ofautomatic and non-automatic apparatus, irrespective of type, from theconsumer's point of view may be discussed. The fundamental ideaunderlying the employment of a non-automatic generator is that the wholeof the calcium carbide put into the apparatus shall be decomposed intoacetylene as soon after the charge is inserted as is natural in thecircumstances; so that after a very brief interval of time the generatingchambers shall contain nothing but spent lime and water, and the holderbe as full of gas as is ever desirable. In an automatic apparatus, thefundamental idea is that the generating chamber, or one at least ofseveral generating chambers, shall always contain a considerable quantityof undecomposed carbide, and some receptacle always contain a store ofwater ready to attack that carbide, so that whenever a demand for gasshall arise everything may be ready to meet it. Inasmuch as acetylene isan inflammable gas, it possesses all the properties characteristic ofinflammable gases in general; one of which is that it is always liable totake fire in presence of a spark or naked light, and another of which isthat it is always liable to become highly explosive in presence of anaked light or spark if, accidentally or otherwise, it becomes mixed withmore than a certain proportion of air. On the contrary, in the completeabsence of liquid or vaporised water, calcium carbide is almost as inerta body as it is possible to imagine: for it will not take fire, andcannot in any circumstances be made to explode. Hence it may be urgedthat a non-automatic generator, with its holder always containing a largevolume of the actually inflammable and potentially explosive acetylene, must invariably be more dangerous than an automatic apparatus which hasless or practically no ready-made gas in it, and which simply containswater in one chamber and unaltered calcium carbide in another. But whenthe generating vessels and the holder of a non-automatic apparatus areproperly designed and constructed, the gas in the latter is acetylenepractically free from air, and therefore while being, as acetyleneinevitably is, inflammable, is devoid of explosive properties, alwaysassuming, as must be the case in a water-sealed holder, that thetemperature of the gas is below 780° C. ; and also assuming, as mustalways be the case in good plant, that the pressure under which the gasis stored remains less than two atmospheres absolute. It is perfectlytrue that calcium carbide is non-inflammable and non-explosive, that itis absolutely inert and incapable of change; but so comprehensive anassertion only applies to carbide in its original drum, or in someimpervious vessel to which moisture and water have no access. Until it isexhausted, an automatic acetylene generator contains carbide in one placeand water in another, dependence being put upon some mechanicalarrangement to prevent the two substances coming into contactprematurely. Many of the devices adopted by builders of acetyleneapparatus for keeping the carbide and water separate, and for mixing themin the requisite quantities when the proper time arrives, are astrustworthy, perhaps, as it is possible for any automatic gear to be; butsome are objectionably complicated, and a few are positively inefficient. There are two difficulties which the designer of automatic mechanism hasto contend with, and it is doubtful whether he always makes a sufficientallowance for them. The first is that not only must calcium carbide andliquid water be kept out of premature contact, but that moisture, orvapour of water, must not be allowed to reach the carbide; oralternatively, that if water vapour reaches the carbide too soon, theundesired reaction shall not determine overheating, and the liberated gasbe not wasted or permitted to become a source of danger. The seconddifficulty encountered by the designer of automata is so to construct hisapparatus that it shall behave well when attended to by completelyunskilled labour, that it shall withstand gross neglect and resistpositive ill-treatment or mismanagement. If the automatic principle isadopted in any part of an acetylene apparatus it must be adoptedthroughout, so that as far as possible--and with due knowledge and skillit is completely possible--nothing shall be left dependent upon thememory and common sense of the gasmaker. For instance, it must not benecessary to shut a certain tap, or to manipulate several cocks beforeopening the carbide vessel to recharge it; it must not be possible forgas to escape backwards out of the holder; and either the carbide-feedgear or the water-supply mechanism (as the case may be) must beautomatically locked by the mere act of taking the cover off the carbidestore, or of opening the sludge-cock at the bottom. It would be anadvantage, even, if the purifiers and other subsidiary items of the plantwere treated similarly, arranging them in such fashion that gas should beautomatically prevented from escaping out of the rest of the apparatuswhen any lid was removed. In fact, the general notion of interlocking, which has proved so successful in railway signal-cabins and incarburetted water gas-plant for the prevention of accidents duo tocarelessness or overnight, might be copied in principle throughout anacetylene installation whenever the automatic system is employed. It is no part of the present argument, to allege that automaticgenerators are, and must always be, inherently dangerous. Automaticdevices of a suitable kind may be found in plenty which are remarkablysimple and highly trustworthy; but it would be too bold a statement tosay that any such arrangement is incapable of failure, especially whenput into the hands of a person untrained in the superintendence ofmachinery. The more reliable a piece of automatic mechanism proves itselfto be, the more likely is it to give trouble and inconvenience andutterly to destroy confidence when it does break down; because the betterit has behaved in the past, and the longer it has lasted withoutrequiring adjustment, the less likely is it that the attendant will be athand when failure occurs. By suitable design and by an intelligentemployment of safety-valves and blow-off pipes (which will be discussedin their proper place) it is quite easy to avoid the faintest possibilityof danger arising from an increase of pressure or an improperaccumulation of gas inside the plant or inside the building containingthe plant; but every time such a safety-valve or blow-off pipe comes intoaction a waste of gas occurs, which means a sacrifice of economy, andshows that the generator is not working as it should. As glass is a fragile and brittle substance, and as it is not capable ofbearing large, rapid, and oft-repeated alterations of temperature inperfect safety, it is not a suitable material for the construction ofacetylene apparatus or of portions thereof. Hence it follows that agenerator must be built of some non-transparent material which preventsthe interior being visible when the apparatus is at work. Although it iscomparatively easy, by the aid of a lamp placed outside the generator-shed in such a position as to throw its beams of light through a windowupon the plant inside, to charge a generator after dark; and although itis possible, without such assistance, by methodical habits and asystematic arrangement of utensils inside the building to charge agenerator even in perfect darkness, such an operation is to bedeprecated, for it is apt to lead to mistakes, it prevents any slightderangement in the installation from being instantly noticed, and itoffers a temptation to the attendant to break rules and to take a nakedlight with him. On all those grounds, therefore, it is highly desirablethat every manipulation connected with a generator shall be effectedduring the daytime, and that the apparatus-house shall be locked upbefore nightfall. But owing to the irregular habits engendered by modernlife it is often difficult to know, during any given day, how much gaswill be required in the ensuing evening; and it therefore becomesnecessary always to have, as ready-made acetylene, or as carbide in aproper position for instant decomposition, a patent or latent store ofgas more than sufficient in quantity to meet all possible requirements. Now, as already stated, a non-automatic apparatus has its store ofmaterial in the form of gas in a holder; and since this is preferablyconstructed on the rising or telescopic principle, a mere inspection ofthe height of the bell--on which, if preferred, a scale indicating itscontents in cubic feet or in burner-hours may be marked--suffices to showhow near the plant is to the point of exhaustion. In many types ofautomatic apparatus the amount of carbide remaining undecomposed at anymoment is quite unknown, or at best can only be deduced by a tedious andinexact calculation; although in some generators, where the store ofcarbide is subdivided into small quantities, or placed in severaldifferent receptacles, an inspection of certain levers or indicatorsgives an approximate idea as to the capacity of the apparatus for furthergas production. In any case the position of a rising holder is the mostobvious sign of the degree of exhaustion of a generator; and therefore, to render absolutely impossible a failure of the light during an evening, a non-automatic generator fitted with a rising holder is best. Since calcium carbide is a solid body having a specific gravity of 2. 2, water being unity, and since 1 cubic foot of water weighs 62. 4 lb. , inround numbers 137 lb. Of _compact_ carbide only occupy 1 cubic footof space. Again, since acetylene is a gas having a specific gravity of0. 91, air being unity, and since the specific gravity of air, water beingunity, is 0. 0013, the specific gravity of acetylene, water being unity, is roughly O. 00116. Hence 1 cubic foot of acetylene weighs roughly 0. 07lb. Furthermore, since 1 lb. Of good carbide evolves 5 cubic feet of gason decomposition with water, acetylene stored at atmospheric pressureoccupies roundly 680 times as much space as the carbide from which it hasbeen evolved. This figure by no means represents the actual state ofaffairs in a generator, because, as was explained in the previouschapter, a carbide vessel cannot be filled completely with solid; and, indeed, were it so "filled, " in ordinary language, much of its spacewould be still occupied with air. Nevertheless it is incontrovertiblethat an acetylene plant calculated to supply so many burners for so longa period of time must be very much larger if it is constructed on thenon-automatic principle, when the carbide is decomposed all at once, thanif the automatic system is adopted, when the solid remains unattackeduntil a corresponding quantity of gas is required for combustion. Clearlyit is the storage part of a non-automatic plant alone which must be somuch larger; the actual decomposing chambers may be of the same size oreven smaller, according to the system of generation to which theapparatus belongs. In practice this extra size of the non-automatic plantcauses it to exhibit two disadvantages in comparison with automaticapparatus, disadvantages which are less serious than they appear, or thanthey may easily be represented to be. In the first place, the non-automatic generator requires more space for its erection. If acetylenewere an illuminating agent suitable for adoption by dwellers in city orsuburb, where the back premises and open-air part of the messuage arereduced to minute proportions or are even non-existent, this objectionmight well be fatal. But acetylene is for the inhabitant of a countryvillage or the occupier of an isolated country house; and he has usuallyplenty of space behind his residence which he can readily spare. In thesecond place, the extra size of the non-automatic apparatus makes it moreexpensive to construct and more costly to instal. It is more cosily toconstruct and purchase because of its holder, which must be well built ona firm foundation and accurately balanced; it is more costly to instalbecause a situation must be found for the erection of the holder, and theapparatus-house may have to be made large enough to contain the holder aswell as the generator itself. As regards the last point, it may be saidat once that there is no necessity to place the holder under cover: itmay stand out of doors, as coal-gas holders do in England, for the sealof the tank can easily be rendered frost-proof, and the gas itself is notaffected by changes of atmospheric temperature beyond altering somewhatin volume. In respect of the other objections, it must be remembered thatthe extra expense is one of capital outlay alone, and therefore onlyincreases the cost of the light by an inappreciable amount, representinginterest and depreciation charges on the additional capital expenditure. The increased cost of a year's lighting due to these charges will amountto only 10 or 15 per cent, on the additional capital sunk. The extracapital sunk does not in any way increase the maintenance charges; andif, by having a large holder, additional security and trustworthiness areobtained, or if the holder leads to a definite, albeit illusive, sense ofextra security and trustworthiness, the additional expenditure may wellbe permissible or even advantageous. The argument is sometimes advanced that inasmuch as for the same, or asmaller, capital outlay as is required to instal a non-automaticapparatus large enough to supply at one charging the maximum amount oflight and heat that can ever be needed on the longest winter's night, anautomatic plant adequate to make gas for two or three evenings can belaid down, the latter must be preferable, because the attendant, in thelatter case, will only need to enter the generator-house two or threetimes a week. Such an argument is defective because it ignores theinfluence of habit upon the human being. A watch which must be woundevery day, or a clock which must be wound every week, on a certain day ofthe week, is seldom permitted to run down; but a watch requiring to bere-wound every other day, or a fourteen-day clock (used as such), wouldrarely be kept going. Similarly, an acetylene generator might be chargedonce a week or once a day without likelihood of being forgotten; but theoperation of charging at irregular intervals would certainly prove anuisance. With a non-automatic apparatus containing all its gas in theholder, the attendant would note the position of the bell each morning, and would introduce sufficient carbide to fill the holder full, or partlyfull, as the case might be; with an automatic apparatus he would betempted to trust that the carbide holders still contained sufficientmaterial to last another night. The automatic system of generating acetylene has undoubtedly oneadvantage in those climates where frost tends to occur frequently, butonly to prevail for a short period. As the apparatus is in operationduring the evening hours, the heat evolved will, or can be made to, suffice to protect the apparatus from freezing until the danger haspassed; whereas if the gas is generated of a morning in a non-automaticapparatus the temperature of the plant may fall to that of the atmospherebefore evening, and some portion may freeze unless special precautionsare taken to protect it. It was shown in Chapter II that overheating is one of the chief troublesto be guarded against in acetylene generators, and that the temperatureattained is a function of the speed at which generation proceeds. Seeingthat in an automatic apparatus the rate of decomposition depends on therate at which gas is being burnt, while in a non-automatic generator itis, or may be, under no control, the critic may urge that the reactionmust take place more slowly and regularly, and the maximum temperaturetherefore be lower, when the plant works automatically. This may be trueif the non-automatic generator is unskilfully designed or improperlymanipulated; but it is quite feasible to arrange an apparatus, especiallyone of the carbide-to-water or of the flooded-compartment type, in suchfashion that overheating to an objectionable extent is rendered whollyimpossible. In a non-automatic apparatus the holder is nothing but aholder and may be placed wherever convenient, even at a distance from thegenerating plant; in an automatic apparatus the holder, or a smallsimilarly constructed holder placed before the main storage vessel, hasto act as a water-supply governor, as the releasing gear for certaincarbide-food mechanism, or indeed as the motive power of such mechanism;and accordingly it must be close to the water or carbide store, and moreor less intimately connected by means of levers, or the like, with thereceptacle in which decomposition occurs. Sometimes the holder surrounds, or is otherwise an integral part of, the decomposing chamber, the wholeapparatus being made self-contained or a single structure with the objectof gaining compactness. But it is evident that such methods ofconstruction render additionally awkward, or even hazardous, any repairor petty operation to the generating portion of the plant; while the morecompletely the holder is isolated from the decomposing vessels the moreeasily can they be cleaned, recharged, or mended, without blowing off thestored gas and without interfering with the action of any burners thatmay be alight at the time. Owing to the ingenuity of inventors, and theexperience they have acquired in the construction of automatic acetyleneapparatus during the years that the gas has been in actual employment, itis going too far boldly to assert that non-automatic generators areinvariably to be preferred before their rivals. Still in view of thenature of the labour which is likely to be bestowed on any domesticplant, of the difficulty in having repairs or adjustments done quickly inoutlying country districts, and of the inconvenience, if not risk, attending upon any failure of the apparatus, the greater capital outlay, and the larger space required by non-automatic generators are in mostinstances less important than the economy in space and prime costcharacteristic of automatic machines when the defects of each are weighedfairly in the balance. Indeed, prolonged experience tends to show that aselection between non-automatic and automatic apparatus may frequently bemade on the basis of capacity. A small plant is undoubtedly much moreconvenient if automatic; a very large plant, such as that intended for apublic supply, is certainly better if non-automatic, but between thesetwo extremes choice may be exercised according to local conditions. CONTROL OF THE CHEMICAL REACTION. --Coming now to study the principlesunderlying the construction of an acetylene generator more closely itwill be seen that as acetylene is produced by bringing calcium carbideinto contact with water, the chemical reaction may be started either byadding the carbide to the water, or by adding the water to the carbide. Similarly, at least from the theoretical aspect, the reaction, may becaused to stop by ceasing to add carbide to water, or by ceasing to addwater to carbide. Apparently if water is added by degrees to carbide, until the carbide is exhausted, the carbide must always be in excess; andmanifestly, if carbide is added in small portions to water, the watermust always be in excess, which, as was argued in Chapter II. , isemphatically the more desirable position of affairs. But it in quitesimple to have carbide present in large excess of the water introducedwhen the whole generator is contemplated, and yet to have the wateralways in chemical excess in the desired manner; because to realise theadvantages of having water in excess, it is only necessary to subdividethe total charge of carbide into a number of separate charges which areeach so small that more than sufficient water to decompose and flood oneof them is permitted to enter every time the feed mechanism comes intoplay, or (in a non-automatic apparatus) every time the water-cock isopened; so arranging the charges that each one is protected from thewater till its predecessor, or its predecessor, have been whollydecomposed. Thus it is possible to regard either the carbide or the wateras the substance which has to be brought into contact with the other inspecified quantity. It is perhaps permissible to repeat that in theconstruction of an automatic generator there is no advantage to be gainedfrom regulating the supply of both carbide and water, because just as themutual decomposition will begin immediately any quantity of the one meetsany quantity of the other, so the reaction will cease (except in one caseowing to "after-generation") directly the whole of that material which isnot in chemical excess has been consumed-quite independently of theamount of the other material left unattacked. Being a liquid, andpossessing as such no definite shape or form of its own irrespective ofthe vessel in which it is held, water is by far the more convenient ofthe two substances to move about or to deliver in predetermined volume tothe decomposing chamber. A supply of water can be started instantaneouslyor cut oil as promptly by the movement of a cock or valve of the usualdescription; or it may be allowed to run down a depending pipe inobedience to the law of gravitation, and stopped from running down such apipe by opposing to its passage a gas pressure superior to thatgravitational force. In any one of several obvious ways the supply ofwater to a mass of carbide may be controlled with absolute certainty, andtherefore it should apparently follow that the make of acetylene shouldbe under perfect control by controlling the water current. On the otherhand, unless made up into balls or cartridges of some symmetrical form, calcium carbide exists in angular masses of highly irregular shape andsize. Its lumps alter in shape and size directly liquid water or moisturereaches them; a loose more or loss gritty powder, or a damp cohesive mud, being produced which is well calculated to choke any narrow aperture orto jam any moving valve. It is more difficult, therefore, by mechanicalagency to add a supply of carbide to a mass of water than to introduce asupply of water to a stationary mass of carbide; and far more difficultstill to bring the supply of carbide under perfect control with thecertainty that the movement shall begin and stop immediately the propertime arrives. But assuming the mechanical difficulties to be satisfactorily overcome, the plan of adding carbide to a stationary mass of water has severalchemical advantages, first, because, however the generator beconstructed, water will be in excess throughout the whole time of gasproduction; and secondly, because the evolution of acetylene willactually cease completely at the moment when the supply of carbide isinterrupted. There is, however, one particular type of generator in whichas a matter of fact the carbide is the moving constituent, viz. , the"dipping" apparatus (cf. _infra_), to which these remarks do notapply; but this machine, as will be seen directly, is, illogicallyperhaps, but for certain good reasons, classed among the water-to-carbideapparatus. All the mechanical advantages are in favour, as justindicated, of making water the moving substance; and accordingly, whenclassified in the present manner, a great majority of the generators nowon the markets are termed water-to-carbide apparatus. Their disadvantagesare twofold, though these may be avoided or circumvented: in all typessave one the carbide is in excess at the immediate place and time ofdecomposition; and in all types without exception the carbide in thewhole of the generator is in excess, so that the phenomenon of "after-generation" occurs with more or less severity. As explained in the lastchapter, after-generation is the secondary production of acetylene whichtakes place more or less slowly after the primary reaction is finished, proceeding either between calcium hydroxide, merely damp lime, or dampgas and calcium carbide, with an evolution of more acetylene. As it ispossible, and indeed usual, to fit a holder of some capacity even to anautomatic generator, the simple fact that more acetylene is liberatedafter the main reaction is over does not matter, for the gas can besafely stored without waste and entirely without trouble or danger. Thereal objection to after-generation is the difficulty of controlling thetemperature and of dissipating the heat with which the reaction isaccompanied. It will be evident that the balance of advantage, weighingmechanical simplicity against chemical superiority, is somewhat evenbetween carbide-to-water and water-to-carbide generators of the propertype; but the balance inclines towards the former distinctly in the easeof non-automatic apparatus, and points rather to the latter whenautomatism is desired. In the early days of the industry it would havebeen impossible to speak so favourably of automatic carbide-to-watergenerators, for they were at first constructed with absurdly complicatedand unreliable mechanism; but now various carbide-feed gears have beendevised which seem to be trustworthy even when carbide not in cartridgeform is employed. NON-AUTOMATIC CARBIDE-TO-WATER GENERATORS. --There is little to be said inthe present place about the principles underlying the construction ofnon-automatic generators. Such apparatus may either be of the carbide-to-water or the water-to-carbide type. In the former, lumps of carbide aredropped by hand down a vertical or sloping pipe or shoot, which opens atits lower end below the water-level of the generating chamber, and whichis fitted below its mouth with a deflector to prevent the carbide fromlodging immediately underneath that mouth. The carbide falls through thewater which stands in the shoot itself almost instantaneously, but duringits momentary descent a small quantity of gas is evolved, which producesan unpleasant odour unless a ventilating hood is fixed above the upperend of the tube. As the ratio of cubical contents to superficial area ofa lump is greater as the lump itself is larger, and as only the outersurface of the lump can be attacked by the water in the shoot during itsdescent, carbide for a hand-fed carbide-to-water generator should be infairly large masses--granulated material being wholly unsuitable--andthis quite apart from the fact that large carbide is superior to small ingas-making capacity, inasmuch as it has not suffered the inevitableslight deterioration while being crushed and graded to size. If carbideis dropped too rapidly into such a generator which is not provided with afalse bottom or grid for the lumps to rest upon, the solid is apt todescend among a mass of thick lime sludge produced at a former operation, which lies at the bottom of the decomposing chamber; and here it may beprotected from the cooling action of fresh water to such an extent thatits surface is baked or coated with a hard layer of lime, whileoverheating to a degree far exceeding the boiling-point of water mayoccur locally. When, however, it falls upon a grid placed some distanceabove the bottom of the water vessel, the various convection currents setup as parts of the liquid become warm, and the mechanical agitationsproduced by the upward current of gas rinse the spent lime from thecarbide, and entirely prevent overheating, unless the lumps areexcessively large in size. If the carbide charged into a hand-fedgenerator is in very large lumps there is always a possibility thatoverheating may occur in the centre of the masses, due to the baking ofthe exterior, even if the generator is fitted with a reaction grid. Manifestly, when carbide in lumps of reasonable size is dropped intoexcess of water which is not merely a thick viscid cream of lime, thetemperature cannot possibly exceed the boiling-point--_i. E. _, 100°C. --provided always the natural convection currents of the water areproperly made use of. The defect which is, or rather which may be, characteristic of a hand-fedcarbide-to-water generator is a deficiency of gas yield due tosolubility. At atmospheric temperatures and pressure 10 volumes of waterdissolve 11 volumes of acetylene, and were the whole of the water in alarge generator run to waste often, a sensible loss of gas would ensue. If the carbide falls nearly to the bottom of the water column, the risinggas is forced to bubble through practically the whole of the liquid, sothat every opportunity is given it to dissolve in the manner indicatedtill the liquid is completely saturated. The loss, however, is not nearlyso serious as is sometimes alleged, because (1) the water becomes heatedand so loses much of its solvent power; and (2) the generator is workedintermittently, with sufficiently long intervals to allow the spent limeto settle into a thick cream, and only that thick cream is run off, whichrepresents but a small proportion of the total water present. Moreover, ahand-fed carbide-to-water generator will work satisfactorily with onlyhalf a gallon [Footnote: The United States National Board of FireUnderwriters stipulates for the presence of 1 (American) gallon of waterfor every 1 lb. Of carbide before such an apparatus is "permitted. " Thisquantity of liquid might retain nearly 4 per cent. Of the total acetyleneevolved. Even this is an exaggeration; for neither her, nor in thecorresponding figure given in the text, is any allowance made for thediminution in solvent power of the water as it becomes heated by thereaction. ] of liquid present for every 1 lb. Of carbide decomposed, andwere all this water run off and a fresh quantity admitted before eachfresh introduction of carbide, the loss of acetylene by dissolution couldnot exceed 2 per cent. Of the total make, assuming the carbide to becapable of yielding 5 cubic feet of gas per lb. Admitting, however, thatsome loss of gas does occur in this manner, the defect is partly, if notwholly, neutralised by the concomitant advantages of the system: (1)granted that the generator is efficiently constructed, decomposition ofthe carbide is absolutely complete, so that no loss of gas occurs in thisfashion; (2) the gas is evolved at a low temperature, so that it isunaccompanied, by products of polymerisation, which may block the leadingpipes and must reduce the illuminating power; (3) the acetylene is notmixed with air (as always happens at the first charging of a water-to-carbide apparatus), which also lowers the illuminating power; and (4) thegas is freed from two of its three chief impurities, viz. , ammonia andsulphuretted hydrogen, in the generating chamber itself. To prevent theloss of acetylene by dissolution, carbide-to-water generators areoccasionally fitted with a reaction grid placed only just below thewater-level, so that the acetylene has no more than 1 inch or so ofliquid to bubble through. The principle is wrong, because hot water beinglighter than cold, the upper layers may be raised to the boiling-point, and even converted into steam, while the bulk of the liquid still remainscold; and if the water actually surrounding the carbide is changed intovapour, nearly all control over the temperature attending the reaction islost. The hand-fed carbide-to-water generator is very simple and, as alreadyindicated, has proved itself perhaps the best type of all for theconstruction of very large installations; but the very simplicity of thegenerator has caused it more than once to be built in a manner that hasnot given entire satisfaction. As shown at L in Fig. 6, p. 84, thegenerator essentially consists of a closed cylindrical vesselcommunicating at its top with a separate rising holder. At one side asdrawn, or disposed concentrically if so preferred, is an open-mouthedpipe or shoot (American "shute") having its lower open extremity belowthe water-level. Into this shoot are dropped by hand or shovel lumps ofcarbide, which fall into the water and there suffer decomposition. As thebottom of the shoot is covered with water, which, owing to the smalleffective gas pressure in the generator given by the holder, stands a fewinches higher in the shoot than in the generator, gas cannot escape fromthe shoot; because before it could do so the water in the generator wouldhave to fall below the level of the point _a_, being either drivenout through the shoot or otherwise. Since the point _b_ of the shootextends further into the generator than _a_, the carbide dropscentrally, and as the bubbles of gas rise vertically, they have noopportunity of ascending into the shoot. In practice, the generator isfitted with a conical bottom for the collection of the lime sludge andwith a cock or other aperture at the apex of the cone for the removal ofthe waste product. As it is not desirable that the carbide should beallowed to fall directly from the shoot into the thicker portion of thesludge within the conical part of the generator, one or more grids isusually placed in the apparatus as shown by the dotted lines in thesketch. It does not seem that there is any particular reason for theemployment of more than one grid, provided the size of the carbidedecomposed is suited to the generator, and provided the mesh of the gridis suited to the size of the carbide. A great improvement, however, ismade if the grid is carried on a horizontal spindle in such a way that itcan be rocked periodically in order to assist in freeing the lumps ofcarbide from the adhering particles of lime. As an alternative to themovable grid, or even as an adjunct thereto, an agitator scraping theconical sides of the generator may be fitted which also assists inensuring a reasonably complete absence of undecomposed carbide from thesludge drawn off at intervals. A further point deserves attention. Ifconstructed in the ideal manner shown in Fig. 6 removal of some of thesludge in the generator would cause the level of the liquid to descendand, by carelessness, the level might fall below the point _a_ atthe base of the shoot. In these circumstances, if gas were unable toreturn from the holder, a pressure below that of the atmosphere would beestablished in the gas space of the generator and air would be drawn inthrough the shoot. This air might well prove a source of danger whengeneration was started again. Any one of three plans may be adopted toprevent the introduction of air. A free path may be left on the gas-mainpassing from the generator to the holder so that gas may be free toreturn and so to maintain the usual positive pressure in the decomposingvessel; the sludge may be withdrawn into some vessel so small in capacitythat the shoot cannot accidentally become unsealed; or the waterspace ofthe generator may be connected with a water-tank containing a ball-valveattached to a constant service of water be that liquid runs in as quicklyas sludge is removed, and the level remains always at the same height. The first plan is only a palliative and has two defects. In the firstplace, the omission of any non-return valve between, the generator andthe next item in the train of apparatus is objectionable of itself; inthe second place, should a very careless attendant withdraw too muchliquid, the shoot might become unsealed and the whole contents of theholder be passed into the air of the building containing the apparatusthrough the open mouth of the shoot. The second plan is perfectly sound, but has the practical defect of increasing the labour of cleaning thegenerator. The third plan is obviously the best. It can indeed be adoptedwhere no real constant service of water is at hand by connecting thegenerator to a water reservoir of relatively large size and by making thelatter of comparatively large transverse area, in proportion to itsdepth; so that the escape of even a largo volume of water from thereservoir may not involve a large reduction in the level at which itstands there. The dust that always clings to lumps of carbide naturally decomposes withextreme rapidity when the material is thrown into the shoot of a carbide-to-water generator, and the sudden evolution of gas so produced has onmore than one occasion seriously alarmed the attendant on the plant. Moreover, to a trifling extent the actual superficial layers of thecarbide suffer attack before the lumps reach the true interior of thegenerator, and a small loss of gas thereby occurs through the open mouthof the shoot. To remove these objections to the hand-fed generator it hasbecome a common practice in large installations to cause the lower end ofthe shoot to dip under the level of some oil contained in an appropriatereceptacle, the carbide falling into a basket carried upon a horizontalspindle. The basket and its support are so arranged that when a suitablecharge of carbide has been dropped into it, a partial rotation of anexternal hand-wheel lifts the basket and carbide out of the oil into anair-tight portion of the generator where the surplus oil can drain awayfrom the lumps. A further rotation of the hand-wheel then tips the basketover a partition inside the apparatus, allowing the carbide to fall intothe actual decomposing chamber. This method of using oil has theadvantage of making the evolution of acetylene on a large scale appear toproceed more quietly than usual, and also of removing the dust from thecarbide before it reaches the water of the generator. The oil itselfobviously does not enter the decomposing chamber to any appreciableextent and therefore does not contaminate the final sludge. The wholeprocess accordingly lies to be favourably distinguished from those othermethods of employing oil in generators or in the treatment of carbidewhich are referred to elsewhere in this book. NON-AUTOMATIC WATER-TO-CARBIDE GENERATORS. --The only principle underlyingthe satisfactory design of a non-automatic water-to-carbide generator isto ensure the presence of water in excess at the spot where decompositionis taking place. This may be effected by employing what is known as the"flooded-compartment" system of construction, _i. E. _, by subdividingthe total carbide charge into numerous compartments arranged eithervertically or horizontally, and admitting the water in interruptedquantities, each more than sufficient thoroughly to decompose andsaturate the contents of one compartment, rather than in a slow, steadystream. It would be quite easy to manage this without adopting anymechanism of a moving kind, for the water might be stored in a tank keptfull by means of a ball-valve, and admitted to an intermediate reservoirin a slow, continuous current, the reservoir being fitted with aninverted syphon, on the "Tantalus-cup" principle, so that it should firstfill itself up, and then suddenly empty into the pipe leading to thecarbide container. Without this refinement, however, a water-to-carbidegenerator, with subdivided charge, behaves satisfactorily as long as eachseparate charge of carbide is so small that the heat evolved on itsdecomposition can be conducted away from the solid through the water-jacketed walls of the vessel, or as the latent heat of steam, withsufficient rapidity. Still it must be remembered that a water-to-carbidegenerator, with subdivided charge, does not belong to the flooded-compartment type if the water runs in slowly and continuously: it is thensimply a "contact" apparatus, and may or may not exhibit overheating, aswell as the inevitable after-generation. All generators of the water-to-carbide type, too, must yield a gas containing some air in the earlierportions of their make, because the carbide containers can only be filledone-third or one-half full of solid. Although the proportion of air sopassed into the holder may be, and usually is, far too small in amount torender the gas explosive or dangerous in the least degree, it may well besufficient to reduce the illuminating power appreciably until it is sweptout of the service by the purer gas subsequently generated. Moreover, allwater-to-carbide generators are liable, as just mentioned, to producesufficient overheating to lower the illuminating power of the gaswhenever they are wilfully driven too fast, or when they are reputed bytheir makers to be of a higher productive capacity than they actuallyshould be; and all water-to-carbide generators, excepting those where thecarbide is thoroughly soaked in water at some period of their operation, are liable to waste gas by imperfect decomposition. DEVICES TO SECURE AUTOMATIC ACTION, --The devices which are commonlyemployed to render a generator automatic in action, that is to say, tocontrol the supply of one of the two substances required in theintermittent evolution of gas, may be divided into two broad classes: (A)those dependent upon the position of a rising-holder bell, and (B) thosedependent upon the gas pressure inside the apparatus. As the bell of arising holder descends in proportion as its gaseous contents areexhausted, it may (A^1) be fitted with some laterally projecting pinwhich, arrived at a certain position, actuates a series of rods orlevers, and either opens a cock on the water-supply pipe or releases amechanical carbide-feed gear, the said cock being closed again or thefeed-gear thrown out of action when the pin, rising with the bell, oncemore passes a certain position, this time in its upward path. Secondly(A^2), the bell may be made to carry a perforated receptacle containingcarbide, which is dipped into the water of the holder tank each time thebell falls, and is lifted out of the water when it rises again. Thirdly(A^3), by fitting inside the upper part of the bell a false interior, conical in shape, the descent of the bell may cause the level of thewater in the holder tank to rise until it is above some lateral aperturethrough which the liquid may escape into a carbide container placedelsewhere. These three methods are represented in the annexed diagram(Fig. 1). In Al the water-levels in the tank and bell remain always at_l_, being higher in the tank than in the bell by a distancecorresponding with the pressure produced by the bell itself. As the bellfalls a pin _X_ moves the lever attached to the cock on the water-pipe, and starts, or shuts off, a current passing from a store-tank orreservoir to a decomposing vessel full of carbide. It is also possible tomake _X_ work some releasing gear which permits carbide to fall intowater--details of this arrangement are given later on. In A^1 the waterin the tank serves as a holder seal only, a separate quantity beingemployed for the purposes of the chemical reaction. This arrangement hasthe advantage that the holder water lasts indefinitely, except forevaporation in hot weather, and therefore it may be prevented fromfreezing by dissolving in it some suitable saline body, or by mixing withit some suitable liquid which lowers its point of solidification. It willbe observed, too, that in A^1 the pin _X_, which derives its motivepower from the surplus weight of the falling bell, has always preciselythe same amount of work to do, viz. , to overcome the friction of the plugof the water-cock in its barrel. Hence at all times the pressureobtaining in the service-pipe is uniform, except for a slight jerkmomentarily given each time the cock is opened or closed. When _X_actuates a carbide-feed arrangement, the work it does may or may not varyon different occasions, as will appear hereafter. In A^2 the bell itselfcarries a perforated basket of carbide, which is submerged in the waterwhen the bell falls, and lifted out again when it rises. As the carbideis thus wetted from below, the lower portion of the mass soon becomes alayer of damp slaked lime, for although the basket is raised completelyabove the water-level, much liquid adheres to the spent carbide bycapillary attraction. Hence, even when the basket is out of the water, acetylene is being produced, and it is produced in circumstances whichprevent any control over the temperature attained. The water clinging tothe lower part of the basket is vaporised by the hot, half-spent carbide, and the steam attacks the upper part, so that polymerisation of the gasand baking of the carbide are inevitable. In the second place, thepressure in the service-pipe attached to A^2 depends as before upon thenet weight of the holder bell; but here that net weight is made up of theweight of the bell itself, that of the basket, and that of the carbide itcontains. Since the carbide is being gradually converted into damp slakedlime, it increases in weight to an indeterminate extent as the generatorin exhausted; but since, on the other hand, some lime may be washed outof the basket each time it is submerged, and some of the smallerfragments of carbide may fall through the perforations, the basket tendsto decrease in weight as the generator is exhausted. Thus it happens inA^2 that the combined weight of bell plus basket plus contents is whollyindefinite, and the pressure in the service becomes so irregular that aseparate governor must be added to the installation before the burnerscan be expected to behave properly. In the third place, the water in thetank serves both for generation and for decomposition, and this involvesthe employment of some arrangement to keep its level fairly constant lestthe bell should become unsealed, while protection from frost by saline orliquid additions is impossible. A^2 is known popularly as a "dipping"generator, and it will be seen to be defective mechanically and badchemically. In both A^1 and A^2 the bell is constructed of thin sheet-metal, and it is cylindrical in shape; the mass of metal in it istherefore negligible in comparison with the mass of water in the tank, and so the level of the liquid is sensibly the same whether the bell behigh or low. In A^3 the interior of the bell is fitted with a circularplate which cuts off its upper corners and leaves a circumferential space_S_ triangular in vertical section. This space is always full ofair, or air and water, and has to be deducted from the available storagecapacity of the bell. Supposing the bell transparent, and viewing it fromabove, its effective clear or internal diameter will be observed to besmaller towards the top than near the bottom; or since the space _S_is closed both against the water and against the gas, the walls of thebell may be said to be thicker near its top. Thus it happens that as thebell descends into the water past the lower angle of _S_, it beginsto require more space for itself in the tank, and so it displaces thewater until the levels rise. When high, as shown in the sketch markedA^3(a), the water-level is at _l_, below the mouth of a pipe_P_; but when low, as in A^3(b), the water is raised to the point_l'_, which is above _P_. Water therefore flows into _P_, whence it reaches the carbide in an attached decomposing chamber. Herealso the water in the tank is used for decomposition as well as forsealing purposes, and its normal level must be maintained exactly at_l_, lest the mouth of _P_ should not be covered whenever thebell falls. [Illustration: FIG. 1. --TYPICAL METHODS OF AUTOMATIC GENERATIONCONTROLLED BY BELL GASHOLDER. ] The devices employed to render a generator automatic which depend uponpressure (B) are of three main varieties: (B^1) the water-level in thedecomposing chamber may be depressed by the pressure therein until itssurface falls below a stationary mass of carbide; (B^2) the level in awater-store tank may be depressed until it falls below the mouth of apipe leading to the carbide vessel; (B^3) the current of water passingdown a pipe to the decomposing chamber may be interrupted by the actionof a pressure superior to the force of gravitation. These arrangementsare indicated roughly in Fig. 2. In B^1, D is a hollow cylinder closed atall points except at the cock G and the hole E, which are always belowthe level of the water in the annulus F, the latter being open to the airat its top. D is rigidly fastened to the outer vessel F so that it cannotmove vertically, and the carbide cage is rigidly fastened to D. Normallythe water-levels are at _l_, and the liquid has access to thecarbide through perforations in the basket. Acetylene is thus produced;but if G is shut, the gas is unable to escape, and so it pressesdownwards upon the water until the liquid falls in D to the dotted line_l"_, rising in F to the dotted line _l'_. The carbide is thenout of water, and except for after-generation, evolution of gas ceases. On opening G more or less fully, the water more or less quickly reachesits original position at _l_, and acetylene is again produced. Manifestly this arrangement is identical with that of A^2 as regards theperiodical immersion of the carbide holder in the liquid; but it is evenworse than the former mechanically because there is no rising holder inB^1, and the pressure in the service is never constant. B^2 representsthe water store of an unshown generator which works by pressure. Itconsists of a vessel divided vertically by means of a partition having asubmerged hole N. One-half, H, is cloned against the atmosphere, butcommunicates with the gas space of the generator through L; the otherhalf, K, is open to the air. M is a pipe leading water to the carbide. When gas is being burnt as fast as, or faster than, it is being evolved, the pressure in the generator is small, the level of the water stands at_l_, and the mouth of M is below it. When the pressure rises bycessation of consumption, that pressure acts through L upon the water inH, driving it down in H and up in K till it takes the positions_l"_, and _l'_, the mouth of M being then above the surface. Itshould be observed that in the diagrams B^1 and B^3, the amount ofpressure, and the consequent alteration in level, is grossly exaggeratedto gain clearness; one inch or less in both cases may be sufficient tostart or retard evolution of acetylene. Fig. B^3 is somewhat ideal, butindicates the principle of opposing gas pressure to a supply of waterdepending upon gravitation; a method often adopted in the construction ofportable acetylene apparatus. The arrangement consists of an upper tankcontaining water open to the air, and a lower vessel holding carbideclosed everywhere except at the pipe P, which leads to the burners, andat the pipe S, which introduces water from the store-tank. If the cock atT is closed, pressure begins to rise in the carbide holder until it issufficient to counterbalance the weight of the column of water in thepipe S, when a further supply is prevented until the pressure sinksagain. This idea is simply an application of the displacement-holderprinciple, and as such is defective (except for vehicular lamps) byreason of lack of uniformity in pressure. [Illustration: FIG. 2. --TYPICAL METHODS OF AUTOMATIC GENERATIONCONTROLLED BY INTERNAL GAS PRESSURE. ] DISPLACEMENT GASHOLDERS. --An excursion may here be made for the purposeof studying the action of a displacement holder, which in its mostelementary form is shown at C. It consists of an upright vessel open atthe top, and divided horizontally into two equal portions by a partition, through which a pipe descends to the bottom of the lower half. At the topof the closed lower compartment a tube is fixed, by means of which gascan be introduced below the partition. While the cock is open to the air, water is poured in at the open top till the lower compartment iscompletely full, and the level of the liquid is at _l_. If now, gasis driven in through the side tube, the water is forced downwards in thelower half, up through the depending pipe till it begins to fill theupper half of the holder, and finally the upper half is full of water andthe lower half of gas an shown by the levels _l'_ and _l"_. Butthe force necessary to introduce gas into such an apparatus, whichconversely is equal to the force with which the apparatus strives toexpel its gaseous contents, measured in inches of water, is the distanceat any moment between the levels _l'_ and _l"_; and as theseare always varying, the effective pressure needed to fill the apparatus, or the effective pressure given by the apparatus, may range from zero toa few inches less than the total height of the whole holder. Adisplacement holder, accordingly, may be used either to store a varyingquantity of gas, or to give a steady pressure just above or just below acertain desired figure; but it will not serve both purposes. If it isemployed as a holder, it in useless as a governor or pressure regulator;if it is used as a pressure regulator, it can only hold a certain fixedvolume of gas. The rising holder, which is shown at A^1 in Fig. 1(neglecting the pin X, &c. ) serves both purposes simultaneously; whethernearly full or nearly empty, it gives a constant pressure--a pressuresolely dependent upon its effective weight, which may be increased byloading its crown or decreased by supporting it on counterpoises to anyextent that may be required. As the bell of a rising holder moves, itmust be provided with suitable guides to keep its path vertical; theseguides being arranged symmetrically around its circumference and carriedby the tank walls. A fixed control rod attached to the tank over which atube fastened to the bell slides telescope-fashion is sometimes adopted;but such an arrangement is in many respects less admirable than theformer. Two other devices intended to give automatic working, which are scarcelycapable of classification among their peers, may be diagrammaticallyshown in Fig. 3. The first of these (D) depends upon the movements of aflexible diaphragm. A vessel (_a_) of any convenient size and shapeis divided into two portions by a thin sheet of metal, leather, caoutchouc, or the like. At its centre the diaphragm is attached by someair-tight joint to the rod _c_, which, held in position by suitableguides, is free to move longitudinally in sympathy with the diaphragm, and is connected at its lower extremity with a water-supply cock or acarbide-feed gear. The tube _e_ opens at its base into the gas spaceof the generator, so that the pressure below the diaphragm in _a_ isthe same as that elsewhere in the apparatus, while the pressure in_a_ above the diaphragm is that of the atmosphere. Being flexibleand but slightly stretched, the diaphragm is normally depressed by theweight of _c_ until it occupies the position _b_; but if thepressure in the generator (_i. E. _, in _e_) rises, it lifts thediaphragm to somewhat about the position _b'_--the extent ofmovement being, as usual, exaggerated in the sketch. The movement of thediaphragm is accompanied by a movement of the rod _c_, which can beemployed in any desirable way. In E the bell of a rising holder of theordinary typo is provided with a horizontal striker which, when the belldescends, presses against the top of a bag _g_ made of any flexiblematerial, such as india-rubber, and previously filled with water. Liquidis thus ejected, and may be caused to act upon calcium carbide in someadjacent vessel. The sketch is given because such a method of obtainingan intermittent water-supply has at one time been seriously proposed; butit is clearly one which cannot be recommended. [Illustration: FIG. 3. --TYPICAL METHODS OF AUTOMATIC GENERATIONCONTROLLED BY A FLEXIBLE DIAPHRAM OR BAG. ] ACTION OF WATER-TO-CARBIDE GENERATORS. --Having by one or other of themeans described obtained a supply of water intermittent in character, itremains to be considered how that supply may be made to approach thecarbide in the generator. Actual acetylene apparatus are so various inkind, and merge from one type to another by such small differences, thatit is somewhat difficult to classify them in a simple and intelligiblefashion. However, it may be said that water-to-carbide generators, _i. E. _, such as employ water as the moving material, may be dividedinto four categories: (F^1) water is allowed to fall as single drops oras a fine stream upon a mass of carbide--this being the "drip" generator;(F^2) a mass of water is made to rise round and then recede from astationary vessel containing carbide--this being essentially identical inall respects save the mechanical one with the "dip" or "dipping"generator shown in A^2, Fig. 1; (F^3) a supply of water is permitted torise round, or to flow upon, a stationary mass of carbide without everreceding from the position it has once assumed--this being the "contact"generator; and (F^4) a supply of water is admitted to a subdivided chargeof carbide in such proportion that each quantity admitted is in chemicalexcess of the carbide it attacks. With the exception of F^2, which hasalready been illustrated as A^2 Fig. 1, or as B^1 in Fig. 2, thesemethods of decomposing carbide are represented in Figs. 4 and 5. It willbe observed that whereas in both F^1 and F^3 the liberated acetylenepasses off at the top of the apparatus, or rather from the top of thenon-subdivided charge of carbide, in F^1 the water enters at the top, andin F^3 it enters at the bottom. Thus it happens that the mixture ofacetylene and steam, which is produced at the spot where the primarychemical reaction is taking place, has to travel through the entire massof carbide present in a generator belonging to type F^3, while in F^1 thedamp gas flows directly to the exit pipe without having to penetrate thelumps of solid. Both F^1 and F^3 exhibit after-generation caused by areaction between the liquid water mechanically clinging to the mass ofspent lime and the excess of carbide to an approximately equal extent;but for the reason just mentioned, after-generation due to a reactionbetween the vaporised water accompanying the acetylene first evolved andthe excess of carbide is more noticeable in F^3 than in F^1; and it isprecisely this latter description of after-generation which leads tooverheating of the most ungovernable kind. Naturally both F^1 and F^3 canbe fitted with water jackets, as is indicated by the dotted lines in thesecond sketch; but unless the generating chamber in quite small and theevolution of gas quite slow, the cooling action of the jacket will notprove sufficient. As the water in F^1 and F^3 is not capable of backwardmotion, the decomposing chambers cannot be employed as displacementholders, as is the case in the dipping generator pictured at B^1, Fig. 2. They must be coupled, accordingly, to a separate holder of thedisplacement or, preferably, of the rising type; and, in order that thegas evolved by after-generation may not be wasted, the automaticmechanism must cut off the supply of water to the generator by the timethat holder is two-thirds or three-quarters full. [Illustration: FIG. 4. --TYPICAL METHODS OF DECOMPOSING CARBIDE (WATER TOCARBIDE). ] [Illustration: FIG. 5. --TYPICAL METHODS OF DECOMPOSING CARBIDE (WATER TOCARBIDE). ] The diagrams G, H, and K in Figs. 4 and 5 represent three differentmethods of constructing a generator which belongs either to the contacttype (F^3) if the supply of water is essentially continuous, _i. E. _, if less is admitted at each movement of the feeding mechanism than issufficient to submerge the carbide in each receptacle; or to the flooded-compartment type (F') if the water enters in large quantities at a time. In H the main carbide vessel is arranged horizontally, or nearly so, andeach partition dividing it into compartments is taller than itspredecessor, so that the whole of the solid in (1) must be decomposed, and the compartment entirely filled with liquid before it can overflowinto (2), and so on. Since the carbide in all the later receptacles isexposed to the water vapour produced in that one in which decompositionis proceeding at any given moment, at least at its upper surface, someafter-generation between vapour and carbide occurs in H; but a partialcontrol over the temperature may be obtained by water-jacketing thecontainer. In G the water enters at the base and gas escapes at the top, the carbide vessels being disposed vertically; hero, perhaps, more after-generation of the same description occurs, as the moist gas streams roundand over the higher baskets. In K, the water enters at the top and mustcompletely fill basket (1) before it can run down the depending pipe into(2); but since the gas also leaves the generator at the top, the latercarbide receptacles do not come in contact with water vapour, but areleft practically unattacked until their time arrives for decomposition bymeans of liquid water. K, therefore, is the best arrangement of parts toavoid after-generation, overheating, and polymerisation of the acetylenewhether the generator be worked as a contact or as a flooded-compartmentapparatus; but it may be freely admitted that the extent of theoverheating due to reaction between water vapour and carbide may be keptalmost negligible in either K, H, or G, provided the partitions in thecarbide container be sufficient in number--provided, that is to say, thateach compartment holds a sufficiently small quantity of carbide; andprovided that the quantity of water ultimately required to fill eachcompartment is relatively so large that the temperature of the liquidnever approaches the boiling-point where vaporisation is rapid. The typeof generator indicated by K has not become very popular, but G is fairlycommon, whilst H undoubtedly represents the apparatus which is mostgenerally adopted for use in domestic and other private installations inthe United Kingdom and the Continent of Europe. The actual generatorsmade according to the design shown by H usually have a carbide receptacledesigned in the form of a semi-cylindrical or rectangular vessel of steelsliding fairly closely into an outside container, the latter being eitherbuilt within the main water space of the entire apparatus or placedwithin a separate water-jacketed casing. Owing to its shape and thesliding motion with which the carbide receptacle is put into thecontainer these generators are usually termed "drawer" generators. Incomparison with type G, the drawer generator H certainly exhibits a lowerrise in temperature when gas is evolved in it at a given speed and whenthe carbide receptacles are constructed of similar dimensions. It is verydesirable that the whole receptacle should be subdivided into asufficient number of compartments and that it should be effectivelywater-cooled from outside. It would also be advantageous if the water-supply were so arranged that the generator should be a true flooded-compartment apparatus, but experience has nevertheless shown thatgenerators of type H do work very well when the water admitted to thecarbide receptacle, each time the feed comes into action, is not enoughto flood the carbide in one of the compartments. Above a certain sizedrawer generators are usually constructed with two or even more completedecomposing vessels, arrangements being such that one drawer can be takenout for cleaning, whilst the other is in operation. When this is the casea third carbide receptacle should always be employed so that it may bedry, lit to receive a charge of carbide, and ready to insert in theapparatus when one of the others is withdrawn. The water-feed shouldalways be so disposed that the attendant can see at a glance which of thetwo (or more) carbide receptacles is in action at any moment, and itshould be also so designed that the supply is automatically diverted tothe second receptacle when the first is wholly exhausted and back againto the first (unless there are more than two) when the carbide in thesecond is entirely gasified. In the sketches G, H, and K, the total spaceoccupied by the various carbide receptacles is represented as beingconsiderably smaller than the capacity of the decomposing chamber. Werethis method of construction copied in actual acetylene apparatus, thefirst makes of gas would be seriously (perhaps dangerously) contaminatedwith air. In practice the receptacles should fit so tightly into theouter vessel and into one another that when loaded to the utmost extentpermissible--space being left for the swelling of the charge and for thepassage of water and gas--but little room should be left for theretention of air in the chamber. ACTION OF CARBIDE-TO-WATER GENERATORS. --The methods which may be adoptedto render a generator automatic when carbide is employed as the movingmaterial are shown at M, N, and P, in Fig. 6; but the precise devicesused in many actual apparatus are so various that it is difficult toportray them generically. Moreover it is desirable to subdivide automaticcarbide-to-water generators, according to the size of the carbide theyare constructed to take, into two or three classes, which are termedrespectively "large carbide-feed, " "small carbide-feed, " and "granulatedcarbide-feed" apparatus. (The generator represented at L does not reallybelong to the present class, being non-automatic and fed by hand; but thesketch is given for completeness. ) M is an automatic carbide-feedgenerator having its store of carbide in a hopper carried by the rising-holder bell. The hopper is narrowed at its mouth, where it is closed by aconical or mushroom valve _d_ supported on a rod held in suitableguides. When the bell falls by consumption of gas, it carries the valveand rod with it; but eventually the button at the base of _c_strikes the bottom of the generator, or some fixed distributing plate, and the rod can descend no further. Then, when the bell falls lower, themushroom _d_ rises from its seat, and carbide drops from the hopperinto the water. This type of apparatus has the defect characteristic ofA^2, Fig. 1; for the pressure in the service steadily diminishes as theeffective weight of bell plus hopper decreases by consumption of carbide. But it has also two other defects--(1) that ordinary carbide is tooirregular in shape to fall smoothly through the narrow annular spacebetween the valve and its seat; (2) that water vapour penetrates into thehopper, and liberates some gas there, while it attacks the lumps ofcarbide at the orifice, producing dust or causing them to stick together, and thus rendering the action of the feed worse than ever. Most of thesedefects can be avoided by using granulated carbide, which is more uniformin size and shape, or by employing a granulated and "treated" carbidewhich has been dipped in some non-aqueous liquid to make it lesssusceptible to the action of moisture. Both these plans, however, areexpensive to adopt; first, because of the actual cost of granulating or"treating" the carbide; secondly, because the carbide deteriorates ingas-making capacity by its inevitable exposure to air during thegranulating or "treating" process. The defects of irregularity ofpressure and possible waste of gas by evolution in the hopper may beovercome by disposing the parts somewhat differently; making the holderan annulus round the hopper, or making it cylindrical with the hopperinside. In this case the hopper is supported by the main portion of theapparatus, and does not move with the bell: the rod and valve being giventheir motion in some fashion similar to that figured. Apparatus designedin accordance with the sketch M, or with the modification just described, are usually referred to under the name of "hopper" generators. On severaloccasions trouble has arisen during their employment owing to the jammingof the valve, a fragment of carbide rather larger than the rest of thematerial lodging between the lips of the hopper and the edges of themushroom valve. This has been followed by a sudden descent of all thecarbide in the store into the water beneath, and the evolution of gas hassometimes been too rapid to pass away at the necessary speed into theholder. The trouble is rendered even more serious should the whole chargeof carbide fall at a time when, by neglect or otherwise, the body of thegenerator contains much lime sludge, the decomposition then proceedingunder exceptionally bad circumstances, which lead to the production of anexcessively high temperature. Hopper generators are undoubtedly veryconvenient for certain purposes, chiefly, perhaps, for the constructionof table-lamps and other small installations. Experience tends to showthat they may be employed, first, provided they are designed to takegranulated carbide--which in comparison with larger grades is much moreuniform and cylindrical in shape--and secondly, provided the quantity ofcarbide in the hopper does not exceed a few pounds. The phenomenon of thesudden unexpected descent of the carbide, popularly known as "dumping, "can hardly be avoided with carbide larger in size than the granulatedvariety; and since the results of such an accident must increase inseverity with the size of the apparatus, a limit in their capacity isdesirable. [Illustration: FIG. 6. --TYPICAL METHODS OF DECOMPOSING CARBIDE (CARBIDETO WATER). ] When it is required to construct a carbide-feed generator of large sizeor one belonging to the large carbide-feed pattern, it is preferable toarrange the store in a different manner. In N the carbide is held in aconsiderable number of small receptacles, two only of which are shown inthe drawing, provided with detachable lids and hinged bottoms kept shutby suitable catches. At proper intervals of time those catches insuccession are knocked on one side by a pin, and the contents of thevessel fall into the water. There are several methods available foroperating the pins. The rising-holder bell may be made to actuate a trainof wheels which terminate in a disc revolving horizontally on a verticalaxis somewhere just below the catches; and this wheel may bear aneccentric pin which hits each catch as it rotates. Alternatively thecarbide boxes may be made to revolve horizontally on a vertical axis bythe movements of the bell communicated through a clutch; and thus eachbox in succession may arrive at a certain position where the catch isknocked aside by a fixed pin. The boxes, again, may revolve vertically ona horizontal axis somewhat like a water-wheel, each box having its bottomopened, or, by a different system of construction, being bodily upset, when it arrives at the bottom of its circular path. In no case, however, are the carbide receptacles carried by the bell, which is a totallydistinct part of the apparatus; and therefore in comparison with M, thepressure given by the bell is much more uniform. Nevertheless, if thesystem of carbide boxes moves at all, it becomes easier to move bydecrease in weight and consequent diminution in friction as the totalcharge is exhausted; and accordingly the bell has less work to do duringthe later stages of its operation. For this reason the plan actuallyshown at N is preferable, since the work done by the moving pin, _i. E. _, by the descending bell, is always the same. P represents acarbide-feed effected by a spiral screw or conveyor, which, revolvedperiodically by a moving bell, draws carbide out of a hopper of anydesired size and finally drops it into a shoot communicating with agenerating chamber such as that shown in L. Here the work done by thebell is large, as the friction against the blades of the screw and thewalls of the horizontal tube is heavy; but that amount of work mustalways be essentially identical. The carbide-feed may similarly beeffected by means of some other type of conveyor instead of the spiralscrew, such as an endless band, and the friction in these cases may besomewhat less than with the screw, but the work to be done by the bellwill always remain large, whatever type of conveyor may be adopted. Afurther plan for securing a carbide-feed consists in employing someextraneous driving power to propel a charge of carbide out of a reservoirinto the generator. Sometimes the propulsive effort is obtained from atrain of clockwork, sometimes from a separate supply of water under highpressure. The clockwork or the water power is used either to drive apiston travelling through the vessel containing the carbide so that theproper quantity of material is dropped over the open mouth of a shoot, orto upset one after another a series of carbide receptacles, or to performsome analogous operation. In these cases the pin or other device fittedto the acetylene apparatus itself has nothing to do beyond releasing themechanism in question, and therefore the work required from the bell isbut small. The propriety of employing a generator belonging to theselatter types must depend upon local conditions, _e. G. _, whether theowner of the installation has hydraulic power on a small scale (aconstant supply of water under sufficient pressure) at disposal, orwhether he does not object to the extra labour involved in the periodicalwinding up of a train of clockwork. It must be clear that all these carbide-feed arrangements have the defectin a more or less serious degree of leaving the carbide in the mainstorage vessel exposed to the attack of water vapour rising from thedecomposing chamber, for none of the valves or operating mechanism can bemade quite air-tight. Evolution of gas produced in this way does notmatter in the least, because it is easy to return the gas so liberatedinto the generator or into the holder; while the extent of the action, and the consequent production of overheating, will tend to be less thanin generators such as those shown in G and H of Figs. 4 and 5, inasmuchas the large excess of water in the carbide-feed apparatus prevents theliquid arriving at a temperature at which it volatilises rapidly. Themain objection to the evolution of gas in the carbide vessel of acarbide-to-water generator depends on the danger that the smooth workingof the feed-gear may be interfered with by the formation of dust or bythe aggregation of the carbide lumps. USE OF OIL IN GENERATORS. --Calcium carbide is a material which is onlycapable of attack for the purpose of evolving acetylene by a liquid thatis essentially water, or by one that contains some water mixed with it. Oils and the like, or even such non-aqueous liquids as absolute alcohol, have no effect upon carbide, except that the former naturally make itgreasy and somewhat more difficult to moisten. This last property hasbeen found of service in acetylene generation, especially on the smallscale; for if carbide is soaked in, or given a coating of, some oil, fat, or solid hydrocarbon like petroleum, cocoanut oil, or paraffin wax, thesubstance becomes comparatively indifferent towards water vapour or themoisture present in the air, while it still remains capable of complete, albeit slow, decomposition by liquid water when completely immersedtherein. The fact that ordinary calcium carbide is attacked so quickly bywater is really a defect of the substance; for it is to this extremerapidity of reaction that the troubles of overheating are due. Now, ifthe basket in the generator B^1 of Fig. 2, or, indeed, the carbide storein any of the carbide-to-water apparatus, is filled with a carbide whichhas been treated with oil or wax, as long as the water-level stands at_l'_ and _l"_ or the carbide still remains in the hopper, it isessentially unattacked by the vapour arising from the liquid; butdirectly the basket is submerged, or the lumps fall into the water, acetylene is produced, and produced more slowly and regularly thanotherwise. Again, oils do not mix with water, but usually float thereon, and a mass of water covered by a thick film or layer of oil does notevaporate appreciably. If, now, a certain quantity of oil, say lampparaffin or mineral lubricating oil, is poured on to the water in B^1, Fig. 2, it moves upwards and downwards with the water. When the watertakes the position _l_, the oil is driven upwards away from thebasket of carbide, and acetylene is generated in the ordinary manner; butwhen the water falls to _l"_ the oil descends also, rinses off muchof the adhering water from the carbide lumps, covers them with a greasyfilm, and almost entirely stops generation till it is in turn washed offby the next ascent of the water. Similarly, if the carbide in generatorsF, G, and H (also K) has been treated with a solid or semi-solid grease, it is practically unattacked by the stream of warm damp gas, and is onlydecomposed when the liquid itself arrives in the basket. For the samereason treated carbide can be kept for fairly long periods of time, evenin a drum with badly fitting lid, without suffering much deterioration bythe action of atmospheric moisture. The problem of acetylene generationis accordingly simplified to a considerable degree by the use of suchtreated carbide, and the advantage becomes more marked as the plantdecreases in size till a portable apparatus is reached, because thesmaller the installation the more relatively expensive or inconvenient isa large holder for surplus gas. The one defect of the method is the extracost of such treated carbide; and in English conditions ordinary calciumcarbide is too expensive to permit of any additional outlay upon theacetylene if it is to compete with petroleum or the product of a tinycoal-gas works. The extra cost of using treated carbide falls upon therevenue account, and is much more noticeable than that of a large holder, which is capital expenditure. When fluid oil is employed in a generatorof type B^1, evolution of gas becomes so regular that any holder beyondthe displacement one which the apparatus itself constitutes is actuallyunnecessary, though still desirable; but B^1, with or without oil, stillremains a displacement apparatus, and as such gives no constant pressure. It must be admitted that the presence of oil so far governs the evolutionof gas that the movement of the water, and the consequent variation ofpressure, is rendered very small; still a governor or a rising holderwould be required to give the best result at the burners. One point inconnexion with the use of liquid oil must not be overlooked, viz. , theextra trouble it may give in the disposal of the residues. This matterwill be dealt with more fully in Chapter V. ; here it is sufficient to saythat as the oil does not mix with the water but floats on the surface, care has to be taken that it is not permitted to enter any open stream. The foregoing remarks about the use of oil manifestly only apply to thosecases where it is used in quantity and where it ultimately becomes mixedwith the sludge or floats on the water in the decomposing chamber. Theemployment of a limpid oil, such as paraffin, as an intermediate liquidinto which carbide is introduced on its way to the water in thedecomposing vessel of a hand-fed generator in the manner described onpage 70 is something quite different, because, except for triflinglosses, one charge of oil should last indefinitely. RISING GASHOLDERS. --Whichever description of holder is employed in anacetylene apparatus, the gas is always stored over, or in contact with, aliquid that is essentially water. This introduces three subjects forconsideration: the heavy weight of a large body of liquid, the loss ofgas by dissolution in that liquid, and the protection of that liquid fromfrost in the winter. The tanks of rising holders are constructed in twodifferent ways. In one the tank is a plain cylindrical vessel somewhatlarger in diameter than the bell which floats in it; and since there mustbe nearly enough water in the tank to fill the interior of the bell whenthe latter assumes its lowest position, the quantity of water isconsiderable, its capacity for dissolving acetylene is large, and theamount of any substance that may have to be added to it to lower itsfreezing-point becomes so great as to be scarcely economical. All thesedefects, including that of the necessity for very substantial foundationsunder the holder to support its enormous weight, may be overcome byadopting the second method of construction. It is clear that the water inthe centre of the tank is of no use, --all that is needed being a narrowtrough for the bell to work in. Large rising holders are thereforeadvantageously built with a tank formed in the shape of an annulus, theeffective breadth of which is not more than 2 or 3 inches, the centreportion being roofed over so as to prevent escape of gas. The sameprinciple may be retained with modified details by fitting inside a plaincylindrical tank a "dummy" or smaller cylinder, closed by a flat orcurved top and fastened water- and air-tight to the bottom of the mainvessel. The construction of annular tanks or the insertion of a "dummy"may be attended with difficulty if the tank is wholly or partly sunkbelow the ground level, owing to the lifting force of water in thesurrounding soil. Where a steel tank is sunk, or a masonry tank isconstructed, regard must be paid, both in the design of the tank and inthe manner of construction, to the level of the underground water in theneighbourhood, as in certain cases special precautions will be needed toavoid trouble from the pressure of the water on the outside of the tankuntil it is balanced by the pressure of the water with which the tank isfilled. So far as mere dissolution of gas is concerned, the loss may bereduced by having a circular disc of wood, &c. , a little smaller indiameter than the boll, floating on the water of a plain tank. EFFECT OF STORAGE IN GASHOLDER ON ACETYLENE. --It is perfectly true, ashas been stated elsewhere, that the gas coming from an acetylenegenerator loses some of its illuminating power if it is stored over waterfor any great length of time; such loss being given by Nichols as 94 percent, in five months, and having been found by one of the authors as 0. 63per cent. Per day--figures which stand in fair agreement with oneanother. This wastage is not due to any decomposition of the acetylene incontact with water, but depends on the various solubilities of thedifferent gases which compose the product obtained from commercialcalcium carbide. Inasmuch as an acetylene evolved in the best generatorcontains some foreign ingredients, and inasmuch as an inferior productcontains more (_cf. _ Chapter V. ), the contents of a holder are neverpure; but as those contents are principally made up of acetylene itself, that gas stands at a higher partial pressure in the holder than theimpurities. Since acetylene is more soluble in water than any of itsdiluents or impurities, sulphuretted hydrogen and ammonia excepted, andsince the solubility of all gases increases as the pressure at which theyare stored rises, the true acetylene in an acetylene holder dissolves inthe water more rapidly and comparatively more copiously than theimpurities; and thus the acetylene tends to disappear and the impuritiesto become concentrated within the bell. Simultaneously at the outer partof the seal, air is dissolved in the water; and by processes of diffusionthe air so dissolved passes through the liquid from the outside to theinside, where it escapes into the bell, while the dissolved acetylenesimilarly passes from the inside to the outside of the seal, and theremingles with the atmosphere. Thus, the longer a certain volume ofacetylene is stored over water, the more does it become contaminated withthe constituents of the atmosphere and with the impurities originallypresent in it; while as the acetylene is much more soluble than itsimpurities, more gas escapes from, than enters, the holder by diffusion, and so the bulk of stored gas gradually diminishes. However, the figurespreviously given show that this action is too slow to be noticeable inpractice, for the gas is never stored for more than a few days at a time. The action cannot be accepted as a valid argument against the employmentof a holder in acetylene plant. Such deterioration and wastage of gas maybe reduced to some extent by the use of a film of some cheap andindifferent oil floating on the water inside an acetylene holder; theeconomy being caused by the lower solubility of acetylene in oils than inaqueous liquids not saturated with some saline material. Probably almostany oil would answer equally well, provided it was not volatile at thetemperature of the holder, and that it did not dry or gum on standing, _e. G. _, olive oil or its substitutes; but mineral lubricating oil isnot so satisfactory. It is, however, not necessary to adopt this methodin practice, because the solvent power of the liquid in the seal can bereduced by adding to it a saline body which simultaneously lowers itsfreezing-point and makes the apparatus more trustworthy in winter. FREEZING OF GASHOLDER SEAL. --The danger attendant upon the congelation ofthe seal in an acetylene holder is very real, not so much because of thefear that the apparatus may be burst, which is hardly to be expected, asbecause the bell will be firmly fixed in a certain position by the ice, and the whole establishment lighted by the gas will be left in darkness. In these circumstances, hurried and perhaps injudicious attempts may bemade to thaw the seal by putting red-hot bars into it or by lightingfires under it, or the generator-house may be thoughtlessly entered witha naked light at a time when the apparatus is possibly in disorderthrough the loss of storage-room for the gas it is evolving. Should aseal ever freeze, it must be thawed only by the application of boilingwater; and the plant-house must be entered, if daylight has passed, inperfect darkness or with the assistance of an outside lamp whiningthrough a closed window. [Footnote: By "closed window" is to beunderstood one incapable of being opened, fitted with one or twothicknesses of stout glass well puttied in, and placed in a wall of thehouse as far as possible from the door. ] There are two ways of preventingthe seal from freezing. In all large installations the generator-housewill be fitted with a warm-water heating apparatus to protect the portionof the plant where the carbide is decomposed, and if the holder is alsoinside the same building it will naturally be safe. If it is outside, oneof the flow-pipes from the warming apparatus should be led into and roundthe lowest part of the seal, care being taken to watch for, or to provideautomatic arrangements for making good, loss of water by evaporation. Ifthe holder is at a distance from the generator-house, or if for any otherreason it cannot easily be brought into the warming circuit, the seal canbe protected in another way; for unlike the water in the generator, thewater in the holder-seal will perform its functions equally well howevermuch it be reduced in temperature, always providing it is maintained inthe liquid condition. There are numerous substances which dissolve in, ormix with, water, and yield solutions or liquids that do not solidifyuntil their temperature falls far below that of the natural freezing-point. Assuming that those substances in solution do not attack theacetylene, nor the metal of which the holder is built, and are not tooexpensive, choice may be made between them at will. Strictly speaking thecost of using them is small, because unless the tank is leaky they lastindefinitely, not evaporating with the water as it is vaporised into thegas or into the air. The water-seal of a holder standing within thegenerator-house may eventually become so offensive to the nostrils thatthe liquid has to be renewed; but when this happens it is due to theaccumulation in the water of the water-soluble impurities of the crudeacetylene. If, as should be done, the gas is passed through a washer orcondenser containing much water before it enters the holder thesulphuretted hydrogen and ammonia will be extracted, and the seal willnot acquire an obnoxious odour for a very long time. Four principal substances have been proposed for lowering the freezing-point of the water in an acetylene-holder seal; common salt (sodiumchloride), calcium chloride (not chloride of lime), alcohol (methylatedspirit), and glycerin. A 10 per cent. Solution of common salt has aspecific gravity of 1. 0734, and does not solidify above -6° C. Or 21. 2°F. ; a 15 per cent. Solution has a density of 1. 111, and freezes at -10°C. Or 14° F. Common salt, however, is not to be recommended, as itssolutions always corrode iron and steel vessels more or less quickly. Alcohol, in its English denatured form of methylated spirit, is stillsomewhat expensive to use, but it has the advantage of not increasing theviscosity of the water; so that a frost-proof mixture of alcohol andwater will flow as readily through minute tubes choked with needle-valves, or through felt and the like, or along wicks, as will plainwater. For this reason, and for the practically identical one that it isquite free from dirt or insoluble matter, diluted spirit is speciallysuitable for the protection of the water in cyclists' acetylene lamps, [Footnote: As will appear in Chapter XIII. , there is usually no holder ina vehicular acetylene lamp, all the water being employed eventually forthe purpose of decomposing the carbide. This does not affect the presentquestion. Dilute alcohol does not attack calcium carbide so energeticallyas pure water, because it stands midway between pure water and purealcohol, which is inert. The attack, however, of the carbide is ascomplete as that of pure water, and the slower speed thereof is amanifest advantage in any holderless apparatus. ] where strict economy isless important than smooth working. For domestic and larger installationsit is not indicated. As between calcium chloride and glycerin there islittle to choose; the former will be somewhat cheaper, but the latterwill not be prohibitively expensive if the high-grade pure glycerins ofthe pharmacist are avoided. The following tables show the amount of eachsubstance which must be dissolved in water to obtain a liquid of definitesolidifying point. The data relating to alcohol were obtained by Pictet, and those for calcium chloride by Pickering. The latter are materiallydifferent from figures given by other investigators, and perhaps it wouldbe safer to make due allowance for this difference. In Germany theAcetylene Association advocates a 17 per cent. Solution of calciumchloride, to which Frank ascribes a specific gravity of 1. 134, and afreezing-point of -8° C. Or 17. 6° F. _Freezing-Points of Dilute Alcohol. _ _________________________________________________________| | | || Percentage of | Specific Gravity. | Freezing-point. || Alcohol. | | ||_______________|___________________|_____________________|| | | | || | | Degs. C. | Degs. F. || 4. 8 | 0. 9916 | -2. 0 | +28. 4 || 11. 3 | 0. 9824 | 5. 0 | 23. 0 || 16. 4 | 0. 9761 | 7. 5 | 18. 5 || 18. 8 | 0. 9732 | 9. 4 | 15. 1 || 20. 3 | 0. 9712 | 10. 6 | 12. 9 || 22. 1 | 0. 9689 | 12. 2 | 10. 0 || 24. 2 | 0. 9662 | 14. 0 | 6. 8 || 26. 7 | 0. 9627 | 16. 0 | 3. 2 || 29. 9 | 0. 9578 | 18. 9 | -2. 0 ||_______________|___________________|__________|__________| _Freezing-Points of Dilute Glycerin. _ _________________________________________________________| | | || Percentage of | Specific Gravity. | Freezing-point. || Glycerin. | | ||_______________|___________________|_____________________|| | | | || | | Degs. C. | Degs. F. || 10 | 1. 024 | -1. 0 | +30. 2 || 20 | 1. 051 | 2. 5 | 27. 5 || 30 | 1. 075 | 6. 0 | 21. 2 || 40 | 1. 105 | 17. 5 | 0. 5 || 50 | 1. 127 | 31. 3 | -24. 3 ||_______________|___________________|__________|__________| _Freezing-Points of Calcium Chloride Solutions. _ _________________________________________________________| | | || Percentage of | Specific Gravity. | Freezing-point. || CaCl_2. | | ||_______________|___________________|_____________________|| | | | || | | Degs. C. | Degs. F. || 6 | 1. 05 | -3. 0 | +26. 6 || 8 | 1. 067 | 4. 3 | 24. 3 || 10 | 1. 985 | 5. 9 | 21. 4 || 12 | 1. 103 | 7. 7 | 18. 1 || 14 | 1. 121 | 9. 8 | 14. 4 || 16 | 1. 140 | 12. 2 | 10. 0 || 18 | 1. 159 | 15. 2 | 4. 6 || 20 | 1. 170 | 18. 6 | -1. 5 ||_______________|___________________|__________|__________| Calcium chloride will probably be procured in the solid state, but it canbe purchased as a concentrated solution, being sold under the name of"calcidum" [Footnote: This proprietary German article is a liquid whichbegins to solidify at -42° C. (-43. 6° F. ), and is completely solid at-56° C. (-69)° F. ). Diluted with one-third its volume of water, itfreezes between -20° and -28° C. (-4° and-l8. 4° F. ). The makers recommendthat it should be mixed with an equal volume of water. Another materialknown as "Gefrierschutzflüssigkeit" and made by the Flörsheim chemicalworks, freezes at -35° C. (-3° F. ). Diluted with one-quarter its volumeof water, it solidifies at -18° C. (-0. 4° F. ); with equal parts of waterit freezes at -12° C. (10. 4° F. ). A third product, called "calcidumoxychlorid, " has been found by Caro and Saulmann to be an impure 35 percent. Solution of calcium chloride. Not one of these is suitable foraddition to the water used in the generating chamber of an acetyleneapparatus, the reasons for this having already been mentioned. ] for theprotection of gasholder seals. Glycerin itself resembles a strongsolution of calcium chloride in being a viscid, oily-looking liquid; andboth are so much heavier than water that they will not mix with furtherquantities unless they are thoroughly agitated therewith. Either may bepoured through water, or have water floated upon it, without anyappreciable admixture taking place; and therefore in first adding them tothe seal great care must be taken that they are uniformly distributedthroughout the liquid. If the whole contents of the seal cannotconveniently be run into an open vessel in which the mixing can beperformed, the sealing water must be drawn off a little at a time and acorresponding quantity of the protective reagent added to it. Care mustbe taken also that motives of economy do not lead to excessive dilutionof the reagent; the seal must be competent to remain liquid under theprolonged influence of the most severe frost ever known to occur in theneighbourhood where the plant is situated. If the holder is placed out ofdoors in an exposed spot where heavy rains may fall on the top of thebell, or where snow may collect there and melt, the water is apt to rundown into the seal, diluting the upper layers until they lose the frost-resisting power they originally had. This danger may be prevented byerecting a sloping roof over the bell crown, or by stirring up the sealand adding more preservative whenever it has been diluted with rainwater. Quite small holders would probably always be placed inside thegenerator-house, where their seals may be protected by the same means asare applied to the generator itself. It need hardly be said that allremarks about the dangers incidental to the freezing of holder seals andthe methods for obviating them refer equally to every item in theacetylene plant which contains water or is fitted with a water-sealedcover; only the water which is actually used for decomposing the calciumcarbide cannot be protected from frost by the addition of calciumchloride or glycerin--that water must be kept from falling to its naturalfreezing-point. From Mauricheau-Beaupré's experiments, referred to onpage 106, it would appear that a further reason for avoiding an additionof calcium chloride to the water used for decomposing carbide should liein the danger of causing a troublesome production of froth within thegenerator. It will be convenient to digress here for the purpose of considering howthe generators of an acetylene apparatus themselves should be protectedfrom frost; but it may be said at the outset that it is impossible to laydown any fixed rules applicable to all cases, since local conditions, such as climate, available resources, dimensions, and exposed orprotected position of the plant-house vary so largely in differentsituations. In all important installations every item of the plant, except the holder, will be collected in one or two rooms of a singlebuilding constructed of brick or other incombustible material. Assumingthat long-continued frost reigns at times in the neighbourhood, the wholeof such a building, with the exception of one apartment used as a carbidestore only, is judiciously fitted with a heating arrangement like thoseemployed in conservatories or hothouses; a system of pipes in which warmwater is kept circulating being run round the walls of each chamber nearthe floor. The boiler, heated with coke, paraffin, or even acetylene, must naturally be placed in a separate room of the apparatus-house havingno direct (indoor) communication with the rooms containing thegenerators, purifiers, &c. Instead of coils of pipe, "radiators" of theusual commercial patterns may be adopted; but the immediate source ofheat should be steam, or preferably hot water, and not hot air orcombustion products from the stove. In exposed situations, where theholder is out of doors, one branch of the flow-pipe should enter andtravel round the seal as previously suggested. Most large countryresidences are already provided with suitable heating apparatus forwarming the greenhouses, and part of the heat may be capable of diversioninto the acetylene generator-shed if the latter is erected in aconvenient spot. In fact, if any existing hot-water warming appliancesare already at hand, and if they are powerful enough to do a little morework, it may be well to put the generator-building in such a positionthat it can be efficiently supplied with artificial warmth from thoseboilers; for any extra length of main necessary to lead the gas into theresidence from a distant generator will cost less on the revenue accountthan the fuel required to feed a special heating arrangement. In smallerinstallations, especially such as are to be found in mild climates, itmay be possible to render the apparatus-house sufficiently frost-proofwithout artificial heat by building it partly underground, fitting itwith a double skylight in place of a window for the entrance of daylight, and banking up its walls all round with thick layers of earth. The housemust have a door, however, which must open outwards and easily, so thatno obstacle may prevent a hurried exit in emergencies. Such a door canhardly be made very thick or double without rendering it heavy anddifficult to open; and the single door will be scarcely capable ofprotecting the interior if the frost is severe and prolonged. Ventilators, too, must be provided to allow of the escape of any gas thatmay accidentally issue from the plant during recharging, &c. ; and someaperture in the roof will be required for the passage of the vent pipe orpipes, which, in certain types of apparatus, move upwards and downwardswith the bell of the holder. These openings manifestly afford facilitiesfor the entry of cold air, so that although this method of protectinggenerator-houses has proved efficient in many places, it can only beconsidered inferior to the plan of installing a proper heatingarrangement. Occasionally, where local regulations do not forbid, theentire generator-house may be built as a "lean-to" against some brickwall which happens to be kept constantly warm, say by having a furnace ora large kitchen stove on its other side. In less complicated installations, where there are only two distinctitems in the plant to be protected from frost--generator and holder--orwhere generator and holder are combined into one piece of apparatus, other methods of warming become possible. As the reaction between calciumcarbide and water evolves much heat, the most obvious way of preventingthe plant from freezing is to economise that heat, _i. E. _, to retainas much of it as is necessary within the apparatus. Such a process, clearly, is only available if the plant is suitable in external form, ispractically self-contained, and comprises no isolated vessels containingan aqueous liquid. It is indicated, therefore, rather for carbide-to-water generators, or for water-to-carbide apparatus in which the carbidechambers are situated inside the main water reservoir--any apparatus, infact, where much water is present and where it is all together in onereceptacle. Moreover, the method of heat economy is suited forapplication to automatic generators rather than to those belonging to theopposite system, because automatic apparatus will be generating gas, andconsequently evolving heat, every evening till late at night--just at thetime when frost begins to be severe. A non-automatic generator willusually be at work only in the mornings, and its store of heat willaccordingly be much more difficult to retain till nightfall. With theobject of storing up the heat evolved in the generator, it must becovered with some material possessed of the lowest heat-conducting powerpossible; and the proper positions for that material in order ofdecreasing importance are the top, sides, and bottom of the plant. Thegenerator may either be covered with a thick layer of straw, carpet, flannel, or the like, as is done in the protection of exposed water-pipes; or it may be provided with a jacket filled with some liquid. Inview of the advisability of not having any organic or combustiblematerial near the generator, the solid substances just mentioned maypreferably be replaced by one of those partially inorganic compositionssold for "lagging" steam-pipes and engine-cylinders, such as "Fossilmeal. " Indeed, the exact nature of the lagging matters comparativelylittle, because the active substance in retaining the heat in theacetylene generator or the steam-pipe is the air entangled in the poresof the lagging; and therefore the value of any particular materialdepends mainly on its exhibiting a high degree of porosity. The idea offitting a water jacket round an acetylene generator is not altogethergood, but it may be greatly improved upon by putting into the jacket astrong solution of some cheap saline body which has the property ofseparating from its aqueous solution in the form of crystals containingwater of crystallisation, and of evolving much heat in so separating. This method of storing much heat in a small space where a fire cannot belighted is in common use on some railways, where passengers' foot-warmersare filled with a strong solution of sodium acetate. When sodium acetateis dissolved in water it manifestly exists in the liquid state, and it ispresumably present in its anhydrous condition (i. E. , not combined withwater of crystallisation). The common crystals are solid, and contain 3molecules of water of crystallisation--also clearly in the solid state. Now, the reaction NaC_2H_3O_2 + 3H_2O = NaC_2H_3O_2. 3H_2O (anhydrous acetate) (crystals) evolves 4. 37 calories (Berthelot), or 1. 46 calorie for each molecule ofwater; and whereas 1 kilo. Of water only evolves 1 large calorie of heatas its temperature falls 1° C. , 18 grammes of water (1 gramme-molecule)evolve l. 46 large calorie when they enter into combination with anhydroussodium acetate to assist in forming crystals--and this 1. 46 calorie mayeither be permitted to warm the mass of crystals, or made to do usefulwork by raising the temperature of some adjacent substance. Sodiumacetate crystals dissolve in 3. 9 parts by weight of water at 6° C. (43°F. ) or in 2. 4 parts at 37° C. (99° F. ). If, then, a jacket round anacetylene apparatus is filled with a warm solution of sodium acetatecrystals in (say) 3 parts by weight of water, the liquid will crystallisewhen it reaches some temperature between 99° and 43° F. ; but when thegenerator comes into action, the heat liberated will change the mass ofcrystals into a liquid without raising its sensible temperature toanything like the extent that would happen were the jacket full of simplewater. Not being particularly warm to the touch, the liquefied product inthe jacket will not lose much heat by radiation, &c. , into thesurrounding air; but when the water in the generator falls again (afterevolution of acetylene ceases) the contents of the jacket will also cool, and finally will begin to crystallise once more, passing a large amountof low-temperature heat into the water of the generator, and safelymaintaining it for long periods of time at a temperature suitable for thefurther evolution of gas. Like the liquid in the seal of an isolatedgasholder, the liquid in such a jacket will last indefinitely; andtherefore the cost of the sodium acetate in negligible. Another method of keeping warm the water in any part of an acetyleneinstallation consists in piling round the apparatus a heap of freshstable manure, which, as is well known, emits much heat as it rots. Wherehorses are kept, such a process may be said to cost nothing. It has theadvantage over methods of lagging or jacketing that the manure can bethrown over any pipe, water-seal, washing apparatus, &c. , even if theplant is constructed in several separate items. Unfortunately the ammoniaand the volatile organic compounds which are produced during the naturaldecomposition of stable manure tend seriously to corrode iron and steel, and therefore this method of protecting an apparatus from frost shouldonly be employed temporarily in times of emergency. CORROSION IN APPARATUS. --All natural water is a solution of oxygen andmay be regarded also as a weak solution of the hypothetical carbonicacid. It therefore causes iron to rust more or less quickly; and since nopaint is absolutely waterproof, especially if it has been applied to asurface already coated locally with spots of rust, iron and steel cannotbe perfectly protected by its aid. More particularly at a few inchesabove and below the normal level of the water in a holder, therefore, themetal soon begins to exhibit symptoms of corrosion which may eventuallyproceed until the iron is eaten away or becomes porous. One method ofprolonging the life of such apparatus is to give it fresh coats of paintperiodically; but unless the old layers are removed where they havecracked or blistered, and the rust underneath is entirely scraped off(which is practically impossible), the new paint films will not last verylong. Another more elegant process for preserving any metal like ironwhich is constantly exposed to the attack of a corrosive liquid, andwhich is readily applicable to acetylene holders and their tanks, dependson the principle of galvanic action. When two metals in good electricalcontact are immersed in some liquid that is capable of attacking both, only that metal will be attacked which is the more electro-positive, orwhich (the same thing in other words) is the more readily attacked by theliquid, evolving the more heat during its dissolution. As long as thisaction is proceeding, as long, that is, as some of the more electro-positive material is present, the less electro-positive material will notsuffer. All that has to be done, therefore, to protect the walls of anacetylene-holder tank and the sides of its bell is to hang in the seal, supported by a copper wire fastened to the tank walls by a trustworthyelectrical joint (soldering or riveting it), a plate or rod of some moreelectro-positive metal, renewing that plate or rod before it is entirelyeaten away. [Footnote: Contact between the bell and the rod may beestablished by means of a flexible metallic wire; or a separate rod mightbe used for the bell itself. ] If the iron is bare or coated with lead(paint may be overlooked), the plate may be zinc; if the iron isgalvanised, _i. E. _, coated with zinc, the plate may be aluminium oran alloy of aluminium and zinc. The joint between the copper wire and thezinc or aluminium plate should naturally be above the water-level. Theforegoing remarks should be read in conjunction with what was said inChapter II. , about the undesirability of employing a soft soldercontaining lead in the construction of an acetylene generator. Here it isproposed intentionally to set up a galvanic couple to prevent corrosion;there, with the same object in view, the avoidances of galvanic action iscounselled. The reason for this difference is self-evident; here aforeign metal is brought into electrical contact with the apparatus inorder that the latter may be made electro-negative; but when a joint issoldered with lead, the metal of the generator is unintentionally madeelectro-positive. Here the plant is protected by the preferentialcorrosion of a cheap and renewable rod; in the former case the plant isencouraged to rust by the unnecessary presence of an improperly selectedmetal. OTHER ITEMS IN GENERATING PLANT. --It has been explained in Chapter II. That the reaction between calcium carbide and water is very tumultuous incharacter, and that it occurs with great rapidity. Clearly, therefore, the gas comes away from the generator in rushes, passing into the nextitem of the plant at great speed for a time, and then ceasing altogether. The methods necessarily adopted for purifying the crude gas are treatedof in Chapter V. ; but it is manifest now that no purifying material canprove efficient unless the acetylene passes through it at a uniform rate, and at one which is as slow as other conditions permit. For this reasonthe proper position of the holder in an acetylene installation is beforethe purifier, and immediately after the condenser or washer which adjoinsthe generator. By this method of design the holder is filled upirregularly, the gas passing into it sometimes at full speed, sometimesat an imperceptible rate; but if the holder is well balanced and guidedthis is a matter of no consequence. Out of the holder, on the other hand, the gas issues at a rate which is dependent upon the number and capacityof the burners in operation at any moment; and in ordinary conditionsthis rate is so much more uniform during the whole of an evening than therate at which the gas is evolved from the carbide, that a purifier placedafter the holder is given a far better opportunity of extracting theimpurities from the acetylene than it would have were it situated beforethe holder, as is invariably the case on coal-gas works. For many reasons, such as capacity for isolation when being recharged orrepaired, it is highly desirable that each item in an acetylene plantshall be separated, or capable of separation, from its neighbours; andthis observation applies with great force to the holder and thedecomposing vessel of the generator. In all large plants each vesselshould be fitted with a stopcock at its inlet and, if necessary, one atits outlet, being provided also with a by-pass so that it can be thrownout of action without interfering with the rest of the installation. Inthe best practice the more important vessels, such as the purifiers, willbe in duplicate, so that unpurified gas need not be passed into theservice while a solitary purifier is being charged afresh. In smallerplants, where less skilled labour will probably be bestowed on theapparatus, and where hand-worked cocks are likely to be neglected ormisused, some more, automatic arrangement for isolating each item isdesirable. There are two automatic devices which may be employed for thepurposes in view, the non-return valve and the water-seal. The non-returnvalve is simply a mushroom or ball valve without handle, lifted off itsseat by gas passing from underneath whenever the pressure of the gasexceeds the weight of the valve, but falling back on to its seat andclosing the pipe when the pressure decreases or when pressure above isgreater than that below. The apparatus works perfectly with a clean gasor liquid which is not corrosive; but having regard to the possiblepresence of tarry products, lime dust, or sludge, condensed water loadedwith soluble impurities, &c. , in the acetylene, a non-return valve is notthe best device to adopt, for both it and the hand-worked cock or screw-down valve are liable to stick and give trouble. The best arrangement inall respects, especially between the generator and the holder, is awater-seal. A water-seal in made by leading the mouth of a pipedelivering gas under the level of water in a suitable receptacle, so thatthe issuing gas has to bubble through the liquid. Gas cannot passbackwards through the pipe until it has first driven so much liquidbefore it that the level in the seal has fallen below the pipe's mouth;and if the end of the pipe is vertical more pressure than can possibly beproduced in the apparatus is necessary to effect this. Omitting the sidetube _b_, one variety of water-seal is shown at D in Fig. 7 on page103. The water being at the level _l_, gas enters at _a_ andbubbles through it, escaping from the apparatus at _c_. It cannotreturn from _c_ to _a_ without driving the water out of thevessel till its level falls from _f_ to _g_; and since the areaof the vessel is much greater than that of the pipe, so great a fall inthe vessel would involve a far greater rise in _a_. It is clear thatsuch a device, besides acting as a non-return valve, also fulfils twoother useful functions: it serves to collect and retain all the liquidmatter that may be condensed in the pipe _a_ from the spot at whichit was originally level or was given a fall to the seal, as well as thatcondensing in _c_ as far as the spot where _c_ dips again; andit equally acts as a washer to the gas, especially if the orifice_g_ of the gas-inlet pipe is not left with a plain mouth asrepresented in the figure, but terminates in a large number of smallholes, the pipe being then preferably prolonged horizontally, with minuteholes in it so as to distribute the gas throughout the entire vessel. Such an apparatus requires very little attention. It may with advantagebe provided with the automatic arrangement for setting the water-levelshown at _d_ and _e_. _d_ is a tunnel tube extendingalmost to the bottom of the vessel, and _e_ is a curved run-off pipeof the form shown. The lower part of the upper curve in _e_ is abovethe level _f_, being higher than _f_ by a distance equal tothat of the gas pressure in the pipes; and therefore when water is pouredinto the funnel it fills the vessel till the internal level reaches_f_, when the surplus overflows of itself. The operation thus notonly adjusts the quantity of water present to the desired level so that_a_ cannot become unsealed, but it also renews the liquid when ithas become foul and nearly saturated with dissolved and condensedimpurities from the acetylene. It would be a desirable refinement to givethe bottom of the vessel a slope to the mouth of _e_, or to someother spot where a large-bore draw-off cock could be fitted for thepurpose of extracting any sludge of lime, &c. , that may collect. Byhaving such a water-seal, or one simpler in construction, between thegenerator and the holder, the former may be safely opened at any time forrepairs, inspection, or the insertion of a fresh charge of carbide whilethe holder is full of gas, and the delivery of acetylene to the burnersat a specified pressure will not be interrupted. If a cock worked by handwere employed for the separation of the holder from the generator, andthe attendant were to forget to close it, part or all of the acetylene inthe holder would escape from the generator when it was opened ordisconnected. Especially when a combined washer and non-return valve followsimmediately after a generator belonging to the shoot type, and the mouthof the shoot is open to the air in the plant-house, it is highlydesirable that the washer shall be fitted with some arrangement of anautomatic kind for preventing the water level rising much above itsproper position. The liquid in a closed washer tends to rise as theapparatus remains in use, water vapour being condensed within it andliquid water, or froth of lime, being mechanically carried forward by thestream of acetylene coming from the decomposing chamber. In course oftime, therefore, the vertical depth to which the gas-inlet pipe in thewasher is sealed by the liquid increases; and it may well be thateventually the depth in question, plus the pressure thrown by the holderbell, may become greater than the pressure which can be set up inside thegenerator without danger of gas slipping under the lower edge of theshoot. Should this state of things arise, the acetylene can no longerforce its way through the washer into the holder bell, but will escapefrom the mouth of the shoot; filling the apparatus-house with gas, andoffering every opportunity for an explosion if the attendant disobeysorders and takes a naked light with him to inspect the plant. It is indispensable that every acetylene apparatus shall be fitted with asafety-valve, or more correctly speaking a vent-pipe. The generator musthave a vent-pipe in case the gas-main leading to the holder should becomeblocked at any time, and the acetylene which continues to be evolved inall water-to-carbide apparatus, even after the supply of water has beencut off be unable to pass away. Theoretically a non-automatic apparatusdoes not require a vent-pipe in its generator because all the gas entersthe holder immediately, and is, or should be, unable to return throughthe intermediate water seal; practically such a safeguard is absolutelynecessary for the reason given. The holder must have a safety-valve incase the cutting-off mechanism of the generator fails to act, and moregas passes into it than it can store. Manifestly the pressure of the gasin a water-sealed holder or in any generator fitted with a water-sealedlid cannot rise above that corresponding with the depth of water in theseal; for immediately the pressure, measured in inches of water, equalsthe depth of the sealing liquid, the seal will be blown out, and the gaswill escape. Such an occurrence, however, as the blowing of a seal mustnever be possible in any item of an acetylene plant, more especially inthose items that are under cover, for the danger that the issuing gasmight be fired or might produce suffocation would be extremely great. Typical simple forms of vent-pipe suitable for acetylene apparatus areshown in Fig. 7. In each case the pipe marked "vent" is the so-calledsafety-valve; it is open at its base for the entry of gas, and open atits top for the escape of the acetylene into the atmosphere, such topbeing in all instances carried through the roof of the generator-houseinto the open air, and to a spot distant from any windows of that houseor of the residence, where it can prove neither dangerous nor a nuisanceby reason of its odour. At A is represented the vent-pipe of adisplacement vessel, which may either be part of a displacement holder orof a generator working on the displacement principle. The vent-pipe isrigidly fixed to the apparatus. If gas is generated within the closedportion of the holder or passes through it, and if the pressure so set upremains less than that which is needed to move the water from the level_l_ to the levels _l'_ and _l"_, the mouth of the pipe isunder water, and acetylene cannot enter it; but immediately such anamount of gas is collected, or such pressure is produced that theinterior level sinks below _l"_, which is that of the mouth of thepipe, it becomes unsealed, and the surplus gas freely escapes. There aretwo minor points in connexion with this form of vent-pipe oftenoverlooked. At the moment when the water arrives at _l"_ in theclosed half of the apparatus, its level in the interior of the vent-pipestands at _l'_, identical with that in the open hall of theapparatus (for the mouth of the vent-pipe and the water in the open hallof the apparatus are alike exposed to the pressure of the atmosphereonly). When the water, then, descends just below _l"_ there is anamount of water inside the pipe equal in height to the distance between_l'_ and _l"_; and before the acetylene can escape, it musteither force this water as a compact mass out of the upper mouth of thevent-pipe (which it is clearly not in a position to do), drive it out ofthe upper mouth a little at a time, or bubble through it till the wateris gradually able to run downwards out of the pipe as its lower openingis more fully unsealed. In practice the acetylene partly bubbles throughthis water and partly drives it out of the mouth of the pipe; on someoccasions temporarily yielding irregular pressures at the burners whichcause them to jump, and always producing a gurgling noise in the vent-pipe which in calculated to alarm the attendant. If the pipe is too smallin diameter, and especially if its lower orifice is cut off perfectlyhorizontal and constricted slightly, the water may refuse to escape fromthe bottom altogether, and the pipe will fail to perform its allottedtask. It is better therefore to employ a wide tube, and to cut off itsmouth obliquely, or to give its lower extremity the shape of an invertedfunnel. At the half of the central divided drawing marked B (Fig. 7) isshown a precisely similar vent-pipe affixed to the bell of a risingholder, which behaves in an identical fashion when by the rising of thebell its lower end is lifted out of the water in the tank. The featuresdescribed above as attendant, upon the act of unsealing of thedisplacement-holder vent-pipe occur here also, but to a less degree; forthe water remaining in the pipe at the moment of unsealing is only thatwhich corresponds with the vertical distance between _l'_ and_l"_, and in a rising holder this is only a height always equal tothe pressure given by the bell. Nevertheless this form of vent-pipeproduces a gurgling noise, and would be better for a trumpet-shapedmouth. A special feature of the pipe in B is that unless it is placedsymmetrically about the centre of the bell its weight tends to throw thebell out of the vertical, and it may have to be supported at its upperpart; conversely, if the pipe is arranged concentrically in the bell, itmay be employed as part of the guiding arrangement of the bell itself. Manifestly, as the pipe must be long enough to extend through the roof ofthe generator-house, its weight materially increases the weight of thebell, and consequently the gas pressure in the service; this fact is notobjectionable provided due allowance is made for it. So tall a vent-pipe, however, seriously raises the centre of gravity of the bell and may makeit top-heavy. To work well the centre of gravity of a holder bell shouldbe as low as possible, any necessary weighting being providedsymmetrically about its circumference and close to its bottom edge. Thewhole length of an ascending vent-pipe need not be carried by the risingbell, because the lower portion, which must be supported by the bell, canbe arranged to slide inside a wider length of pipe which is fixed to theroof of the generator-house at the point where it passes into the openair. [Illustration: FIG. 7. --TYPICAL FORMS OF VENT-PIPES OR SAFETY-VALVES. ] A refinement upon this vent-pipe is represented at C, where it is rigidlyfastened to the tank of the holder, and has its internal aperture alwaysabove the level of the water in the apparatus. Rigidly fixed to the crownof the bell is a tube of wider diameter, _h_, which is closed at itsupper end. _h_ is always full of gas, and its mouth is normallybeneath the level of the water in the seal; but when the bell rises toits highest permissible position, the mouth of _h_ comes above thewater, and communication is opened between the holder and the outeratmosphere. No water enters the vent-pipe from the holder, and thereforeno gurgling or irregular pressure is produced. Another excellentarrangement of a vent-pipe, suggested by Klinger of Gumpoldskirchen, isshown at D, a drawing which has already been partly considered as awasher and water-seal. For the present purpose the main vessel and itsvarious pipes are so dimensioned that the vertical height _g_ to_f_ is always appreciably greater than the gas pressure in theservice or in the generator or gasholder to which it is connected. Inthese circumstances the gas entering at _a_ depresses the water inthe pipe below the level _f_ to an extent equal to the pressure atwhich it enters that pipe--an extent normally less than the distance_f_ to _g_; and therefore gas never passes into the body of thevessel, but travels away by the side tube _b_ (which in formerreferences to this drawing was supposed to be absent). If, however, thepressure at _a_ exceeds that of the vertical height _f_ to_g_, gas escapes at _g_ through the water, and is then free toreach the atmosphere by means of the vent _c_. As before, _d_serves to charge the apparatus with water, and _e_ to ensure aproper amount being added. Clearly no liquid can enter the vent-pipe inthis device. Safety-valves such as are added to steam-boilers and thelike, which consist of a weighted lever holding a conical valve downagainst its seat, are not required in acetylene apparatus, for thesimpler hydraulic seals discussed above can always be fitted whereverthey may be needed. It should be noticed that these vent-pipes only comeinto operation in emergencies, when they are required to act promptly. Noeconomy is to be effected by making them small in diameter. For obviousreasons the vent-pipe of a holder should have a diameter equal to that ofthe gas-inlet tube, and the vent-pipe of a generator be equal in size tothe gas-leading tube. FROTHING IN GENERATORS. --A very annoying trouble which crops up every nowand then during the evolution of acetylene consists in the production oflarge masses of froth within the generator. In the ordinary way, decomposition of carbide is accompanied by a species of effervescence, but the bubbles should break smartly and leave the surface of the liquidreasonably free from foam. Sometimes, however, the bubbles do not break, but a persistent "head" of considerable height is formed. Furtherproduction of gas only increases the thickness of the froth until itrises so high that it is carried forward through the gas-main into thenext item of the plant. The froth disappears gradually in the pipes, butleaves in them a deposit of lime which sooner or later causesobstructions by accumulating at the angles and dips; while during itspresence in the main the steady passage of gas to the holder isinterrupted and the burners may even be made to jump. Manifestly thedefect is chiefly, if not always, to be noticed in the working ofcarbide-to-water generators. The phenomenon has been examined byMauricheau-Beaupré, who finds that frothing is not characteristic of purecarbide and that it cannot be attributed to any of the impuritiesnormally present in commercial carbide. If, however, the carbide containscalcium chloride, frothing is liable to occur. A 0. 1 per cent. Solutionof calcium chloride appears to yield some foam when carbide is decomposedin it, and a 1 per cent. Solution to foam in a pronounced manner. In theabsence of calcium chloride, the main cause of frothing seems to be thepresence in the generator of new paint or tar. If a generator is takeninto use before the paint in any part of it which becomes moistened bywarm lime-water has had opportunity of drying thoroughly hard, frothingis certain to occur; and even if the carbide has been stored for only ashort time in a tin or drum which has been freshly painted, a productionof froth will follow when it is decomposed in water. The products of thepolymerisation of acetylene also tend to produce frothing, but not tosuch an extent as the turpentine in paint and the lighter constituents ofcoal-tar. Carbide stored even temporarily in a newly painted tin frothson decomposition because it has absorbed among its pores some of thevolatile matter given off by the paint during the process of desiccation. THE "DRY" PROCESS OF GENERATION. --A process for generating acetylene, totally different in principle from those hitherto considered, has beenintroduced in this country. According to the original patents of G. J. Atkins, the process consisted in bringing small or powdered carbide intomechanical contact with some solid material containing water, the waterbeing either mixed with the solid reagent or attached to it as water ofcrystallisation. Such reagents indeed were claimed as crude starch andthe like, the idea being to recover a by-product of pecuniary value. Nowthe process seems to be known only in that particular form in whichgranulated carbide is treated with crystallised sodium carbonate, _i. E. _, common washing soda. Assuming the carbide employed to bechemically pure and the reaction between it and the water ofcrystallisation contained in ordinary soda crystals to proceedquantitatively, the production of acetylene by the dry process should berepresented by the following chemical equation: 5CaC_2 + Na_2CO_3. 10H_2O = 5C_2H_2 + 5Ca(OH)_2 + Na_2CO_3. On calculating out the molecular weights, it will be seen that 286 partsof washing soda should suffice for the decomposition of 320 parts of purecalcium carbide, or in round numbers 9 parts of soda should decompose 10parts of carbide. In practice, however, it seems to be found that from 1to 1. 5 parts of soda are needed for every part of carbide. The apparatus employed is a metal drum supported on a hollow horizontalspindle, one end of which is closed and carries a winch handle, and theother end of which serves to withdraw the gas generated in the plant. Thedrum is divided into three compartments by means of two verticalpartitions so designed that when rotation proceeds in one particulardirection portions of the two reagents stored in one end compartment passinto the centre compartment; whereas when rotation proceeds in theopposite direction, the material in the centre compartment is merelymixed together, partly by the revolution of the drum, partly with theassistance of a stationary agitator slung loosely from the centralspindle. The other end compartment contains coke or sawdust or other drymaterial through which the gas passes for the removal of lime or otherdust carried in suspension as it issues from the generating compartment. The gas then passes through perforations into the central spindle, oneend of which is connected by a packed joint with a fixed pipe, whichleads to a seal or washer containing petroleum. Approached from atheoretical standpoint, it will be seen that this method of generationentirely sacrifices the advantages otherwise accruing from the use ofliquid water as a means for dissipating the heat of the chemicalreaction, but on the other hand, inasmuch as the substances are bothsolid, the reaction presumably occurs more slowly than it would in thepresence of liquid water; and moreover the fact that the water employedto act upon the carbide is in the solid state and also more or lesscombined with the rest of the sodium carbonate molecule, means that, perunit of weight, the water decomposed must render latent a larger amountof heat than it would were it liquid. Experiments made by one of theauthors of this book tend to show that the gas evolved from carbide bythe dry process contains rather less phosphorus than it might in otherconditions of generation, and as a fact gas made by the dry process isordinarily consumed without previous passage through any chemicalpurifying agent. It is obvious, however, that the use of the churndescribed above greatly increases the labour attached to the productionof the gas; while it is not clear that the yield per unit weight ofcarbide decomposed should be as high as that obtained in wet generation. The inventor has claimed that his by-product should be valuable andsaleable, apparently partly on the ground that it should contain causticsoda. Evidence, however, that a reaction between the calcium oxide orhydroxide and the sodium carbonate takes place in the prevailingconditions is not yet forthcoming, and the probabilities are that suchdecomposition would not occur unless the residue were largely dilutedwith water. [Footnote: The oldest process employed for manufacturingcaustic soda consisted in mixing a solution of sodium carbonate withquick or slaked lime, and it has been well established that thecausticisation of the soda will not proceed when the concentration of theliquid is greater than that corresponding with a specific gravity ofabout 1-10, _i. E. _, when the liquid contains more than some 8 to 10per cent, of sodium hydroxide. ] Conversely there are some grounds forbelieving that the dry residue is less useful than an ordinary wetresidue for horticultural purposes, and also for the production ofwhitewash. From a financial standpoint, the dry process suffers owing tothe expense involved in the purchase of a second raw material, for whichbut little compensation can be discovered unless it is proved that theresidue is intrinsically more valuable than common acetylene-lime and canbe sold or used advantageously by the ordinary owner of an installation. The discarding of the chemical purifier at the present day is a move ofwhich the advantage may well be overrated. ARTIFICIAL LIGHTING OF GENERATOR SHEDS. --It has already been argued thatall normal or abnormal operations in connexion with an acetylenegenerating plant should be carried out, if possible, by daylight; and ithas been shown that on no account must a naked light ever be taken insidethe house containing such a plant. It will occasionally happen, however, that the installation must be recharged or inspected after nightfall. Inorder to do this in safety, a double window, incapable of being opened, should be fitted in one wall of the house, as far as possible from thedoor, and in such a position that the light may fall on to all thenecessary places. Outside this window may be suspended an ordinary hand-lantern burning oil or paraffin; or, preferably, round this window may bebuilt a closed lantern into which some source of artificial light may bebrought. If the acetylene plant has an isolated holder of considerablesize, there is no reason at all why a connexion should not be made withthe service-pipes, and an acetylene flame be used inside this lantern;but with generators of the automatic variety, an acetylene light is notso suitable, because of the fear that gas may not be available preciselyat the moment when it is necessary to have light in the shed. It would, however, be a simple matter to erect an acetylene burner inside thelantern in such a way that when needed an oil-lamp or candle could beused instead. Artificial internal light of any kind is best avoided; theonly kind permissible being an electric glow-lamp. If this is employed, it should be surrounded by a second bulb or gas-tight glass jacket, andpreferably by a wire cage as well; the wires leading to it must becarefully insulated, and all switches or cut-outs (which may produce aspark) must be out of doors. The well-known Davy safety or miner's lampis not a trustworthy instrument for use with acetylene because of(_a_) the low igniting-point of acetylene; (_b_) the hightemperature of its flame; and (_c_) the enormous speed at which theexplosive wave travels through a mixture of acetylene and air. For thesereasons the metallic gauze of the Davy lamp is not so efficient aprotector of the flame as it is in cases of coal-gas, methane, &c. Moreover, in practice, the Davy lamp gives a poor light, and unless inconstant use is liable to be found out of order when required. It should, however, be added that modern forms of the safety lamp, in which thelight is surrounded by a stout glass chimney and only sufficient gauze isused for the admission of fresh air and for the escape of the combustionproducts, appear quite satisfactory when employed in an atmospherecontaining some free acetylene. CHAPTER IV THE SELECTION OF AN ACETYLENE GENERATOR In Chapter II. An attempt has been made to explain the physical andchemical phenomena which accompany the interaction of calcium carbide andwater, and to show what features in the reaction are useful and whatinconvenient in the evolution of acetylene on a domestic or larger scale. Similarly in Chapter III. Have been described the various typical deviceswhich may be employed in the construction of different portions ofacetylene plant, so that the gas may be generated and stored under thebest conditions, whether it is evolved by the automatic or by the non-automatic system. This having been done, it seemed of doubtful utility toinclude in the first edition of this work a long series of illustrationsof such generators as had been placed on the markets by British, French, German, and American makers. It would have been difficult withinreasonable limits to have reproduced diagrams of all the generators thathad been offered for sale, and absolutely impossible within the limits ofa single hand-book to picture those which had been suggested or patented. Moreover, some generating apparatus appeared on the market ephemerally;some was constantly being modified in detail so as to alter parts whichexperience or greater knowledge had shown the makers to be in need ofalteration, while other new apparatus was constantly being brought out. On these and other grounds it did not appear that much good purpose wouldhave been served by describing the particular apparatus which at thattime would have been offered to prospective purchasers. It seemed bestthat the latter should estimate the value and trustworthiness ofapparatus by studying a section of it in the light of the generalprinciples of construction of a satisfactory generator as enunciated inthe book. While the position thus taken by the authors in 1903 wouldstill not be incorrect, it has been represented to them that it wouldscarcely be inconsistent with it to give brief descriptions of some ofthe generators which are now being sold in Great Britain and a few othercountries. Six more years' experience in the design and manufacture ofacetylene plant has enabled the older firms of manufacturers to fix uponcertain standard patterns for their apparatus, and it may confidently beanticipated that many of these will survive a longer period. Faultydevices and designs have been weeded out, and there are lessons of thepast as well as theoretical considerations to guide the inventor of a newtype of generator. On those grounds, therefore, an attempt has now beenmade to give brief descriptions, with sectional views, of a number of thegenerators now on the market in Great Britain. Moreover, as the firstedition of this book found many readers in other countries, in several ofwhich there is greater scope for the use of acetylene, it has beendecided to describe also a few typical or widely used foreign generators. All the generators described must stand or fall on their merits, whichcannot be affected by any opinion expressed by the authors. In thedescriptions, which in the first instance have generally been furnishedby the manufacturers of the apparatus, no attempt has therefore been madeto appraise the particular generators, and comparisons and eulogisticcomments have been excluded. The descriptions, however, wouldnevertheless have been somewhat out of place in the body of this book;they have therefore been relegated to a special Appendix. It has, ofcourse, been impossible to include the generators of all even of theEnglish manufacturers, and doubtless many trustworthy ones have remainedunnoticed. Many firms also make other types of generators in addition tothose described. It must not be assumed that because a particular make ofgenerator is not mentioned it is necessarily faulty. The apparatusdescribed may be regarded as typical or well known, and workable, but itis not by reason of its inclusion vouched for in any other respect by theauthors. The Appendix is intended, not to bias or modify the judgment ofthe would-be purchaser of a generator, but merely to assist him inascertaining what generators there are now on the market. The observations on the selection of a generator which follow, as well asany references in other chapters to the same matter, have been madewithout regard to particular apparatus of which a description may (or maynot) appear in the Appendix. With this premise, it may be stated that theintending purchaser should regard the mechanism of a generator as shownin a sectional view or on inspection of the apparatus itself. If thegenerator is simple in construction, he should be able to understand itsmethod of working at a glance, and by referring it to the type(_vide_ Chapter III. ) to which it belongs, be able to appraise itsutility from a chemical and physical aspect from what has already beensaid. If the generator is too complicated for ready understanding of itsmode of working, it is not unlikely to prove too complicated to behavewell in practice. Not less important than the mechanism of a generator isgood construction from the mechanical point of view, _i. E. _, whetherstout metal has been employed, whether the seams and joints are wellfinished, and whether the whole apparatus has been built in the workman-like fashion which alone can give satisfaction in any kind of plant. Bearing these points in mind, the intending purchaser may find assistancein estimating the mechanical value of an apparatus by perusing theremainder of this chapter, which will be devoted to elaborating at lengththe so-called scientific principles underlying the construction of asatisfactory generator, and to giving information on the mechanical andpractical points involved. It is perhaps desirable to remark that there is scarcely any feature inthe generation of acetylene from calcium carbide and water--certainly noimportant feature--which introduces into practice principles not alreadyknown to chemists and engineers. Once the gas is set free it ranks simplyas an inflammable, moisture-laden, somewhat impure, illuminating andheat-giving gas, which has to be dried, purified, stored, and led to theplace of combustion; it is in this respect precisely analogous to coal-gas. Even the actual generation is only an exothermic, or heat-producing, reaction between a solid and a liquid, in which rise of temperature andpressure must be prevented as far as possible. Accordingly there is nofundamental or indispensable portion of an acetylene apparatus whichlends itself to the protection of the patent laws; and even the details(it may be said truthfully, if somewhat cynically) stand in patentabilityin inverse ratio to their simplicity and utility. During the early part of 1901 a Committee appointed by the British HomeOffice, "to advise as to the conditions of safety to which acetylenegenerators should conform, and to carry out tests of generators in themarket in order to ascertain how far those conform with such conditions, "issued a circular to the trade suggesting that apparatus should be sentthem for examination. In response, forty-six British generators weresubmitted for trial, and were examined in a fashion which somewhatexceeded the instructions given to the Committee, who finally reported tothe Explosives Department of the Home Office in a Blue Book, No. Cd. 952, which can be purchased through any bookseller. This report comprises anappendix in which most of the apparatus are illustrated, and it includesthe result of the particular test which the Committee decided to apply. Qualitatively the test was useful, as it was identical in all instances, and only lacks full utility inasmuch as the trustworthiness of theautomatic mechanism applied to such generators as were intended to workon the automatic system was not estimated. Naturally, a completevaluation of the efficiency of automatic mechanism cannot be obtainedfrom one or even several tests, it demands long-continued watching; but ageneral notion of reliability might have been obtained. Quantitatively, however, the test applied by the Committee is not so free from reproach, for, from the information given, it would appear to have been less fairto some makers of apparatus than to others. Nevertheless the report isvaluable, and indicates the general character of the most importantapparatus which were being offered for sale in the United Kingdom in1900-1901. It is not possible to give a direct answer to the question as to which isthe best type of acetylene generator. There are no generators made byresponsible firms at the present time which are not safe. Some may beeasier to charge and clean than others; some require more frequentattention than others; some have moving parts less likely to fail, whenhandled carelessly, than others; some have no moving mechanism to fail. For the illumination of a large institution or district where one man canbe fully occupied in attending to the plant, cleaning, lighting, andextinguishing the lamps, or where other work can be found for him so asto leave him an hour or so every day to look after the apparatus, thehand-fed carbide-to-water generator L (Fig. 6) has many advantages, andis probably the best of all. In smaller installations choice must be madefirst between the automatic and the non-automatic principle--theadvantages most frequently lying with the latter. If a non-automaticgenerator is decided upon, the hand carbide-feed or the flooded-compartment apparatus is almost equally good; and if automatism isdesired, either a flooded-compartment machine or one of the mosttrustworthy types of carbide-feed apparatus may be taken. There arecontact apparatus on the markets which appear never to have giventrouble, and those are worthy of attention. Some builders advocate theirown apparatus because the residue is solid and not a cream. If there isany advantage in this arising from greater ease in cleaning andrecharging the generator and in disposing of the waste, that advantage isusually neutralised by the fear that the carbide may not have been whollydecomposed within the apparatus; and whereas any danger arising fromimperfectly spent carbide being thrown into a closed drain may beprevented by flooding the residue with plenty of water in an open vessel, imperfect decomposition in the generator means a deficiency in the amountof gas evolved from a unit weight of solid taken or purchased. In fact, setting on one side apparatus which belong to a notoriously defectivesystem and such as are constructed in large sizes on a system that isonly free from overheating, &c. , in small sizes; setting aside allgenerators which are provided with only one decomposing chamber when theyare of a capacity to require two or more smaller ones that can moreefficiently be cooled with water jackets; and setting aside any form ofplant which on examination is likely to exhibit any of the more seriousobjections indicated in this and the previous chapters, there iscomparatively little to choose, from the chemical and physical points ofview, between the different types of generators now on the markets. Aselection may rather be made on mechanical grounds. The generator must bewell able to produce gas as rapidly as it will ever be required duringthe longest or coldest evening; it must be so large that several morebrackets or burners can be added to the service after the installation iscomplete. It must be so strong that it will bear careless handling andthe frequent rough manipulation of its parts. It must be built of stoutenough material not to rust out in a few years. Each and all of its partsmust be accessible and its exterior visible. Its pipes, both for gas andsludge, must be of large bore (say 1 inch), and fitted at every dip withan arrangement for withdrawing into some closed vessel the moisture, &c. , that may condense. The number of cocks, valves, and moving parts must bereduced to a minimum; cocks which require to be shut by hand beforerecharging must give way to water-seals. It must be simple in all itsparts, and its action intelligible at a glance. It must be easy tocharge--preferably even by the sense of touch in darkness. It must beeasy to clean. The waste lime must be easily removed. It must be sofitted with vent-pipes that the pressure can never rise above that atwhich it is supposed to work. Nevertheless, a generator in which thesevent-pipes are often brought into use is badly constructed and wasteful, and must be avoided. The water of the holder seal should be distinct fromthat used for decomposing the carbide; and those apparatus where theholder is entirely separated from the generator are preferable to such asare built all in one, even if water-seals are fitted to prevent return ofgas. Apparatus which is supposed to be automatic should be made perfectlyautomatic, the water or the carbide-feed being locked automaticallybefore the carbide store, the decomposing chamber, or the sludge-cock canbe opened. The generating chamber must always be in communication withthe atmosphere through a water-sealed vent-pipe, the seal of which, ifnecessary, the gas can blow at any time. All apparatus should be fittedwith rising holders, the larger the better. Duplicate copies of printedinstructions should be demanded of the maker, one copy being kept in thegenerator-house, and the other elsewhere for reference in emergencies. These instructions must give simple and precise information as to whatshould be done in the event of a breakdown as well as in the normalmanipulation of the plant. Technical expressions and descriptions ofparts understood only by the maker must be absent from these rules. ADDENDUM. BRITISH AND FOREIGN REGULATIONS FOR THE CONSTRUCTION AND INSTALLATION OFACETYLENE GENERATING PLANT Dealing with the "conditions which a generator should fulfil before itcan be considered as being safe, " the HOME OFFICE COMMITTEE of 1901before mentioned write as follows: 1. The temperature in any part of the generator, when run at the maximumrate for which it is designed, for a prolonged period, should not exceed130° C. This may be ascertained by placing short lengths of wire, drawnfrom fusible metal, in those parts of the apparatus in which heat isliable to be generated. 2. The generator should have an efficiency of not less than 90 per cent. , which, with carbide yielding 5 cubic feet per pound, would imply a yieldof 4. 5 cubic feet for each pound of carbide used. 3. The size of the pipes carrying the gas should be proportioned to themaximum rate of generation, so that undue back pressure from throttlingmay not occur. 4. The carbide should be completely decomposed in the apparatus, so thatlime sludge discharged from the generator shall not be capable ofgenerating more gas. 5. The pressure in any part of the apparatus, on the generator side ofthe holder, should not exceed that of 20 inches of water, and on theservice side of same, or where no gasholder is provided, should notexceed that of 5 inches of water. 6. The apparatus should give no tarry or other heavy condensationproducts from the decomposition of the carbide. 7. In the use of a generator regard should be had to the danger ofstoppage of passage of the gas and resulting increase of pressure whichmay arise from the freezing of the water. Where freezing may beanticipated, steps should be taken to prevent it. 8. The apparatus should be so constructed that no lime sludge can gainaccess to any pipes intended for the passage of gas or circulation ofwater. 9. The use of glass gauges should be avoided as far as possible, and, where absolutely necessary, they should be effectively protected againstbreakage. 10. The air space in a generator before charging should be as small aspossible. 11. The use of copper should be avoided in such parts of the apparatus asare liable to come in contact with acetylene. The BRITISH ACETYLENE ASSOCIATION has drawn up the following list ofregulations which, it suggests, shall govern the construction ofgenerators and the installation of piping and fittings: 1. Generators shall be so constructed that, when used in accordance withprinted instructions, it shall not he possible for any undecomposedcarbide to remain in the sludge removed therefrom. 2. The limit of pressure in any part of the generator shall not exceedthat of 20 inches of water, subject to the exception that if it be shownto the satisfaction of the Executive of the Acetylene Association thathigher pressures up to 50 inches of water are necessary in certaingenerators, and are without danger, the Executive may, with the approvalof the Home Office, grant exemption for such generators, with or withoutconditions. 3. The limit of pressure in service-pipes, within the house, shall notexceed 10 inches of water. 4. Except when used for special industrial purposes, such as oxy-acetylene welding, factories, lighthouses, portable apparatus containingnot more than four pounds of carbide, and other special conditions asapproved by the Association, the acetylene plant, such as generators, storage-holders, purifiers, scrubbers, and for washers, shall be in asuitable and well-ventilated outhouse, in the open, or in a lean-to, having no direct communication with a dwelling-house. A blow-off pipe orsafety outlet shall be arranged in such a manner as to carry off into theopen air any overmake of gas and to open automatically if pressure beincreased beyond 20 inches water column in the generating chamber orbeyond 10 inches in the gasholder, or beyond the depth of any fluid sealon the apparatus. 5. Generators shall have sufficient storage capacity to make a seriousblow-off impossible. 6. Generators and apparatus shall be made of sufficiently strong materialand be of good workmanship, and shall not in any part be constructed ofunalloyed copper. 7. It shall not be possible under any conditions, even by wrongmanipulation of cocks, to seal the generating chamber hermetically. 8. It shall not be possible for the lime sludge to choke any of the gas-pipes in the apparatus, nor water-pipes if such be alternately used assafety-valves. 9. In the use of a generator, regard shall be had to the danger ofstoppage of passage of the gas, and resulting increase of pressure, whichmay arise from the freezing of the water. Where freezing may beanticipated, steps shall be taken to prevent it. 10. The use of glass gauges shall be avoided as far as possible, andwhere absolutely necessary they shall be effectively protected againstbreakage. 11. The air space in the generator before charging shall be as small aspossible, _i. E. _, the gas in the generating chamber shall notcontain more than 8 per cent. Of air half a minute after commencement ofgeneration. A sample of the contents, drawn from the holder any timeafter generation has commenced, shall not contain an explosive mixture, _i. E. _, more than 18 per cent, of air. This shall not apply to theinitial charges of the gasholder, when reasonable precautions are taken. 12. The apparatus shall produce no tarry or other heavy condensationproducts from the decomposition of the carbide. 13. The temperature of the gas, immediately on leaving the charge, shallnot exceed 212° F. (100° C. ) 14. No generator shall be sold without a card of instructions suitablefor hanging up in some convenient place. Such instructions shall be ofthe most detailed nature, and shall not presuppose any expert knowledgewhatever on the part of the operator. 15. Notice to be fixed on Generator House Door, "NO LIGHTS OR SMOKINGALLOWED. " 16. Every generator shall have marked clearly upon the outside astatement of the maximum number of half cubic foot burners and the chargeof carbide for which it is designed. 17. The Association strongly advise the use of an efficient purifier withgenerating plant for indoor lighting. 18. No composition piping shall be used in any part of a permanentinstallation. 19. Before being covered in, all pipe-work (main and branches) shall betested in the following manner: A special acetylene generator, giving apressure of at least 10 inches water column in a gauge fixed on thefurthest point from the generator, shall be connected to the pipe-work. All points shall be opened until gas reaches them, when they shall beplugged and the main cock on the permanent generator turned off, but allintermediate main cocks shall be open in order to test underground mainand all connexions. The gauge must not show a loss after generator hasbeen turned off for at least two hours. 20. After the fittings (pendants, brackets, &c. ) have been fixed and allburners lighted, the gas shall be turned off at the burners and the wholeinstallation shall be re-tested, but a pressure of 5 inches shall bedeemed sufficient, which shall not drop lower than to 4-1/2 inches on thegauge during one hour's test. 21. No repairs to, or alterations in, any part of a generator, purifier, or other vessel which has contained acetylene shall be commenced, nor, except for recharging, shall any such part or vessel be cleaned out untilit has been completely filled with water, so as to expel any acetylene ormixture of acetylene and air which may remain in the vessel, and maycause a risk of explosion. _Recommendation_. --It being the general practice to store carbide inthe generator-house, the Association recommend that the carbide shall beplaced on a slightly raised platform above the floor level. THE BRITISH FIRE OFFICES COMMITTEE in the latest revision, dated July 15, 1907, of its Rules and Regulations _re_ artificial lighting oninsured premises, includes the following stipulations applicable toacetylene: Any apparatus, except as below, for generating, purifying, enriching, compressing or storing gas, must be either in the open or in a buildingused for such purposes only, not communicating directly with any buildingotherwise occupied. An acetylene portable apparatus is allowed, provided it holds a charge ofnot more than 2 lb. Of carbide. A cylinder containing not more than 20 cubic feet of acetylene compressedand (or) dissolved in accordance with an Order of Secretary of Stateunder the Explosives Act, 1875, is allowed. The use of portable acetylene lamps containing charges of carbideexceeding the limit of 2 lb. Allowed under these Rules (the averagecharge being about 18 lb. ) is allowed in the open or in buildings incourse of erection. Liquid acetylene must not be used or stored on the premises. The pipe, whether flexible or not, connecting an incandescent gas lamp tothe gas-supply must be of metal with metal connexions. (The reference in these Rules to the storage of carbide has been quotedin Chapter II. (page 19). ) These rules are liable to revision from time to time. The GERMAN ACETYLENE VEREIN has drawn up (December 1904) the followingcode of rules for the construction, erection, and manipulation ofacetylene apparatus: I. _Rules for Construction. _ 1. All apparatus for the generation, purification, and storage ofacetylene must be constructed of sheet or cast iron. Holder tanks may bebuilt of brick. 2. When bare, galvanised, or lead-coated sheet-iron is used, the sides ofgenerators, purifiers, condensers, holder tanks, and (if present) washersand driers must be built with the following gauges as minima: Holder bells. All other apparatus. Up to 7 cubic feet capacity 0. 75 mm. 1. 00 mm. From 7 to 18 " 1. 00 1. 25From 18 to 53 " 1. 25 1. 50Above 53 " 1. 50 2. 00 When not constructed of cast-iron, the bottoms, covers, and "manhole"lids must be 0. 5 mm. Thicker in each respective size. In all circumstances, the thickness of the walls--especially in the caseof apparatus not circular in horizontal section--must be such thatalteration in shape appears impossible, unless deformation is guardedagainst in other ways. Generators must be so constructed that when they are being charged thecarbide cannot fall into the residue which has already been gasified; andthe residues must always be capable of easy, complete, and safe removal. 3. Generators, purifiers, and holders must be welded, riveted or foldedat the seams; soft solder is only permissible as a tightening material. 4. Pipes delivering acetylene, or uniting the apparatus, must be cast- orwrought-iron. Unions, cocks, and valves must not be made of copper; butthe use of brass and bronze is permitted. 5. When cast-iron is employed, the rules of the German Gas and WaterEngineers are to be followed. 6. In generators where the whole amount of carbide introduced is notgasified at one time, it must be possible to add fresh water or carbidein safety, without interfering with the action of the apparatus. In suchgenerators the size of the gasholder space is to be calculated accordingto the quantity of carbide which can be put into the generator. For every1 kilogramme of carbide the available gasholder space must be: for thefirst 50 kilos. , 20 litres; for the next 50 kilos. , 15 litres; foramounts above 100 kilos. , 10 litres per kilo. [One kilogramme may betaken as 2. 2 lb. , and 28 litres as 1 cubic foot. ] The generator must be large enough to supply the full number of normal(10-litre) burners with gas for 5 hours; the yield of acetylene beingtaken at 290 litres per kilo. [4. 65 cubic feet per lb. ] The gasholder space of apparatus where carbide is not stored must be atleast 30 litres for every normal (10-litre) flame. 7. The gasholder must be fitted with an appliance for removing any gaswhich may be generated (especially when the apparatus is first broughtinto action) after the available space is full. This vent must have adiameter at least equal to the inlet pipe of the holder. 8. Acetylene plant must be provided with purifying apparatus whichcontains a proper purifying material in a suitable condition. 9. The dimensions of subsidiary apparatus, such as washers, purifiers, condensers, pipes, and cocks must correspond with the capacity of theplant. 10. Purifiers and washers must be constructed of materials capable ofresisting the attack of the substances in them. 11. Every generator must bear a plate giving the name of the maker, orthe seller, and the maximum number of l0-litre lights it is intended tosupply. If all the carbide put into the generator is not gasified at onetime, the plate must also state the maximum weight of carbide in thecharge. The gasholder must also bear a plate recording the maker's orseller's name, as well as its storage capacity. 12. Rules 1 to 11 do not apply to portable apparatus serving up to twolights, or to portable apparatus used only out of doors for the lightingof vehicles or open spaces. II. _Rules for Erection_ 1. Acetylene apparatus must not be erected in or under rooms occupied orfrequented (passages, covered courts, &c. ) by human beings. Generatorsand holders must only be erected in apartments covered with light roofs, and separated from occupied rooms, barns, and stables by a fire-proofwall, or by a distance of 15 feet. Any wall is to be considered fire-proof which is built of solid brick, without openings, and one side ofwhich is "quite free. " Apparatus may be erected in barns and stables, provided the space required is partitioned off from the remainder by afire-proof wall. 2. The doors of apparatus sheds must open outwards, and must notcommunicate directly with rooms where fires and artificial lights areused. 3. Apparatus for the illumination of showmen's booths, "merry-go-rounds, "shooting galleries, and the like must be erected outside the tents, andbe inaccessible to the public. 4. Permanent apparatus erected in the open air must be at least 15 feetfrom an occupied building. 5. Apparatus sheds must be fitted at their highest points with outletventilators of sufficient size; the ventilators leading straight throughthe roof into the open air. They must be so arranged that the escapinggases and vapours cannot enter rooms or chimneys. 6. The contacts of any electrical warning devices must be outside theapparatus shed. 7. Acetylene plants must be prevented from freezing by erection in frost-free rooms, or by the employment of a heating apparatus or other suitableappliance. The heat must only be that of warm water or steam. Furnacesfor the heating appliance must be outside the rooms containinggenerators, their subsidiary apparatus, or holders; and must be separatedfrom such rooms by fire-proof walls. 8. In one of the walls of the apparatus shed--if possible not that havinga door--a window must be fitted which cannot be opened; and outside thatwindow an artificial light is to be placed. In the usual way acetylenelighting may be employed; but a lamp burning paraffin or oil, or alantern enclosing a candle, must always be kept ready for use inemergencies. In all circumstances internal lighting is forbidden. 9. Every acetylene installation must be provided with a main cock, placedin a conveniently accessible position so that the whole of the servicemay be cut off from the plant. 10. The seller of an apparatus must provide his customer with a sectionaldrawing, a description of the apparatus, and a set of rules for attendingto it. These are to be supplied in duplicate, and one set is to be kepthanging up in the apparatus shed. III. Rules for Working the Apparatus. 1. The apparatus must only be opened by daylight for addition of water. If the generator is one of those in which the entire charge of carbide isnot gasified at once, addition of fresh carbide must only be made bydaylight. 2. All work required by the plant, or by any portion of it, and allordinary attendance needed must be performed by daylight. 3. All water-seals must be carefully kept full. 4. When any part of an acetylene apparatus or a gas-meter freezes, notwithstanding the precautions specified in II. , 7, it must be thawedonly by pouring hot water into or over it; flames, burning fuel, or red-hot iron bars must not be used. 5. Alterations to any part of an apparatus which involve the operationsof soldering or riveting, &c. , _i. E. _, in which a fire must be used, or a spark may be produced by the impact of hammer on metal, must only becarried out by daylight in the open air after the apparatus has beentaken to pieces. First of all the plant must be freed from gas. This isto be done by filling every part with water till the liquid overflows, leaving the water in it for at least five minutes before emptying itagain. 6. The apparatus house must not be used for any other operation, noremployed for the storage of combustible articles. It must be efficientlyventilated, and always kept closed. A notice must be put upon the doorthat unauthorised persons are not permitted to enter. 7. It in forbidden to enter the house with a burning lantern or lamp, tostrike matches, or to smoke therein. 8. A search for leaks in the pipes must not be made with the aid of alight. 9. Alterations to the service must not be made while the pipes are underpressure, but only after the main cock has been shut. 10. If portable apparatus, such as described in I. , 12, are connected tothe burners with rubber tube, the tube must be fortified with an internalor external spiral of wire. The tube must be fastened at both ends to thecocks with thread, copper wire, or with ring clamps. 11. The preparation, storage, and use of compressed or liquefiedacetylene is forbidden. By compressed acetylene, however, is only to beunderstood gas compressed to a pressure exceeding one effectiveatmosphere. Acetylene compressed into porous matter, with or withoutacetone, is excepted from this prohibition. 12. In the case of plants serving 50 lights or less, not more than 100kilos. Of carbide in closed vessels may be kept in the apparatus housebesides the drum actually in use. A fresh drum is not to be opened before the previous one has been two-thirds emptied. Opened drums must be closed with an iron watertight lidcovering the entire top of the vessel. In the case of apparatus supplying over 500 lights, only one day'sconsumption of carbide must be kept in the generator house. In otherrespects the store of carbide for such installations is to be treated asa regular carbide store. 13. Carbide drums must not be opened with the aid of a flame or a red-hotiron instrument. 14. Acetylene apparatus must only be attended to by trustworthy andresponsible persons. The rules issued by the AUSTRIAN GOVERNMENT in 1905 for the installationof acetylene plant and the use of acetylene are divided into generalenactments relating to acetylene, and into special enactments in regardto the apparatus and installation. The general enactments state that: 1. The preparation and use of liquid acetylene is forbidden. 2. Gaseous acetylene, alone, in admixture, or in solution, must not becompressed above 2 atmospheres absolute except under special permission. 3. The storage of mixtures of acetylene with air or other gasescontaining or evolving free oxygen is forbidden. 4. A description of every private plant about to be installed must besubmitted to the local authorities, who, according to its size andcharacter, may give permission for it to be installed and brought intouse either forthwith or after special inspection. Important alterationsto existing plant must be similarly notified. 5. The firms and fitters undertaking the installation of acetylene plantmust be licensed. The special enactments fall under four headings, viz. , (_a_)apparatus; (_b_) plant houses; (_c_) pipes; (_d_)residues. In regard to apparatus it is enacted that: 1. The type of apparatus to be employed must be one which has beenapproved by one of certain public authorities in the country. 2. A drawing and description of the construction of the apparatus and ashort explanation of the method of working it must be fixed in aconspicuous position under cover in the apparatus house. The notice mustalso contain approved general information as to the properties of calciumcarbide and acetylene, precautions that must be observed to guard againstpossible danger, and a statement of how often the purifier will requireto be recharged. 3. The apparatus must be marked with the name of the maker, the year ofits construction, the available capacity of the gasholder, and themaximum generating capacity per hour. 4. Each constituent of the plant must be proportioned to the maximumhourly output of gas and in particular the available capacity of theholder must be 75 per cent. Of the latter. The apparatus must not bedriven above its nominal productive capacity. 5. The productive capacity of generators in which the gasholder has to beopened or the bell removed before recharging, or for the removal ofsludge, must not exceed 50 litres per hour, nor may the charge of carbideexceed 1 kilo. 6. Generators exceeding 50 litres per hour productive capacity must bearranged so that they can be freed from air before use. 7. Generators exceeding 1500 litres per hour capacity must be arranged sothat the acetylene, contained in the parts of the apparatus which have tobe opened for recharging or for the removal of sludge, can be removedbefore they are opened. 8. Automatic generators of which the decomposing chambers are builtinside the gasholder must not exceed 300 litres per hour productivecapacity. 9. Generators must be arranged so that after-generation cannot produceobjectionable results. 10. The holder of carbide-to-water generators must be large enough totake all the gas which may be produced by the introduction of one chargeof carbide without undue pressure ensuing. 11. The maximum pressure permissible in any part of the apparatus is 1. 1atmosphere absolute. 12. The temperature in the gas space of a generator must never exceed 80°C. 13. Generating apparatus, &c. , must be constructed in a workmanlikemanner of metal capable of resisting rust and distortion, and, where themetal comes in contact with carbide or acetylene, it must not be one(copper in particular) which forms an explosive compound with the gas. Cocks and screw connexions, &c. , of brass, bronze, &c. , must always bekept clean. Joints exposed to acetylene under pressure must be made byriveting or welding except that in apparatus not exceeding 100 litres perhour productive capacity double bending may be used. 14. Every apparatus must be fitted with a safety-valve or vent-pipeterminating in a safe place in the open, and of adequate size. 15. Every apparatus must be provided with an efficient purifier so fittedthat it may be isolated from the rest of the plant and with dueconsideration of the possible action of the purifying material upon themetal used. 16. Mercury pressure gauges are prohibited. Liquid gauges, if used mustbe double the length normally needed, and with a cock which in automaticapparatus must be kept shut while it is in action. 17. Proper steps must always be taken to prevent the apparatus freezing. In the absence of other precautions water-seals and pressure-gauges mustbe filled with liquid having a sufficiently low freezing-point andwithout action on acetylene or the containing vessel. 18. Signal devices to show the position of the gasholder bell must not becapable of producing sparks inside the apparatus house. 19. Leaks must not be sought for with an open flame and repairs requiringthe use of a blow-pipe, &c. , must only be carried out after the apparatushas been taken to pieces or freed from gas by flooding. 20. Apparatus must only be attended to by trustworthy and responsibleadults. 21. Portable apparatus holding not more than 1 kilo. Of carbide and ofnot more than 50 litres per hour productive capacity, and apparatus fixedand used out of doors are exempt from the foregoing regulations exceptNos. 11 and 12, and the first part of 13. In regard to (_b_), plant houses, it is enacted that: 1. Rooms containing acetylene apparatus must be of ample size, used forno other purpose, have water-tight floors, be warmed without fireplacesor chimneys, be lighted from outside through an air-tight window by anindependent artificial light, have doors opening outwards, efficientventilation and a store of sand or like material for fire extinction. Strangers must be warned away. 2. Apparatus of not more than 300 litres per hour productive capacity maybe erected in basements or annexes of dwelling houses, but if of over 50litres per hour capacity must not be placed under rooms regularlyfrequented. Rooms regularly frequented and those under the same must notbe used. 3. Apparatus of more than 300 litres per hour productive capacity must beerected in an independent building at least 15 feet distant from otherproperty, which building, unless it is at least 30 feet distant, must beof fire-proof material externally. 4. Gasholders exceeding 280 cubic foot in capacity must be in a detachedroom or in the open and inaccessible to strangers, and at least 30 feetfrom other property and with lightning conductors. 5. In case of fire the main cock must not be shut until it is ascertainedthat no one remains in the room served with the gas. 6. All acetylene installations must be known to the local fire brigade. In regard to (_c_), pipes, it is enacted that: 1. Mains for acetylene must be separated from the generating apparatus bya cock, and under a five-minute test for pressure must not show a fall ofover eight-tenths inch when the pressure is 13. 8 inches, or three timesthe working pressure, whichever is greater. 2. The pipes must as a rule be of iron, though lead may be used wherethey are uncovered and not exposed to risk of injury. Rubber connexionsmay only be used for portable apparatus, and attached to a terminal onthe metal pipes provided with a cock, and be fastened at both ends sothat they will not slip off the nozzles. In regard to (_d_), residues, it is enacted that special open orwell-ventilated pits must be provided for their reception when theapparatus exceeds 300 litres per hour productive capacity. With smallerapparatus they may be discharged into cesspools if sufficiently diluted. The ITALIAN GOVERNMENT regulations in regard to acetylene plant aredivided into eight sections. The first of these relates to the productionand use of liquid and compressed acetylene. The production and use ofliquid acetylene is prohibited except under the provisions of the lawsrelating to explosives. Neat acetylene must not be compressed to morethan l-1/2 atmospheres except that an absolute pressure of 10 atmospheresis allowed when the gas is dissolved in acetone or otherwise renderedfree from risk. Mixtures of acetylene with air or oxygen are forbidden, irrespective of the pressure or proportions. Mixtures of acetylene withhydrocarbons, carbonic oxide, hydrogen and inert gases are permittedprovided the proportion of acetylene does not exceed 50 per cent. Nor theabsolute pressure 10 atmospheres. The second section relates to acetylene installations, which areclassified in four groups, viz. , (_a_) fixed or portable apparatussupplying not more than thirty burners consuming 20 litres per hour;(_b_) private installations supplying between 30 and 200 suchburners; (_c_) public or works installations supplying between 30and 200 such burners; (_d_) installations supplying more than 200such burners. The installations must comply with the following general conditions: 1. No part of the generator when working at its utmost capacity shouldattain a temperature of more than 100° C. 2. The carbide must be completely decomposed in the apparatus so that noacetylene can be evolved from the residue. The residues must be dilutedwith water before being discharged into drains or cesspools, and sludgestorage-pits must be in the open. 3. The apparatus must preclude the escape of lime into the gas and waterconnexions. 4. Glass parts must be adequately protected. 5. Rubber connexions between the generator, gasholder, and main areabsolutely prohibited with installations supplying more than 30 burners. 6. Cocks must be provided for cutting off the main and connexions fromthe generator and gasholder. 7. Each burner must have an independent tap. 8. Generators of groups (_b_), (_c_), and (_d_) must beconstructed so that no after-generation of acetylene can take placeautomatically and that any surplus gas would in any case be carried outof the generator house by a vent-pipe. The third section deals with generator houses, which must be wellventilated and light; must not be used for any other purpose except tostore one day's consumption of carbide, not exceeding 300 kilos. ; must befire-proof; must have doors opening outwards; and the vent-pipes mustterminate at a safe place in the open. Apparatus of group (_b_) mustnot be placed in a dwelling-room and only in an adjoining room if thegasholder is of less than 600 litres capacity. Apparatus of group(_c_) must be in an independent building which must be at least 33feet from occupied premises if the capacity of the gasholder is 6000litres and upwards. Half this distance suffices for gasholders containing600 to 6000 litres. These distances may be reduced at the discretion ofthe local authorities provided a substantial partition wall at least 1foot thick is erected. Apparatus of group (_d_) must be at least 50feet from occupied premises and the gasholder and generator must not bein the same building. The fourth section deals with the question of authorisation for theinstallation of acetylene plant. Apparatus of group (_a_) may beinstalled without obtaining permission from any authorities. In regard toapparatus of the other groups, permission for installation must beobtained from local or other authorities. The fifth section relates to the working of acetylene plant. It makes theconcessionaires and owners of the plant responsible for the manipulationand supervision of the apparatus, and for the employment of suitableoperators, who must not be less than 18 years of age. The sixth section relates to the inspection of acetylene plant from timeto time by inspectors appointed by the local or other authorities. Apparatus of group (_a_) is not subject to these periodicalinspections. The seventh section details the fees payable for the inspection ofinstallations and carbide stores, and fixes the penalties for non-compliance with the regulations. The eighth section refers to the notification of the position anddescription of all carbide works, stores, and acetylene installations tothe local authorities. The HUNGARIAN GOVERNMENT rules for the construction and examination ofacetylene plant forbid the use of copper and of its alloys; cocks, however, may be made of a copper alloy. The temperature in the gas spaceof a fixed generator must not exceed 50° C. , in that of a portableapparatus 80° C. The maximum effective pressure permissible is 0. 15atmosphere. The CONSEIL D'HYGIÈNE DE LA SEINE IN FRANCE allows a maximum pressure of1. 5 metres, i. E. , 59 inches, of water column in generators used for theordinary purposes of illumination; but apparatus intended to supply gasto the low-pressure oxy-acetylene blowpipe (see Chapter IX. ) may developup to 2. 5 metres, or 98. 5 inches of water pressure, provided copper andits alloys are entirely excluded from the plant and from the delivery-pipes. The NATIONAL BOARD OF FIRE UNDERWRITERS OF THE UNITED STATES OF AMERICAhas issued a set of rules and requirements, of which those relating toacetylene generators and plant are reproduced below. The underwritersstate that, "To secure the largest measure of safety to life andproperty, these rules for the installation of acetylene gas machines mustbe observed. " RULES FOR THE INSTALLATION AND USE OF ACETYLENE GAS GENERATORS. [Footnote: The "gallon" of these rules is, of course, the Americangallon, which is equal to 0. 83 English standard gallon. ] The use of liquid acetylene or gas generated therefrom is absolutelyprohibited. Failure to observe these rules is as liable to endanger life as property. To secure the largest measure of safety to life and property, thefollowing rules for the installation of acetylene gas machines must beobserved. _Class A. --Stationary Automatic Apparatus. _ 1. FOUNDATIONS. --(_a_) Must, where practicable, be of brick, stone, concrete or iron. If necessarily of wood they shall be extra heavy, located in a dry place and open to the circulation of air. The ordinary board platform is not satisfactory. Wooden foundations shallbe of heavy planking, joists or timbers, arranged so that the air willcirculate around them so as to form a firm base. (_b_) Must be so arranged that the machine will be level and unequalstrain will not be placed on the generator or connexions. 2. LOCATION. --(_a_) Generators, especially in closely built updistricts should preferably be placed outside of insured buildings ingenerator houses constructed and located in compliance with Rule 9. (_b_) Generators must be so placed that the operating mechanism willhave room for free and full play and can be adjusted without artificiallight. They must not be subject to interference by children or carelesspersons, and if for this purpose further enclosure is necessary, it mustbe furnished by means of slatted partitions permitting the freecirculation of air. (_c_) Generators which from their construction are renderedinoperative during the process of recharging must be so located that theycan be recharged without the aid of artificial light. (_d_) Generators must be placed where water will not freeze. 3. ESCAPES OR RELIEF-PIPES. --Each generator must be provided with anescape or relief-pipe of ample size; no such pipe to be less than 3/4-inch internal diameter. This pipe shall be substantially installed, without traps, and so that any condensation will drain back to thegenerator. It must be carried to a suitable point outside the building, and terminate in an approved hood located at least 12 feet above groundand remote from windows. The hood must be constructed in such a manner that it cannot beobstructed by rain, snow, ice, insects or birds. 4. CAPACITY. --(_a_) Must be sufficient to furnish gas continuouslyfor the maximum lighting period to all lights installed. A lightingperiod of at least 5 hours shall be provided for in every case. (_b_) Generators for conditions of service requiring lighting periodof more than 5 hours must be of sufficient capacity to avoid rechargingat night. The following ratings will usually be found advisable. (i) For dwellings, and where machines are always used intermittently, thegenerator must have a rated capacity equal to the total number of burnersinstalled. (ii) For stores, opera houses, theatres, day-run factories, and similarservice, the generator must have a rated capacity of from 30 to 50 percent, in excess of the total number of burners installed. (iii) For saloons and all night or continued service, the generator musthave a rated capacity of from 100 to 200 per cent. In excess of the totalnumber of burners installed. (_c_) A small generator must never be installed to supply a largenumber of lights, even though it seems probable that only a few lightswill be used at a time. _An overworked generator adds to the cost ofproducing acetylene gas_. 5. CARBIDE CHARGES. --Must be sufficient to furnish gas continuously forthe maximum lighting period to all burners installed. In determiningcharges lump carbide must be estimated as capable of producing 4-1/2cubic foot of gas to the pound, commercial 1/4-inch carbide 4 cubic feetof gas to the pound, and burners must be considered as requiring at least25 per cent. More than their rated consumption of gas. 6. BURNERS. --Burners consuming one-half of a cubic foot of gas per hourare considered standard in rating generators. Those having a greater orless capacity will decrease or increase the number of burners allowablein proportion. Burners usually consume from 25 to 100 per cent. More than their ratedconsumption of gas, depending largely on the working pressure. The so-called 1/2-foot burner when operated at pressures of from 20- to 25-tenths inches water column (2 to 2-1/2 inches) is usually used with besteconomy. 7. PIPING. --(_a_) Connexions from generators to service-pipes mustbe made with right and left thread nipples or long thread nipples withlock nuts. All forms of unions are prohibited. (_b_) Piping must, as far as possible, be arranged so that anymoisture will drain back to the generator. If low points occur ofnecessity in any piping, they must be drained through tees into drip cupspermanently closed with screw caps or plugs. No pet-cocks shall be used. (_c_) A valve and by-pass connexion must be provided from theservice-pipe to the blow-off for removing the gas from the holder in caseit should be necessary to do so. (_d_) The schedule of pipe sizes for piping from generators toburners should conform to that commonly used for ordinary gas, but in nocase must the feeders be smaller than three-eighths inch. The following schedule is advocated: 3/8 inch pipe, 26 feet, three burners. 1/2 inch pipe, 30 feet, six burners. 3/4 inch pipe, 50 feet, twenty burners. 1 inch pipe, 70 feet, thirty-five burners. 1-1/4 inch pipe, 100 feet, sixty burners. 1-1/2 inch pipe, 150 feet, one hundred burners. 2 inch pipe, 200 feet, two hundred burners. 2-1/2 inch pipe, 300 feet, three hundred burners. 3 inch pipe, 450 feet, four hundred and fifty burners, 3-1/2 inch pipe, 500 feet, six hundred burners. 4 inch pipe, 600 feet, seven hundred and fifty burners. (_e_) Machines of the carbide-feed type must not be fitted withcontinuous drain connexions leading to sewers, but must discharge intosuitable open receptacles which may have such connections. (_f_) Piping must be thoroughly tested both before and after theburners have been installed. It must not show loss in excess of 2 incheswithin twelve hours when subjected to a pressure equal to that of 15inches of mercury. (_g_) Piping and connexions must be installed by persons experiencedin the installation of acetylene apparatus. 8. CARE AND ATTENDANCE. --In the care of generators designed for alighting period of more than five hours always clean and recharge thegenerating chambers at regular stated intervals, regardless of the numberof burners actually used. Where generators are not used throughout the entire year always removeall water and gas and clean thoroughly at the end of the season duringwhich they are in service. It is usually necessary to take the bell portion out and invert it so asto allow all gas to escape. This should never be done in the presence ofartificial light or fire of any kind. Always observe a regular time, during daylight hours only, for attendingto and charging the apparatus. In charging the generating chambers of water-feed machines clean allresiduum carefully from the containers and remove it at once from thebuilding. Separate from the mass any unslacked carbide remaining andreturn it to the containers, adding now carbide as required. Be carefulnever to fill the containers over the specified mark, as it is importantto allow for the swelling of the carbide when it comes in contact withwater. The proper action and economy of the machine are dependent on thearrangement and amount of carbide placed in the generator. Carefullyguard against the escape of gas. Whenever recharging with carbide always replenish the water-supply. Never deposit residuum or exhausted material from water-feed machines insewer-pipes or near inflammable material. Always keep water-tanks and water-seals filled with clean water. Never test the generator or piping for leaks with a flame, and neverapply flame to an outlet from which the burner has been removed. Never use a lighted match, lamp, candle, lantern or any open light nearthe machine. Failure to observe the above cautions is as liable to endanger life asproperty. 9. OUTSIDE GENERATOR HOUSES. --(_a_) Outside generator houses shouldnot be located within 5 feet of any opening into, nor shall they opentoward any adjacent building, and must be kept under lock and key. (_b_) The dimensions must be no greater than the apparatus requiresto allow convenient room for recharging and inspection of parts. Thefloor must be at least 12 inches above grade and the entire structurethoroughly weather-proof. (_c_) Generator houses must be thoroughly ventilated, and anyartificial heating necessary to prevent freezing shall be done by steamor hot-water systems. (_d_) Generator houses must not be used for the storage of calciumcarbide except in accordance with the rules relating to that subject(_vide_ Chapter II. ). _Class B. --Stationary Non-Automatic Apparatus_. 10. FOUNDATIONS. --(_a_) Must be of brick, stone or concrete. (_b_) Must be so arranged that the machine will be level and so thatstrain will not be brought upon the connexions. 11. GAS-HOUSES. --(_a_) Must be constructed entirely of non-combustible material and must not be lighted by any system ofillumination involving open flames. (_b_) Must be heated, where artificial heating is necessary toprevent freezing, by steam or hot-water systems, the heater to be locatedin a separate building, and no open flames to be permitted withingenerator enclosures. (_c_) Must be kept closed and locked excepting during daylighthours. (_d_) Must be provided with a permanent and effective system ofventilation which will be operative at all times, regardless of theperiods of operation of the plant. 12. ESCAPE-PIPES. --Each generator must be provided with a vent-pipe ofample size, substantially installed, without traps. It must be carried toa suitable point outside the building and terminate in an approved hoodlocated at least 12 feet above ground and remote from windows. The hood must be constructed in such a manner that it cannot beobstructed by rain, snow, ice, insects or birds. 13. CARE AND MAINTENANCE. --All charging and cleaning of apparatus, generation of gas and execution of repairs must be done during daylighthours only, and generators must not be manipulated or in any way tamperedwith in the presence of artificial light. This will require gasholders of a capacity sufficient to supply alllights installed for the maximum lighting period, without the necessityof generation of gas at night or by artificial light. In the operation of generators of the carbide-feed type it is importantthat only a limited amount of carbide be fed into a given body of water. An allowance of at least one gallon of generating water per pound ofcarbide must be made in every case, and when this limit has been reachedthe generator should be drained and flushed, and clean water introduced. These precautions are necessary to avoid over-heating during generationand accumulation of hard deposits of residuum in the generating chamber. (Rule 14, referring to the storage of carbide, has been quoted in ChapterII. (page 19)). RULES FOR THE CONSTRUCTION OF GENERATORS. The following Rules are intended to provide only against the morehazardous defects usually noted in apparatus of this kind. The Rules donot cover all details of construction nor the proper proportioning ofparts, and devices which comply with these requirements alone are notnecessarily suitable for listing as permissible for use. These points areoften only developed in the examination required before permission isgiven for installation. _Class A. --Stationary Apparatus for Isolated Installations. _ 15. GENERAL RULES. GENERATORS. --(_a_) Must be made of iron or steel, and in a manner and of material to insure stability and durability. (_b_) Must be automatically regulated and uniform in their action, producing gas only as immediate consumption demands, and so designed thatgas is generated without producing sufficient heat to cause yellowdiscoloration of residuum (which will occur at about 500° F. ) or abnormalpressure at any stage of the process when using carbide of any degree offineness. The presence of excessive heat tends to change the chemical character ofthe gas and may even cause its ignition, while in machines of thecarbide-feed type, finely divided carbide will produce excessive pressureunless provision is made to guard against it. (_c_) Must be so arranged that during recharging, back flow of gasfrom the gasholder will be automatically prevented, or so arranged thatit will be impossible to charge the apparatus without first closing thesupply-pipe to the gasholder, and to the other generating chambers ifseveral are used. This is intended to prevent the dangerous escape of gas. (_d_) The water or carbide supply to the generating chamber must beso arranged that gas will be generated long enough in advance of theexhaustion of the supply already in the gasholder to allow the using ofall lights without exhausting such supply. This provides for the continuous working of the apparatus under allconditions of water-feed and carbide charge, and it obviates theextinction of lights through intermittent action of the machine. (_e_) No valves or pet-cocks opening into the room from the gas-holding part or parts, the draining of which will allow an escape of gas, are permitted, and condensation from all parts of the apparatus must beautomatically removed without the use of valves or mechanical workingparts. Such valves and pet-cocks are not essential; their presence increases thepossibility of leakage. The automatic removal of condensation from theapparatus is essential to the safe working of the machine. U-traps opening into the room from the gas-holding parts must not be usedfor removal of condensation. All sealed drip connexions must be soarranged as to discharge gas to the blow-off when blown out, and theseals must be self-restoring upon relief of abnormal pressure. (_f_) The apparatus must be capable of withstanding fire fromoutside causes. Sheet-metal joints must be double-seamed or riveted and thoroughlysweated with solder. Pipes must be attached to sheet-metal with lock-nutsor riveted flanges. This prohibits the use of wood or of joints relying entirely upon solder. (_g_) Gauge glasses, the breakage of which would allow the escape ofgas, must not be used. (_h_) The use of mercury seals is prohibited. Mercury has been found unreliable as a seal in acetylene apparatus. (_i_)Combustible oils must not be used in connexion with theapparatus. (_j_) The construction must be such that liquid seals shall notbecome thickened by the deposit of lime or other foreign matter. (_k_) The apparatus must be constructed so that accidental siphoningof water will be impossible. (_l_) Flexible tubing, swing joints, unions, springs, mechanicalcheck-valves, chains, pulleys, stuffing-boxes and lead or fusible pipingmust not be used on acetylene apparatus except where failure of suchparts will not vitally affect the working or safety of the machine. Floats must not be used excepting in cases where failure will result onlyin rendering the machine inoperative. (_m_) Every machine must be plainly marked with the maximum numberof lights it is designed to supply, the amount of carbide necessary for asingle charge, the manufacturer's name and the name of the machine. 16. GENERATING CHAMBERS. --(_a_) Must be constructed of galvanisediron or steel not less than No. 24 U. S. Standard gauge in thickness forcapacities up to and including 20 gallons, not less than No. 22 U. S. Standard gauge for capacities between 20 and 75 gallons, and not lessthan No. 20 U. S. Standard gauge for capacities in excess of 75 gallons. (_b_) Must each be connected with the gasholder in such a mannerthat they will, at all times, give open connexion either to the gasholderor to the blow-off pipe to the outer air. This prevents dangerous pressure within or the escape of gas from thegenerating chamber. (_c_) Must be so constructed that not more than 5 pounds of carbidecan be acted upon at once, in machines which apply water in smallquantities to the carbide. This tends to reduce the danger of overheating and excessive after-generation by providing for division of the carbide charges in machinesof this type. (_d_) Must be provided with covers having secure fastenings to holdthem properly in place and those relying on a water-seal must besubmerged in at least 12 inches of water. Water-seal chambers for coversdepending on a water-seal must be 1-1/2 inches wide and 15 inches deep, excepting those depending upon the filling of the seal chambers for thegeneration of gas, where 9 inches will be sufficient. (_e_) Must be so designed that the residuum will not clog or affectthe working of the machine and can conveniently be handled and removed. (_f_) Must be provided with suitable vent connexions to the blow-offpipe so that residuum may be removed and the generating water replacedwithout causing siphoning or introducing air to the gasholder uponrecharging. This applies to machines of the carbide-feed type. (_g_) Feed mechanism for machines of the carbide-feed type must beso designed that the direct fall of carbide from the carbide holder intothe water of the generator is prevented at all positions of the feedmechanisms; or, when actuated by the rise and fall of a gas-bell, must beso arranged that the feed-valve will not remain open after the landing ofthe bell, and so that the feed valve remains inoperative as long as thefilling opening on the carbide hopper remains open. Feed mechanisms mustalways be far enough above the water-level to prevent clogging from theaccumulation of damp lime. For this purpose the distance should be notless than 10 inches. 17. CARBIDE CHAMBERS. --(_a_) Must be constructed of galvanised ironor steel not less than No. 24 U. S. Standard gauge in thickness forcapacities up to and including 50 pounds and not less than No. 22 U. S. Standard gauge for capacities in excess of 50 pounds. (_b_) Must have sufficient carbide capacity to supply the fullnumber of burners continuously and automatically during the maximumlighting period. This rule removes the necessity of recharging or attending to the machineat improper hours. Burners almost invariably require more than theirrated consumption of gas, and carbide is not of staple purity, and thereshould therefore be an assurance of sufficient quantity to last as longas light is needed. Another important consideration is that in someestablishments burners are called upon for a much longer period oflighting than in others, requiring a generator of greater gas-producingcapacity. Machines having several generating chambers must automaticallybegin generation in each upon exhaustion of the preceding chamber. (_c_) Must be arranged so that the carbide holders or charges may beeasily and entirely removed in case of necessity. 18. GASHOLDERS. --(_a_) Must be constructed of galvanised iron orsteel not less than No. 24 U. S. Standard gauge in thickness forcapacities up to and including 20 gallons, not less than No. 22 U. S. Standard gauge for capacities between 20 and 75 gallons, and not lessthan No. 20 U. S. Standard gauge for capacities in excess of 75 gallons. Gas-bells, if used, may be two gauges lighter than holders. Condensation chambers, if placed under holders, to be of same gauge asholders. (_b_) Must be of sufficient capacity to contain all gas generatedafter all lights have been extinguished. If the holder is too small and blows off frequently after the lights areextinguished there is a waste of gas. This may suggest improper workingof the apparatus and encourage tampering. (_c_) Must, when constructed on the gasometer principle, be soarranged that when the gas-bell is filled to its maximum with gas atnormal pressure its lip or lower edge will extend at least 9 inches belowthe inner water-level. (_d_) Must, when constructed on the gasometer principle, have thedimensions of the tank portion so related to those of the bell that apressure of at least 11 inches will be necessary before gas can be forcedfrom the holder. (_e_) The bell portion of a gasholder constructed on the gasometerprinciple must be provided with a substantial guide to its upwardmovement, preferably in the centre of the holder, carrying a stop actingto chock the bell 1 inch above the normal blow-off point. This tends to insure the proper action of the bell and decreases theliability of escaping gas. (_f_) A space of at least three-quarters of an inch must be allowedbetween the sides of the tank and the bell. (_g_) All water-seals must be so arranged that the water-level maybe readily seen and maintained. 19. WATER-SUPPLY. --(_a_) The supply of water to the generator forgenerating purposes must not be taken from the water-seal of anygasholder constructed on the gasometer principle, unless the feedmechanism is so arranged that the water-seals provided for in Rules 18, (_c_), (_d_), and (_e_) may be retained under allconditions. This provides for the proper level of water in the gasholder. (_b_) In cases where machines of the carbide-feed type are suppliedwith water from city water-mains or house-pipes, the pipe connexion mustdischarge into the regularly provided filling trap on the generator andnot through a separate continuous connexion leading into the generatingchamber. This is to prevent the expulsion of explosive mixtures through thefilling trap in refilling. 20. RELIEFS OR SAFETY BLOW-OFFS. --(_a_) Must in all cases beprovided, and must afford free vent to the outer air for any over-production of gas, and also afford relief in case of abnormal pressure inthe machine. Both the above-mentioned vents may be connected, with the same escape-pipe. (_b_) Must be of at least 3/4-inch internal diameter and be providedwith suitable means for connecting to the pipe loading outside of thebuilding. (_c_) Must be constructed without valves or other mechanical workingparts. (_d_) Apparatus requiring pressure regulators must be provided withan additional approved safety blow-off attachment located between thepressure regulator and the service-pipes and discharging to the outerair. This is intended to prevent the possibility of undue pressure in theservice-pipes due to failure of the pressure regulator. 21. PRESSURES. --(_a_) The working pressure at the generator must notvary more than ten-tenths (1) inch water column under all conditions ofcarbide charge and feed, and between the limits of no load and 50 percent. Overload. (_b_) Apparatus not requiring pressure regulators must be soarranged that the gas pressure cannot exceed sixty-tenths (6) incheswater column. This requires the use of the pressure relief provided for in Rule No. 20(_a_). (_c_) Apparatus requiring pressure regulators must be so arrangedthat the gas pressure cannot exceed three pounds to the square inch. The pressure limit of 3 pounds is taken since that is the pressurecorresponding to a water column about 6 feet high, which is about, thelimit in point of convenience for water-sealed reliefs. 22. AIR MIXTURES. --Generators must be so arranged as to contain theminimum amount of air when first started or recharged, and no device orattachment facilitating or permitting mixture of air with the gas priorto consumption, except at the burners, shall be allowed. Owing to the explosive properties of acetylene mixed with air, machinesmust be so designed that such mixtures are impossible. 23. PURIFIERS. --(_a_) Must be constructed of galvanised iron orsteel not less than No. 24 U. S. Standard gauge in thickness. (_b_) Where installed, purifiers must conform to the general rulesfor the construction of other acetylene apparatus and allow the freepassage of gas. (_c_) Purifiers must contain no carbide for drying purposes. (_d_) Purifiers must be located inside of gasholders, or, wherenecessarily outside, must have no hand-holes which can be opened withoutfirst shutting off the gas-supply. 24. PRESSURE REGULATORS. --(_a_) Must conform to the rules for theconstruction of other acetylene apparatus so far as they apply and mustnot be subject to sticking or clogging. (_b_) Must be capable of maintaining a uniform pressure, not varyingmore than four-tenths inch water column, at any load within their rating. (_c_) Must be installed between valves in such a manner as tofacilitate inspection and repairs. _Class B. --Stationary Apparatus for Central Station Service. _ Generators of over 300 lights capacity for central station service arenot required to be automatic in operation. Generators of less than 300lights capacity must be automatic in operation and must comply in everyrespect with the requirements of Class A. 25. GENERAL RULES. GENERATORS. --(_a_) Must be substantiallyconstructed of iron or steel and be protected against depreciation by aneffective and durable preventive of corrosion. Galvanising is strongly recommended as a protection against oxidation, and it may to advantage be reinforced by a thorough coating of asphaltumor similar material. (_b_) Must contain no copper or alloy of copper in contact withacetylene, excepting in valves. (_c_) Must be so arranged that generation will take place withoutoverheating; temperatures in excess of 500° F. To be consideredexcessive. (_d_) Must be provided with means for automatic removal ofcondensation from gas passages. (_e_) Must be provided with suitable protection against freezing ofany water contained in the apparatus. No salt or other corrosive chemical is permissible as a protectionagainst freezing. (_f_) Must in general comply with the requirements governing theconstruction of apparatus for isolated installations so far as they areapplicable. (_g_) Must be so arranged as to insure correct procedure inrecharging and cleaning. (_h_) Generators of the carbide-feed type must be provided with someform of approved measuring device to enable the attendant to determinewhen the maximum allowable quantity of carbide has been fed into thegenerating chamber. In the operation of generators of this type an allowance of at least 1gallon of clean generating water per pound of carbide should be made, andthe generator should be cleaned after slaking of every full charge. Wherelump carbide is used the lumps may become embedded in the residuum, ifthe latter is allowed to accumulate at the bottom of the generatingchamber, causing overheating from slow and restricted generation, andrendering the mass more liable to form a hard deposit and bring severestresses upon the walls of the generator by slow expansion. 26. GENERATING CHAMBERS. --(_a_) Must each be connected with thegasholder in such a manner that they will, at all times, give openconnexion either to the gasholder or to the blow-off pipe into the outerair. (_b_) Must be so arranged as to guard against appreciable escape ofgas to the room at any time during the introduction of the charges. (_c_) Must be so designed that the residuum will not clog or affectthe operation of the machine and can conveniently be handled and removed. (_d_) Must be so arranged that during the process of cleaning andrecharging the back-flow of gas from the gasholder or other generatingchambers will be automatically prevented. 27. GASHOLDERS. --(_a_) Must be of sufficient capacity to contain atleast 4 cubic feet of gas per 1/2-foot burner of the rating. This is to provide for the requisite lighting period without thenecessity of making gas at night, allowance being made for theenlargement of burners caused by the use of cleaners. (_b_) Must be provided with suitable guides to direct the movementof the bell throughout its entire travel. 28. PRESSURE RELIEFS. --Must in all cases be provided, and must be soarranged as to prevent pressure in excess of 100-tenths (10) inches watercolumn in the mains. 29. PRESSURES. --Gasholders must be adjusted to maintain a pressure ofapproximately 25-tenths (2. 5) inches water column in the mains. CHAPTER V THE TREATMENT OF ACETYLENE AFTER GENERATION IMPURITIES IN CALCIUM CARBIDE. --The calcium carbide manufactured at thepresent time, even when of the best quality commercially obtainable, isby no means a chemically pure substance; it contains a large number offoreign bodies, some of which evolve gas on treatment with water. To aconsiderable extent this statement will probably always remain true inthe future; for in order to make absolutely pure carbide it would benecessary for the manufacturer to obtain and employ perfectly pure lime, carbon, and electrodes in an electric furnace which did not suffer attackduring the passage of a powerful current, or he would have to devise someprocess for simultaneously or subsequently removing from his carbidethose impurities which were derived from his impure raw materials or fromthe walls of his furnace--and either of these processes would increasethe cost of the finished article to a degree that could hardly be borne. Beside the impurities thus inevitably arising from the calcium carbidedecomposed, however, other impurities may be added to acetylene by theaction of a badly designed generator or one working on a wrong system ofconstruction; and therefore it may be said at once that the crude gascoming from the generating plant is seldom fit for immediate consumption, while if it be required for the illumination of occupied rooms, it mustinvariably be submitted to a rigorous method of chemical purification. IMPURITIES OF ACETYLENE. --Combining together what may be termed thecarbide impurities and the generator impurities in crude acetylene, theforeign bodies are partly gaseous, partly liquid, and partly solid. Theymay render the gas dangerous from the point of view of possibleexplosions; they, or the products derived from them on combustion, may beharmful to health if inspired, injurious to the fittings and decorationsof rooms, objectionable at the burner orifices by determining, orassisting in, the formation of solid growths which distort the flame andso reduce its illuminating power; they may give trouble in the pipes bycondensing from the state of vapour in bends and dips, or by depositing, if they are already solid, in angles, &c. , and so causing stoppages; orthey may be merely harmful economically by acting as diluents to theacetylene and, by having little or no illuminating value of themselves, causing the gas to emit less light than it should per unit of volumeconsumed, more particularly, of course, when the acetylene is not burntunder the mantle. Also, not being acetylene, or isomeric therewith, theyrequire, even if they are combustible, a different proportion of oxygenfor their perfect combustion; and a good acetylene jet is only calculatedto attract precisely that quantity of air to the flame which a gas havingthe constitution C_2H_2 demands. It will be apparent without argumentthat a proper system of purification is one that is competent to removethe carbide impurities from acetylene, so far as that removal isdesirable or necessary; it should not be called upon to extract thegenerator impurities, because the proper way of dealing with them is, tothe utmost possible extent, to prevent their formation. The soleexception to this rule is that of water-vapour, which invariablyaccompanies the best acetylene, and must be partially removed as soon asconvenient. Vapour of water almost always accompanies acetylene from thegenerator, even when the apparatus does not belong to those systems ofworking where liquid water is in excess, this being due to the fact thatin a generator where the carbide is in excess the temperature tends torise until part of the water is vapourised and carried out of thedecomposing chamber before it has an opportunity of reacting with theexcess of carbide. The issuing gas is therefore more or less hot, and itusually comes from the generating chamber saturated with vapour, thequantity needed so to saturate it rising as the temperature of the gasincreases. Practically speaking, there is little objection to thepresence of water-vapour in acetylene beyond the fear of deposition ofliquid in the pipes, which may accumulate till they are partially orcompletely choked, and may even freeze and burst them in very severeweather. Where the chemical purifiers, too, contain a solid materialwhich accidentally or intentionally acts as a drier by removing moisturefrom the acetylene, it is a waste of such comparatively expensivematerial to allow gas to enter the purifier wetter than need be. EXTRACTION OF MOISTURE. --In all large plants the extraction of themoisture may take place in two stages. Immediately after the generator, and before the washer if the generator requires such an apparatus tofollow it, a condenser is placed. Here the gas is made to travel somewhatslowly through one or more pipes surrounded with cold air or water, or ismade to travel through a space containing pipes in which cold water iscirculating, the precise method of constructing the condenser beingperfectly immaterial so long as the escaping gas has a temperature notappreciably exceeding that of the atmosphere. So cooled, however, the gasstill contains much water-vapour, for it remains saturated therewith atthe temperature to which it is reduced, and by the inevitable law ofphysics a further fall in temperature will be followed by a furtherdeposition of liquid water from the acetylene. Manifestly, if theinstallation is so arranged that the gas can at no part of the serviceand on no occasion fall to a lower temperature than that at which itissues from the condenser, the removal of moisture as effected by such acondenser will be sufficient for all practical purposes; but at least inall large plants where a considerable length of main is exposed to theair, a more complete moisture extractor must be added to the plant, orwater will be deposited in the pipes every cold night in the winter. Itis, however, useless to put a chemical drier, or one more searching inits action than a water-cooled condenser, at so early a position in theacetylene plant, because the gas will be subsequently stored in a water-sealed holder, where it will most probably once again be saturated withmoisture from the seal. When such generators are adopted as require tohave a specific washer placed after them in order to remove the water-soluble impurities, _e. G. _, those in which the gas does not actuallybubble through a considerable quantity of liquid in the generatingchamber itself, it is doubtful whether a separate condenser is altogethernecessary, because, as the water in the washer can easily be kept at theatmospheric temperature (by means of water circulating in pipes orotherwise), the gas will be brought to the atmospheric temperature in thewasher, and at that temperature it cannot carry with it more than acertain fixed proportion of moisture. The notion of partially drying agas by causing it to pass through water may appear paradoxical, but acomprehension of physical laws will show that it is possible, and willprove efficient in practice, when due attention is given to the factsthat the gas entering the washer is hot, and that it is subsequently tobe stored over water in a holder. GENERATOR IMPURITIES. --The generator impurities present in the crudestacetylene consist of oxygen and nitrogen, _i. E. _, the mainconstituents of air, the various gaseous, liquid, and semi-solid bodiesdescribed in Chapter II. , which are produced by the polymerising anddecomposing action of heat upon the carbide, water, and acetylene in theapparatus, and, whenever the carbide is in excess in the generator, somelime in the form of a very fine dust. In all types of water-to-carbideplant, and in some automatic carbide-feed apparatus, the carbide chambermust be disconnected and opened each time a fresh charge has to beinserted; and since only about one-third of the space in the containercan be filled with carbide, the remaining two-thirds are left full ofair. It is easy to imagine that the carbide container of a smallgenerator might be so large, or loaded with so small a quantity ofcarbide, or that the apparatus might in other respects be so badlydesigned, that the gas evolved might contain a sufficient proportion ofair to render it liable to explode in presence of a naked light, or of atemperature superior to its inflaming-point. Were a cock, however, whichshould have been shut, to be carelessly left open, an escape of gas from, rather than an introduction of air into, the apparatus would follow, because the pressure in the generator is above that of the atmosphere. Asis well known, roughly four-fifths by volume of the air consist ofnitrogen, which is non-inflammable and accordingly devoid of danger-conferring properties; but in all flames the presence of nitrogen isharmful by absorbing much of the heat liberated, thus lowering thetemperature of that flame, and reducing its illuminating power far moreseriously. On the other hand, a certain quantity of air in acetylenehelps to prevent burner troubles by acting as a mere diluent (albeit aninferior one to methane or marsh-gas), and therefore it has been proposedintentionally to add air to the gas before consumption, such a processbeing in regular use on the large scale in some places abroad. As Eitnerhas shown (Chapter VI. ) that in a 3/4-inch pipe acetylene ceases to beexplosive when mixed with less than 47. 7 per cent. Of air, an amount of, say, 40 per cent. Or less may in theory be safely added to acetylene; butin practice the amount of air added, if any, would have to be muchsmaller, because the upper limit of explosibility of acetylene-airmixtures is not rigidly fixed, varying from about 50 per cent. Of airwhen the mixture is in a small vessel, and fired electrically to about 25per cent. Of air in a large vessel approached with a flame. Moreover, safely to prepare such mixtures, after the proportion of air had beendecided upon, would require the employment of some additional perfectlytrustworthy automatic mechanism to the plant to draw into the apparatus aquantity of air strictly in accordance with the volume of acetylene made--a pair of meters geared together, one for the gas, the other for theair--and this would introduce extra complexity and extra expense. On thewhole the idea cannot be recommended, and the action of the British HomeOffice in prohibiting the use of all such mixtures except thoseunavoidably produced in otherwise good generators, or in burners of theordinary injector type, is perfectly justifiable. The derivation andeffect of the other gaseous and liquid generator impurities in acetylenewere described in Chapter II. Besides these, very hot gas has been foundto contain notable amounts of hydrogen and carbon monoxide, both of whichburn with non-luminous flames. The most plausible explanation of theirorigin has been given by Lewes, who suggests that they may be formed bythe action of water-vapour upon very hot carbide or upon carbon separatedtherefrom as the result of previous dissociation among the gases present;the steam and the carbon reacting together at a temperature of 500° C. Orthereabouts in a manner resembling that of the production of water-gas. The last generator impurity is lime dust, which is calcium oxide orhydroxide carried forward by the stream of gas in a state of extremelyfine subdivision, and is liable to be produced whenever water actsrapidly upon an excess of calcium carbide. This lime occasionally appearsin the alternative form of a froth in the pipes leading directly from thegenerating chamber; for some types of carbide-to-water apparatus, decomposing certain kinds of carbide, foam persistently when the liquidin them becomes saturated with lime, and this foam or froth is remarkablydifficult to break up. FILTERS. --It has just been stated that the purifying system added to anacetylene installation should not be called upon to remove thesegenerator impurities; because their appearance in quantity indicates afaulty generator, which should be replaced by one of better action. Onthe contrary, with the exception of the gases which are permanent atatmospheric temperature--hydrogen, carbon monoxide, nitrogen, and oxygen--and which, once produced, must remain in the acetylene (lowering itsilluminating value, but giving no further trouble), extraction of thesegenerator impurities is quite simple. The dust or froth of lime will beremoved in the washer where the acetylene bubbles through water--the dustitself can be extracted by merely filtering the gas through cotton-wool, felt, or the like. The least volatile liquid impurities will be removedpartly in the condenser, partly in the washer, and partly by themechanical dry-scrubbing action of the solid purifying material in thechemical purifier. To some extent the more volatile liquid bodies will beremoved similarly; but a complete extraction of them demands theemployment of some special washing apparatus in which the crude acetyleneis compelled to bubble (in finely divided streams) through a layer ofsome non-volatile oil, heavy mineral lubricating oil, &c. ; for thoughsoluble in such oil, the liquid impurities are not soluble in, nor dothey mix with, water; and since they are held in the acetylene asvapours, a simple passage through water, or through water-cooled pipes, does not suffice for their recovery. It will be seen that a sufficientremoval of these generator impurities need throw no appreciable extralabour upon the consumer of acetylene, for he can readily select a typeof generator in which their production is reduced to a minimum; while acotton-wool or coke filter for the gas, a water washer, which is alwaysuseful in the plant if only employed as a non-return valve between thegenerator and the holder, and the indispensable chemical purifiers, willtake out of the acetylene all the remaining generator impurities whichneed, and can, be extracted. CARBIDE IMPURITIES. --Neglecting very minute amounts of carbon monoxideand hydrogen (which may perhaps come from cavities in the calcium carbideitself), as being utterly insignificant from the practical point of view, the carbide impurities of the gas fall into four main categories: thosecontaining phosphorus, those containing sulphur, those containingsilicon, and those containing gaseous ammonia. The phosphorus in the gascomes from calcium phosphide in the calcium carbide, which is attacked bywater, and yields phosphoretted hydrogen (or phosphine, as it will betermed hereafter). The calcium phosphide, in its turn, is produced in theelectric furnace by the action of the coke upon the phosphorus inphosphatic lime--all commercially procurable lime and some varieties ofcoke (or charcoal) containing phosphates to a larger or smaller extent. The sulphur in the gas comes from aluminium sulphide in the carbide, which is produced in the electric furnace by the interaction ofimpurities containing aluminium and sulphur (clay-like bodies, &c. )present in the lime and coke; this aluminium sulphide is attacked bywater and yields sulphuretted hydrogen. Even in the absence of aluminiumcompounds, sulphuretted hydrogen may be found in the gases of anacetylene generator; here it probably arises from calcium sulphide, foralthough the latter is not decomposed by water, it gradually changes inwater into calcium sulphydrate, which appears to suffer decomposition. When it exists in the gas the silicon is derived from certain silicidesin the carbide; but this impurity will be dealt with by itself in a laterparagraph. The ammonia arises from the action of the water uponmagnesium, aluminium, or possibly calcium nitride in the calcium carbide, which are bodies also produced in the electric furnace or as the carbideis cooling. In the gas itself the ammonia exists as such; the phosphorusexists mainly as phosphine, partly as certain organic compoundscontaining phosphorus, the exact chemical nature of which has not yetbeen fully ascertained; the sulphur exists partly as sulphurettedhydrogen and partly as organic compounds analogous, in all probability, to those of phosphorus, among which Caro has found oil of mustard, andcertain bodies that he regards as mercaptans. [Footnote: It will beconvenient to borrow the phrase used in the coal-gas industry, callingthe compounds of phosphorus other than phosphine "phosphorus compounds, "and the compounds of sulphur other than sulphuretted hydrogen "sulphurcompounds. " The "sulphur compounds" of coal-gas, however, consist mainlyof carbon bisulphide, which is certainly not the chief "sulphur compound"in acetylene, even if present to any appreciable extent. ] The precise wayin which these organic bodies are formed from the phosphides andsulphides of calcium carbide is not thoroughly understood; but the systemof generation employed, and the temperature obtaining in the apparatus, have much to do with their production; for the proportion of the totalphosphorus and sulphur found in the crude gas which exists as "compounds"tends to be greater as the generating plant yields a higher temperature. It should be noted that ammonia and sulphuretted hydrogen have oneproperty in common which sharply distinguishes them from the sulphur"compounds, " and from all the phosphorus compounds, including phosphine. Ammonia and sulphuretted hydrogen are both very soluble in water, thelatter more particularly in the lime-water of an active acetylenegenerator; while all the other bodies referred to are completelyinsoluble. It follows, therefore, that a proper washing of the crude gasin water should suffice to remove all the ammonia and sulphurettedhydrogen from the acetylene; and as a matter of fact those generators inwhich the gas is evolved in presence of a large excess of water, and inwhich it has to bubble through such water, yield an acetylene practicallyfree from ammonia, and containing nearly all the sulphur which it doescontain in the state of "compounds. " It must also be remembered thatchemical processes which are perfectly suited to the extraction ofsulphuretted hydrogen and phosphine are not necessarily adapted for theremoval of the other phosphorus and sulphur compounds. WASHERS. --In designing a washer for the extraction of ammonia andsulphuretted hydrogen it is necessary to see that the gas is brought intomost intimate contact with the liquid, while yet no more pressure thancan possibly be avoided is lost. Subdivision of the gas stream may beeffected by fitting the mouth of the inlet-pipe with a rose having alarge number of very small holes some appreciable distance apart, or bybending the pipe to a horizontal position and drilling it on its uppersurface with numbers of small holes. Another method is to force the gasto travel under a series of partitions extending just below the water-level, forming the lower edges of those partitions either perfectlyhorizontal or with small notches like the teeth of a saw. One volume ofpure water only absorbs about three volumes of sulphuretted hydrogen atatmospheric temperatures, but takes up some 600 volumes of gaseousammonia; and as ammonia always accompanies the sulphuretted hydrogen, thelatter may be said to be absorbed in the washer by a solution of ammonia, a liquid in which sulphuretted hydrogen is much more soluble. Therefore, since water only dissolves about an equal volume of acetylene, the liquidin the washer will continue to extract ammonia and sulphuretted hydrogenlong after it is saturated with the hydrocarbon. For this reason, _i. E. _, to avoid waste of acetylene by dissolution in the cleanwater of the washer, the plan is sometimes adopted of introducing waterto the generator through the washer, so that practically the carbide isalways attacked by a liquid saturated with acetylene. Provided the liquidin the generator does not become seriously heated, there is no objectionto this arrangement; but if the water is heated strongly in the generatorit loses much or all of its solvent properties, and the impurities may bedriven back again into the washer. Clearly if the waste lime of thegenerator occurs as a dry or damp powder, the plan mentioned is not to berecommended; but when the waste lime is a thin cream--water being inlarge excess--it may be adopted. If the generator produces lime dustamong the gas, and if the acetylene enters the washer through minuteholes, a mechanical filter to remove the dust must be inserted betweenthe generator and the washer, or the orifices of the leading pipe will bechoked. Whenever a water-cooled condenser is employed after thegenerator, in which the gas does not come in contact with the water, thatliquid may always be used to charge the generator. For compactness andsimplicity of parts the water of the holder seal is occasionally used asthe washing liquid, but unless the liquid of the seal is constantlyrenewed it will thus become offensive, especially if the holder is undercover, and it will also act corrosively upon the metal of the tank andbell. The water-soluble impurities in acetylene will not be removedcompletely by merely standing over the holder seal for a short time, andit is not good practice to pass unnecessarily impure gas into a holder. [Footnote: This is not a contradiction of what has been said in ChapterIII. About the relative position of holder and chemical purifiers, because reference is now being made to ammonia and sulphuretted hydrogenonly. ] HARMFULNESS OF IMPURITIES. --The reasons why the carbide impurities mustbe removed from acetylene before it is burned have now to be explained. From the strictly chemical point of view there are three compounds ofphosphorus, all termed phosphoretted hydrogen or phosphine: a gas, PH_3;a liquid, P_2H_4; and a solid, P_4H_2. The liquid is spontaneouslyinflammable in presence of air; that is to say, it catches fire of itselfwithout the assistance of spark or flame immediately it comes in contactwith atmospheric oxygen; being very volatile, it is easily carried asvapour by any permanent gas. The gaseous phosphine is not actuallyspontaneously inflammable at temperatures below 100° C. ; but it oxidisesso rapidly in air, even when somewhat diluted, that the temperature mayquickly rise to the point of inflammation. In the earliest days of theacetylene industry, directly it was recognised that phosphine alwaysaccompanies crude acetylene from the generator, it was believed thatunless the proportion were strictly limited by decomposing only a carbidepractically free from phosphides, the crude acetylene might exhibitspontaneously inflammable properties. Lewes, indeed, has found that asample of carbide containing 1 per cent of calcium phosphide gave(probably by local decomposition--the bulk of the phosphide sufferingattack first) a spontaneously inflammable gas; but when examiningspecimens of commercial carbide the highest amount of phosphine hediscovered in the acetylene was 2. 3 per cent, and this gas was notcapable of self-inflammation. According to Bullier, however, acetylenemust contain 80 per cent of phosphine to render it spontaneouslyinflammable. Berdenich has reported a case of a parcel of carbide whichyielded on the average 5. 1 cubic foot of acetylene per lb. , producing gaswhich contained only 0. 398 gramme of phosphorus in the form of phosphineper cubic metre (or 0. 028 per cent. Of phosphine) and was spontaneouslyinflammable. But on examination the carbide in question was found to bevery irregular in composition, and some lumps produced acetylenecontaining a very high proportion of phosphorus and silicon compounds. Nodoubt the spontaneous inflammability was due to the exceptional richnessof these lumps in phosphorus. As manufactured at the present day, calciumcarbide ordinarily never contains an amount of phosphide sufficient torender the gas dangerous on the score of spontaneous inflammability; butshould inferior material ever be put on the markets, this danger mighthave to be guarded against by submitting the gas evolved from it tochemical analysis. Another risk has been suggested as attending the useof acetylene contaminated with phosphine (and to a minor degree withsulphuretted hydrogen), viz. , that being highly toxic, as theyundoubtedly are, the gas containing them might be extremely dangerous tobreathe if it escaped from the service, or from a portable lamp, unconsumed. Anticipating what will be said in a later paragraph, theworst kind of calcium carbide now manufactured will not yield a gascontaining more than 0. 1 per cent. By volume of sulphuretted hydrogen and0. 05 per cent. Of phosphine. According to Haldane, air containing 0. 07per cent. Of sulphuretted hydrogen produces fatal results on man if it isbreathed for some hours, while an amount of 0. 2 per cent. Is fatal in 1-1/2 minutes. Similar figures for phosphine cannot be given, becausepoisoning therewith is very rare or quite unknown: the cases of "phossy-jaw" in match factories being caused either by actual contact with yellowphosphorus or by inhalation of its vapour in the elemental state. However, assuming phosphine to be twice as toxic as sulphurettedhydrogen, its effect in crude acetylene of the above-mentionedcomposition will be equal to that of the sulphuretted hydrogen, so thatin the present connexion the gas may be said to be equally toxic with asample of air containing 0. 2 per cent. Of sulphuretted hydrogen, whichkills in less than two minutes. But this refers only to crude acetyleneundiluted with air; and being a hydrocarbon--being in fact neither oxygennor common air--acetylene is irrespirable of itself though largely devoidof specific toxic action. Numerous investigations have been made of theamount of acetylene (apart from its impurities) which can be breathed insafety; but although these point to a probable recovery after a fairlylong-continued respiration of an atmosphere charged with 30 per cent. Ofacetylene, the figure is not trustworthy, because toxicologicalexperiments upon animals seldom agree with similar tests upon man. Ifcrude acetylene were diluted with a sufficient proportion of air toremove its suffocating qualities, the percentage of specifically toxicingredients would be reduced to a point where their action might beneglected; and short of such dilution the acetylene itself would in allprobability determine pathological effects long before its impuritiescould set up symptoms of sulphur and phosphorus poisoning. Ammonia is objectionable in acetylene because it corrodes brass fittingsand pipes, and because it is partially converted (to what extent isuncertain) into nitrous and nitric acids as it passes through the flame. Sulphur is objectionable in acetylene because it is converted intosulphurous and sulphuric anhydrides, or their respective acids, as itpasses through the flame. Phosphorus is objectionable because in similarcircumstances it produces phosphoric anhydride and phosphoric acid. Eachof these acids is harmful in an occupied room because they injure thedecorations, helping to rot book-bindings, [Footnote: It is only fair tostate that the destruction of leather bindings is commonly due to tracesof sulphuric acid remaining in the leather from the production employedin preparing it, and is but seldom caused directly by the products ofcombustion coming from gas or oil. ] tarnishing "gold-leaf" ornaments, andspoiling the colours of dyed fabrics. Each is harmful to the humansystem, sulphuric and phosphoric anhydrides (SO_3, and P_4O_10) acting asspecific irritants to the lungs of persons predisposed to affections ofthe bronchial organs. Phosphorus, however, has a further harmful action:sulphuric anhydride is an invisible gas, but phosphoric anhydride is asolid body, and is produced as an extremely fine, light, white voluminousdust which causes a haze, more or less opaque, in the apartment. [Footnote: Lewes suggests that ammonia in the gas burnt may assist in theproduction of this haze, owing to the formation of solid ammonium saltsin the state of line dust. ] Immediately it comes in contact withatmospheric moisture phosphoric anhydride is converted into phosphoricacid, but this also occurs at first as a solid substance. The solidityand visibility of the phosphoric anhydride and acid are beneficial inpreventing highly impure acetylene being unwittingly burnt in a room;but, on the other hand, being merely solids in suspension in the air, thecombustion products of phosphorus are not so easily carried away from theroom by the means provided for ventilation as are the products of thecombustion of sulphur. Phosphoric anhydride is also partly deposited inthe solid state at the burner orifices, perhaps actually corroding thesteatite jets, and always assisting in the deposition of carbon from anypolymerised hydrocarbons in the acetylene; thus helping the carbon toblock up or distort those orifices. Whenever the acetylene is to be burnton the incandescent system under a mantle of the Welsbach or other type, phosphorus, and possibly sulphur, become additionally objectionable, andrigorous extraction is necessary. As is well known, the mantle iscomposed of the oxides of certain "rare earths" which owe their practicalvalue to the fact that they are non-volatile at the temperature of thegas-flame. When a gas containing phosphorus is burnt beneath such amantle, the phosphoric anhydride attacks those oxides, partiallyconverting them into the respective phosphates, and these bodies are lessrefractory. A mantle exposed to the combustion products of crudeacetylene soon becomes brittle and begins to fall to pieces, occasionallyshowing a yellowish colour when cold. The actual advantage of burningacetylene on the incandescent system is not yet thoroughly established--in this country at all events; but it is clear that the process will notexhibit any economy (rather the reverse) unless the plant is providedwith most capable chemical purifiers. Phosphorus, sulphur, and ammoniaare not objectionable in crude acetylene because they confer upon the gasa nauseous odour. From a well-constructed installation no acetyleneescapes unconsumed: the gas remains wholly within the pipes until it isburnt, and whatever odour it may have fails to reach the human nostrils. A house properly piped for acetylene will be no more conspicuous by itsodour than a house properly piped for coal-gas. On the contrary, the factthat the carbide impurities of acetylene, which, in the absolutely purestate, is a gas of somewhat faint, hardly disagreeable, odour, do conferupon that gas a persistent and unpleasant smell, is distinctlyadvantageous; for, owing to that odour, a leak in the pipes, an unclosedtap, or a fault in the generating plant is instantly brought to theconsumer's attention. A gas wholly devoid of odour would be extremelydangerous in a house, and would have to be scented, as is done in thecase of non-carburetted water-gas when it is required for domesticpurposes. AMOUNTS OF IMPURITIES AND SCOPE OF PURIFICATION. --Partly for the reasonwhich has just been given, and partly on the ground of expense, acomplete removal of the impurities from crude acetylene is not desirable. All that need be done is to extract sufficient to deprive the gas of itsinjurious effects upon lungs, decorations, and burners. As it stands, however, such a statement is not sufficiently precise to be useful eitherto consumers of acetylene or to manufacturers of plant, and some more orless arbitrary standard must be set up in order to define the compositionof "commercially pure" acetylene, as well as to gauge the efficiency ofany process of purification. In all probability such limit may bereasonably taken at 0. 1 milligramme of either sulphur or phosphorus(calculated as elementary bodies) per 1 litre of acetylene, _i. E. _, 0. 0-1. 1 grain per cubic foot; a quantity which happens to correspondalmost exactly with a percentage by weight of 0. 01. Owing to the atomicweights of these substances, and the very small quantities beingconsidered, the same limit hardly differs from that of 0. 01 per cent. Byweight of sulphuretted hydrogen or of phosphine--it being alwaysrecollected that the sulphur and phosphorus do not necessarily exist inthe gas as simple hydrides. Keppeler, however, has suggested the higherfigure of 0. 15 milligramme of either sulphur or phosphorus per litre ofacetylene (=0. 066 grain per cubic foot) for the maximum amount of theseimpurities permissible in purified acetylene. He adopts this standard onthe basis of the results of observations of the amounts of sulphur andphosphorus present in the gas issuing from a purifier charged withheratol at the moment when the last layer of the heratol is beginning tochange colour. No limit has been given for the removal of the ammonia, partly because that impurity can more easily, and without concomitantdisadvantage, be extracted entirely; and partly because it is usuallyremoved in the washer and not in the true chemical purifier. According to Lewes, the maximum amount of ammonia found in the acetylenecoming from a dripping generator is 0. 95 gramme per litre, while incarbide-to-water gas it is 0. 16 gramme: 417 and 70. 2 grains per cubicfoot respectively. Rossel and Landriset have found 4 milligrammes (1. 756grains [Footnote: Milligrammes per litre; grains per cubic foot. It isconvenient to remember that since 1 cubic foot of water weighs 62. 321 x16 - 997. 14 avoirdupois ounces, grammes per litre are approximately equalto oz. Per cubic foot; and grammes per cubic metre to oz. Per 1000 cubicfeet. ]) to be the maximum in water-to-carbide gas, and none to occur incarbide-to-water acetylene. Rossel and Landriset return the minimumproportion of sulphur, calculated as H_2S, found in the gaseous state inacetylene when the carbide has not been completely flooded with water at1. 18 milligrammes per litre, or 0. 52 grain per cubic foot; and thecorresponding maxima at 1. 9 milligrammes, or 0. 84 grain. In carbide-to-water gas, the similar maxima are 0. 23 milligramme or 0. 1 grain. Asalready stated, the highest proportion of phosphine yet found inacetylene is 2. 3 per cent. (Lewes), which is equal to 32. 2 milligrammesof PH_3 per litre or 14. 13 grains per cubic foot (Polis); but this sampledated from 1897. Eitner and Keppeler record the minimum proportion ofphosphorus, calculated as PH_3, found in crude acetylene, as 0. 45milligramme per litre, and the maximum as 0. 89 milligramme per litre; inEnglish terms these figures are 0. 2 and 0. 4 grain per cubic foot. On anaverage, however, British and Continental carbide of the present day maybe said to give a gas containing 0. 61 milligramme of phosphoruscalculated as PH_3 per litre and 0. 75 milligramme of sulphur calculatedas H_2S. In other units these figures are equal to 0. 27 grain of PH_3 and0. 33 grain of H_2S per 1 cubic foot, or to 0. 041 per cent. By volume ofPH_3 and 0. 052 per cent. Of H_2S. Yields of phosphorus and sulphur muchhigher than these will be found in the journals and books, but suchanalytical data were usually obtained in the years 1896-99, before themanufacture of calcium carbide had reached its present degree ofsystematic control. A commercial specimen of carbide was seen by one ofthe authors as late as 1900 which gave an acetylene containing 1. 12milligramme of elementary sulphur per litre, i. E. , 0. 096 per cent, byvolume, or 0. 102 per cent, by volume of H_2S; but the phosphorus showedthe low figure of 0. 36 milligramme per litre (0. 031 per cent, of P or0. 034 per cent, of PH_3 by volume). The British Acetylene Association's regulations relating to carbide ofcalcium (_vide_ Chap. XIV. ) contain a clause to the effect that"carbide which, when properly decomposed, yields acetylene containingfrom all phosphorus compounds therein more than 0. 05 per cent, by volumeof phosphoretted hydrogen, may be refused by the buyer. " This limit isequivalent to 0. 74 milligramme of phosphorus calculated as PH_3 perlitre. A latitude of 0. 01 per cent, is, however, allowed for theanalysis, so that the ultimate limit on which carbide could be rejectedis: 0. 06 volume per cent. Of PH_3, or 0. 89 milligramme of phosphorus perlitre. The existence in appreciable quantity of combined silicon as a normalimpurity in acetylene seems still open to doubt. Calcium carbidefrequently contains notable quantities of iron and other silicides; butalthough these bodies are decomposed by acids, yielding hydrogensilicide, or siliciuretted hydrogen, they are not attacked by plainwater. Nevertheless Wolff and Gerard have found hydrogen silicide incrude acetylene, and Lewes looks upon it as a common impurity in smallamounts. When it occurs, it is probably derived, as Vigouroux hassuggested, from "alloys" of silicon with calcium, magnesium, andaluminium in the carbide. The metallic constituents of these substanceswould naturally be attacked by water, evolving hydrogen; and thehydrogen, in its nascent state, would probably unite with the liberatedsilicon to form hydrogen silicide. Many authorities, including Keppeler, have virtually denied that silicon compounds exist in crude acetylene, while the proportion 0. 01 per cent. Has been given by other writers asthe maximum. Caro, however, has stated that the crude gas almostinvariably contains silicon, sometimes in very small quantities, butoften up to the limit of 0. 8 per cent. ; the failure of previousinvestigators to discover it being due to faulty analytical methods. Carohas seen one specimen of (bad) carbide which gave a spontaneouslyinflammable gas although it contained only traces of phosphine; itsinflammability being caused by 2. 1 per cent. Of hydrogen silicide. Practically speaking, all the foregoing remarks made about phosphineapply equally to hydrogen silicide: it burns to solid silicon oxide(silica) at the burners, is insoluble in water, and is spontaneouslyinflammable when alone or only slightly diluted, but never occurs in goodcarbide in sufficient proportion to render the acetylene itselfinflammable. According to Caro the silicon may be present both ashydrogen silicide and as silicon "compounds. " A high temperature in thegenerator will favour the production of the latter; an apparatus in whichthe gas is washed well in lime-water will remove the bulk of the former. Fraenkel has found that magnesium silicide is not decomposed by water oran alkaline solution, but that dilute hydrochloric acid acts upon it andspontaneously inflammable hydrogen silicide results. If it may be assumedthat the other silicides in commercial calcium carbide also behave inthis manner it is plain that hydrogen silicide cannot occur in crudeacetylene unless the gas is supposed to be hurried out of the generatorbefore the alkaline water therein has had time to decompose any traces ofthe hydrogen silicide which is produced in the favouring conditions ofhigh temperature sometimes prevailing. Mauricheau-Beaupré has failed tofind silica in the products of combustion of acetylene from carbide ofvarying degrees of purity. He found, however, that a mixture of strongnitric and hydrochloric acids (_aqua regia_), if contaminated withtraces of phosphoric acid, dissolved silica from the glass of laboratoryvessels. Consequently, since phosphoric acid results from the phosphinein crude acetylene when the gas is passed through aqua regia, silica maybe found on subsequently evaporating the latter. But this, silica, hefound, was derived from the glass and not through the oxidation ofsilicon compounds in the acetylene. It is possible that some of theearlier observers of the occurrence of silicon compounds in crudeacetylene may have been misled by the solution of silica from the glassvessels used in their investigations. The improbability of recognisablequantities of silicon compounds occurring in acetylene in any ordinaryconditions of generation is demonstrated by a recent study by Fraenkel ofthe composition of the deposit produced on reflectors exposed to theproducts of combustion of a sample of acetylene which afforded a hazewhen burnt. The deposit contained 51. 07 per cent. Of phosphoric acid, butno silica. The gas itself contained from 0. 0672 to 0. 0837 per cent. Byvolume of phosphine. PURIFYING MATERIALS. --When acetylene first began to be used as a domesticilluminant, most generator builders denied that there was any need forthe removal of these carbide impurities from the gas, some going so faras to assert that their apparatus yielded so much purer an acetylene thanother plant, where purification might be desirable, that an addition of aspecial purifier was wholly unnecessary. Later on the more responsiblemembers of the trade took another view, but they attacked the problem ofpurification in a perfectly empirical way, either employing some purelymechanical scrubber filled with some moist or dry porous medium, orperhaps with coke or the like wetted with dilute acid, or they simplyborrowed the processes adopted in the purification of coal-gas. At firstsight it might appear that the more simple methods of treating coal-gasshould be suitable for acetylene; since the former contains two of theimpurities--sulphuretted hydrogen and ammonia--characteristic of crudeacetylene. After removing the ammonia by washing with water, therefore, it was proposed to extract the sulphur by passing the acetylene throughthat variety of ferric hydroxide (hydrated oxide of iron) which is soserviceable in the case of coal-gas. The idea, however, was quiteunsound: first, because it altogether ignores the phosphorus, which isthe most objectionable impurity in acetylene, but is not present in coal-gas; secondly, because ferric hydroxide is used on gasworks to extract ina marketable form the sulphur which occurs as sulphuretted hydrogen, andtrue sulphuretted hydrogen need not exist in well-generated and well-washed acetylene to any appreciable extent; thirdly, because ferrichydroxide is not employed by gasmakers to remove sulphur compounds (thisis done with lime), being quite incapable of extracting them, or theanalogous sulphur compounds of crude acetylene. About the same time three other processes based on somewhat betterchemical knowledge were put forward. Pictet proposed leading the gasthrough a strong solution of calcium chloride and then through strongsulphuric acid, both maintained at a temperature of -20° to -40° C. , finally washing the gas in a solution of some lead salt. Proof that suchtreatment would remove phosphorus to a sufficient degree is notaltogether satisfactory; but apart from this the necessity of maintainingsuch low temperatures, far below that of the coldest winter's night, renders the idea wholly inadmissible for all domestic installations. Willgerodt suggested removing sulphuretted hydrogen by means of potassiumhydroxide (caustic potash), then absorbing the phosphine in brominewater. For many reasons this process is only practicable in thelaboratory. Bergé and Reychler proposed extracting both sulphurettedhydrogen and phosphine in an acid solution of mercuric chloride(corrosive sublimate). The poisonousness of this latter salt, apart fromall other objections, rules such a method out. BLEACHING POWDER. --The next idea, first patented by Smith of Aberdeen, but fully elaborated by Lunge and Cedercreutz, was to employ bleaching-powder [Footnote: Bleaching-powder is very usually called chloride oflime; but owing to the confusion which is constantly arising in the mindsof persons imperfectly acquainted with chemistry between chloride of limeand chloride of calcium--two perfectly distinct bodies--the lessambiguous expression "bleaching-powder" will be adopted here. ] either inthe solid state or as a liquid extract. The essential constituent ofbleaching-powder from the present aspect is calcium hypochlorite, whichreadily oxidises sulphuretted hydrogen, and more particularly phosphine, converting them into sulphuric and phosphoric acids, while the acetyleneis practically unattacked. In simple purifying action the material provedsatisfactory; but since high-grade commercial bleaching-powder containssome free chlorine, or some is set free from it in the purifier under theinfluence of the passing gas, the issuing acetylene was found to containchlorine, free or combined; and this, burning eventually to hydrochloricacid, is hardly less harmful than the original sulphur compounds. Moreover, a mixture of acetylene, chlorine, and air is liable to catchfire of itself when exposed to bright sunlight; and therefore the use ofa bleaching-powder purifier, or rather the recharging thereof, was notunattended by danger in the early days. To overcome these defects, thevery natural process was adopted of diluting the bleaching-powder, suchdiluent also serving to increase the porosity of the material. A veryunsuitable substance, however, was selected for the purpose, viz. , sawdust, which is hygroscopic organic, and combustible. Owing to theexothermic chemical action between the impurities of the acetylene andthe bleaching-powder, the purifying mass became heated; and thus not onlywere the phenomena found in a bad generator repeated in the purifyingvessel, but in presence of air and light (as in emptying the purifier), the reaction proceeded so rapidly that the heat caused inflammation ofthe sawdust and the gas, at least on one occasion an actual fire takingplace which created much alarm and did some little damage. For a time, naturally, bleaching-powder was regarded as too dangerous a material tobe used for the purification of crude acetylene; but it was soondiscovered that danger could be avoided by employing the substance in aproper way. HERATOL, FRANKOLINE, ACAGINE AND PURATYLENE. --Setting aside as unworthyof attention certain compositions offered as acetylene purifyingmaterials whose constitution has not been divulged or whose action hasnot been certified by respectable authority, there are now threeprincipal chemical reagents in regular use. Those are chromic acid, cuprous chloride (sub- or proto-chloride of copper), and bleaching-powder. Chromic acid is employed in the form of a solution acidified withacetic or hydrochloric acid, which, in order to obtain the advantages(_see_ below) attendant upon the use of a solid purifying material, is absorbed in that highly porous and inert description of silica knownas infusorial earth or "kieselguhr. " This substance was first recommendedby Ullmann, and is termed commercially "heratol" As sold it containssomewhere about 136 grammes of chromic acid per kilo. Cuprous chloride isused as a solution in strong hydrochloric acid mixed with ferricchloride, and similarly absorbed in kieselguhr. From the name of itsproposer, this composition is called "frankoline. " It will be shown inChapter VI. That the use of metallic copper in the construction ofacetylene apparatus is not permissible or judicious, because the gas isliable to form therewith an explosive compound known as copper acetylide;it might seem, therefore, that the employment of a copper salt forpurification courts accident. The objection is not sound, because theacetylide is not likely to be produced except in the presence of ammonia;and since frankoline is a highly acid product, the ammonia is convertedinto its chloride before any copper acetylide can be produced. As aspecial acetylene purifier, bleaching-powder exists in at least two chiefmodifications. In one, known as "acagine, " it is mixed with 15 per cent. Of lead chromate, and sometimes with about the same quantity of bariumsulphate; the function of the latter being simply that of a diluent, while to the lead chromate is ascribed by its inventor (Wolff) the powerof retaining any chlorine that may be set free from the bleaching-powderby the reduction of the chromic acid. The utility of the lead chromate inthis direction has always appeared doubtful; and recently Keppeler hasargued that it can have no effect upon the chlorine, inasmuch as in thespent purifying material the lead chromate may be found in its originalcondition unchanged. The second modification of bleaching-powder isdesignated "puratylene, " and contains calcium chloride and quick orslaked lime. It is prepared by evaporating to dryness under diminishedpressure solutions of its three ingredients, whereby the finishedmaterial is given a particularly porous nature. It will be observed that both heratol and frankoline are powerfully acid, whence it follows they are capable of extracting any ammonia that mayenter the purifier; but for the same reason they are liable to actcorrosively upon any metallic vessel in which they are placed, and theytherefore require to be held in earthenware or enamelled receivers. Butsince they are not liquid, the casing of the purifier can be safelyconstructed of steel or cast iron. Puratylene also removes ammonia byvirtue of the calcium chloride in it. Acagine would probably pass theammonia; but this is no real objection, as the latter can be extracted bya preliminary washing in water. Heratol changes, somewhat obscurely, incolour as it becomes spent, its original orange tint, due to the chromicacid, altering to a dirty green, characteristic of the reduced salts ofchromium oxide. Frankoline has been asserted to be capable ofregeneration or revivification, _i. E. _, that when spent it may berendered fit for further service by being exposed to the air for a time, as is done with gas oxide; this, however, may be true to some extent withthe essential constituents of frankoline, but the process is notavailable with the commercial solid product. Of all these materials, heratol is the most complete purifier of acetylene, removing phosphorusand sulphur most rapidly and thoroughly, and not appreciably diminishingin speed or efficiency until its chromic acid is practically quite usedup. On the other hand, heratol does act upon pure acetylene to someextent; so that purifiers containing it should be small in size andfrequently recharged. In one of his experiments Keppeler found that 13per cent. Of the chromic acid in heratol was wasted by reacting withacetylene. As this waste of chromic acid involves also a correspondingloss of gas, small purifiers are preferable, because at any moment theyonly contain a small quantity of material capable of attacking theacetylene itself. Frankoline is very efficacious as regards thephosphorus, but it does not wholly extract the sulphur, leaving, according to Keppeler, from 0. 13 to 0. 20 gramme of the latter in everycubic metre of the gas. It does not attack acetylene itself; and if, owing to its free hydrochloric acid, it adds any acid vapours to thepurified gas, these vapours may be easily removed by a subsequent passagethrough a vessel containing lime or a carbide drier. Both beingessentially bleaching-powder, acagine and puratylene are alike inremoving phosphorus to a satisfactory degree; but they leave some sulphurbehind. Acagine evidently attacks acetylene to a slight extent, asKeppeler has found 0. 2 gramme of chlorine per cubic metre in the issuinggas. Although some of these materials attack acetylene slightly, and someleave sulphur in the purified gas, they may be all considered reasonablyefficient from the practical point of view; for the loss of trueacetylene is too small to be noticeable, and the quantity of sulphur notextracted too trifling to be harmful or inconvenient. They may be valued, accordingly, mainly by their price, proper allowance being made for thequantity of gas purified per unit weight of substance taken. Thisquantity of gas must naturally vary with the proportion of phosphorus andsulphur in the crude acetylene; but on an average the composition ofunpurified gas is what has already been given above, and so the figuresobtained by Keppeler in his investigation of the subject may be accepted. In the annexed table these are given in two forms: (1) the number oflitres of gas purified by 1 kilogramme of the substance, (2) the numberof cubic feet purified per lb. It should be noted that the volumes of gasrefer to a laboratory degree of purification; in practice they may all beincreased by 10 or possibly 20 per cent. _________________________________________________| | | || | Litres | Cubic Feet || | per Kilogramme. | per Lb. ||______________|___________________|______________|| | | || Heratol | 5, 000 | 80 || Frankoline | 9, 000 | 144 || Puratylene | 10, 000 | 160 || Acagine | 13, 000 | 208 ||______________|___________________|______________| Another method of using dry bleaching-powder has been proposed byPfeiffer. He suggests incorporating it with a solution of some lead salt, so that the latter may increase the capacity of the calcium hypochloriteto remove sulphur. Analytical details as to the efficiency of thisprocess have not been given. During 1901 and 1902 Bullier and Maquennepatented a substance made by mixing bleaching-powder with sodiumsulphate, whereby a double decomposition occurs, sodium hypochlorite, which is equally efficient with calcium hypochlorite as a purifyingmaterial, being produced together with calcium sulphate, which, beingidentical with plaster of Paris, sets into a solid mass with the excessof water present, and is claimed to render the whole more porous. Thisprocess seemed open to objection, because Blagden had shown that asolution of sodium hypochlorite was not a suitable purifying reagent inpractice, since it was much more liable to add chlorine to the gas thancalcium hypochlorite. The question how a solidified modification ofsodium hypochlorite would behave in this respect has been investigated byKeppeler, who found that the Bullier and Maquenne material imparted morechlorine to the gas which had traversed it than other hypochloritepurifying agents, and that the partly foul material was liable to causeviolent explosions. About the same time Rossel and Landriset pointed outthat purification might be easily effected in all generators of thecarbide-to-water pattern by adding to the water of the generator itself aquantity of bleaching-powder equivalent to 5 to 20 grammes for every 1kilogramme of carbide decomposed, claiming that owing to the large amountof liquid present, which is usually some 4 litres per kilogramme ofcarbide (0. 4 gallon per lb. ), no nitrogen chloride could be produced, andthat owing to the dissolved lime in the generator, chlorine could not beadded to the gas. The process is characterised by extreme simplicity, noseparate purifier being needed, but it has been found that anintroduction of bleaching-powder in the solid condition is liable tocause an explosive combination of acetylene and chlorine, while the useof a solution is attended by certain disadvantages. Granjon has proposedimpregnating a suitable variety of wood charcoal with chlorine, with orwithout an addition of bleaching-powder; then grinding the product topowder, and converting it into a solid porous mass by the aid of cement. The material is claimed to last longer than ordinary hypochloritemixtures, and not to add chlorine to the acetylene. SUBSIDIARY PURIFYING MATERIALS. --Among minor reagents suggested aspurifying substances for acetylene may be mentioned potassiumpermanganate, barium peroxide, potassium bichromate, sodium plumbate andarsenious oxide. According to Benz the first two do not remove thesulphuretted hydrogen completely, and oxidise the acetylene to someextent; while potassium bichromate leaves some sulphur and phosphorusbehind in the gas. Sodium plumbate has been suggested by Morel, but it isa question whether its action on the impurities would not be too violentand whether it would be free from action on the acetylene itself. The useof arsenious oxide dissolved in a strong acid, and the solution absorbedin pumice or kieselguhr has been protected by G. F. Jaubert. Thephosphine is said to combine with the arsenic to form an insolublebrownish compound. In 1902 Javal patented a mixture of 1 part ofpotassium permanganate, 5 of "sulphuric acid, " and 1 of water absorbed in4 parts of infusorial earth. The acid constantly neutralised by theammonia of the crude gas is as constantly replaced by fresh acid formedby the oxidation of the sulphuretted hydrogen; and this free acid, actingupon the permanganate, liberates manganese peroxide, which is claimed todestroy the phosphorus and sulphur compounds present in the crudeacetylene. ÉPURÈNE. --A purifying material to which the name of épurène has beengiven has been described, by Mauricheau-Beaupré, as consisting of amixture of ferric chloride and ferric oxide in the proportion of 2molecules, or 650 parts, of the former with one molecule, or 160 parts, of the latter, together with a suitable quantity of infusorial earth. Inthe course of preparation, however, 0. 1 to 0. 2 per cent. Of mercuricchloride is introduced into the material. This mercuric chloride is saidto form an additive compound with the phosphine of the crude acetylene, which compound is decomposed by the ferric chloride, and the mercuricchloride recovered. The latter therefore is supposed to act only as acarrier of the phosphine to the ferric chloride and oxide, by which it isoxidised according to the equation: 8Fe_2Cl_6 + 4Fe_2O_3 + 3PH_3 = 12Fe_2Cl_4 + 3H_3PO_4. Thus the ultimate products are phosphoric acid and ferrous chloride, which on exposure to air is oxidised to ferric chloride and oxide. It issaid that this revivification of the fouled or spent épurène takes placein from 20 to 48 hours when it is spread in the open in thin layers, orit may be partially or wholly revivified _in situ_ by adding a smallproportion of air to the crude acetylene as it enters the purifier. Theaddition of 1 to 2 per cent. Of air, according to Mauricheau-Beaupré, suffices to double the purifying capacity of one charge of the material, while a larger proportion would achieve its continuous revivification. Épurène is said to purify 10, 000 to 11, 000 litres of crude acetylene perkilogramme, or, say, 160 to 176 cubic feet per pound, when the acetylenecontains on the average 0. 05 per cent, by volume of phosphine. For employment in all acetylene installations smaller than those whichserve complete villages, a solid purifying material is preferable to aliquid one. This is partly due to the extreme difficulty of subdividing astream of gas so that it shall pass through a single mass of liquid insmall enough bubbles for the impurities to be removed by the time the gasarrives at the surface. This time cannot be prolonged without increasingthe depth of liquid in the vessel, and the greater the depth of liquid, the more pressure is consumed in forcing the gas through it. Perfectpurification by means of fluid reagents unattended by too great aconsumption of pressure is only to be effected by a mechanical scrubbersuch as is used on coal-gas works, wherein, by the agency of externalpower, the gas comes in contact with large numbers of solid surfaces keptconstantly wetted; or by the adoption of a tall tower filled with porousmatter or hollow balls over which a continuous or intermittent stream ofthe liquid purifying reagent is made to trickle, and neither of thesedevices is exactly suited to the requirements of a domestic acetyleneinstallation. When a solid material having a proper degree of porosity oraggregation is selected, the stream of gas passing through it is brokenup most thoroughly, and by employing several separate layers of suchmaterial, every portion of the gas is exposed equally to the action ofthe chemical reagent by the time the gas emerges from the vessel. Theamount of pressure so consumed is less than that in a liquid purifierwhere much fluid is present; but, on the other hand, the loss of pressureis absolutely constant at all times in a liquid purifier, provided thehead of liquid is maintained at the same point. A badly chosen solidpurifying agent may exhibit excessive pressure absorption as it becomespartly spent. A solid purifier, moreover, has the advantage that it maysimultaneously act as a drier for the gas; a liquid purifier, in whichthe fluid is mainly water, obviously cannot behave in a similar fashionFor thorough purification it is necessary that the gas shall actuallystream through the solid material; a mere passage over its surface isneither efficient nor economical of material. DISPOSITION OF PURIFYING MATERIAL. --Although much has been written, andsome exaggerated claims made, about the maximum, volume of acetylene acertain variety of purifying material will treat, little has been saidabout the method in which such a material should be employed to obtainthe best results. If 1 lb. Of a certain substance will purify 200 cubicfeet of normal crude acetylene, that weight is sufficient to treat thegas evolved from 40 lb. Of carbide; but it will only do so provided it isso disposed in the purifier that the gas does not pass through it at toohigh a speed, and that it is capable of complete exhaustion. In the coal-gas industry it is usually assumed that four layers of purifyingmaterial, each having a superficial area of 1 square foot, are theminimum necessary for the treatment of 100 cubic feet of gas per hour, irrespective of the nature of the purifying material and of the impurityit is intended to extract. If there is any sound basis for thisgeneralization, it should apply equally to the purification of acetylene, because there is no particular reason to imagine that the removal ofphosphine by a proper substance should occur at an appreciably differentspeed from the removal of carbon dioxide, sulphuretted hydrogen, andcarbon bisulphide by lime, ferric oxide, and sulphided lime respectively, Using the coal gas figures, then, for every 10 cubic feet of acetylenegenerated per hour, a superficial area of (4 x 144 / 10) 57. 6 squareinches of purifying material is required. In the course of Keppeler'sresearch upon different purifying materials it is shown that 400 grammesof heratol, 360 grammes of frankoline, 250 grammes of acagine, and 230grammes of puratylene each occupy a space of 500 cubic centimetres whenloosely loaded into a purifying vessel, and from these data, thefollowing table has been calculated: __________________________________________________________| | | | || | Weight | Weight | Cubic Inches || | per Gallon | per Cubic Foot | Occupied || | in Lbs. | in Lbs. | per Lb. ||_____________|____________|________________|______________|| | | | || Water | 10. 0 | 62. 321 | 27. 73 || Heratol | 8. 0 | 49. 86 | 31. 63 || Frankoline | 7. 2 | 41. 87 | 38. 21 || Acagine | 6. 0 | 31. 16 | 55. 16 || Puratylene | 4. 6 | 28. 67 | 60. 28 ||_____________|____________|________________|______________| As regards the minimum weight of material required, data have been givenby Pfleger for use with puratylene. He states that 1 Kilogramme of thatsubstance should be present for every 100 litres of crude acetyleneevolved per hour, 4 kilogrammes being the smallest quantity put into thepurifier. In English units these figures are 1 lb. Per 1. 5 cubic feet perhour, with 9 lb. As a minimum, which is competent to treat 1. 1 cubic feetof gas per hour. Thus it appears that for the purification of the gascoming from any generator evolving up to 14 cubic feet of acetylene perhour a weight of 9 lb of puratylene must be charged into the purifier, which will occupy (60. 28 / 9) 542 cubic inches of space; and it must beso spread out as to present a total superficial area of (4 x 144 x 14 /100) 80. 6 square inches to the passing gas. It follows, therefore, thatthe material should be piled to a depth of (542 / 80. 6) 6. 7 inches on asupport having an area of 80. 6 square inches; but inasmuch as such adepth is somewhat large for a small vessel, and as several layers arebetter than one, it would be preferable to spread out these 540 cubicinches of substance on several supports in such a fashion that a totalsurface of 80. 6 square inches or upwards should be exhibited. Thesefigures may obviously be manipulated in a variety of ways for the designof a purifying vessel; but, to give an example, if the ordinarycylindrical shape be adopted with four circular grids, each having aclear diameter of 8 inches (_i. E. _, an area of 50. 3 square inches), and if the material is loaded to a depth of 3 inches on each, there wouldbe a total volume of (50. 3 x 3 x 4) = 604 cubic inches of puratylene inthe vessel, and it would present a total area of (50. 3 x 4) = 201 squareinches to the acetylene. At Keppeler's estimation such an amount ofpuratylene should weigh roughly 10 lb. , and should suffice for thepurification of the gas obtained from 320 lb. Of ordinary carbide; while, applying the coal-gas rule, the total area of 201 square inches shouldrender such a vessel equal to the purification of acetylene passingthrough it at a speed not exceeding (201 / 5. 76) = 35 cubic feet perhour. Remembering that it is minimum area in square inches of purifyingmaterial that must govern the speed at which acetylene may be passedthrough a purifier, irrespective probably of the composition of thematerial; while it is the weight of material which governs the ultimatecapacity of the vessel in terms of cubic feet of acetylene or pounds ofcarbide capable of purification, these data, coupled with Keppeler'sefficiency table, afford means for calculating the dimensions of thepurifying vessel to be affixed to an installation of any desired numberof burners. There is but little to say about the design of the vesselfrom the mechanical aspect. A circular horizontal section is more likelyto make for thorough exhaustion of the material. The grids should becapable of being lifted out for cleaning. The lid may be made tighteither by a clamp and rubber or leather washer, or by a liquid seal. Ifthe purifying material is not hygroscopic, water, calcium chloridesolution, or dilute glycerin may be used for sealing purposes; but if thematerial, or any part of it, does absorb water, the liquid in the sealshould be some non-aqueous fluid like lubricating oil. Clamped lids aremore suitable for small purifiers, sealed lids for large vessels. Caremust be taken that condensation products cannot collect in the purifyingvessel. If a separate drying material is employed in the same purifierthe space it takes must be considered separately from that needed by theactive chemical reagent. When emptying a foul purifier it should berecollected that the material may be corrosive, and being saturated withacetylene is likely to catch fire in presence of a light. Purifiers charged with heratol are stated, however, to admit of a morerapid flow of the gas through them than that stated above for puratylene. The ordinary allowance is 1 lb. Of heratol for every cubic foot per hourof acetylene passing, with a minimum charge of 7 lb. Of the material. Asthe quantity of material in the purifier is increased, however, the flowof gas per hour may be proportionately increased, _e. G. _, a purifiercharged with 132 lb. Of heratol should purify 144 cubic feet of acetyleneper hour. In the systematic purification of acetylene, the practical questionarises as to how the attendant is to tell when his purifiers approachexhaustion and need recharging; for if it is undesirable to pass crudegas into the service, it is equally undesirable to waste so comparativelyexpensive a material as a purifying reagent. In Chapter XIV. It will beshown that there are chemical methods of testing for the presence, ordetermining the proportion, of phosphorus and sulphur in acetylene; butthese are not suitable for employment by the ordinary gas-maker. Heil hasstated that the purity of the gas may be judged by an inspection of itsatmospheric flame as given by a Bunsen burner. Pure acetylene gives aperfectly transparent moderately dark blue flame, which has an inner coneof a pale yellowish green colour; while the impure gas yields a longerflame of an opaque orange-red tint with a bluish red inner zone. Itshould be noted, however, that particles of lime dust in the gas maycause the atmospheric flame to be reddish or yellowish (by presence ofcalcium or sodium) quite apart from ordinary impurities; and for variousother reasons this appearance of the non-luminous flame is scarcely to berelied upon. The simplest means of ascertaining definitely whether apurifier is sufficiently active consists in the use of the test-papersprepared by E. Merck of Darmstadt according to G. Keppeler'sprescription. These papers, cut to a convenient size, are put up in smallbooks from which they may be torn one at a time. In order to test whethergas is sufficiently purified, one of the papers is moistened withhydrochloric acid of 10 per cent. Strength, and the gas issuing from apet-cock or burner orifice is allowed to impinge on the moistened part. The original black or dark grey colour of the paper is changed to whiteif the gas contains a notable amount of impurity, but remains unchangedif the gas is adequately purified. The paper consists of a speciallyprepared black porous paper which has been dipped in a solution ofmercuric chloride (corrosive sublimate) and dried. Moistening the paperwith hydrochloric acid provides in a convenient form for applicationBergé's solution for the detection of phosphine (_vide_ ChapterXIV. ). The Keppeler test-papers turn white when the gas contains eitherammonia, phosphine, siliciuretted hydrogen, sulphuretted hydrogen ororganic sulphur compounds, but with carbon disulphide the change is slow. Thus the paper serves as a test for all the impurities likely to occur inacetylene. The sensitiveness of the test is such that gas containingabout 0. 15 milligramme of sulphur, and the same amount of phosphorus, perlitre (= 0. 0655 grain per cubic foot) imparts in five minutes a distinctwhite mark to the moistened part of the paper, while gas containing 0. 05milligramme of sulphur per litre (= 0. 022 grain per cubic foot) gives intwo minutes a dull white mark visible only by careful inspection. If, therefore, a distinct white mark appears on moistened Keppeler paper whenit is exposed for five minutes to a jet of acetylene, the latter isinadequately purified. If the gas has passed through a purifier, thistest indicates that the material is not efficient, and that the purifierneeds recharging. The moistening of the Keppeler paper with hydrochloricacid before use is essential, because if not acidified the paper ismarked by acetylene itself. The books of Keppeler papers are put up in acase which also contains a bottle of acid for moistening them as requiredand are obtainable wholesale of E. Merek, 16 Jewry Street, London, E. C. , and retail of the usual dealers in chemicals. If Keppeler's test-papersare not available, the purifier should be recharged as a matter ofroutine as soon as a given quantity of carbide--proportioned to thepurifying capacity of the charge of purifying material--has been usedsince the last recharging. Thus the purifier may conveniently containenough material to purify the gas evolved from two drums of carbide, inwhich case it would need recharging when every second drum of carbide isopened. REGULATIONS AS TO PURIFICATION. --The British AcetyleneAssociation has issued the following set of regulations as to purifyingmaterial and purifiers for acetylene: Efficient purifying material and purifiers shall comply with thefollowing requirements: (1) The purifying material shall remove phosphorus and sulphur compoundsto a commercially satisfactory degree; _i. E. _, not to a greaterdegree than will allow easy detection of escaping gas through its odour. (2) The purifying material shall not yield any products capable ofcorroding the gas-mains or fittings. (3) The purifying material shall, if possible, be efficient as a dryingagent, but the Association does not consider this an absolute necessity. (4) The purifying material shall not, under working conditions, becapable of forming explosive compounds or mixtures. It is understood, naturally, that this condition does not apply to the unavoidable mixtureof acetylene and air formed when recharging the purifier. (5) The apparatus containing the purifying material shall be simple inconstruction, and capable of being recharged by an inexperienced personwithout trouble. It shall be so designed as to bring the gas into propercontact with the material. (6) The containers in purifiers shall be made of such materials as arenot dangerously affected by the respective purifying materials used. (7) No purifier shall be sold without a card of instructions suitable orhanging up in some convenient place. Such instructions shall be of themost detailed nature, and shall not presuppose any expert knowledgewhatever on the part of the operator. Reference also to the abstracts of the official regulations as toacetylene installations in foreign countries given in Chapter IV. Willshow that they contain brief rules as to purifiers. DRYING. --It has been stated in Chapter III. That the proper position forthe chemical purifiers of an acetylene plant is after the holder; andthey therefore form the last items in the installation unless a "station"governor and meter are fitted. It is therefore possible to use them alsoto remove the moisture in the gas, if a material hygroscopic in nature isemployed to charge them. This should be true more particularly withpuratylene, which contains a notable proportion of the very hygroscopicbody calcium chloride. If a separate drier is desirable, there are twomethods of charging it. It may be filled either with some hygroscopicsubstance such as porous calcium chloride or quicklime in very coarsepowder, which retains the water by combining with it; or the gas may beled through a vessel loaded with calcium carbide, which will manifestlyhold all the moisture, replacing it by an equivalent quantity of(unpurified) acetylene. The objection is sometimes urged against thislatter method, that it restores to the gas the nauseous odour and theotherwise harmful impurities it had more or less completely lost in thepurifiers; but as regards the first point, a nauseous odour is not, ashas previously been shown, objectionable in itself, and as regards thesecond, the amount of impurities added by a carbide drier, being strictlylimited by the proportion of moisture in the damp gas, is too small to benoticeable at the burners or elsewhere. As is the case with purification, absolute removal of moisture is not called for; all that is needed is toextract so much that the gas shall never reach its saturation-point inthe inaccessible parts of the service during the coldest winter's night. Any accessible length of main specially exposed to cold may besafeguarded by itself; being given a steady fall to a certain point(preferably in a frost-free situation), and there provided with acollecting-box from which the deposited liquid can be removedperiodically with a pump or otherwise. FILTRATION. --The gas issuing from the purifier or drier is very liable tohold in suspension fine dust derived from the purifying or dryingmaterial used. It is essential that thin dust should be abstracted beforethe gas reaches the burners, otherwise it will choke the orifices andprevent them functioning properly. Consequently the gas should passthrough a sufficient layer of filtering material after it has traversedthe purifying material (and drier if one is used). This filteringmaterial may be put either as a final layer in the purifier (or drier), or in a separate vessel known as a filter. Among filtering materials incommon use may be named cotton-wool, fine canvas or gauze, felt andasbestos-wool. The gas must be fairly well dried before it enters thefilter, otherwise the latter will become choked with deposited moisture, and obstruct the passage of the gas. Having now described the various items which go to form a well-designedacetylene installation, it may be useful to recapitulate briefly, withthe object of showing the order in which they should be placed. From thegenerator the gas passes into a condenser to cool it and to remove anytarry products and large quantities of water. Next it enters a washingapparatus filled with water to extract water-soluble impurities. If thegenerator is of the carbide-to-water pattern, the condenser may beomitted, and the washer is only required to retain any lime froth and toact as a water-seal or non-return valve. If the generator does not washthe gas, the washer must be large enough to act efficiently as such, andbetween it and the condenser should be put a mechanical filter to extractany dust. From the washer the acetylene travels to the holder. From theholder it passes through one or two purifiers, and from there travels tothe drier and filter. If the holder does not throw a constant pressure, or if the purifier and drier are liable to cause irregularities, agovernor or pressure regulator must be added after the drier. Theacetylene is then ready to enter the service; but a station meter (thelast item in the plant) is useful as giving a means of detecting any leakin the delivery-pipes and in checking the make of gas from the amount ofcarbide consumed. If the gas is required for the supply of a district, astation meter becomes quite necessary, because the public lamps will befed with gas at a contract rate, and without the meter there would be nocontrol over the volume of acetylene they consume. Where the gas finallyleaves the generating-house, or where it enters the residence, a full-waystopcock should be put on the main. GENERATOR RESIDUES. --According to the type of generator employed thewaste product removed therefrom may vary from a dry or moist powder to athin cream or milk of lime. Any waste product which is quite liquid inits consistency must be completely decomposed and free from particles ofcalcium carbide of sensible magnitude; in the case of more solidresidues, the less fluid they are the greater is the improbability (orthe less is the evidence) that the carbide has been wholly spent withinthe apparatus. Imperfect decomposition of the carbide inside thegenerator not only means an obvious loss of economy, but its presenceamong the residues makes a careful handling of them essential to avoidaccident owing to a subsequent liberation of acetylene in someunsuitable, and perhaps closed, situation. A residue which is notconspicuously saturated with water must be taken out of the generator-house into the open air and there flooded with water, being left in someuncovered receptacle for a sufficient time to ensure all the acetylenebeing given off. A residue which is liquid enough to flow should be rundirectly from the draw-off cock of the generator through a closed pipe tothe outside; where, if it does not discharge into an open conduit, thewaste-pipe must be trapped, and a ventilating shaft provided so that nogas can blow back into the generator-house. DISPOSAL OF RESIDUES. --These residues have now to be disposed of. In somecircumstances they can be put to a useful purpose, as will be explainedin Chapter XII. ; otherwise, and always perhaps on the small scale--certainly always if the generator overheats the gas and yields tar amongthe spent lime--they must be thrown into a convenient place. It should beremembered that although methods of precipitating sewage by adding lime, or lime water, to it have frequently been used, they have not provedsatisfactory, partly because the sludge so obtained is peculiarlyobjectionable in odour, and partly because an excess of lime yields aneffluent containing dissolved lime, which among other disadvantages isharmful to fish. The plan of running the liquid residues of acetylenemanufacture into any local sewerage system which may be found in theneighbourhood of the consumer's premises, therefore, is very convenientto the consumer; but is liable to produce complaints if the sewage isafterwards treated chemically, or if its effluent is passed untreatedinto a highly preserved river; and the same remark applies in a lesserdegree if the residues are run into a private cesspool the liquidcontents of which automatically flow away into a stream. If, however, thecesspool empties itself of liquid matter by filtration or percolationthrough earth, there can be no objection to using it to hold the limesludge, except in so far as it will require more frequent emptying. Onthe whole, perhaps the best method of disposing of these residues is torun them into some open pit, allowing the liquid to disappear byevaporation and percolation, finally burying the solid in some spot whereit will be out of the way. When a large carbide-to-water generator isworked systematically so as to avoid more loss of acetylene by solutionin the excess of liquid than is absolutely necessary, the liquid residuescoming from it will be collected in some ventilated closed tank wherethey can settle quietly. The clear lime-water will then be pumped backinto the generator for further use, and the almost solid sludge will beready to be carried to the pit where it is to be buried. Special caremust be taken in disposing of the residues from a generator in which oilis used to control evolution of gas. Such oil floats on the aqueousliquid; and a very few drops spread for an incredible distance as anexceedingly thin film, causing those brilliant rainbow-like colours whichare sometimes imagined to be a sign of decomposing organic matter. Theliquid portions of these residues must be led through a pit fitted with adepending partition projecting below the level at which the water isconstantly maintained; all the oil then collects on the first side of thepartition, only water passing underneath, and the oil may be withdrawnand thrown away at intervals. CHAPTER VI THE CHEMICAL AND PHYSICAL PROPERTIES OF ACETYLENE It will only be necessary for the purpose of this book to indicate themore important chemical and physical properties of acetylene, and, inparticular, those which have any bearing on the application of acetylenefor lighting purposes. Moreover, it has been found convenient to discussfully in other chapters certain properties of acetylene, and in regard tosuch properties the reader is referred to the chapters mentioned. PHYSICAL PROPERTIES. --Acetylene is a gas at ordinary temperatures, colourless, and, when pure, having a not unpleasant, so-called "ethereal"odour. Its density, or specific gravity, referred to air as unity, hasbeen found experimentally by Leduc to be 0. 9056. It is customary to adoptthe value 0. 91 for calculations into which the density of the gas enters(_vide_ Chapter VII. ). The density of a gas is important not onlyfor the determination of the size of mains needed to convey it at a givenrate of flow under a given pressure, as explained in Chapter VII. , butalso because the volume of gas which will pass through small orifices ina given time depends on its density. According to Graham's well-known lawof the effusion of gases, the velocity with which a gas effuses variesdirectly as the square root of the difference of pressure on the twosides of the opening, and inversely as the square root of the density ofthe gas. Hence it follows that the volume of gas which escapes through aporous pipe, an imperfect joint, or a burner orifice is, provided thepressure in the gas-pipe is the same, a function of the square root ofthe density of the gas. Hence this density has to be taken intoconsideration in the construction of burners, i. E. , a burner required topass a gas of high density must have a larger orifice than one for a gasof low density, if the rate of flow of gas is to be the same under thesame pressure. This, however, is a question for the burner manufacturers, who already make special burners for gases of different densities, and itneed not trouble the consumer of acetylene, who should always use burnersdevised for the consumption of that gas. But the Law of effusionindicates that the volume of acetylene which can escape from a leakysupply-pipe will be less than the volume of a gas of lower density, _e. G. _, coal-gas, if the pressure in the pipe is the same for both. This implies that on an extensive distributing system, in which forpractical reasons leakage is not wholly avoidable, the loss of gasthrough leakage will be less for acetylene than for coal-gas, given thesame distributing pressure. If _v_ = the loss of acetylene from adistributing system and _v'_ = the loss of coal-gas from a similarsystem worked at the same pressure, both losses being expressed involumes (cubic feet) per hour, and the coal-gas being assumed to have adensity of 0. 04, then (1) (_v_/_v'_) = (0. 40 / 0. 91)^(1/2) = 0. 663 or, _v_ = 0. 663_v'_, which signifies that the loss of acetylene by leakage under the sameconditions of pressure, &c. , will be only 0. 663 times that of the loss ofcoal-gas. In practice, however, the pressures at which the gases areusually sent through mains are not identical, being greater in the caseof acetylene than in that of coal-gas. Formula (1) therefore requirescorrection whenever the pressures are different, and calling the pressureat which the acetylene exists in the main _p_, and the correspondingpressure of the coal-gas _p'_, the relative losses by leakage are-- (2) (_v_/_v'_) = (0. 40 / 0. 91)^(1/2) x (_p_/_p'_)^(1/2) _v_ = 0. 663_v'_ x (_p_/_p'_)^(1/2) It will be evident that whenever the value of the fraction(_p_/_p'_)^(1/2), is less than 1. 5, _i. E. _, whenever the pressure ofthe acetylene does not exceed double that of the coal-gas present inpipes of given porosity or unsoundness, the loss of acetylene will beless than that of coal-gas. This is important, especially in the case oflarge village acetylene installations, where after a time it would beimpossible to avoid some imperfect joints, fractured pipes, &c. , throughout the extensive distributing mains. The same loss of gas byleakage would represent a far higher pecuniary value with acetylene thanwith coal-gas, because the former must always be more costly per unit ofvolume than the latter. Hence it is important to recognise that the rateof leakage, _cœteris paribus_, is less with acetylene, and it isalso important to observe the economical advantage, at least in terms ofgas or calcium carbide, of sending the acetylene into the mains at as lowa pressure as is compatible with the length of those mains and thecharacter of the consumers' burners. As follows from what will be said inChapter VII. , a high initial pressure makes for economy in the prime costof, and in the expense of laying, the mains, by enabling the diameter ofthose mains to be diminished; but the purchase and erection of thedistributing system are capital expenses, while a constant expenditureupon carbide to meet loss by leakage falls upon revenue. The critical temperature of acetylene, _i. E. _, the temperature belowwhich an abrupt change from the gaseous to the liquid state takes placeif the pressure is sufficiently high, is 37° C. , and the criticalpressure, _i. E. _, the pressure under which that change takes placeat that temperature, is nearly 68 atmospheres. Below the criticaltemperature, a lower pressure than this effects liquefaction of the gas, _i. E. _, at 13. 5° C. A pressure of 32. 77 atmospheres, at 0° C. , 21. 53atmospheres (Ansdell, _cf. _ Chapter XI. ). These data are ofcomparatively little practical importance, owing to the fact that, asexplained in Chapter XI. , liquefied acetylene cannot be safely utilised. The mean coefficient of expansion of gaseous acetylene between 0° C. And100° C. , is, under constant pressure, 0. 003738; under constant volume, 0. 003724. This means that, if the pressure is constant, 0. 003738represents the increase in volume of a given mass of gaseous acetylenewhen its temperature is raised one degree (C. ), divided by the volume ofthe same mass at 0° C. The coefficients of expansion of air are: underconstant pressure, 0. 003671; under constant volume, 0. 003665; and thoseof the simple gases (nitrogen, hydrogen, oxygen) are very nearly thesame. Strictly speaking the table given in Chapter XIV. , for facilitatingthe correction of the volume of gas measured over water, is not quitecorrect for acetylene, owing to the difference in the coefficients ofexpansion of acetylene and the simple gases for which the table was drawnup, but practically no appreciable error can ensue from its use. It is, however, for the correction of volumes of gases measured at differenttemperatures to one (normal) temperature, and, broadly, for determiningthe change of volume which a given mass of the gas will undergo withchange of temperature, that the coefficient of expansion of a gas becomesan important factor industrially. Ansdell has found the density of liquid acetylene to range from 0. 460 at-7° C. To 0. 364 at +35. 8° C. , being 0. 451 at 0° C. Taking the volume ofthe liquid at -7° as unity, it becomes 1. 264 at 35. 8°, and thence Ansdellinfers that the mean coefficient of expansion per degree is 0. 00489° forthe total range of pressure. " Assuming that the liquid was under the samepressure at the two temperatures, the coefficient of expansion per degreeCentigrade would be 0. 00605, which agrees more nearly with the figure0. 007 which is quoted, by Fouché As mentioned before, data referring toliquid (_i. E. _, liquefied) acetylene are of no practical importance, because the substance is too dangerous to use. They are, however, interesting in so far as they indicate the differences in propertiesbetween acetylene converted into the liquid state by great pressure, andacetylene dissolved in acetone under less pressure; which differencesmake the solution fit for employment. It may be observed that as thesolution of acetylene in acetone is a liquid, the acetylene must existtherein as a liquid; it is, in fact, liquid acetylene in a state ofdilution, the diluent being an exothermic and comparatively stable body. The specific heat of acetylene is given by M. A. Morel at 0. 310, thoughhe has not stated by whom the value was determined. For the purpose of acalculation in Chapter III. The specific heat at constant pressure wasassumed to be 0. 25, which, in the absence of precise information, appearssomewhat more probable as an approximation to the truth. The ratio(_k_ or C_p/C_v ) of the specific heat at constant pressure to thatat constant volume has been found by Maneuvrier and Fournier to be 1. 26;but they did not measure the specific heat itself. [Footnote: The ratio1. 26 _k_ or (C_p/C_v) has been given in many text-books as the valueof the specific heat of acetylene, whereas this value should obviously beonly about one-fourth or one-fifth of 1. 26. By employing the ordinary gas laws it is possible approximately tocalculate the specific heat of acetylene from Maneuvrier and Fournier'sratio. Taking the molecular weight of acetylene as 26, we have 26 C_p - 26 C_v = 2 cal. , and C_p = 1. 26 C_v. From this it follows that C_p, _i. E. _, the specific heat at constantpressure of acetylene, should be 0. 373. ] It will be seen that this valuefor _k_ differs considerably from the corresponding ratio in thecase of air and many common gases, where it is usually 1. 41; the figureapproaches more closely that given for nitrous oxide. For the specificheat of calcium carbide Carlson quotes the following figures: 0° 1000° 1500° 2000° 2500° 3000° 3500°0. 247 0. 271 0. 296 0. 325 0. 344 0. 363 0. 381 The molecular volume of acetylene is 0. 8132 (oxygen = 1). According to the international atomic weights adopted in 1908, themolecular weight of acetylene is 26. 016 if O = 16; in round numbers, asordinarily used, it is 26. Employing the latest data for the weight of 1litre of dry hydrogen and of dry normal air containing 0. 04 per cent. Ofcarbon dioxide at a temperature of 0° C. And a barometric pressure of 760mm. In the latitude of London, viz. , 0. 089916 and 1. 29395 grammesrespectively (Castell-Evans), it now becomes possible to give the weightof a known volume of dry or moist acetylene as measured under statedconditions with some degree of accuracy. Using 26. 016 as the molecularweight of the gas (O = 16), 1 litre of dry acetylene at 0° C. And 760 mm. Weighs 1. 16963 grammes, or 1 gramme measures 0. 854973 litre. From this itfollows that the theoretical specific gravity of the gas at 0°/0° C. Is0. 9039 (air = 1), a figure which may be compared with Leduc'sexperimental value of 0. 9056. Taking as the coefficient of expansion atconstant pressure the figure already given, viz. , 0. 003738, the weightsand measures of dry and moist acetylene observed under British conditions(60° F. And 30 inches of mercury) become approximately: Dry. Saturated. 1 litre . . . 1. 108 grm. . . 1. 102 grm. 1 gramme . . . 0. 902 litre. . . 0. 907 litre. 1000 cubic feet . 69. 18 lb. . . . 68. 83 lb. It should be remembered that unless the gas has been passed through achemical drier, it is always saturated with aqueous vapour, the amount ofwater present being governed by the temperature and pressure. The 1 litreof moist acetylene which weighs 1. 102 gramme at 60° F. And 30 inches ofmercury, contains 0. 013 gramme of water vapour; and therefore the weightof dry acetylene in the 1 litre of moist gas is 1. 089 gramme. Similarly, the 68. 83 pounds which constitute the weight of 1000 cubic feet of moistacetylene, as measured under British standard conditions, are composed ofalmost exactly 68 pounds of dry acetylene and 0. 83 pound of water vapour. The data required in calculating the mass of vapour in a known volume ofa saturated gas at any observed temperature and pressure, _i. E. _, inreducing the figures to those which represent the dry gas at any other(standard) temperature and pressure, will be found in the text-books ofphysical chemistry. It is necessary to recollect that since coal-gas ismeasured wet, the factors given in the table quoted in Chapter XIV. Fromthe "Notification of the Gas Referees" simply serve to convert the volumeof a wet gas observed under stated conditions to the equivalent volume ofthe same wet gas at the standard conditions mentioned. HEAT OF COMBUSTION, &C--Based on Berthelot and Matignon's value for theheat of combustion which is given on a subsequent page, viz. , 315. 7 largecalories per molecular weight of 26. 016 grammes, the calorific power ofacetylene under different conditions is shown in the following table: Dry. Dry. Saturated. 0° C. & 760 mm. 60° F & 30 ins. 60° F. & 30 ins. 1 gramme 12. 14 cals. 12. 14 cals. 12. 0 cals. 1 litre 14. L9 " 13. 45 " 13. 22 "1 cubic foot 40. 19 " 380. 8 " 374. 4 " The figures in the last column refer to the dry acetylene in the gas, nocorrection having been made for the heat absorbed by the water vapourpresent. As will appear in Chapter X. , the average of actualdeterminations of the calorific value of ordinary acetylene is 363 largecalories or 1440 B. Th. U. Per cubic foot. The temperature of ignition ofacetylene has been generally stated to be about 480° C. V. Meyer andMünch in 1893 found that a mixture of acetylene and oxygen ignitedbetween 509° and 515° C. Recent (1909) investigations by H. B. Dixon andH. F. Coward show, however, that the ignition temperature in neat oxygenis between 416° and 440° (mean 428° C. ) and in air between 406° and 440°, with a mean of 429° C. The corresponding mean temperature of ignitionfound by the same investigators for other gases are: hydrogen, 585°;carbon monoxide, moist 664°, dry 692°; ethylene, in oxygen 510°, in air543°; and methane, in oxygen between 550° and 700°, and in air, between650° and 750° C. Numerous experiments have been performed to determine the temperature ofthe acetylene flame. According to an exhaustive research by L. Nichols, when the gas burns in air it attains a maximum temperature of 1900° C. ±20°, which is 120° higher than the temperature he found by a similarmethod of observation for the coal-gas flame (fish-tail burner). LeChatelier had previously assigned to the acetylene flame a temperaturebetween 2100° and 2400°, while Lewes had found for the dark zone 459°, for the luminous zone 1410°, and for the tip 1517° C, Féry and Mahlerhave also made measurements of the temperatures afforded by acetylene andother fuels, some of their results being quoted below. Féry employed hisoptical method of estimating the temperature, Mahler a process devised byMallard and Le Chatelier. Mahler's figures all relate to flames suppliedwith air at a temperature of 0° C. And a constant pressure of 760 mm. Hydrogen . . . . . . . . . . . 1900 1960Carbon monoxide . . . . . . . . . -- 2100Methane . . . . . . . . . . . -- _ 1850Coal-gas (luminous) . . . . . . . . 1712 | " (atmospheric, with deficient supply of air) . 1812 | 1950 " (atmospheric, with full supply of air) . . 1871 _|Water-gas . . . . . . . . . . -- 2000Oxy-coal-gas blowpipe . . . . . . . 2200 --Oxy-hydrogen blowpipe . . . . . . . 2420 --Acetylene . . . . . . . . . . 2548 2350Alcohol . . . . . . . . . . . 1705 1700Alcohol (in Denayrouze Bunsen) . . . . . 1862 --Alcohol and petrol in equal parts . . . . 2053 --Crude petroleum (American) . . . . . . -- 2000Petroleum spirit " . . . . . . . -- 1920Petroleum oil " . . . . . . . -- 1660 Catani has published the following determinations of the temperatureyielded by acetylene when burnt with cold and hot air and also withoxygen: Acetylene and cold air . . . . . . 2568° C. " air at 500° C . . . . 2780° C. " air at 1000° C . . . . 3000° C. " oxygen . . . . . . 4160° C. EXPLOSIVE LIMITS. --The range of explosibility of mixtures of acetyleneand air has been determined by various observers. Eitner's figures forthe lower and upper explosive limits, when the mixture, at 62. 6° F. , isin a tube 19 mm. In diameter, and contains 1. 9 per cent. Of aqueousvapour, are 3. 35 and 52. 3 per cent. Of acetylene (_cf. _ Chapter X. ). In this case the mixture was fired by electric spark. In wider vessels, the upper explosive limit, when the mixture was fired by a Bunsen flame, was found to be as high as 75 per cent. Of acetylene. Eitner also foundthat when 13 of the 21 volumes of oxygen in air are displaced by carbondioxide, a mixture of such "carbon dioxide air" with acetylene isinexplosive in all proportions. Also that when carbon dioxide is added toa mixture of acetylene and air, an explosion no longer occurs when thecarbon dioxide amounts to 46 volumes or more to every 54 volumes of air, whatever may be the proportion of acetylene in the mixture. [Footnote:According to Caro, if acetylene is added to a mixture composed of 55 percent. By volume of air and 45 per cent. Of carbon dioxide, the whole isonly explosive when the proportion of acetylene lies between 5. 0 and 5. 8per cent. Caro has also quoted the effect of various inflammable vapoursupon the explosive limits of acetylene, his results being referred to inChapter X. ] These figures are valuable in connexion with the preventionof the formation of explosive mixtures of air and acetylene when newmains or plant are being brought into operation (_cf. _ ChapterVII. ). Eitner has also shown, by direct investigation on mixtures ofother combustible gases and air, that the range of explosibility isgreatly reduced by increase in the proportion of aqueous vapour present. As the proportion of aqueous vapour in gas standing over water increaseswith the temperature the range of explosibility of mixtures of acombustible gas and air is naturally and automatically reduced when thetemperature rises, provided the mixture is in contact with water. Thus at17. 0° C. , mixtures of hydrogen, air, and aqueous vapour containing from9. 3 to 65. 0 per cent, of hydrogen are explosive, whereas at 78. 1° C. , provided the mixture is saturated with aqueous vapour, explosion occursonly when the percentage of hydrogen in the mixture is between 11. 2 and21. 9. The range of explosibility of mixtures of acetylene and air issimilarly reduced by the addition of aqueous vapour (though the exactfigures have not been experimentally ascertained); and hence it followsthat when the temperature in an acetylene generator in which water is inexcess, or in a gasholder, rises, the risk of explosion, if air is mixedwith the gas, is automatically reduced with the rise in temperature byreason of the higher proportion of aqueous vapour which the gas willretain at the higher temperature. This fact is alluded to in Chapter II. Acetone vapour also acts similarly in lowering the upper explosive limitof acetylene (_cf. _ Chapter XI. ). It may perhaps be well to indicate briefly the practical significance ofthe range of explosibility of a mixture of air and a combustible gas, such as acetylene. The lower explosive limit is the lowest percentage ofcombustible gas in the mixture of it and air at which explosion willoccur in the mixture if a light or spark is applied to it. If thecombustible gas is present in the mixture with air in less than thatpercentage explosion is impossible. The upper explosive limit is thehighest percentage of combustible gas in the mixture of it and air atwhich explosion will occur in the mixture if a light or spark is appliedto it. If the combustible gas is present in the mixture with air in morethan that percentage explosion is impossible. Mixtures, however, in whichthe percentage of combustible gas lies between these two limits willexplode when a light or spark is applied to them; and the comprehensiveterm "range of explosibility" is used to cover all lying between the twoexplosive limits. If, then, a naked light is applied to a vesselcontaining a mixture of a combustible gas and air, in which mixture theproportion of combustible gas is below the lower limit of explosibility, the gas will not take fire, but the light will continue to burn, derivingits necessary oxygen from the excess of air present. On the other hand, if a light is applied to a vessel containing a mixture of a combustiblegas and air, in which mixture the proportion of combustible gas is abovethe upper limit of explosibility, the light will be extinguished, andwithin the vessel the gaseous mixture will not burn; but it may burn atthe open mouth of the vessel as it comes in contact with the surroundingair, until by diffusion, &c. , sufficient air has entered the vessel toform, with the remaining gas, a mixture lying within the explosivelimits, when an explosion will occur. Again, if a gaseous mixturecontaining less of its combustible constituent than is necessary toattain the lower explosive limit escapes from an open-ended pipe and alight is applied to it, the mixture will not burn as a useful compactflame (if, indeed, it fires at all); if the mixture contains more of itscombustible constituent than is required to attain the upper explosivelimit, that mixture will burn quietly at the mouth of the pipe and willbe free from any tendency to fire back into the pipe--assuming, ofcourse, that the gaseous mixture within the pipe is constantly travellingtowards the open end. If, however, a gaseous mixture containing aproportion of its combustible constituent which lies between the lowerand the upper explosive limit of that constituent escapes from an open-ended pipe and a light is applied, the mixture will fire and the flamewill pass back into the pipe, there to produce an explosion, unless theorifice of the said pipe is so small as to prevent the explosive wavepassing (as is the case with a proper acetylene burner), or unless thepipe itself is so narrow as appreciably to alter the range ofexplosibility by lowering the upper explosive limit from its normalvalue. By far the most potent factor in altering the range of explosibility ofany gas when mixed with air is the diameter of the vessel containing ordelivering such mixture. Le Chatelier has investigated this point in thecase of acetylene, and his values are reproduced overleaf; they arecomparable among themselves, although it will be observed that hisabsolute results differ somewhat from those obtained by Eitner which arequoted later: _Explosive Limits of Acetylene mixed with Air. _--(Le Chatelier. ) ___________________________________________________________| | | || | Explosive Limits. | || Diameter of Tube |_______________________| Range of || in Millimetres. | | | Explosibility. || | Lower. | Upper. | ||__________________|___________|___________|________________|| | | | || | Per Cent. | Per Cent. | Per Cent. || 40 | 2. 9 | 64 | 61. 1 || 30 | 3. 1 | 62 | 58. 9 || 20 | 3. 5 | 55 | 51. 5 || 6 | 4. 0 | 40 | 36. 0 || 4 | 4. 5 | 25 | 20. 5 || 2 | 5. 0 | 15 | 10. 0 || 0. 8 | 7. 7 | 10 | 2. 3 || 0. 5 | . . . | . . . | . . . ||__________________|___________|___________|________________| Thus it appears that past an orifice or constriction 0. 5 mm. In diameterno explosion of acetylene can proceed, whatever may be the proportionsbetween the gas and the air in the mixture present. With every gas the explosive limits and the range of explosibility arealso influenced by various circumstances, such as the manner of ignition, the pressure, and other minor conditions; but the following figures formixtures of air and different combustible gases were obtained by Eitnerunder similar conditions, and are therefore strictly comparable one withanother. The conditions were that the mixture was contained in a tube 19mm. (3/4-inch) wide, was at about 60° to 65° F. , was saturated withaqueous vapour, and was fired by electric spark. _Table giving the Percentage by volume of Combustible Gas in a Mixtureof that Gas and Air corresponding with the Explosive Limits of such aMixture. _--(Eitner. ) ____________________________________________________________________| | | | || Description of | Lower | Upper | Difference between the || Combustible Gas. | Explosive | Explosive | Lower and Upper Limits, || | Limit. | Limit. | showing the range || | | | covered by the || | | | Explosive Mixtures. ||__________________|___________|___________|_________________________|| | | | || | Per Cent. | Per Cent. | Per Cent. || Carbon monoxide | 16. 50 | 74. 95 | 58. 45 || Hydrogen | 9. 45 | 66. 40 | 57. 95 || Water-gas | | | || (uncarburetted) | 12. 40 | 66. 75 | 54. 35 || ACETYLENE | 3. 35 | 52. 30 | 48. 95 || Coal-gas | 7. 90 | 19. 10 | 11. 20 || Ethylene | 4. 10 | 14. 60 | 10. 50 || Methane | 6. 10 | 12. 80 | 6. 70 || Benzene (vapour) | 2. 65 | 6. 50 | 3. 85 || Pentane " | 2. 40 | 4. 90 | 2. 50 || Benzoline " | 2. 40 | 4. 90 | 2. 50 ||__________________|___________|___________|_________________________| These figures are of great practical significance. They indicate that amixture of acetylene and air becomes explosive (_i. E. _, will explodeif a light is applied to it) when only 3. 35 per cent. Of the mixture isacetylene, while a similar mixture of coal-gas and air is not explosiveuntil the coal-gas reaches 7. 9 per cent. Of the mixture. And again, airmay be added to coal-gas, and it does not become explosive until thecoal-gas is reduced to 19. 1 per cent. Of the mixture, while, on thecontrary, if air is added to acetylene, the mixture becomes explosive assoon as the acetylene has fallen to 52. 3 per cent. Hence the immenseimportance of taking precautions to avoid, on the one hand, the escape ofacetylene into the air of a room, and, on the other hand, the admixtureof air with the acetylene in any vessel containing it or any pipe throughwhich it passes. These precautions are far more essential with acetylenethan with coal-gas. The table shows further how great is the danger ofexplosion if benzene, benzoline, or other similar highly volatilehydrocarbons [Footnote: The nomenclature of the different volatilespirits is apt to be very confusing. "Benzene" is the proper name for themost volatile hydrocarbon derived from coal-tar, whose formula is C_6H_6. Commercially, benzene is often known as "benzol" or "benzole"; but itwould be generally advantageous if those latter words were only used tomean imperfectly rectified benzene, _i. E. _, mixtures of benzene withtoluene, &c. , such as are more explicitly understood by the terms "90. Sbenzol" and "50. S benzol. " "Gasoline, " "carburine, " "petroleum ether, ""benzine, " "benzoline, " "petrol, " and "petroleum spirit" all refer tomore or less volatile (the most volatile being mentioned first) and moreor less thoroughly rectified products obtained from petroleum. They aremixtures of different hydrocarbons, the greater part of them having thegeneral chemical formula C_nH_2n+2 where n = 5 or more. None of them is adefinite chemical compound as is benzene; when n = 5 only the product ispentane. These hydrocarbons are known to chemists as "paraffins, ""naphthenes" being occasionally met with; while a certain proportion ofunsaturated hydrocarbons is also present in most petroleum spirits. Thehydrocarbons of coal-tar are "aromatic hydrocarbons, " their genericformula being C_nH_2^n-6, where n is never less than 6. ] are allowed tovaporise in a room in which a light may be introduced. Less of the vapourof these hydrocarbons than of acetylene in the air of a room brings themixture to the lower explosive limit, and therewith subjects it to therisk of explosion. This tact militates strongly against the use of suchhydrocarbons within a house, or against the use of air-gas, which, asexplained in Chapter I. , is air more or less saturated with the vapour ofvolatile hydrocarbons. Conversely, a combustible gas, such as acetylene, may be safely "carburetted" by these hydrocarbons in a properlyconstructed apparatus set up outside the dwelling-house, as explained inChapter X. , because there would be no air (as in air-gas) in the pipes, &c. , and a relatively large escape of carburetted acetylene would berequired to produce an explosive atmosphere in a room. Moreover, theodour of the acetylene itself would render the detection of a leak fareasier with carburetted acetylene than with air-gas. N. Teclu has investigated the explosive limits of mixtures of air withcertain combustible gases somewhat in the same manner as Eitner, viz. : byfiring the mixture in an eudiometer tube by means of an electric spark. He worked, however, with the mixture dry instead of saturated withaqueous vapour, which doubtless helps to account for the differencebetween his and Eitner's results. _Table giving the Percentages by volume of Combustible Gas in aDehydrated Mixture of that Gas and Air between which the Explosive Limitsof such a Mixture lie. _--(Teclu). ____________________________________________________________________| | | || | Lower Explosive Limit. | Upper Explosive Limit. || Description of |________________________|________________________|| Combustible Gas. | | || | Per Cent. Of Gas. | Per Cent. Of Gas. ||__________________|________________________|________________________|| | | || ACETYLENE | 1. 53-1. 77 | 57. 95-58. 65 || Hydrogen | 9. 73-9. 96 | 62. 75-63. 58 || Coal-gas | 4. 36-4. 82 | 23. 35-23. 63 || Methane | 3. 20-3. 67 | 7. 46- 7. 88 ||__________________|________________________|________________________| Experiments have been made at Lechbruch in Bavaria to ascertain directlythe smallest proportion of acetylene which renders the air of a roomexplosive. Ignition was effected by the flame resulting when a pad ofcotton-wool impregnated with benzoline or potassium chlorate was fired byan electrically heated wire. The room in which most of the tests weremade was 8 ft. 10 in. Long, 6 ft. 7 in. Wide, and 6 ft. 8 in. High, andhad two windows. When acetylene was generated in this room in normalconditions of natural ventilation through the walls, the volume generatedcould amount to 3 per cent. Of the air-space of the room withoutexplosion ensuing on ignition of the wool, provided time elapsed forequable diffusion, which, moreover, was rapidly attained. Further, it wasfound that when the whole of the acetylene which 2 kilogrammes or 4. 4 lb. Of carbide (the maximum permissible charge in many countries for aportable lamp for indoor use) will yield was liberated in a room, adestructive explosion could not ensue on ignition provided the air-spaceexceeded 40 cubic metres or 1410 cubic feet, or, if the evolved gas wereuniformly diffused, 24 cubic metres or 850 cubic feet. When the walls ofthe room were rendered impervious to air and gas, and acetylene wasliberated, and allowed time for diffusion, in the air of the room, anexplosion was observed with a proportion of only 2-1/2 per cent. Ofacetylene in the air. _Solubility of Acetylene in Various Liquids. _ _____________________________________________________________________| | | | || | | Volumes of | || | Tem- | Acetylene | || Solvent. |perature. |dissolved by| Authority. || | | 100 Vols. | || | | of Solvent. | ||___________________________|_________|____________|__________________|| | | | || | Degs. C | | || Acetone . . . . | 15 | 2500 | Claude and Hess || " . . . . | 50 | 1250 | " || Acetic acid; alcohol . | 18 | 600 | Berthelot || Benzoline; chloroform . | 18 | 400 | " || Paraffin oil . . . | 0 | 103. 3 | E. Muller || " . . . | 18 | 150 | Berthelot || Olive oil . . . . | -- | 48 | Fuchs and Schiff || Carbon bisulphide . . | 18 | 100 | Berthelot || " tetrachloride . | 0 | 25 | Nieuwland || Water (at 4 65 atmospheres| | | || pressure) . . | 0 | 160 | Villard || " (at 755 mm. Pressure)| 12 | 118 | Berthelot || " (760 mm. Pressure) . | 12 | 106. 6 | E. Müller || " " . | 15 | 110 | Lewes || " " . | 18 | 100 | Berthelot || " " . | -- | 100 | E. Davy (in 1836)|| " " . | 19. 5 | 97. 5 | E. Müller || Milk of lime: about 10 | | | || grammes of calcium hy- | 5 | 112 | Hammerschmidt || droxide per 100 c. C. . | | | and Sandmann || " " " | 10 | 95 | " || " " " | 20 | 75 | " || " " " | 50 | 38 | " || " " " | 70 | 20 | " || " " " | 90 | 6 | " || Solution of common salt, 5%| 19 | 67. 9 | " || (sodium chloride) " | 25 | 47. 7 | " || " 20%| 19 | 29. 6 | " || " " | 25 | 12. 6 | " || "(nearly saturated, | | | || 26%) . . | 15 | 20. 6 | " || "(saturated, sp. Gr. | | | || 1-21) . . | 0 | 22. 0 | E. Müller || " " " | 12 | 21. 0 | " || " " " | 18 | 20. 4 | " || Solution of calcium | | | Hammerschmidt || chloride (saturated) . | 15 | 6. 0 | and Sandmann || Bergé and Reychler's re- | | | || agent . . . . | -- | 95 | Nieuwland ||___________________________|_________|____________|__________________| SOLUBILITY. --Acetylene is readily soluble in many liquids. It isdesirable, on the one hand, as indicated in Chapter III. , that the liquidin the seals of gasholders, &c. , should be one in which acetylene issoluble to the smallest degree practically attainable; while, on theother hand, liquids in which acetylene is soluble in a very high degreeare valuable agents for its storage in the liquid state. Hence it isimportant to know the extent of the solubility of acetylene in a numberof liquids. The tabular statement (p. 179) gives the most trustworthyinformation in regard to the solubilities under the normal atmosphericpressure of 760 mm. Or thereabouts. The strength of milk of lime quoted in the above table was obtained bycarefully allowing 50 grammes of carbide to interact with 550 c. C. Ofwater at 5° C. A higher degree of concentration of the milk of lime wasfound by Hammerschmidt and Sandmann to cause a slight decrease in theamount of acetylene held in solution by it. Hammerschmidt and Sandmann'sfigures, however, do not agree well with others obtained by Caro, who hasalso determined the solubility of acetylene in lime-water, using first, aclear saturated lime-water prepared at 20° C. And secondly, a milk oflime obtained by slaking 10 grammes of quicklime in 100 c. C. Of water. Asbefore, the figures relate to the volumes of acetylene dissolved atatmospheric pressure by 100 volumes of the stated liquid. _________________________________________________| | | || Temperature. | Lime-water. | Milk of Lime. ||_______________|_______________|_________________|| | | || Degs C. | | || 0 | 146. 2 | 152. 6 || 5 | 138. 5 | -- || 15 | 122. 8 | 134. 8 || 50 | 43. 9 | 62. 6 || 90 | 6. 2 | 9. 2 ||_______________|_______________|_________________| Figures showing the solubility of acetylene in plain water at differenttemperatures have been published in Landolt-Börnstein's Physico-Chemical Tables. These are reproduced below. The "Coefficient ofAbsorption" is the volume of the gas, measured at 0° C. And a barometricheight of 760 mm. Taken up by one volume of water, at the statedtemperature, when the gas pressure on the surface, apart from the vapourpressure of the water itself, is 760 mm. The "Solubility" is the weightof acetylene in grammes taken up by 100 grammes of water at the statedtemperature, when the total pressure on the surface, including that ofthe vapour pressure of the water, is 760 mm. _____________________________________________| | | || Temperature. | Coefficient of | Solubility. || | Absorption. | ||______________|________________|_____________|| | | || Degs. C. | | || 0 | 1. 73 | 0. 20 || 1 | 1. 68 | 0. 19 || 2 | 1. 63 | 0. 19 || 3 | 1. 58 | 0. 18 || 4 | 1. 53 | 0. 18 || 5 | 1. 49 | 0. 17 || 6 | 1. 45 | 0. 17 || 7 | 1. 41 | 0. 16 || 8 | 1. 37 | 0. 16 || 9 | 1. 34 | 0. 15 || 10 | 1. 31 | 0. 15 || 11 | 1. 27 | 0. 15 || 12 | 1. 24 | 0. 14 || 13 | 1. 21 | 0. 14 || 14 | 1. 18 | 0. 14 || 15 | 1. 15 | 0. 13 || 16 | 1. 13 | 0. 13 || 17 | 1. 10 | 0. 13 || 18 | 1. 08 | 0. 12 || 19 | 1. 05 | 0. 12 || 20 | 1. 03 | 0. 12 || 21 | 1. 01 | 0. 12 || 22 | 0. 99 | 0. 11 || 23 | 0. 97 | 0. 11 || 24 | 0. 95 | 0. 11 || 25 | 0. 93 | 0. 11 || 26 | 0. 91 | 0. 10 || 27 | 0. 89 | 0. 10 || 28 | 0. 87 | 0. 10 || 29 | 0. 85 | 0. 10 || 30 | 0. 84 | 0. 09 ||______________|________________|_____________| Advantage is taken, as explained in Chapter XI. , of the high degree ofsolubility of acetylene in acetone, to employ a solution of the gas inthat liquid when acetylene is wanted in a portable condition. Thesolubility increases very rapidly with the pressure, so that under apressure of twelve atmospheres acetone dissolves about 300 times itsoriginal volume of the gas, while the solubility also increases greatlywith a reduction in the temperature, until at -80° C. Acetone takes up2000 times its volume of acetylene under the ordinary atmosphericpressure. Further details of the valuable qualities of acetone as asolvent of acetylene are given in Chapter XI. , but it may here beremarked that the successful utilisation of the solvent power of acetonedepends to a very large extent on the absolute freedom from moisture ofboth the acetylene and the acetone, so that acetone of 99 per cent. Strength is now used as the solvent. Turning to the other end of the scale of solubility, the most valuableliquids for serving as seals of gasholders, &c. , are readily discernible. Far superior to all others is a saturated solution of calcium chloride, and this should be selected as the confining liquid whenever it isimportant to avoid dissolution of acetylene in the liquid as far as maybe. Brine comes next in order of merit for this purpose, but it isobjectionable on account of its corrosive action on metals. Olive oilshould, according to Fuchs and Schiff, be of service where a salineliquid is undesirable; mineral oil seems useless. Were they concordant, the figures for milk of lime would be particularly useful, because thismaterial is naturally the confining liquid in the generating chambers ofcarbide-to-water apparatus, and because the temperature of the liquidrises through the heat evolved during the generation of the gas(_vide_ Chapters II. And III. ). It will be seen that these figureswould afford a means of calculating the maximum possible loss of gas bydissolution when a known volume of sludge is run off from a carbide-to-water generator at about any possible temperature. According to Garelli and Falciola, the depression in the freezing-pointof water caused by the saturation of that liquid with acetylene is 0. 08°C. , the corresponding figure for benzene in place of water being 1. 40° C. These figures indicate that 100 parts by weight of water should dissolve0. 1118 part by weight of acetylene at 0° C. , and that 100 parts ofbenzene should dissolve about 0. 687 part of acetylene at 5° C. In otherwords, 100 volumes of water at the freezing-point should dissolve 95volumes of acetylene, and 100 volumes of benzene dissolve some 653volumes of the gas. The figure calculated for water in this way is lowerthan that which might be expected from the direct determinations at othertemperatures already referred to; that for benzene may be compared withBerthelot's value of 400 volumes at 18° C. Other measurements of thesolubility of acetylene in water at 0° C. Have given the figure 0. 1162per cent. By weight. TOXICITY. --Many experiments have been made to determine to what extentacetylene exercises a toxic action on animals breathing air containing alarge proportion of it; but they have given somewhat inconclusiveresults, owing probably to varying proportions of impurities in thesamples of acetylene used. The sulphuretted hydrogen and phosphine whichare found in acetylene as ordinarily prepared are such powerful toxicagents that they would always, in cases of "acetylene" poisoning, belargely instrumental in bringing about the effects observed. Acetylene_per se_ would appear to have but a small toxic action; for theprincipal toxic ingredient in coal-gas is carbon monoxide, which does notoccur in sensible quantity in acetylene as obtained from calcium carbide. The colour of blood is changed by inhalation of acetylene to a brightcherry-red, just as in cases of poisoning by carbon monoxide; but this isdue to a more dissolution of the gas in the haemoglobin of the blood, sothat there is much more hope of recovery for a subject of acetylenepoisoning than for one of coal-gas poisoning. Practically the risk ofpoisoning by acetylene, after it has been purified by one of the ordinarymeans, is _nil_. The toxic action of the impurities of crudeacetylene is discussed in Chapter V. Acetylene is an "endothermic" compound, as has been mentioned in ChapterII. , where the meaning of the expression endothermic is explained. It hasthere been indicated that by reason of its endothermic nature it isunsafe to have acetylene at either a temperature of 780° C. And upwards, or at a pressure of two atmospheres absolute, or higher. If thattemperature or that pressure is exceeded, dissociation (_i. E. _, decomposition into its elements), if initiated at any spot, will extendthrough the whole mass of acetylene. In this sense, acetylene at or above780° C. , or at two or more atmospheres pressure, is explosive in theabsence of air or oxygen, and it is thereby distinguished from themajority of other combustible gases, such as the components of coal-gas. But if, by dilution with another gas, the partial pressure of theacetylene is reduced, then the mixture may be subjected to a higherpressure than that of two atmospheres without acquiring explosiveness, asis fully shown in Chapter XI. Thus it becomes possible safely to compressmixtures of acetylene and oil-gas or coal-gas, whereas unadmixedacetylene cannot be safely kept under a pressure of two atmospheresabsolute or more. In a series of experiments carried out by Dupré onbehalf of the British Home Office, and described in the Report onExplosives for 1897, samples of moist acetylene, free from air, butapparently not purified by any chemical process, were exposed to theinfluence of a bright red-hot wire. When the gas was held in thecontaining vessel at the atmospheric pressure then obtaining, viz. , 30. 34inches (771 mm. ) of mercury, no explosion occurred. When the pressure wasraised to 45. 34 inches (1150 mm. ), no explosion occurred; but when thepressure was further raised to 59. 34 inches (1505 mm. , or very nearly twoatmospheres absolute) the acetylene exploded, or dissociated into itselements. Acetylene readily polymerises when heated, as has been stated in ChapterII. , where the meaning of the term "polymerisation" has been explained. The effects of the products of the polymerisation of acetylene on theflame produced when the gas is burnt at the ordinary acetylene burnershave been stated in Chapter VIII. , where the reasons therefor have beenindicated. The chief primary product of the polymerisation of acetyleneby heat appears to be benzene. But there are also produced, in some casesby secondary changes, ethylene, methane, naphthalene, styrolene, anthracene, and homologues of several of these hydrocarbons, while carbonand hydrogen are separated. The production of these bodies by the actionof heat on acetylene is attended by a reduction of the illuminative valueof the gas, while owing to the change in the proportion of air requiredfor combustion (_see_ Chapter VIII. ), the burners devised for theconsumption of acetylene fail to consume properly the mixture of gasesformed by polymerisation from the acetylene. It is difficult to comparethe illuminative value of the several bodies, as they cannot all beconsumed economically without admixture, but the following tableindicates approximately the _maximum_ illuminative value obtainablefrom them either by combustion alone or in admixture with some non-illuminating or feebly-illuminating gas: ________________________________________________| | | || | | Candles per || | | Cubic Foot ||______________|___________________|_____________|| | | || | | (say) || Acetylene | C_2H_2 | 50 || Hydrogen | H_2 | 0 || Methane | CH_4 | 1 || Ethane | C_2H_6 | 7 || Propane | C_3H_8 | 11 || Pentane | C_5H_12 (vapour) | 35 || Hexane | C_6H_14 " | 45 || Ethylene | C_2H_4 | 20 || Propylene | C_3H_6 | 25 || Benzene | C_6H_6 (vapour) | 200 || Toluene | C_7H_8 " | 250 || Naphthalene | C_10H_8 " | 400 ||______________|___________________|_____________| It appears from this table that, with the exception of the threehydrocarbons last named, no substance likely to be formed by the actionof heat on acetylene has nearly so high an illuminative value--volume forvolume--as acetylene itself. The richly illuminating vapours of benzeneand naphthalene (and homologues) cannot practically add to theilluminative value of acetylene, because of the difficulty of consumingthem without smoke, unless they are diluted with a large proportion offeebly- or non-illuminating gas, such as methane or hydrogen. Thepractical effect of carburetting acetylene with hydrocarbon vapours willbe shown in Chapter X. To be disastrous so far as the illuminatingefficiency of the gas is concerned. Hence it appears that no conceivableproducts of the polymerisation of acetylene by heat can result in itsilluminative value being improved--even presupposing that the burnerscould consume the polymers properly--while practically a considerabledeterioration of its value must ensue. The heat of combustion of acetylene was found by J. Thomson to be 310. 57large calories per gramme-molecule, and by Berthelot to be 321. 00calories. The latest determination, however, made by Berthelot andMatignon shows it to be 315. 7 calories at constant pressure. Taking theheat of formation of carbon dioxide from diamond carbon at constantpressure as 94. 3 calories (Berthelot and Matignon), which is equal to97. 3 calories from amorphous carbon, and the heat of formation of liquidwater as 69 calories; this value for the heat of combustion of acetylenemakes its heat of formation to be 94. 3 x 2 + 69 - 315. 7 = -58. 1 largecalories per gramme-molecule (26 grammes) from diamond carbon, or -52. 1from amorphous carbon. It will be noticed that the heat of combustion ofacetylene is greater than the combined heats of combustion of itsconstituents; which proves that heat has been absorbed in the union ofthe hydrogen and carbon in the molecule, or that acetylene isendothermic, as elsewhere explained. These calculations, and others givenin Chapter IX. , will perhaps be rendered more intelligible by thefollowing table of thermochemical phenomena: _______________________________________________________________| | | | || Reaction. | Diamond | Amorphous | || | Carbon. | Carbon. | ||________________________________|_________|___________|________|| | | | || (1) C (solid) + O . . . | 26. 1 | 29. 1 | . . . || (2) C (solid) + O_2 . . . | 94. 3 | 97. 3 | . . . || (3) CO + O (2 - 1) . . . | . . . | . . . | 68. 2 || (4) Conversion of solid carbon | | | || into gas (3 - 1) . . . | 42. 1 | 39. 1 | . . . || (5) C (gas) + O (1 + 4) . . | . . . | . . . | 68. 2 || (6) Conversion of amorphous | | | || carbon to diamond . . | . . . | . . . | 3. 0 || (7) C_2 + H_2 . . . . | -58. 1 | -52. 1 | . . . || (8) C_2H_2 + 2-1/2O_2 . . | . . . | . . . | 315. 7 ||________________________________|_________|___________|________| W. G. Mixter has determined the heat of combustion of acetylene to be312. 9 calories at constant volume, and 313. 8 at constant pressure. UsingBerthelot and Matignon's data given above for amorphous carbon, thisrepresents the heat of formation to be -50. 2 (Mixter himself calculatesit as -51. 4) calories. By causing compressed acetylene to dissociateunder the influence of an electric spark, Mixter measured its heat offormation as -53. 3 calories. His corresponding heats of combustion ofethylene are 344. 6 calories (constant volume) and 345. 8 (constantpressure); for its heat of formation he deduces a value -7. 8, andexperimentally found one of about -10. 6 (constant pressure). THE ACETYLENE FLAME. --It has been stated in Chapter I. That acetyleneburnt in self-luminous burners gives a whiter light than that afforded byany other artificial illuminant, because the proportion of the variousspectrum colours in the light most nearly resembles the correspondingproportion found in the direct rays of the sun. Calling the amount ofmonochromatic light belonging to each of the five main spectrum colourspresent in the sun's rays unity in succession, and comparing the amountwith that present in the light obtained from electricity, coal-gas, andacetylene, Münsterberg has given the following table for the compositionof the several lights mentioned: ______________________________________________________________________| | | | | || | Electricity | Coal-Gas | Acetylene | || |________________|__________________|_______________|_______|| Colour | | | | | | | || in | | | | | | With | || Spectrum. | Arc. | Incan- | Lumin- | Incan- | Alone. | 3 per | Sun- || | | descent. | ous. | descent. | | Cent. | light. || | | | | | | Air. | ||__________|______|_________|________|_________|_______|_______|_______|| | | | | | | | || Red | 2. 09 | 1. 48 | 4. 07 | 0. 37 | 1. 83 | 1. 03 | 1 || Yellow | 1. 00 | 1. 00 | 1. 00 | 0. 90 | 1. 02 | 1. 02 | 1 || Green | 0. 99 | 0. 62 | 0. 47 | 4. 30 | 0. 76 | 0. 71 | 1 || Blue | 0. 87 | 0. 91 | 1. 27 | 0. 74 | 1. 94 | 1. 46 | 1 || Violet | 1. 08 | 0. 17 | 0. 15 | 0. 83 | 1. 07 | 1. 07 | 1 || Ultra- | | | | | | | || Violet | 1. 21 | . . . | . . . | . . . | . . . | . . . | 1 ||__________|______|_________|________|_________|_______|_______|_______| These figures lack something in explicitness; but they indicate thegreater uniformity of the acetylene light in its proportion of rays ofdifferent wave-lengths. It does not possess the high proportion of greenof the Welsbach flame, or the high proportion of red of the luminous gas-flame. It is interesting to note the large amount of blue and violetlight in the acetylene flame, for these are the colours which are chieflyconcerned in photography; and it is to their prominence that acetylenehas been found to be so very actinic. It is also interesting to note thatan addition of air to acetylene tends to make the light even more likethat of the sun by reducing the proportion of red and blue rays to nearerthe normal figure. H. Erdmann has made somewhat similar calculation, comparing the light ofacetylene with that of the Hefner (amyl acetate) lamp, and with coal-gasconsumed in an Argand and an incandescent burner. Consecutively takingthe radiation of the acetylene flame as unity for each of the spectrumcolours, his results are: __________________________________________________________________| | | | || | | | Coal-Gas || Colour in | Wave-Lengths, | |_______________________|| Spectrum | uu | Hefner Light | | || | | | Argand | Incandescent ||___________|_______________|______________|________|______________|| | | | | || Red | 650 | 1. 45 | 1. 34 | 1. 03 || Orange | 610 | 1. 22 | 1. 13 | 1. 00 || Yellow | 590 | 1. 00 | 1. 00 | 1. 00 || Green | 550 | 0. 87 | 0. 93 | 0. 86 || Blue | 490 | 0. 72 | 1. 27 | 0. 92 || Violet | 470 | 0. 77 | 1. 35 | 1. 73 ||___________|_______________|______________|________|______________| B. Heise has investigated the light of different flames, includingacetylene, by a heterochromatic photometric method; but his resultsvaried greatly according to the pressure at which the acetylene wassupplied to the burner and the type of burner used. Petroleum affordslight closely resembling in colour the Argand coal-gas flame; andelectric glow-lamps, unless overrun and thereby quickly worn out, givevery similar light, though with a somewhat greater preponderance ofradiation in the red and yellow. ____________________________________________________________________| | | || | Percent of Total | || Light. | Energy manifested | Observer. || | as Light. | ||____________________________|___________________|___________________|| | | || Candle, spermaceti . . | 2. 1 | Thomsen || " paraffin . . . | 1. 53 | Rogers || Moderator lamp . . . | 2. 6 | Thomsen || Coal-gas . . . . . | 1. 97 | Thomsen || " . . . . . | 2. 40 | Langley || " batswing . . . | 1. 28 | Rogers || " Argand . . . | 1. 61 | Rogers || " incandesce . . | 2 to 7 | Stebbins || Electric glow-lamp . . | about 6 | Merritt || " " . . | 5. 5 | Abney and Festing || Lime light (new) . . . | 14 | Orehore || " (old) . . . | 8. 4 | Orehore || Electric arc . . . . | 10. 4 | Tyndall; Nakano || " . . . . | 8 to 13 | Marks || Magnesium light . . . | 12. 5 | Rogers || Acetylene . . . . | 10. 5 | Stewart and Hoxie || " (No. 0 slit burner | 11. 35 | Neuberg || " (No. 00000 . . | | || Bray fishtail) | 13. 8 | Neuberg || " (No. 3 duplex) . | 14. 7 | Neuberg || Geissler tube . . . | 32. 0 | Staub ||____________________________|___________________|___________________| Violle and Féry, also Erdmann, have proposed the use of acetylene as astandard of light. As a standard burner Féry employed a piece ofthermometer tube, cut off smoothly at the end and having a diameter of0. 5 millimetre, a variation in the diameter up to 10 per cent. Being ofno consequence. When the height of the flame ranged from 10 to 25millimetres the burner passed from 2. 02 to 4. 28 litres per hour, and theilluminating power of the light remained sensibly proportional to theheight of the jet, with maximum variations from the calculated value of±0. 008. It is clear that for such a purpose as this the acetylene must beprepared from very pure carbide and at the lowest possible temperature inthe generator. Further investigations in this direction should bewelcome, because it is now fairly easy to obtain a carbide of standardquality and to purify the gas until it is essentially pure acetylene froma chemical point of view. L. W. Hartmann has studied the flame of a mixture of acetylene withhydrogen. He finds that the flame of the mixture is richer in light ofshort wave-lengths than that of pure acetylene, but that the colour ofthe light does not appear to vary with the proportion of hydrogenpresent. Numerous investigators have studied the optical or radiant efficiency ofartificial lights, _i. E. _, the proportion of the total heat pluslight energy emitted by the flame which is produced in the form ofvisible light. Some results are shown in the table on the previous page. Figures showing the ratio of the visible light emitted by variousilluminants to the amount of energy expended in producing the light andalso the energy equivalent of each spherical Hefner unit evolved havebeen published by H. Lux, whose results follow: _______________________________________________________________________| | | | | || | Ratio of | Ratio of | Mean | Energy || | Light | Light | Spherical | Equiva- || Light. | emitted to | emitted to | Illuminat- | lent to 1 || | Total | Energy | ing Power. | Spherical || | Radiation. | Impressed. | Hefners. | Hefner in || | | | | Watts. ||____________________|____________|____________|____________|___________|| | | | | || | Per Cent. | Per Cent. | | || Hefner lamp | 0. 89 | 0. 103 | 0. 825 | 0. 108 || Paraffin lamp, 14" | 1. 23 | 0. 25 | 12. 0 | 0. 105 || ACETYLENE, 7. 2 | | | | || litre burner | 6. 36 | 0. 65 | 6. 04 | 0. 103 || Coal-gas incandes- | | | | || cent, upturned | 2. 26-2. 92 | 0. 46 | 89. 6 | 0. 037 || " incandes- | | | | || cent, inverted | 2. 03-2. 97 | 0. 51 | 82. 3 | 0. 035 || Carbon filament | | | | || glow-lamp | 3. 2-2. 7 | 2. 07 | 24. 5 | 0. 085 || Nernst lamp | 5. 7 | 4. 21-3. 85 | 91. 9 | 0. 073 || Tantalum lamp | 8. 5 | 4. 87 | 26. 7 | 0. 080 || Osram lamp | 9. 1 | 5. 36 | 27. 4 | 0. 075 || Direct-current arc | 8. 1 | 5. 60 | 524 | 0. 047 || " " enclosed | 2. 0 | 1. 16 | 295 | 0. 021 || Flame arc, yellow | 15. 7 | 13. 20 | 1145 | 0. 041 || " " white | 7. 6 | 6. 66 | 760 | 0. 031 || Alternating- | | | | || current arc | 3. 7 | 1. 90 | 89 | 0. 038 || Uviol mercury | | | | || vapour lamp | 5. 8 | 2. 24 | 344 | 0. 015 || Quartz lamp | 17. 6 | 6. 00 | 2960 | 0. 014 ||____________________|____________|____________|____________|___________| CHEMICAL PROPERTIES. --It is unnecessary for the purpose of this work togive an exhaustive account of the general chemical reactions of acetylenewith other bodies, but a few of the more important must be referred to. Since the gases are liable to unite spontaneously when brought intocontact, the reactions between, acetylene and chlorine require attention, first, because of the accidents that have occurred when using bleaching-powder (_see_ Chapter V. ) as a purifying material for the crude gas;secondly, because it has been proposed to manufacture one of the productsof the combination, viz. , acetylene tetrachloride, on a large scale, andto employ it as a detergent in place of carbon tetrachloride or carbondisulphide. Acetylene forms two addition products with chlorine, C_2H_2Cl_2, and C_2H_2Cl_4. These are known as acetylene dichloride andtetrachloride respectively, or more systematically as dichlorethylene andtetrachlorethane. One or both of the chlorides is apt to be produced whenacetylene comes into contact with free chlorine, and the reactionsometimes proceeds with explosive violence. The earliest writers, such asE. Davy, Wöhler, and Berthelot, stated that an addition of chlorine toacetylene was invariably followed by an explosion, unless the mixture wasprotected from light; whilst later investigators thought the two gasescould be safely mixed if they were both pure, or if air was absent. Owingto the conflicting nature of the statements made, Nieuwland determined in1905 to study the problem afresh; and the annexed account is chieflybased on his experiments, which, however, still fail satisfactorily toelucidate all the phenomena observed. According to Nieuwland's results, the behaviour of mixtures of acetylene and chlorine appears capricious, for sometimes the gases unite quietly, although sometimes they explode. Acetylene and chlorine react quite quietly in the dark and at lowtemperatures; and neither a moderate increase in temperature, nor theadmission of diffused daylight, nor the introduction of small volumes ofair, is necessarily followed by an explosion. Doubtless the presence ofeither light, air, or warmth increases the probability of an explosivereaction, while it becomes more probable still in their joint presence;but in given conditions the reaction may suddenly change from a gentleformation of addition products to a violent formation of substitutionproducts without any warning or manifest cause. When the gases merelyunite quietly, tetrachlorethane, or acetylene tetrachloride, is producedthus: C_2H_2 + 2Cl_2 = C_2H_2Cl_4; but when the reaction is violent some hexachlorethane is formed, presumably thus: 2C_2H_2 + 5Cl_2 = 4HCl + C_2 + C_2Cl_6. The heat evolved by the decomposition of the acetylene by the formationof the hydrochloric acid in the last equation is then propagated amongstthe rest of the gaseous mixture, accelerating the action, and causing theacetylene to react with the chlorine to form more hydrochloric acid andfree carbon thus; C_2H_2 + Cl_2 = 2HCl + C_2. It is evident that these results do not altogether explain the mechanismof the reactions involved. Possibly the formation of substitutionproducts and the consequent occurrence of an explosion is brought aboutby some foreign substance which acts as a catalytic agent. Such substancemay conceivably be one of the impurities in crude acetylene, or the solidmatter of a bleaching-powder purifying material. The experiments at leastindicate the direction in which safety may be sought when bleaching-powder is employed to purify the crude gas, viz. , dilution of the powderwith an inert material, absence of air from the gas, and avoidance ofbright sunlight in the place where a spent purifier is being emptied. Unfortunately Nieuwland did not investigate the action on acetylene ofhypochlorites, which are presumably the active ingredients in bleaching-powder. As will appear in due course, processes have been devised andpatented to eliminate all danger from the reaction between acetylene andchlorine for the purpose of making tetrachlorethane in quantity. Acetylene combines with hydrogen in the presence of platinum black, andethylene and then ethane result. It was hoped at one time that thisreaction would lead to the manufacture of alcohol from acetylene beingachieved on a commercial basis; but it was found that it did not proceedwith sufficient smoothness for the process to succeed, and a number ofhigher or condensation products were formed at the same time. It has beenshown by Erdmann that the cost of production of alcohol from acetylenethrough this reaction must prove prohibitive, and he has indicatedanother reaction which he considered more promising. This is theconversion of acetylene by means of dilute sulphuric acid (3 volumes ofconcentrated acid to 7 volumes of water), preferably in the presence ofmercuric oxide, to acetaldehyde. The yield, however, was notsatisfactory, and the process does not appear to have passed beyond thelaboratory stage. It has also been proposed to utilise the readiness with which acetylenepolymerises on heating to form benzene, for the production of benzenecommercially; but the relative prices of acetylene and benzene would haveto be greatly changed from those now obtaining to make such a schemesuccessful. Acetylene also lends itself to the synthesis of phenol orcarbolic acid. If the dry gas is passed slowly into fuming sulphuricacid, a sulpho-derivative results, of which the potash salt may be throwndown by means of alcohol. This salt has the formula C_2H_4O_2, S_2O_6K_2, and on heating it with caustic potash in an atmosphere of hydrogen, decomposing with excess of sulphuric acid, and distilling, phenol resultsand may be isolated. The product is, however, generally much contaminatedwith carbon, and the process, which was devised by Berthelot, does notappear to have been pursued commercially. Berthelot has also investigatedthe action of ordinary concentrated sulphuric acid on acetylene, andobtained various sulphonic derivatives. Schröter has made similarinvestigations on the action of strongly fuming sulphuric acid onacetylene. These investigations have not yet acquired any commercialsignificance. If a mixture of acetylene with either of the oxides of carbon is ledthrough a red-hot tube, or if a similar mixture is submitted to theaction of electric sparks when confined within a closed vessel at somepressure, a decomposition occurs, the whole of the carbon is liberated inthe free state, while the hydrogen and oxygen combine to form water. Analogous reactions take place when either oxide of carbon is led overcalcium carbide heated to a temperature of 200° or 250° C. , the secondproduct in this case being calcium oxide. The equations representingthese actions are: C_2H_2 + CO = H_2O + 3C 2C_2H_2 + CO_2 = 2H_2O + 5C CaC_2 + CO = CaO + 3C 2CaC_2 + CO_2 = 2CaO + 5C By urging the temperature, or by increasing the pressure at which thegases are led over the carbide, the free carbon appears in the graphiticcondition; at lower temperatures and pressures, it is separated in theamorphous state. These reactions are utilised in Frank's process forpreparing a carbon pigment or an artificial graphite (_cf. _ ChapterXII. ). Parallel decompositions occur between carbon bisulphide and eitheracetylene or calcium carbide, all the carbon of both substances beingeliminated, while the by-product is either sulphuretted hydrogen orcalcium (penta) sulphide. Other organic bodies containing sulphur aredecomposed in the same fashion, and it has been suggested by Ditz that ifcarbide could be obtained at a suitable price, the process might be madeuseful in removing sulphur (_i. E. _, carbon bisulphide and thiophen)from crude benzol, in purifying the natural petroleum oil which containssulphur, and possibly in removing "sulphur compounds" from coal-gas. COMPOUNDS WITH COPPER. By far the most important chemical reactions ofacetylene in connexion with its use as an illuminant or fuel are thosewhich it undergoes with certain metals, notably copper. It is known thatif acetylene comes in contact with copper or with one of its salts, incertain conditions a compound is produced which, at least when dry, ishighly explosive, and will detonate either when warmed or when struck orgently rubbed. The precise mechanism of the reaction, or reactions, between acetylene and copper (or its compounds), and also the characterof the product, or products, obtained have been studied by numerousinvestigators; but their results have been inconclusive and sometimesrather contradictory, so that it can hardly be said that the conditionswhich determine or preclude the formation of an explosive compound andthe composition of the explosive compound are yet known with certainty. Copper is a metal which yields two series of compounds, cuprous andcupric salts, the latter of which contain half the quantity of metal perunit of acid constituent that is found in the former. It should follow, therefore, that there are two compounds of copper with carbon, or coppercarbides: cuprous carbide, Cu_2C_2, and cupric carbide, CuC_2. Acetylenereacts at ordinary temperatures with an ammoniacal solution of any cupricsalt, forming a black cupric compound of uncertain constitution whichexplodes between 50° and 70° C. It is decomposed by dilute acids, yielding some polymerised substances. At more elevated temperatures othercupric compounds are produced which also give evidence of polymerisation. Cuprous carbide or acetylide is the reddish brown amorphous precipitatewhich is the ultimate product obtained when acetylene is led into anammoniacal solution of cuprous chloride. This body is decomposed byhydrochloric acid, yielding acetylene; but of itself it is, in allprobability, not explosive. Cuprous carbide, however, is very unstableand prone to oxidation; so that, given the opportunity, it combines withoxygen or hydrogen, or both, until it produces the copper acetylide, oracetylene-copper, which is explosive--a body to which Blochmann's formulaC_2H_2Cu_2O is generally ascribed. Thus it should happen that the exactnature of the copper acetylene compound may vary according to theconditions in which it has been formed, from a substance that is notexplosive at all at first, to one that is violently explosive; and thedegree of explosiveness should depend on the greater exposure of thecompound to air and moisture, or the larger amount of oxygen and moisturein the acetylene during its contact with the copper or copper salt. Forinstance, Mai has found that freshly made copper acetylide can be heatedto 60° C. Or higher without explosion; but that if the compound isexposed to air for a few hours it explodes on warming, while if warmedwith oxygen it explodes on contact with acetylene. It is said by Mai andby Caro to absorb acetylene when both substances are dry, becoming so hotas to explode spontaneously. Freund and Mai have also observed that whencopper acetylide which has been dried in contact with air for four orfive hours at a temperature of 50° or 60° C. Is allowed to explode in thepresence of a current of acetylene, an explosion accompanied by lighttakes place; but it is always local and is not communicated to the gas, whether the latter is crude or pure. In contact with neutral or acidsolutions of cuprous salts acetylene yields various double compoundsdiffering in colour and crystallising power; but according to Chavastelonand to Caro they are all devoid of explosive properties. Sometimes ayellowish red precipitate is produced in solutions of copper saltscontaining free acid, but the deposit is not copper acetylide, and ismore likely to be, at least in part, a copper phosphide--especially ifthe gas is crude. Hence acid solutions or preparations of copper saltsmay safely be used for the purification of acetylene, as is done in thecase of frankoline, mentioned in Chapter V. It is clear that the amountof free acid in such a material is much more than sufficient toneutralise all the ammonia which may accompany the crude acetylene intothe purifier until the material is exhausted in other respects; andmoreover, in the best practice, the gas would have been washed quite ornearly free from ammonia before entering the purifier. From a practical aspect the possible interaction of acetylene andmetallic copper has been investigated by Gerdes and by Grittner, whoseresults, again, are somewhat contradictory. Gerdes exposed neat acetyleneand mixtures of acetylene with oil-gas and coal-gas to a pressure of nineor ten atmospheres for ten months at ordinary summer and wintertemperatures in vessels made of copper and various alloys. Those metalsand alloys which resisted oxidation in air resisted the attack of thegases, but the more corrodible substances were attacked superficially;although in no instance could an explosive body be detected, nor could anexplosion be produced by heating or hammering. In further experiments theacetylene contained ammonia and moisture and Gerdes found that wherecorrosion took place it was due exclusively to the ammonia, no explosivecompounds being produced even then. Grittner investigated the question byleading acetylene for months through pipes containing copper gauze. Hisconclusions are that a copper acetylide is always produced if impureacetylene is allowed to pass through neutral or ammoniacal solutions ofcopper; that dry acetylene containing all its natural impurities exceptammonia acts to an equal extent on copper and its alloys, yielding theexplosive compound; that pure and dry gas does not act upon copper or itsalloys, although it is possible that an explosive compound may beproduced after a great length of time. Grittner has asserted that anexplosive compound may be produced when acetylene is brought into contactwith such alloys of copper as ordinary brass containing 64. 66 per cent. Of copper, or red brass containing 74. 46 per cent. Of copper, 20. 67 percent. Of zinc, and 4. 64 per cent. Of tin; whereas none is obtained whenthe metal is either "alpaca" containing 64. 44 per cent. Of copper, 18. 79per cent. Of nickel, and 16. 33 per cent. Of zinc, or britannia metalcomposed of 91. 7 per cent. Of copper and 8. 3 per cent. Of tin. Caro hasfound that when pure dry acetylene is led for nine months over sheets orfilings of copper, brass containing 63. 2 per cent. Of copper, red brasscontaining 73. 8 per cent. , so-called "alpaca-metal" containing 65. 3 percent. , and britannia metal containing 90. 2 per cent. Of copper, no actionwhatever takes place at ordinary temperatures; if the gas is moist verysmall quantities of copper acetylide are produced in six months, whatevermetal is tested, but the yield does not increase appreciably afterwards. At high temperatures condensation occurs between acetylene and copper orits alloys, but explosive bodies are not formed. Grittner's statement that crude acetylene, with or without ammonia, actsupon alloys of copper as well as upon copper itself, has thus beencorroborated by Caro; but experience renders it tolerably certain thatbrass (and presumably gun-metal) is not appreciably attacked in practicalconditions. Gerdes' failure to obtain an explosive compound in anycircumstances may very possibly be explained by the entire absence of anyoxygen from his cylinders and gases, so that any copper carbide producedremained unoxidised. Grittner's gas was derived, at least partially, froma public acetylene supply, and is quite likely to have been contaminatedwith air in sufficient quantity to oxidise the original copper compound, and to convert it into the explosive modification. For the foregoing reasons the use of unalloyed copper in the constructionof acetylene generators or in the subsidiary items of the plant, as wellas in burner fittings, is forbidden by statute or some quasi-legalenactment in most countries, and in others the metal has been abandonedfor one of its alloys, or for iron or steel, as the case may be. Grittner's experiments mentioned above, however, probably explain whyeven alloys of copper are forbidden in Hungary. (_Cf. _ Chapter IV. , page 127. ) When acetylene is passed over finely divided copper or iron (obtained byreduction of the oxide by hydrogen) heated to from 130° C. To 250° C. , the gas is more or less completely decomposed, and various products, among which hydrogen predominates, result. Ethane and ethylene areundoubtedly formed, and certain homologues of them and of acetylene, aswell as benzene and a high molecular hydrocarbon (C_7H_6)_n termed"cuprene, " have been found by different investigators. Nearly the samehydrocarbons, and others constituting a mixture approximating incomposition to some natural petroleums, are produced when acetylene ispassed over heated nickel (or certain other metals) obtained by thereduction of the finely divided oxide. These observations are at presentof no technical importance, but are interesting scientifically becausethey have led up to the promulgation of a new theory of the origin ofpetroleum, which, however, has not yet found universal acceptance. CHAPTER VII MAINS AND SERVICE-PIPES--SUBSIDIARY APPARATUS The process by which acetylene is produced, and the methods employed forpurifying it and rendering it fit for consumption in dwelling-rooms, having been dealt with in the preceding pages, the present chapter willbe devoted to a brief account of those items in the plant which liebetween the purifier outlet and the actual burner, including the meter, governor, and pressure gauge; the proper sizes of pipe for acetylene;methods of laying it, joint-making, quality of fittings, &c. ; whilefinally a few words will be said about the precautions necessary whenbringing a new system of pipes into use for the first time. THE METER. --A meter is required either to control the working of acomplete acetylene installation or to measure the volume of gas passingthrough one particular pipe, as when a number of consumers are suppliedthrough separate services under agreement from a central supply plant. The control which may be afforded by the inclusion of a meter in theequipment of a domestic acetylene generating plant is valuable, but inpractice will seldom be exercised. The meter records check the yield ofgas from the carbide consumed in a simple and trustworthy manner, andalso serve to indicate when the material in the purifier is likely to beapproaching exhaustion. The meter may also be used experimentally tocheck the soundness of the service-pipes or the consumption of aparticular burner or group of burners. Altogether it may be regarded as auseful adjunct to a domestic lighting plant, provided full advantage istaken of it. If, however, there is no intention to pay systematicattention to the records of the meter, it is best to omit it from such aninstallation, and so save its initial cost and the slight loss ofpressure which its use involves on the gas passing through it. A domesticacetylene lighting plant can be managed quite satisfactorily without ameter, and as a multiplication of parts is undesirable in an apparatuswhich will usually be tended by someone not versed in technicaloperations, it is on the whole better to omit the meter in such aninstallation. Where the plant is supervised by a technical man, a metermay advisedly be included in the equipment. Its proper position in thetrain of apparatus is immediately after the purifier. A meter must not beused for unpurified or imperfectly purified acetylene, because theimpurities attack the internal metallic parts and ultimately destroythem. The supply of acetylene to various consumers from a centralgenerating station entails the fixing of a meter on each consumer'sservice-pipe, so that the quantity consumed by each may be charged foraccordingly, just as in the case of public coal-gas supplies. There are two types of gas-meter in common use, either of which may, without essential alteration, be employed for measuring the volume ofacetylene passing through a pipe. It is unnecessary to refer here atlength to their internal mechanism, because their manufacture by otherthan firms of professed meter-makers is out of the question, and the userwill be justified in accepting the mechanism as trustworthy and durable. Meters can always be had stamped with the seal of a local authority orother body having duly appointed inspectors under the Sales of Gas Act, and the presence of such a stamp on a meter implies that it has beenofficially examined and found to register quantities accurately, or notvarying beyond 2 per cent. In favour of the seller, or 3 per cent, infavour of the consumer. [Footnote: It may be remarked that when a meter--wet or dry--begins to register incorrectly by reason of old age or wantof adjustment, its error is very often in the direction that benefits thecustomer, _i. E. _, more gas passes through it than the dials record. ]Hence a "stamped" meter may be regarded for practical purposes asaffording a correct register of the quantities of gas passing through it. Except that the use of unalloyed copper in any part of the meter where itmay come in contact with the gas must be wholly avoided, for the reasonthat copper is inadmissible in acetylene apparatus (_see_ ChapterVI. ), the meters ordinarily employed for coal-gas serve quite well foracetylene. Obviously, however, since so very much less acetylene thancoal-gas is consumed per burner, comparatively small meters only will berequired even for large installations of acetylene lighting. This fact isnow recognised by meter-makers, and meters of all suitable sizes can beobtained. It is desirable, if an ordinary coal-gas meter is being boughtfor use with acetylene, to have it subjected to a somewhat more rigoroustest for soundness than is customary before "stamping" but the makerswould readily be able to carry out this additional test. The two types of gas-meter are known as "wet" and "dry. " The case of thewet meter is about hall-filled with water or other liquid, the level ofwhich has to be maintained nearly constant. Several ingenious devices arein use for securing this constancy of level over a more or less extendedperiod, but the necessity for occasional inspection and adjustment of thewater-level, coupled with the stoppage of the passage of gas in the eventof the water becoming frozen, are serious objections to the employment ofthe wet meter in many situations. The trouble of freezing may be avoidedby substituting for the simple water an aqueous solution of glycerin, ormixture of glycerin with water, suitable strengths for which may bededuced from the table relating to the use of glycerin in holder sealsgiven at the close of Chapter III. The dry meter, on the other hand, isvery convenient, because it is not obstructed by the effects of frost, and because it acts for years without requiring attention. It is notsusceptible of adjustment for measuring with so high a degree of accuracyas a good wet meter, but its indications are sufficiently correct to fallwell within the legalised deviations already mentioned. Such errors, perhaps, are somewhat large for so costly and powerful a gas asacetylene, and they would be better reduced; but it is not so very oftenthat a dry meter reaches its limit of inaccuracy. Whether wet or dry, themeter should be fixed in a place where the temperature is tolerablyuniform, otherwise the volumes registered at different times will notbear the same ratio to the mass of gas (or volume at normal temperature), and the registrations will be misleading unless troublesome correctionsto compensate for changes of temperature are applied. THE GOVERNOR, which can be dispensed with in most ordinary domesticacetylene lighting installations provided with a good gasholder of therising-bell type, is designed to deliver the acetylene to a service-pipeat a uniform pressure, identical with that under which the burnersdevelop their maximum illuminating efficiency. It must therefore bothcheek the pressure anterior to it whenever that is above the determinedlimit to which it is set, and deliver to the efferent service-pipeacetylene at a constant pressure whether all or any number of the burnersdown to one only are in use. Moreover, when the pressure anterior to thegovernor falls to or below the determined limit, the governor shouldoffer no resistance--entailing a loss of pressure to the passage of theacetylene. These conditions, which a perfect governor should fulfil, arenot absolutely met by any simple apparatus at present in use, but so faras practical utility is concerned service governors which are readilyobtainable are sufficiently good. They are broadly of two types, viz. , those having a bell floating in a mercury seal, and those having adiaphragm of gas-tight leather or similar material, either the bell orthe diaphragm being raised by the pressure of the gas. The action isessentially the same in both cases: the bell or the diaphragm is soweighted that when the pressure of the gas exceeds the predeterminedlimit the diaphragm or bell is lifted, and, through an attached rod andvalve, brings about a partial closure of the orifice by which the gasflows into the bell or the diaphragm chamber. The valve of the governor, therefore, automatically throttles the gas-way more or less according tothe difference in pressure before and after the apparatus, until at anymoment the gas-way is just sufficient in area to pass the quantity of gaswhich any indefinite number of burners require at their fixed workingpressure; passing it always at that fixed working pressure irrespectiveof the number of burners, and maintaining it constant irrespective of theamount of pressure anterior to the governor, or of any variations in thatanterior pressure. In most patterns of service governor weights may beadded when it is desired to increase the pressure of the effluent gas. Itis necessary, in ordering a governor for an acetylene-supply, to statethe maximum number of cubic feet per hour it will be required to pass, and approximately the pressure at which it will be required to deliverthe gas to the service-pipe. This will usually be between 3 and 5 inches(instead of about 1 inch in the case of coal-gas), and if the anteriorpressure is likely to exceed 10 inches, this fact should be stated also. The mercury-seal governors are usually the more trustworthy and durable, but they are more costly than those with leather diaphragms. The sealshould have twice or thrice the depth it usually has for coal-gas. Thegovernor should be placed where it is readily accessible to the man incharge of the installation, but where it will not be interfered with byirresponsible persons. In large installations, where a number of separatebuildings receive service-pipes from one long main, each service-pipeshould be provided with a governor. GASHOLDER PRESSURE. --In drawing up the specification or scheme of anacetylene installation, it is frequently necessary either to estimate thepressure which a bell gasholder of given diameter and weight will throw, or to determine what should be the weight of the bell of a gasholder ofgiven diameter when the gas is required to be delivered from it at aparticular pressure. The gasholder of an acetylene installation servesnot only to store the gas, but also to give the necessary pressure fordriving it through the posterior apparatus and distributing mains andservice-pipes. In coal-gas works this office is generally given overwholly or in part to a special machine, known as the exhauster, but thismachine could not be advantageously employed for pumping acetylene unlessthe installation were of very great magnitude. Since, therefore, acetylene is in practice always forced through mains and service-pipes invirtue of the pressure imparted to it by the gasholder and since, forreasons already given, only the rising-bell type of gasholder can beregarded as satisfactory, it becomes important to know the relationswhich subsist between the dimensions and weight of a gasholder bell andthe pressure which it "throws" or imparts to the contained gas. The bell must obviously be a vessel of considerable weight if it is towithstand reasonable wear and tear, and this weight will give a certainhydrostatic pressure to the contained gas. If the weight of the bell isknown, the pressure which it will give can be calculated according to thegeneral law of hydrostatics, that the weight of the water displaced mustbe equal to the weight of the floating body. Supposing for the momentthat there are no other elements which will have to enter into thecalculation, then if _d_ is the diameter in inches of the(cylindrical) bell, the surface of the water displaced will have an areaof _d^2_ x 0. 7854. If the level of the water is depressed _p_inches, then the water displaced amounts to _p_(_d^2_ x 0. 7854)cubic inches, and its weight will be (at 62° F. ): (0. 7854_pd^2_ x 0. 03604) = 0. 028302_pd^2_ lb. Consequently a bell which is _d_ inches in diameter, and gives apressure of _p_ inches of water, will weigh 0. 028302_pd^2_ lb. Or, if W = the weight of the bell in lb. , the pressure thrown by it willbe W/0. 028302_d^2_ or 35. 333W/_d^2_. This is the fundamentalformula, which is sometimes given as _p_ = 550W/_d^2_, in whichW = the weight of the bell in tons, and _d_ the diameter in feet. This value of _p_, however, is actually higher than the holder wouldgive in practice. Reductions have to be made for two influences, viz. , the lifting power of the contained gas, which is lighter than air, andthe diminution in the effective weight of so much of the bell as isimmersed in water. The effect of these influences was studied by Pole, who in 1839 drew up some rules for calculating the pressure thrown by agasholder of given dimensions and weight. These rules form the basis ofthe formula which is commonly used in the coal-gas industry, and they maybe applied, _mutatis mutandis_, to acetylene holders. Thecorrections for both the influences mentioned vary with the height atwhich the top of the gasholder bell stands above the level of the waterin the tank. Dealing first with the correction for the lifting power ofthe gas, this, according to Pole, is a deduction of _h_(1 -_d_)/828 where _d_ is the specific gravity of the gas and_h_ the height (in inches) of the top of the gasholder above thewater level. This strictly applies only to a flat-topped bell, and henceif the bell has a crown with a rise equal to about 1/20 of the diameterof the bell, the value of _h_ here must be taken as equal to theheight of the top of the sides above the water-level (= _h'_), plusthe height of a cylinder having the same capacity as the crown, and thesame diameter as the bell, that is to say, _h_=_h'_ +_d_/40 where _d_ = the diameter of the bell. The specificgravity of commercially made acetylene being constantly very nearly 0. 91, the deduction for the lifting power of the gas becomes, for acetylenegasholders, 0. 0001086_h_ + 0. 0000027_d_, where _h_ is theheight in inches of the top of the sides of the bell above the water-level, and _d_ is the diameter of the bell. Obviously this is anegligible quantity, and hence this correction may be disregarded for allacetylene gasholders, whereas it is of some importance with coal-gas andother gases of lower specific gravity. It is therefore wrong to apply toacetylene gasholders formulæ in which a correction for the lifting powerof the gas has been included when such correction is based on the averagespecific gravity of coal-gas, as is the case with many abbreviatedgasholder pressure formulæ. The correction for the immersion of the sides of the bell is of greatermagnitude, and has an important practical significance. Let H be thetotal height in inches of the side of the gasholder, _h_ the heightin inches of the top of the sides of the gasholder above the water-level, and _w_ = the weight of the sides of the gasholder in lb. ; then, forany position of the bell, the proportion of the total height of the sidesimmersed (H - _h_)/H, and the buoyancy is (H - _h_)/H x_w_/S + pi/4_d^2_, in which S = the specific gravity of thematerial of which the bell is made. Assuming the material to be mildsteel or wrought iron, having a specific gravity of 7. 78, the buoyancy is(4_w_(H - _h_)) / (7. 78Hpi_d^2_) lb. Per square inch(_d_ being inches and _w_ lb. ), which is equivalent to(4_w_(H - _h_)) / (0. 03604 x 7. 78Hpi_d^2_) =(4. 54_w_(H - _h_)) / (H_d^2_) inches of water. Hence thecomplete formula for acetylene gasholders is: _p_ = 35. 333W / _d^2_ - 4. 54_w_(H - _h_) /H_d^2_ It follows that _p_ varies with the position of the bell, that is tosay, with the extent to which it is filled with gas. It will be well toconsider how great this variation is in the case of a typical acetyleneholder, as, if the variation should be considerable, provision must bemade, by the employment of a governor on the outlet main or otherwise, toprevent its effects being felt at the burners. Now, according to the rules of the "Acetylen-Verein" (_cf. _ ChapterIV. ), the bells of holders above 53 cubic feet in capacity should havesides 1. 5 mm. Thick, and crowns 0. 5 mm. Thicker. Hence for a holder from150 to 160 cubic feet capacity, supposing it to be 4 feet in diameter andabout 12 feet high, the weight of the sides (say of steel No. 16 S. W. G. =2. 66 lb. Per square foot) will be not less than 12 x 4pi x 2. 66 = 401 lb. The weight of the crown (say of steel No. 14 S. W. G. = 3. 33 lb. Per squarefoot) will be not less than about 12. 7 x 3. 33 = about 42 lb. Hence thetotal weight of holder = 401 + 42 = 443 lb. Then if the holder is full, _h_ is very nearly equal to H, and _p_ = (35. 333 x 443) / 48^2= 6. 79 inches. If the holder stands only 1 foot above the water-level, then _p_ = 6. 79 - (4. 54 x 401 (144 - 12)) / (144 x 48^2) = 6. 79 -0. 72 = 6. 07 inches. The same result can be arrived at without the directuse of the second member of the formula: For instance, the weight of the sides immersed is 11 x 4pi x 2. 66 = 368lb. , and taking the specific gravity of mild steel at 7. 78, the weight ofwater displaced is 368 / 7. 78 = 47. 3 lb. Hence the total effective weightof the bell is 443 - 47. 3 = 395. 7 lb. , and _p_ = (35. 333 x 395. 7) /48^2 = 6. 07 inches. [Footnote: If the sealing liquid in the gasholdertank is other than simple water, the correction for the immersion of thesides of the bell requires modification, because the weight of liquiddisplaced will be _s'_ times as great as when the liquid is water, if _s'_ is the specific gravity of the sealing liquid. For instance, in the example given, if the sealing liquid were a 16 per cent. Solutionof calcium chloride, specific gravity 1. 14 (_vide_ p. 93) instead ofwater, the weight of liquid displaced would be 1. 14 (368 / 7. 78) = 53. 9lb. , and the total effective weight of the bell = 443 - 53. 9 = 389. 1 lb. Therefore _p_ becomes = (35. 333 x 389. 1) / 48^2 = 5. 97 inches, instead of 6. 07 inches. ] The value of _p_ for any position of the bell can thus be arrivedat, and if the difference between its values for the highest and for thelowest positions of the bell exceeds 0. 25 inch, [Footnote: This figure isgiven as an example merely. The maximum variation in pressure must beless than one capable of sensibly affecting the silence, steadiness, andeconomy of the burners and stoves, &c. , connected with the installation. ]a governor should be inserted in the main leading from the holder to theburners, or one of the more or less complicated devices for equalisingthe pressure thrown by a holder as it rises and falls should be added tothe holder. Several such devices were at one time used in connexion withcoal-gas holders, and it is unnecessary to describe them in this work, especially as the governor is practically the better means of securinguniform pressure at the burners. It is frequently necessary to add weight to the bell of a small gasholderin order to obtain a sufficiently high pressure for the distribution ofacetylene. It is best, having regard to the steadiness of the bell, thatany necessary weighting of it should be done near its bottom rim, whichmoreover is usually stiffened by riveting to it a flange or curb ofheavier gauge metal. This flange may obviously be made sufficiently stoutto give the requisite additional weighting. As the flange is constantlyimmersed, its weight must not be added to that of the sides in computingthe value of _w_ for making the correction of pressure in respect ofthe immersion of the bell. Its effective weight in giving pressure to thecontained gas is its actual weight less its actual weight divided by itsspecific gravity (say 7. 2 for cast iron, 7. 78 for wrought iron or mildsteel, or 11. 4 for lead). Thus if _x_ lb. Of steel is added to therim its weight in computing the value of W in the formula _p_ =35. 333W / _d_^2 should be taken as x - x / 7. 78. If the actualweight is 7. 78 lb. , the weight taken for computing W is 7. 78 - 1 = 6. 78lb. THE PRESSURE GAUGE. --The measurement of gas pressure is effected by meansof a simple instrument known as a pressure gauge. It comprises a glass U-tube filled to about half its height with water. The vacant upper half ofone limb is put in communication with the gas-supply of which thepressure is to be determined, while the other limb remains open to theatmosphere. The difference then observed, when the U-tube is heldvertical, between the levels of the water in the two limbs of the tubeindicates the difference between the pressure of the gas-supply and theatmospheric pressure. It is this _difference_ that is meant when the_pressure_ of a gas in a pipe or piece of apparatus is spoken of, and it must of necessity in the case of a gas-supply have a positivevalue. That is to say, the "pressure" of gas in a service-pipe expressesreally by how much the pressure in the pipe _exceeds_ theatmospheric pressure. (Pressures less than the atmospheric pressure willnot occur in connexion with an acetylene installation, unless thegasholder is intentionally manipulated to that end. ) Gas pressures areexpressed in terms of inches head or pressure of water, fractions of aninch being given in decimals or "tenths" of an inch. The expression"tenths" is often used alone, thus a pressure of "six-tenths" means apressure equivalent to 0. 6 inch head of water. The pressure gauge is for convenience provided with an attached scale onwhich the pressures may be directly read, and with a connexion by whichthe one limb is attached to the service-pipe or cock where the pressureis to be observed. A portable gauge of this description is very useful, as it can be attached by means of a short piece of flexible tubing to anytap or burner. Several authorities, including the British AcetyleneAssociation, have recommended that pressure gauges should not be directlyattached to generators, because of the danger that the glass might befractured by a blow or by a sudden access of heat. Such breakage would befollowed by an escape of gas, and might lead to an accident. Fixedpressure gauges, however, connected with every item of a plant areextremely useful, and should be employed in all large installations, asthey afford great aid in observing and controlling the working, and inlocating the exact position of any block. All danger attending their usecan be obviated by having a stopcock between the gauge inlet and theportion of the plant to which it is attached; the said stopcock beingkept closed except when it is momentarily opened to allow of a readingbeing taken. As an additional precaution against its being left open, thestopcock may be provided with a weight or spring which automaticallycloses the gas-way directly the observer's hand is removed from the tap. In the best practice all the gauges will be collected together on a boardfastened in some convenient spot on the wall of the generator-house, eachgauge being connected with its respective item of the plant by means of apermanent metallic tube. The gauges must be filled with pure water, orwith a liquid which does not differ appreciably in specific gravity frompure water, or the readings will be incorrect. Greater legibility will beobtained by staining the water with a few drops of caramel solution, orof indigo sulphate (indigo carmine); or, in the absence of these dyes, with a drop or two of common blue-black writing ink. If they are noterected in perfectly frost-free situations, the gauges may be filled witha mixture of glycerin and pure alcohol (not methylated spirit), with orwithout a certain proportion of water, which will not freeze at anywinter temperature. The necessary mixture, which must have a density ofexactly 1. 00, could be procured from any pharmacist. It is the pressure as indicated by the pressure gauge which is referredto in this book in all cases where the term "pressure of the gas" or thelike is used. The quantity of acetylene which will flow in a given timefrom the open end of a pipe is a function of this pressure, while thequantity of acetylene escaping through a tiny hole or crack or a burnerorifice also depends on this total pressure, though the ratio in thisinstance is not a simple one, owing to the varying influence of frictionbetween the issuing gas and the sides of the orifice. Where, however, acetylene or other gas is flowing through pipes or apparatus there is aloss of energy, indicated by a falling off in the pressure due tofriction, or to the performance of work, such as actuating a gas-meter. The extent of this loss of energy in a given length of pipe or in a meteris measured by the difference between the pressures of the gas at the twoends of the pipe or at the inlet and outlet of the meter. This differenceis the "loss" or "fall" of pressure, due to friction or work performed, and is spoken of as the "actuating" pressure in regard to the passage ofgas through the stretch of pipe or meter. It is a measure of the energyabsorbed in actuating the meter or in overcoming the friction. (Cf. Footnote, Chapter II. , page 54. ) DIMENSIONS OF MAINS. --The diameter of the mains and service-pipes for anacetylene installation must be such that the main or pipe will convey themaximum quantity of the gas likely to be required to feed all the burnersproperly which are connected to it, without an excessive actuatingpressure being called for to drive the gas through the main or pipe. Theflow of all gases through pipes is of course governed by the same generalprinciples; and it is only necessary in applying these principles to aparticular gas, such as acetylene, to know certain physical properties ofthe gas and to make due allowance for their influence. The generalprinciples which govern the flow of a gas through pipes have beenexhaustively studied on account of their importance in relation to thedistribution of coal-gas and the supply of air for the ventilation ofplaces where natural circulation is absent or deficient. It will beconvenient to give a very brief reference to the way in which theseprinciples have been ascertained and applied, and then to proceed to theparticular case of the distribution of acetylene through mains andservice-pipes. The subject of "The Motion of Fluids in Pipes" was treated in a lucid andcomprehensive manner in an Essay by W. Pole in the _Journal of GasLighting_ during 1852, and his conclusions have been generally adoptedby gas engineers ever since. He recapitulated the more important pointsof this essay in the course of some lectures delivered in 1872, and oneor other of these two sources should be consulted for furtherinformation. Briefly, W. Pole treated the question in the followingmanner: The practical question in gas distribution is, what quantity of gas willa given actuating pressure cause to flow along a pipe of given length andgiven diameter? The solution of this question allows of the diameters ofpipes being arranged so that they will carry a required quantity of gas agiven distance under the actuating pressure that is most convenient orappropriate. There are five quantities to be dealt with, viz. : (1) The length of pipe = _l_ feet. (2) The internal diameter of the pipe = _d_ inches. (3) The actuating pressure = _h_ inches of head of water. (4) Thespecific gravity or density of the gas = _d_ times that of air. (5) The quantity of gas passing through the pipe--Q cubic feet per hour. This quantity is the product of the mean velocity of the gas in the pipeand the area of the pipe. The only work done in maintaining the flow of gas along a pipe is thatrequired to overcome the friction of the gas on the walls of the pipe, or, rather, the consequential friction of the gas on itself, and the lawswhich regulate such friction have not been very exhaustivelyinvestigated. Pole pointed out, however, that the existing knowledge onthe point at the time he wrote would serve for the purpose of determiningthe proper sizes of gas-mains. He stated that the friction (1) isproportional to the area of rubbing surface (viz. , pi_ld_); (2)varies with the velocity, in some ratio greater than the first power, butusually taken as the square; and (3) is assumed to be proportional to thespecific gravity of the fluid (viz. , _s_). Thus the force (_f_) necessary to maintain the motion of the gas inthe pipe is seen to vary (1) as pi_ld_, of which pi is a constant;(2) as _v^2_, where _v_ = the velocity in feet per hour; and(3) as _s_. Hence, combining these and deleting the constant pi, itappears that _f_ varies as _ldsv^2_. Now the actuating force is equal to _f_, and is represented by thedifference of pressure at the two ends of the pipe, _i. E. _, theinitial pressure, viz. , that at the place whence gas is distributed orissues from a larger pipe will be greater by the quantity _f_ thanthe terminal pressure, viz. , that at the far end of the pipe where itbranches or narrows to a pipe or pipes of smaller size, or terminates ina burner. The terminal pressure in the case of service-pipes must besettled, as mentioned in Chapter II. , broadly according to the pressureat which the burners in use work best, and this is very different in thecase of flat-flame burners for coal-gas and burners for acetylene. Themost suitable pressure for acetylene burners will be referred to later, but may be taken as equal to p_0 inches head of water. Then, calling theinitial pressure (_i. E. _, at the inlet head of service-pipe) p_1, itfollows that p_1 - p_0 = _f_. Now the cross-section of the pipe hasan area (pi/4)_d^2_, and if _h_ represents the difference ofpressure between the two ends of the pipe per square inch of its area, itfollows that _f_ = _h(pi/4)d^2_. But since _f_ has beenfound above to vary as _ldsv^2_, it is evident that _h(pi/4)d^2_ varies as _ldsv^2_. Hence _v^2_ varies as _hd/ls_, and putting in some constant M, the value of which must be determined byexperiment, this becomes _v^2_ = M_hd/ls_. The value of M deduced from experiments on the friction of coal-gas inpipes was inserted in this equation, and then taking Q = pi/4_d^2v_, it was found that for coal-gas Q = 780(_hd/sl_)^(1/2) This formula, in its usual form, is Q = 1350_d^2_(_hd/sl_)^(1/2) in which _l_ = the length of main in yards instead of in feet. Thisis known as Pole's formula, and has been generally used for determiningthe sizes of mains for the supply of coal-gas. For the following reasons, among others, it becomes prudent to revisePole's formula before employing it for calculations relating toacetylene. First, the friction of the two gases due to the sides of apipe is very different, the coefficient for coal-gas being 0. 003, whereasthat of acetylene, according to Ortloff, is 0. 0001319. Secondly, themains and service-pipes required for acetylene are smaller, _cateriaparibus_, than those needed for coal-gas. Thirdly, the observedspecific gravity of acetylene is 0. 91, that of air being unity, whereasthe density of coal-gas is about 0. 40; and therefore, in the absence ofdirect information, it would be better to base calculations respectingacetylene on data relating to the flow of air in pipes rather than uponsuch as are applicable to coal-gas. Bernat has endeavoured to take theseand similar considerations into account, and has given the followingformula for determining the sizes of pipes required for the distributionof acetylene: Q = 0. 001253_d^2_(_hd/sl_)^(1/2) in which the symbols refer to the same quantities as before, but theconstant is calculated on the basis of Q being stated in cubic metres, lin metres, and d and h in millimetres. It will be seen that the equationhas precisely the same shape as Pole's formula for coal-gas, but that theconstant is different. The difference is not only due to one formulareferring to quantities stated on the metric and the other to the samequantities stated on the English system of measures, but depends partlyon allowance having been made for the different physical properties ofthe two gases. Thus Bernat's formula, when merely transposed from themetric system of measures to the English (_i. E. _, Q being cubic feetper hour, _l_ feet, and _d_ and _h_ inches) becomes Q = 1313. 5_d^2_(_hd/sl_)^(1/2) or, more simply, Q = 1313. 4(_hd^5/sl_)^(1/2) But since the density of commercially-made acetylene is practically thesame in all cases, and not variable as is the density of coal-gas, itsvalue, viz. , 0. 91, may be brought into the constant, and the formula thenbecomes Q = 1376. 9(_hd^5/l_)^(1/2) Bernat's formula was for some time generally accepted as the mosttrustworthy for pipes supplying acetylene, and the last equation gives itin its simplest form, though a convenient transposition is d = 0. 05552(Q^2_l/h_)^(1/5) Bernat's formula, however, has now been generally superseded by one givenby Morel, which has been found to be more in accordance with the actualresults observed in the practical distribution of acetylene. Morel'sformula is D = 1. 155(Q^2_l/h_)^(1/5) in which D = the diameter of the pipe in centimetres, Q = the number ofcubic metres of gas passing per hour, _l_ = the length of pipe inmetres, and _h_ = the loss of pressure between the two ends of thepipe in millimetres. On converting tins formula into terms of the Englishsystem of measures (_i. E. _, _l_ feet, Q cubic feet, and_h_ and _d_ inches) it becomes (i) d = 0. 045122(Q^2_l/h_)^(1/5) At first sight this formula does not appear to differ greatly fromBernat's, the only change being that the constant is 0. 045122 instead of0. 05552, but the effect of this change is very great--for instance, otherfactors remaining unaltered, the value of Q by Morel's formula will be1. 68 times as much as by Bernat's formula. Transformations of Morel'sformula which may sometimes be more convenient to apply than (i) are: (ii) Q = 2312. 2(_hd^5/l_)^(1/2) (iii) _h_ = 0. 000000187011(Q^2_l/d^5_) and (iv) _l_ = 5, 346, 340(_hd^5_/Q^2) In order to avoid as far as possible expenditure of time and labour inrepeating calculations, tables have been drawn up by the authors fromMorel's formulæ which will serve to give the requisite information as tothe proper sizes of pipes to be used in those cases which are likely tobe met with in ordinary practice. These tables are given at the end ofthis chapter. When dealing with coal-gas, it is highly important to bear in mind thatthe ordinary distributing formulæ apply directly only when the pipe ormain is horizontal, and that a rise in the pipe will be attended by anincrease of pressure at the upper end. But as the increase is greater thelower the density of the gas, the disturbing influence of a moderate risein a pipe is comparatively small in the case of a gas of so high adensity as acetylene. Hence in most instances it will be unnecessary tomake any allowance for increase of pressure due to change of level. Wherethe change is very great, however, allowance may advisedly be made on thefollowing basis: The pressure of acetylene in pipes increases by aboutone-tenth of an inch (head of water) for every 75 feet rise in the pipe. Hence where acetylene is supplied from a gasholder on the ground-level toall floors of a house 75 feet high, a burner at the top of the house willordinarily receive its supply at a pressure greater by one-tenth of aninch than a burner in the basement. Such a difference, with therelatively high pressures used in acetylene supplies, is of no practicalmoment. In the case of an acetylene-supply from a central station todifferent parts of a mountainous district, the variations of pressurewith level should be remembered. The distributing formulæ also assume that the pipe is virtually straight;bends and angles introduce disturbing influences. If the bend is sharp, or if there is a right-angle, an allowance should be made if it isdesired to put in pipes of the smallest permissible dimensions. In thecase of the most usual sizes of pipes employed for acetylene mains orservices, it will suffice to reckon that each round or square elbow isequivalent in the resistance it offers to the flow of gas to a length of5 feet of pipe of the same diameter. Hence if 5 feet is added to theactual length of pipe to be laid for every bond or elbow which will occurin it, and the figure so obtained is taken as the value of _l_ informulæ (i), (ii), or (iii), the values then found for Q, _d_, or_h_ will be trustworthy for all practical purposes. It may now be useful to give an example of the manner of using theforegoing formulæ when the tables of sizes of pipes are not available. Let it be supposed that an institution is being equipped for acetylenelighting; that 50 burners consuming 0. 70 cubic foot, and 50 consuming1. 00 cubic foot of acetylene per hour may be required in usesimultaneously; that a pressure of at least 2-1/2 inches is required atall the burners; that for sufficient reasons it is considered undesirableto use a higher distributing pressure than 4 inches at the gasholder, outlet of the purifiers, or initial governor (whichever comes last in thetrain of apparatus); that the gasholder is located 100 feet from the mainbuilding of the institution, and that the trunk supply-pipe through thelatter must be 250 feet in length, and the supplies to the burners, either singly or in groups, be taken from this trunk pipe through shortlengths of tubing of ample size. What should be the diameter of the trunkpipe, in which it will be assumed that ten bonds or elbows are necessary? In the first instance, it is convenient to suppose that the trunk pipemay be of uniform diameter throughout. Then the value of _l_ will be100 (from gasholder to main building) + 250 (within the building) + 50(equivalent of 10 elbows) = 400. The maximum value of Q will be (50 x0. 7) + (50 x 1. 0) = 85; and the value of _h_ will be 1 - 2. 5 - 1. 5. Then using formula (i), we have: d = 0. 045122((85^2 x 400)/1. 5)^(1/5) = 0. 045122(1, 926, 667)^(1/5) = 0. 045122 x 18. 0713 = 0. 8154. The formula, therefore, shows that the pipe should have an internaldiameter of not less than 0. 8154 inch, and consequently 1 inch (the nextsize above 0. 8154 inch) barrel should be used. If the initial pressure(i. E. , at outlet of purifiers) could be conveniently increased from 4 to4. 8 inches, 3/4 inch barrel could be employed for the service-pipe. Butif connexions for burners were made immediately the pipe entered thebuilding, these burners would then be supplied at a pressure of 4. 2inches, while those on the extremity of the pipe would, when all burnerswere in use, be supplied at a pressure of only 2. 5 inches. Such a greatdifference of pressure is not permissible at the several burners, as notype of burner retains its proper efficiency over more than a verylimited range of pressure. It is highly desirable in the case of theordinary Naphey type of burner that all the burners in a house should besupplied at pressures which do not differ by more than half an inch;hence the pipes should, wherever practicable, be of such a size that theywill pass the maximum quantity of gas required for all the burners whichwill ever be in use simultaneously, when the pressure at the first burnerconnected to the pipe after it enters the house is not more than half aninch above the pressure at the burner furthermost removed from the firstone, all the burner-taps being turned on at the time the pressures areobserved. If the acetylene generating plant is not many yards from thebuilding to be supplied, it is a safe rule to calculate the size of pipesrequired on the basis of a fall of pressure of only half an inch from theoutlet of the purifiers or initial governor to the farthermost burner. The extra cost of the larger size of pipe which the application of thisrule may entail will be very slight in all ordinary house installations. VELOCITY OF FLOW IN PIPES. --For various purposes, it is often desirableto know the mean speed at which acetylene, or any other gas, is passingthrough a pipe. If the diameter of the pipe is _d_ inches, itscross-sectional area is _d^2_ x 0. 7854 square inches; and sincethere are 1728 cubic inches in 1 cubic foot, that quantity of gas willoccupy in a pipe whose diameter is _d_ inches a length of 1728/(_d^2_ x 0. 7854) linear inches or 183/_d^2_^ linear feet. If the gas is in motion, and the pipe is delivering Q cubic feet perhour, since there are 3600 seconds of time in one hour, the mean speed ofthe gas becomes 183/_d^2_ x Q/3600 = Q/(19 x 7_d^2_) linear feet per second. This value is interesting in several ways. For instance, taking a roughaverage of Le Chatelier's results, the highest speed at which theexplosive wave proceeds in a mixture of acetylene and air is 7 metres or22 feet per second. Now, even if a pipe is filled with an acetylene-airmixture of utmost explosibility, an explosion cannot travel backwardsfrom B to A in that pipe, if the gas is moving from A to B at a speed ofover 22 feet per second. Hence it may be said that no explosion can occurin a pipe provided Q/(19. 7_d^2_) = 22 or more; _i. E. _, Q/_d^2_=433. 4 In plain language, if the number of cubic feet passing through the pipeper hour divided by the square of the diameter of the pipe is at least433. 4, no explosion can take place within that pipe, even if the gas ishighly explosive and a light is applied to its exit. In Chapter VI. Are given the explosive limits of acetylene-air mixturesas influenced by the diameter of the tube containing them. If wepossessed a similar table showing the speed of the explosive wave inmixtures of known composition, the foregoing formulæ would enable us tocalculate the minimum speed which would insure absence of explosibilityin a supply-pipe of any given diameter throughout its length, or at itsnarrowest part. It would not, however, be possible simply by increasingthe forward speed of an explosive mixture of acetylene and air to a pointexceeding that of its explosion velocity to prevent all danger of firingback in an atmospheric burner tube. A much higher pressure than isusually employed in gas-burners, other than blowpipes, would be needed toconfer a sufficient degree of velocity upon the gas, a pressure whichwould probably fracture any incandescent mantle placed in the flame. SERVICE-PIPES AND MAINS. --The pipes used for the distribution ofacetylene must be sound in themselves, and their joints perfectly tight. Higher pressures generally prevail in acetylene service-pipes within ahouse than in coal-gas service-pipes, while slight leaks are moreoffensive and entail a greater waste of resources. Therefore it isuneconomical, as well as otherwise objectionable, to employ service-pipesor fittings for acetylene which are in the least degree unsound. Unfortunately ordinary gas-barrel is none too sound, nor well-threaded, and the taps and joints of ordinary gas-fittings are commonly leaky. Hence something better should invariably be used for acetylene. What isknown as "water" barrel, which is one gauge heavier than gas-barrel ofthe same size, may be adopted for the service-pipes, but it is better toincur a slight extra initial expense and to use "steam" barrel, which isof still heavier gauge and is sounder than either gas or water-pipe. Allelbows, tees, &c. , should be of the same quality. The fitters' work inmaking the joints should be done with the utmost care, and the sloppywork often passed in the case of coal-gas services must on no account beallowed. It is no exaggeration to say that the success of an acetyleneinstallation, from the consumer's point of view, will largely, if notprincipally, depend on the tightness of the pipes in his house. Thestatement has been made that the "paint" used by gas-fitters, _i. E. _, the mixture of red and white lead ground in "linseed" oil, is not suitable for employment with acetylene, and it has been proposedto adopt a similar material in which the vehicle is castor-oil. No goodreason has been given for the preference for castor-oil, and the troubleswhich have arisen after using ordinary paint may be explained partly onthe very probable assumption that the oil was not genuine linseed, and sodid not dry, and partly on the fact that almost entire reliance wasplaced on the paint for keeping the joint sound. Joints for acetylene, like those for steam and high-pressure water, must be made tight by usingwell-threaded fittings, so as to secure metallic contact between pipe andsocket, &c. ; the paint or spun-yarn is only an additional safeguard. Inmaking a faced joint, washers of (say, 7 lb) lead, or coils of lead-wirearc extremely convenient and quite trustworthy; the packing can be usedrepeatedly. LEAKAGE. --Broadly speaking, it may be said that the commercial success ofany village acetylene-supply--if not that of all large installations--depends upon the leakage being kept within moderate limits. It followsfrom what was stated in Chapter VI. About the diffusion of acetylene, that from pipes of equal porosity acetylene and coal-gas will escape atequal rates when the effective pressure in the pipe containing acetyleneis double that in the pipe containing coal-gas. The loss of coal-gas byleakage is seldom less than 5 per cent. Of the volume passed into themain at the works; and provided a village main delivering acetylene isnot unduly long in proportion to the consumption of gas--or, in otherwords, provided the district through which an acetylene distributing mainpasses is not too sparsely populated--the loss of acetylene should notexceed the same figure. Caro holds that the loss of gas by leakage from avillage installation should be quoted in absolute figures and not as apercentage of the total make as indicated by the works meter, becausethat total make varies so largely at different periods of the year, whilethe factors which determine the magnitude of the leakage are alwaysidentical; and therefore whereas the actual loss of gas remains the same, it is represented to be more serious in the summer than in the winter. Such argument is perfectly sound, but the method of returning leakage asa percentage of the make has been employed in the coal-gas industry formany years, and as it does not appear to have led to any misunderstandingor inconvenience, there is no particular reason for departing from theusual practice in the case of acetylene where the conditions as touniform leakage and irregular make are strictly analogous. Caro has stated that a loss of 15 to 20 litres per kilometre per hour(_i. E. _, of 0. 85 to 1. 14 cubic feet per mile per hour) from anacetylene distributing main is good practice; but it should be noted thatmuch lower figures have been obtained when conditions are favourable andwhen due attention has been devoted to the fitters' work. In one of theGerman village acetylene installations where the matter has beencarefully investigated (Döse, near Cuxhaven), leakage originally occurredat the rate of 7. 3 litres per kilometre per hour in a main 8. 5kilometres, or 5. 3 miles, long and 4 to 2 inches in diameter; but it wasreduced to 5. 2 litres, and then to 3. 12 litres by tightening the plugs ofthe street lantern and other gas cocks. In British units, these figuresare 0. 415, 0. 295, and 0. 177 cubic foot per mile per hour. By calculation, the volume of acetylene generated in this village would appear to havebeen about 23, 000 cubic feet per mile of main per year, and therefore itmay be said that the proportion of gas lost was reduced by attending tothe cocks from 15. 7 per cent, to 11. 3 per cent, and then to 6. 8 per cent. At another village where the main was 2. 5 kilometres long, testsextending over two months, when the public lamps were not in use, showedthe leakage to be 4. 4 litres per kilometre per hour, _i. E. _, 1. 25cubic foot per mile per hour, when the annual make was roughly 46, 000cubic feet per mile of main. Here, the loss, calculated from the directreadings of the works motor, was 4. 65 per cent. When all the fittings, burners excepted, have been connected, the wholesystem of pipes must be tested by putting it under a gas (or air)pressure of 9 or 12 inches of water, and observing on an attachedpressure gauge whether any fall in pressure occurs within fifteen minutesafter the main inlet tap has been shut. The pressure required for thispurpose can be obtained by temporarily weighting the holder, or by theemployment of a pump. If the gauge shows a fall of pressure of onequarter of an inch or more in these circumstances, the pipes must beexamined until the leak is located. In the presence of a meter, theinstallation can conveniently be tested for soundness by throwing intoit, through the meter, a pressure of 12 inches or so of water from theweighted holder, then leaving the inlet cock open, and observing whetherthe index hand on the lowest dial remains perfectly stationary for aquarter of an hour--movement of the linger again indicating a leak. Thesearch for leaks must never be made with a light; if the pipes are fullof air this is useless, if full of gas, criminal in its stupidity. Whilethe whole installation is still under a pressure of 12 inches thrown fromthe loaded holder, whether it contains air or gas, first all the likelyspots (joints, &c. ), then the entire length of pipe is carefully brushedover with strong soapy water, which will produce a conspicuous "soap-bubble" wherever the smallest flaw occurs. The tightness of a system ofpipes put under pressure from a loaded holder cannot be ascertainedsafely by observing the height of the bell, and noting if it falls onstanding. Even if there is no issue of gas from the holder, the positionof the bell will alter with every variation in temperature of the storedgas or surrounding air, and with every movement of the barometer, risingas the temperature rises and as the barometer falls, and _viceversâ_, while, unless the water in the seal is saturated withwhatever gas the holder contains, the bell will steadily drop a little anpart of its contents are lost by dissolution in the liquid. PIPES AND FITTINGS. --As a general rule it is unadvisable to use lead orcomposition pipe for permanent acetylene connexions. If exposed, it isliable to be damaged, and perhaps penetrated by a blow, and if set in thewall and covered with paper or panel it is liable to be pierced if nailsor tacks should at any time be driven into the wall. There is also anincreased risk in case of fire, owing to its ready fusibility. If used atall--and it has obvious advantages--lead or composition piping should belaid on the surface of the walls, &c. , and protected from blows, &c. , bya light wooden casing, outwardly resembling the wooden coverings forelectric lighting wires. It has been a common practice, in laying theunderground mains required for supplying the villages which are lightedby means of acetylene from a central works in different parts of France, to employ lead pipes. The plan is economical, but in view of the dangerthat the main might be flattened by the weight of heavy traction-enginespassing over the roads, or that it might settle into local dips from thesame cause or from the action of subterranean water, in which dips waterwould be constantly condensing in cold weather, the use of lead for thispurpose cannot be recommended. Steam-barrel would be preferable to castpipe, because permanently sound joints are easier to make in the former, and because it is not so brittle. The fittings used for acetylene must have perfectly sound joints andtaps, for the same reasons that the service-pipes must be quite sound. Common gas-fittings will not do, the joints, taps, ball-sockets, &c. , arenot accurately enough ground to prevent leakage. They may in many casesbe improved by regrinding, but often the plug and barrel are so shallowthat it is almost impossible to ensure soundness. It is therefore betterto procure fittings having good taps and joints in the first instance;the barrels should be long, fairly wide, and there should be no sensible"play" between plug and barrel when adjusted so that the plug turnseasily when lightly lubricated. Fittings are now being specially made foracetylene, which is a step in the right direction, because, in additionto superior taps and joints being essential, smaller bore piping andsmaller through-ways to the taps than are required for coal-gas serve foracetylene. It is perhaps advisable to add that wherever a rigid bracketor fitting will answer as well as a jointed one, the latter should on noaccount be used; also water-slide pendants should never be employed, asthey are fruitful of accidents, and their apparent advantages are for themost part illusory. Ball-sockets also should be avoided if possible; ifit is absolutely necessary to have a fitting with a ball-socket, thelatter should have a sleeve made of a short length of sound rubber-tubingof a size to give a close fit, slipped over so as to join the ballportion to the socket portion. This sleeve should be inspected once aquarter at least, and renewed immediately it shows signs of cracking. Generally speaking all the fittings used should be characterised bystructural simplicity; any ornamental or decorative effects desired maybe secured by proper design without sacrifice of the simplicity whichshould always mark the essential and operative parts of the fitting. Flexible connexions between the fixed service-pipe and a semi-portable ortemporary burner may at times be required. If the connexion is forpermanent use, it must not be of rubber, but of the metallic flexibletubing which is now commonly employed for such connexions in the case ofcoal-gas. There should be a tap between the service-pipe and the flexibleconnexion, and this tap should be turned off whenever the burner is outof use, so that the connexion is not at other times under the pressurewhich is maintained in the service-pipes. Unless the connexion is veryshort--say 2 feet or less--there should also be a tap at the burner. These flexible connexions, though serviceable in the case of table-lamps, &c. , of which the position may have to be altered, are undesirable, asthey increase the risk attendant on gas (whether acetylene or otherilluminating gas) lighting, and should, if possible, be avoided. Flexibleconnexions may also be required for temporary use, such as for conveyingacetylene to an optical lantern, and if only occasionally called for, thecost of the metallic flexible tubing will usually preclude its use. Itwill generally be found, however, that the whole connexion in such a casecan be of composition or lead gas-piping, connected up at its two ends bya few inches of flexible rubber tubing. It should be carried along thewalls or over the heads of people who may use the room, rather thanacross the floor, or at a low level, and the acetylene should be turnedon to it only when actually required for use, and turned off at the fixedservice-pipe as soon as no longer required. Quite narrow compositiontubing, say 1/4-inch, will carry all the acetylene required for two orthree burners. The cost of a composition temporary connexion will usuallybe less than one of even common rubber tubing, and it will be safer. Thecomposition tubing must not, of course, be sharply bent, but carried byeasy curves to the desired point, and it should be carefully rolled in aroll of not less than 18 inches diameter when removed. If theseprecautions are observed it may be used very many times. Acetylene service-pipes should, wherever possible, be laid with a fall, which may be very slight, towards a small closed vessel adjoining thegasholder or purifier, in order that any water deposited from the gasowing to condensation of aqueous vapour may run out of the pipe into thatapparatus. Where it is impossible to secure an uninterrupted fall in thatdirection, there should be inserted in the service-pipe, at the lowestpoint of each dip it makes, a short length of pipe turned downwards andterminating in a plug or sound tap. Water condensing in this section ofthe service-pipe will then run down and collect in this drainage-pipe, from which it can be withdrawn at intervals by opening the plug or tapfor a moment. The condensed water is thus removed from the service-pipe, and does not obstruct its through-way. Similar drainage devices may beused at the lowest points of all dips in mains, though there are specialseal-pots which take the place of the cock or plug used to seal the endof the drainage-pipe. Such seal-pots or "syphons" are commonly used onordinary gas-distributing systems, and might be applied in the case oflarge acetylene installations, as they offer facilities for removing thecondensed water from time to time in a convenient and expeditious manner. EXPULSION OF AIR FROM MAINS. --After a service-pipe system has been provedto be sound, it is necessary to expel the air from it before acetylenecan be admitted to it with a view to consumption. Unless the system is avery large one, the expulsion of air is most conveniently effected byforcing from the gasholder preliminary batches of acetylene through thepipes, while lights are kept away from the vicinity. This precaution isnecessary because, while the acetylene is displacing the air in thepipes, they will for some time contain a mixture of air and acetylene inproportions which fall within the explosive limits of such a mixture. Ifthe escaping acetylene caught fire from any adjacent light under theseconditions, a most disastrous explosion would ensue and extend throughall the ramifications of the system of pipes. Therefore the first stepwhen a new system of pipes has to be cleared of air is to see that thereare no lights in or about the house--either fires, lamps, cigars orpipes, candles or other flames. Obviously this work must be done in thedaytime and finished before nightfall. Burners are removed from two ormore brackets at the farthest points in the system from the gasholder, and flexible connexions are temporarily attached to them, and led througha window or door into the open air well clear of the house. One of thebrackets selected should as a rule be the lowest point supplied in thehouse. The gasholder having been previously filled with acetylene, thetap or taps on the pipe leading to the house are turned on, and theacetylene is passed under slight pressure into the system of pipes, andescapes through the aforesaid brackets, of which the taps have beenturned on, into the open. The taps of all other brackets are kept closed. The gas should be allowed to flow thus through the pipes until about fivetimes the maximum quantity which all the burners on the system wouldconsume in an hour has escaped from the open brackets. The taps on thesebrackets are then closed, and the burners replaced. Flexible tubing isthen connected in place of the burners to all the other brackets in thehouse, and acetylene is similarly allowed to escape into the open airfrom each for a quarter of an hour. All taps are then closed, and theburners replaced; all windows in the house are left open wide for half anhour to allow of the dissipation of any acetylene which may haveaccumulated in any part of it, and then, while full pressure from thegasholder is maintained, a tap is turned on and the gas lighted. If itburns with a good, fully luminous flame it may be concluded that thesystem of pipes is virtually free from air, and the installation may beused forthwith as required. If, however, the flame is very feeblyluminous, or if the escaping gas does not light, lights must beextinguished, and the pipes again blown through with acetylene into theopen air. The burner must invariably be in position when a light isapplied, because, in the event of the pipes still containing an explosivemixture, ignition would not be communicated through the small orifices ofthe burner to the mixture in the pipes, and the application of the lightwould not entail any danger of an explosion. Gasfitters familiar with coal-gas should remember, when putting a systemof acetylene pipes into use for the first time, that the range over whichmixtures of acetylene and air are explosive is wider than that over whichmixtures of coal-gas and air are explosive, and that greater care istherefore necessary in getting the pipes and rooms free from a dangerousmixture. The mains for very large installations of acetylene--_e. G. _, forlighting a small town--may advisedly be freed from air by some other planthan simple expulsion of the air by acetylene, both from the point ofview of economy and of safety. If the chimney gases from a neighbouringfurnace are found on examination to contain not more than about 8 percent of oxygen, they may be drawn into the gasholder and forced throughthe pipes before acetylene is admitted to them. The high proportion ofcarbon dioxide and the low proportion of oxygen in chimney gases makes amixture of acetylene and chimney gases non-explosive in any proportions, and hence if the air is first wholly or to a large extent expelled from apipe, main, or apparatus, by means of chimney gases, acetylene may beadmitted, and a much shorter time allowed for the expulsion by it of thecontents of the pipe, before a light is applied at the burners, &c. Thisplan, however, will usually only be adopted in the case of very largepipes, &c. ; but on a smaller scale the air may be swept out of adistributing system by bringing it into connexion with a cylinder ofcompressed or liquefied carbon dioxide, the pressure in which will drivethe gas to any spot where an outlet is provided. As these cylinders of"carbonic acid" are in common employment for preparing aerated waters andfor "lifting" beer, &c. , they are easy to hire and use. TABLE (B). Giving the Sizes of Pipe which should be used in practice for Acetylenewhen the fall of pressure in the Pipe is not to exceed 0. 1 inch. (Basedon Morel's formula. ) _________________________________________________________| | || Cubic Feet of | Diameters of Pipe to be used up to || Acetylene | the lengths indicated. || which the Pipe |_______________________________________|| is required to | | | | | || pass in | 1/4 | 3/8 | 1/2 | 3/4 | 1 || One Hour. | inch. | inch. | inch. | inch. | inch. ||________________|_______|_______|_______|_______|_______|| | | | | | || | Feet. | Feet. | Feet. | Feet. | Feet. || 1 | 520 | 3960 | 16700 | . . . | . . . || 2 | 130 | 990 | 4170 | . . . | . . . || 3 | 58 | 440 | 1850 | . . . | . . . || 4 | 32 | 240 | 1040 | . . . | . . . || 5 | 21 | 150 | 660 | 5070 | . . . || 6 | 14 | 110 | 460 | 3520 | . . . || 7 | 10 | 80 | 340 | 2590 | . . . || 8 | . . . | 62 | 260 | 1980 | . . . || 9 | . . . | 49 | 200 | 1560 | . . . || 10 | . . . | 39 | 160 | 1270 | 5340 || 15 | . . . | 17 | 74 | 560 | 2370 || 20 | . . . | 10 | 41 | 310 | 1330 || 25 | . . . | . . . | 26 | 200 | 850 || 30 | . . . | . . . | 18 | 140 | 590 || 35 | . . . | . . . | 13 | 100 | 430 || 40 | . . . | . . . | 10 | 79 | 330 || 45 | . . . | . . . | . . . | 62 | 260 || 50 | . . . | . . . | . . . | 50 | 210 ||________________|_______|_______|_______|_______|_______| TABLE (A). Showing the Quantities [Q] (in cubic feet) of Acetylene which will passin One Hour through Pipes of various diameters (in inches) underdifferent Falls of Pressure. (Based on Morel's formula. ) ____________________________________________________________________| | | | | | | | | | | | || Diameter | | | | | | | | | | | || of Pipe | 1/4| 3/8| 1/2| 3/4 | 1 | 1 | 1 | 1 | 2 | 2 | 3 || [_d_] = | | | | | | 1/4 | 1/2| 3/4| | 1/2| || inches | | | | | | | | | | | ||__________|____|____|____|_____|_____|_____|____|____|____|____|____|| | || Length | || of Pipe | || [_l_] = | Fall of Pressure in the Pipe [_h_] = 0. 10 inch. || Feet | ||__________|_________________________________________________________|| | | | | | | | | | | | || 10 | 7. 2|19. 9|40. 8|112 |230 |405 | 635| 935|1305|2285|3600|| 25 | 4. 5|12. 6|25. 8| 71. 2|146 |255 | 400| 590| 825|1445|2280|| 50 | 3. 2| 8. 9|18. 3| 50. 3|103 |180 | 285| 420| 585|1020|1610|| 100 | 2. 3| 6. 3|12. 9| 35. 6| 73. 1|127 | 200| 295| 410| 720|1140|| 200 | 1. 6| 4. 4| 9. 1| 25. 2| 51. 7| 90. 3| 142| 210| 290| 510| 805|| 300 | 1. 3| 3. 6| 7. 4| 20. 5| 42. 2| 73. 7| 116| 171| 240| 415| 655|| 400 | 1. 1| 3. 1| 6. 4| 17. 8| 36. 5| 63. 8| 100| 148| 205| 360| 570|| 500 | 1. 0| 2. 8| 5. 8| 15. 9| 32. 7| 57. 1| 90| 132| 185| 320| 510||__________|____|____|____|_____|_____|_____|____|____|____|____|____|| | || Length | || of Pipe | || [_l_] = | Fall of Pressure in the Pipe [_h_] = 0. 25 inch. || Feet | ||__________|_________________________________________________________|| | | | | | | | | | | | || 25 | 7. 2|19. 9|40. 8|112 |230 |405 | 635| 935|1305|2285|3600|| 50 | 5. 1|14. 1|28. 9| 79. 6|163 |285 | 450| 660| 925|1615|2550|| 100 | 3. 6| 9. 9|20. 4| 56. 3|115 |200 | 320| 470| 655|1140|1800|| 250 | 2. 3| 6. 3|12. 9| 35. 6| 73. 1|127 | 200| 295| 410| 720|1140|| 500 | 1. 6| 4. 4| 9. 1| 25. 2| 51. 7| 90. 3| 142| 210| 290| 510| 805|| 1000 | 1. 1| 3. 1| 6. 4| 17. 8| 36. 5| 63. 8| 100| 148| 205| 360| 570||__________|____|____|____|_____|_____|_____|____|____|____|____|____|| | || Length | || of Pipe | || [_l_] = | Fall of Pressure in the Pipe [_h_] = 0. 50 inch. || Feet | ||__________|_________________________________________________________|| | | | | | | | | | | | || 25 |10. 2|28. 1|57. 8|159 |325 |570 | 900|1325|1850|3230|5095|| 50 | 7. 2|19. 9|40. 8|112 |230 |405 | 635| 935|1305|2285|3600|| 100 | 5. 1|14. 1|28. 9| 79. 6|163 |285 | 450| 660| 925|1615|2550|| 250 | 3. 2| 8. 9|18. 3| 50. 3|103 |180 | 285| 420| 585|1020|1610|| 500 | 2. 3| 6. 3|12. 9| 35. 6| 73. 1|127 | 200| 295| 410| 720|1140|| 1000 | 1. 6| 4. 4| 9. 1| 25. 2| 51. 7| 90. 3| 142| 210| 290| 510| 805||__________|____|____|____|_____|_____|_____|____|____|____|____|____|| | || Length | || of Pipe | || [_l_] = | Fall of Pressure in the Pipe [_h_] = 0. 75 inch. || Feet | ||__________|_________________________________________________________|| | | | | | | | | | | | || 50 | 8. 8|24. 4|50. 0|138 |280 |495 | 780|1145|1160|2800|4410|| 100 | 6. 2|17. 2|35. 4| 97. 5|200 |350 | 550| 810|1130|1980|3120|| 250 | 3. 9|10. 9|22. 4| 61. 7|126 |220 | 350| 510| 715|1250|1975|| 500 | 2. 8| 7. 7|15. 8| 43. 6| 89. 5|156 | 245| 360| 505| 885|1395|| 1000 | 2. 0| 5. 4|11. 2| 30. 8| 63. 3|110 | 174| 255| 360| 625| 985|| 2000 | 1. 4| 3. 8| 7. 9| 21. 8| 44. 8| 78. 2| 123| 181| 250| 440| 695||__________|____|____|____|_____|_____|_____|____|____|____|____|____|| | || Length | || of Pipe | || [_l_] = | Fall of Pressure in the Pipe [_h_] = 1. 0 inch. || Feet | ||__________|_________________________________________________________|| | | | | | | | | | | | || 100 | 7. 2|19. 9|40. 8|112 |230 |405 | 635| 935|1305|2285|3600|| 250 | 4. 5|12. 6|25. 8| 71. 2|146 |255 | 400| 590| 825|1445|2280|| 500 | 3. 2| 8. 9|18. 3| 50. 3|103 |180 | 285| 420| 585|1020|1610|| 1000 | 2. 3| 6. 3|12. 9| 35. 6| 73. 1|127 | 200| 295| 410| 720|1140|| 2000 | 1. 6| 4. 4| 9. 1| 25. 2| 51. 7| 90. 3| 142| 210| 290| 510| 805|| 3000 | 1. 3| 3. 6| 7. 4| 20. 5| 42. 2| 73. 7| 116| 171| 240| 415| 655||__________|_________________________________________________________|| | || Length | || of Pipe | || [_l_] = | Fall of Pressure in the Pipe [_h_] = 1. 5 inch. || Feet | ||__________|_________________________________________________________|| | | | | | | | | | | | || 250 | 5. 6|15. 4|31. 6| 87. 2|179 |310 | 495| 725|1010|1770|2790|| 500 | 3. 9|10. 9|22. 4| 61. 7|126 |220 | 350| 510| 715|1250|1975|| 1000 | 2. 8| 7. 7|15. 8| 43. 6| 89. 5|156 | 245| 360| 505| 885|1395|| 2000 | 2. 0| 5. 4|11. 2| 30. 8| 63. 3|110 | 174| 255| 360| 625| 985|| 3000 | 1. 6| 4. 4| 9. 1| 25. 2| 51. 7| 90. 3| 142| 210| 290| 510| 805|| 4000 | 1. 4| 3. 8| 7. 9| 21. 8| 44. 8| 78. 2| 123| 181| 250| 440| 695||__________|____|____|____|_____|_____|_____|____|____|____|____|____|| | || Length | || of Pipe | || [_l_] = | Fall of Pressure in the Pipe [_h_] = 2. 0 inches. || Feet | ||__________|_________________________________________________________|| | | | | | | | | | | | || 500 | 4. 5|12. 6|25. 8| 71. 2|146 |255 | 400| 590| 825|1445|2280|| 1000 | 3. 2| 8. 9|18. 3| 50. 3|103 |180 | 285| 420| 585|1020|1610|| 2000 | 2. 3| 6. 3|12. 9| 35. 6| 73. 1|127 | 200| 295| 410| 720|1140|| 3000 | 1. 8| 5. 1|10. 5| 29. 1| 59. 7|104 | 164| 240| 335| 590| 930|| 4000 | 1. 6| 4. 4| 9. 1| 25. 2| 51. 7| 90. 3| 142| 210| 290| 510| 805|| 5000 | 1. 4| 4. 0| 8. 1| 22. 5| 46. 2| 80. 8| 127| 187| 260| 455| 720|| 6000 | 1. 3| 3. 6| 7. 4| 20. 5| 42. 2| 73. 7| 116| 171| 240| 415| 655||__________|____|____|____|_____|_____|_____|____|____|____|____|____| NOTE. --In order not to impart to the above table the appearance of thequantities having been calculated to a degree of accuracy which has nopractical significance, quantities of less than 5 cubic feet have beenignored when the total quantity exceeds 200 cubic feet, and fractions ofa cubic foot have been included only when the total quantity is less than100 cubic feet. TABLE (C). Giving the Sizes of Pipe which should be used in practice for Acetylenewhen the fall of pressure in the Pipe is not to exceed 0. 25 inch. (Basedon Morel's formula. ) ____________________________________________________________________| | || Cubic feet | || of | || Acetylene | Diameters of Pipe to be used up to the lengths stated. || which the | || Pipe is | || required |_______________________________________________________|| to pass | | | | | | | | || in One | 1/4 | 1/2 | 3/4 | 1 | 1-1/4| 1-1/2| 1-3/4| 2 || Hour | inch. | inch. | inch. | inch. | inch. | inch. | inch. | inch. ||____________|______|______|______|______|______|______|______|______|| | | | | | | | | || | Feet. | Feet. | Feet. | Feet. | Feet. | Feet. | Feet. | Feet. || 2-1/2 | 1580 | 6680 | 50750| . . . | . . . | . . . | . . . | . . . || 5 | 390 | 1670 | 12690| 53160| . . . | . . . | . . . | . . . || 7-1/2 | 175 | 710 | 5610| 23760| . . . | . . . | . . . | . . . || 10 | 99 | 410 | 3170| 13360| 40790| . . . | . . . | . . . || 15 | 41 | 185 | 1410| 5940| 18130| 45110| . . . | . . . || 20 | 24 | 105 | 790| 3350| 10190| 25370| 54840| . . . || 25 | 26 | 67 | 500| 2130| 6520| 16240| 35100| . . . || 30 | 11 | 46 | 350| 1480| 4530| 11270| 24370| 47520|| 35 | . . . | 34 | 260| 1090| 3330| 8280| 17900| 34910|| 40 | . . . | 26 | 195| 830| 2550| 6340| 13710| 26730|| 45 | . . . | 20 | 155| 660| 2010| 5010| 10830| 21120|| 50 | . . . | 16 | 125| 530| 1630| 4060| 8770| 17110|| 60 | . . . | 11 | 88| 370| 1130| 2880| 6090| 11880|| 70 | . . . | . . . | 61| 270| 830| 2070| 4470| 8730|| 80 | . . . | . . . | 49| 210| 630| 1580| 3420| 6680|| 90 | . . . | . . . | 39| 165| 500| 1250| 2700| 5280|| 100 | . . . | . . . | 31| 130| 400| 1010| 2190| 4270|| 150 | . . . | . . . | 14| 59| 180| 450| 970| 1900|| 200 | . . . | . . . | . . . | 33| 100| 250| 540| 1070|| 250 | . . . | . . . | . . . | 21| 65| 160| 350| 680|| 500 | . . . | . . . | . . . | . . . | 16| 40| 87| 170|| 1000 | . . . | . . . | . . . | . . . | . . . | 10| 22| 42||____________|______|______|______|______|______|______|______|______| TABLE (D). Giving the Sizes of Pipe which should be used in practice for AcetyleneMains when the fall of pressure in the Main is not to exceed 0. 5 inch, (Based on Morel's formula. ) ____________________________________________________________________| | || Cubic feet | || of | || Acetylene | Diameters of Pipe to be used up to the lengths stated. || which the | || Main is | || required |_______________________________________________________|| to pass | | | | | | | | || in One | 3/4 | 1 | 1-1/4| 1-1/2| 1-3/4| 2 | 2-1/2| 3 || Hour | inch. | inch. | inch. | inch. | inch. | inch. | inch. | inch. ||____________|______|______|______|______|______|______|______|______|| | | | | | | | | || |Miles. |Miles. |Miles. |Miles. |Miles. |Miles. |Miles. |Miles. || 10 | 5. 05 | . . . | . . . | . . . | . . . | . . . | . . . | . . . || 25 | 0. 80 | 2. 45 | 6. 15 | . . . | . . . | . . . | . . . | . . . || 50 | 0. 20 | 0. 60 | 1. 50 | 3. 30 | 6. 45 | . . . | . . . | . . . || 100 | 0. 05 | 0. 15 | 0. 35 | 0. 80 | 1. 60 | 4. 95 |12. 30 | . . . || 200 | . . . | 0. 04 | 0. 09 | 0. 20 | 0. 40 | 1. 20 | 3. 05 |12. 95 || 300 | . . . | . . . | 0. 04 | 0. 09 | 0. 18 | 0. 55 | 1. 35 | 5. 75 || 400 | . . . | . . . | . . . | 0. 05 | 0. 10 | 0. 30 | 0. 75 | 3. 25 || 500 | . . . | . . | . . . | 0. 03 | 0. 06 | 0. 20 | 0. 50 | 2. 05 || 750 | . . . | . . . | . . . | . . . | 0. 03 | 0. 08 | 0. 20 | 0. 80 || 1100 | . . . | . . . | . . . | . . . | . . . | 0. 05 | 0. 12 | 0. 50 || 1500 | . . . | . . . | . . . | . . . | . . . | 0. 02 | 0. 05 | 0. 23 || 2000 | . . . | . . . | . . . | . . . | . . . | . . . | 0. 03 | 0. 13 || 2500 | . . . | . . . | . . . | . . . | . . . | . . . | 0. 02 | 0. 08 || 5000 | . . . | . . . | . . . | . . . | . . . | . . . | . . . | 0. 03 ||____________|______|______|______|______|______|______|______|______| TABLE (E). Giving the Sizes of Pipe which should be used in practice for AcetyleneMains when the fall of pressure in the Main is not to exceed 1. 0 inch. (Based on Morel's formula. ) __________________________________________________________________| | || Cubic feet | || of | || Acetylene |Diameters of Pipe to be used up to the lengths stated|| which the | || Main is | || required |_____________________________________________________|| to pass | | | | | | | | | || in One | 3/4 | 1 |1-1/4|1-1/2|1-3/4| 2 |2-1/2| 3 | 4 || Hour |inch. |inch. |inch. |inch. |inch. |inch. |inch. |inch. |inch. ||____________|_____|_____|_____|_____|_____|_____|_____|_____|_____|| | | | | | | | | | || |Miles|Miles|Miles|Mile. |Miles|Miles|Miles|Miles|Miles|| 10 | 2. 40|10. 13|30. 90| . . . | . . . | . . . | . . . | . . . | . . . || 25 | 0. 38| 1. 62| 4. 94|12. 30| . . . | . . . | . . . | . . . | . . . || 50 | 0. 09| 0. 40| 1. 23| 3. 07| 6. 65|12. 96| . . . | . . . | . . . || 100 | 0. 02| 0. 10| 0. 30| 0. 77| 1. 66| 3. 24| 9. 88| . . . | . . . || 200 | . . . | 0. 02| 0. 07| 0. 19| 0. 41| 0. 81| 2. 47| 6. 15| . . . || 300 | . . . | 0. 01| 0. 03| 0. 08| 0. 18| 0. 36| 1. 09| 2. 73|11. 52|| 400 | . . . | . . . | 0. 0 | 0. 05| 0. 10| 0. 20| 0. 61| 1. 53| 6. 48|| 500 | . . . | . . . | 0. 0 | 0. 03| 0. 06| 0. 13| 0. 39| 0. 98| 4. 14|| 750 | . . . | . . . | . . . | 0. 01| 0. 03| 0. 05| 0. 17| 0. 43| 1. 84|| 1000 | . . . | . . . | . . . | . . . | 0. 01| 0. 03| 0. 10| 0. 24| 1. 03|| 1500 | . . . | . . . | . . . | . . . | . . . | 0. 01| 0. 01| 0. 11| 0. 46|| 2000 | . . . | . . . | . . . | . . . | . . . | . . . | 0. 02| 0. 06| 0. 26|| 2500 | . . . | . . . | . . . | . . . | . . . | . . . | 0. 01| 0. 04| 0. 16|| 5000 | . . . | . . . | . . . | . . . | . . . | . . . | . . . | 0. 01| 0. 04||____________|_____|_____|_____|_____|_____|_____|_____|_____|_____| CHAPTER VIII COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS--THEIR DISPOSITION NATURE OF LUMINOUS FLAMES. --When referring to methods of obtainingartificial light by means of processes involving combustion or oxidation, the term "incandescence" is usually limited to those forms of burner inwhich some extraneous substance, such as a "mantle, " is raised to abrilliant white heat. Though convenient, the phrase is a mere convention, for all artificial illuminants, even including the electric light, whichexhibit a useful degree of intensity depend on the same principle ofincandescence. Adopting the convention, however, an incandescent burneris one in which the fuel burns with a non-luminous or atmospheric flame, the light being produced by causing that flame to play upon someextraneous refractory body having the property of emitting much lightwhen it is raised to a sufficiently high temperature; while a luminousburner is one in which the fuel is allowed to combine with atmosphericoxygen in such a way that one or more of the constituents in the gasevolves light as it suffers combustion. From the strictly chemical pointof view the light-giving substance in the incandescent flame lastsindefinitely, for it experiences no change except in temperature; whereasthe light-giving substance in a luminous flame lasts but for an instant, for it only evolves light during the act of its combination with theoxygen of the atmosphere. Any fluid combustible which burns with a flamecan be made to give light on the incandescent system, for all suchmaterials either burn naturally, or can be made to burn with a non-luminous flame, which can be employed to raise the temperature of somemantle; but only those fuels can be burnt on the self-luminous systemwhich contain some ingredient that is liberated in the elemental state inthe flame, the said ingredient being one which combines energeticallywith oxygen so as to liberate much local heat. In practice, just as thereare only two or three substances which are suitable for the constructionof an incandescent mantle, so there is only one which renders a flameusefully self-luminous, viz. , carbon; and therefore only such fuels ascontain carbon among their constituents can be burnt so as to producelight without the assistance of the mantle. But inasmuch as it isnecessary for the evolution of light by the combustion of carbon thatthat carbon shall be in the free state, only those carbonaceous fuelsyield light without the mantle in which the carbonaceous ingredient isdissociated into its elements before it is consumed. For instance, alcohol and carbon monoxide are both combustible, and both containcarbon; but they yield non-luminous flames, for the carbon burns tocarbon dioxide in ordinary conditions without assuming the solid form;ether, petroleum, acetylene, and some of the hydrocarbons of coal-gas doemit light on combustion, for part of their carbon is so liberated. Thequantity of light emitted by the glowing substance increases as thetemperature of that substance rises: the gain in light being equal to thefifth or higher power of the gain in heat; [Footnote: Calculated fromabsolute zero. ] therefore unnecessary dissipation of heat from a flame isone of the most important matters to be guarded against if that flame isto be an economical illuminant. But the amount of heat liberated when acertain weight (or volume) of a particular fuel combines with asufficient quantity of oxygen to oxidise it wholly is absolutely fixed, and is exactly the same whether that fuel is made to give a luminous or anon-luminous flame. Nevertheless the atmospheric flame given by a certainfuel may be appreciably hotter than its luminous flame, because theformer is usually smaller than the latter. Unless the luminous flame of arich fuel is made to expose a wide surface to the air, part of its carbonmay escape ultimate combustion; soot or smoke may be produced, and someof the most valuable heat-giving substance will be wasted. But if theflame is made to expose a large surface to the air, it becomes flat orhollow in shape instead of being cylindrical and solid, and therefore inproportion to its cubical capacity it presents to the cold air a largersuperficies, from which loss of heat by radiation, &c. , occurs. Beinglarger, too, the heat produced is less concentrated. It does not fall within the province of the present book to discuss therelative merits of luminous and incandescent lighting; but it may beremarked that acetylene ranks with petroleum against coal-gas, carburetted or non-carburetted water-gas, and semi-water-gas, in showinga comparatively small degree of increased efficiency when burnt under themantle. Any gas which is essentially composed of carbon monoxide orhydrogen alone (or both together) burns with a non-luminous flame, andcan therefore only be used for illuminating purposes on the incandescentsystem; but, broadly speaking, the higher is the latent illuminatingpower of the gas itself when burnt in a non-atmospheric burner, the lessmarked is the superiority, both from the economical and the hygienicaspect, of its incandescent flame. It must be remembered also that only agas yields a flame when it is burnt; the flame of a paraffin lamp and ofa candle is due to the combustion of the vaporised fuel. Methods ofburning acetylene under the mantle are discussed in Chapter IX. ; hereonly self-luminous flames are being considered, but the theoreticalquestion of heat economy applies to both processes. Heat may be lost from a flame in three several ways: by direct radiationand conduction into the surrounding air, among the products ofcombustion, and by conduction into the body of the burner. Loss of heatby radiation and conduction to the air will be the greater as the flameexposes a larger surface, and as a more rapid current of cold air isbrought into proximity with the flame. Loss of heat by conduction, intothe burner will be the greater as the material of which the burner isconstructed is a better conductor of heat, and as the mass of material inthat burner is larger. Loss of heat by passage into the combustionproducts will also be greater as these products are more voluminous; butthe volume of true combustion products from any particular gas is a fixedquantity, and since these products must leave the flame at thetemperature of that flame--where the highest temperature possible isrequisite--it would seem that no control can be had over the quantity ofheat so lost. However, although it is not possible in practice to supplya flame with too little air, lest some of its carbon should escapeconsumption and prove a nuisance, it is very easy without conspicuousinconvenience to supply it with too much; and if the flame is suppliedwith too much, there is an unnecessary volume of air passing through itto dilute the true combustion products, which air absorbs its own properproportion of heat. It is only the oxygen of the air which a flame needs, and this oxygen is mixed with approximately four times its volume ofnitrogen; if, then, only a small excess of oxygen (too little to benoticeable of itself) is admitted to a flame, it is yet harmful, becauseit brings with it four times its volume of nitrogen, which has to beraised to the same temperature as the oxygen. Moreover, the nitrogen andthe excess of oxygen occupy much space in the flame, making it larger, and distributing that fixed quantity of heat which it is capable ofgenerating over an unnecessarily large area. It is for this reason thatany gas gives so much brighter a light when burnt in pure oxygen than inair, (1) because the flame is smaller and its heat more concentrated, and(2) because part of its heat is not being wasted in raising thetemperature of a large mass of inert nitrogen. Thus, if the flame of agas which naturally gives a luminous flame is supplied with an excess ofair, its illuminating value diminishes; and this is true whether thatexcess is introduced at the base of the actual flame, or is added to thegas prior to ignition. In fact the method of adding some air to anaturally luminous gas before it arrives at its place of combustion isthe principle of the Bunsen burner, used for incandescent lighting andfor most forms of warming and cooking stoves. A well-made modernatmospheric burner, however, does not add an excess of air to the flame, as might appear from what has been said; such a burner only adds part ofthe air before and the remainder of the necessary quantity after thepoint of first ignition--the function of the primary supply being merelyto insure thorough admixture and to avoid the production of elementalcarbon within the flame. ILLUMINATING POWER. --It is very necessary to observe that, as thecombined losses of heat from a flame must be smaller in proportion to thetotal heat produced by the flame as the flame itself becomes larger, themore powerful and intense any single unit of artificial light is, themore economical does it become, because economy of heat spells economy oflight. Conversely, the more powerful and intense any single unit of lightis, the more is it liable to injure the eyesight, the deeper and, bycontrast, the more impenetrable are the shadows it yields, and the lesspleasant and artistic is its effect in an occupied room. For economicalreasons, therefore, one large central source of light is best in anapartment, but for physiological and æsthetic reasons a considerablenumber of correspondingly smaller units are preferable. Even in thestreet the economical advantage of the single unit is outweighed by theinconvenience of its shadows, and by the superiority of a number ofevenly distributed small sources to one central large source of lightwhenever the natural transmission of light rays through the atmosphere isinterfered with by mist or fog. The illuminating power of acetylene iscommonly stated to be "240 candles" (though on the same basis Wolff hasfound it to be about 280 candles). This statement means that whenacetylene is consumed in the most advantageous self-luminous burner atthe most advantageous rate, that rate (expressed in cubic feet per hour)is to 5 in the same ratio as the intensity of the light evolved(expressed in standard candles) is to the said "illuminating power. "Thus, Wolff found that when acetylene was burnt in the "0000 Bray" fish-tail burner at the rate of 1. 377 cubic feet per hour, a light of 77candle-power was obtained. Hence, putting x to represent the illuminatingpower of the acetylene in standard candles, we have: 1. 377 / 5 = 77 / x hence x = 280. Therefore acetylene is said to have, according to Wolff, an illuminatingpower of about 280 candles, or according to other observers, whoseresults have been commonly quoted, of 240 candles. The same method ofcalculating the nominal illuminating power of a gas is applied within theUnited Kingdom in the case of all gases which cannot be advantageouslyburnt at the rate of 5 cubic feet per hour in the standard burner(usually an Argand). The rate of 5 cubic feet per hour is specified inmost Acts of Parliament relating to gas-supply as that at which coal-gasis to be burnt in testings of its illuminating power; and theilluminating power of the gas is defined as the intensity, expressed instandard candles, of the light afforded when the gas is burnt at thatrate. In order to make the values found for the light evolved at moreadvantageous rates of consumption by other descriptions of gas--such asoil-gas or acetylene--comparable with the "illuminating power" of coal-gas as defined above, the values found are corrected in the ratio of theactual rate of consumption to 5 cubic feet per hour. In this way the illuminating power of 240 candles has been commonlyassigned to acetylene, though it would be clearer to those unfamiliarwith the definition of illuminating power in the Acts of Parliament whichregulate the testing of coal-gas, if the same fact were conveyed bystating that acetylene affords a maximum illuminating power of 48 candles(_i. E. _, 240 / 5) per cubic foot. Actually, by misunderstanding ofthe accepted though arbitrary nomenclature of gas photometry, it has notinfrequently been assorted or implied that a cubic foot of acetyleneyields a light of 240 candle-power instead of 48 candle-power. It should, moreover, be remembered that the ideal illuminating power of a gas is thehighest realisable in any Argand or flat-flame burner, while the saidburner may not be a practicable one for general use in house lighting. Thus, the burners recommended for general use in lighting by acetylene donot develop a light of 48 candles per cubic foot of gas consumed, butconsiderably less, as will appear from the data given later in thischapter. It has been stated that in order to avoid loss of heat from a flamethrough the burner, that burner should present only a small mass ofmaterial (_i. E. _, be as light in weight as possible), and should beconstructed of a bad heat-conductor. But if a small mass of a materialvery deficient in heat-conducting properties comes in contact with aflame, its temperature rises seriously and may approach that of the baseof the flame itself. In the case of coal-gas this phenomenon is notobjectionable, is even advantageous, and it explains why a burner made ofsteatite, which conducts heat badly, in always more economical (of heatand therefore of light) than an iron one. In the case of acetylene thesame rule should, and undoubtedly does, apply also; but it iscomplicated, and its effect sometimes neutralised, by a peculiarity ofthe gas itself. It has been shown in Chapters II. And VI. That acetylenepolymerises under the influence of heat, being converted into otherbodies of lower illuminating power, together with some elemental carbon. If, now, acetylene is fed into a burner which, being composed of somematerial like steatite possessed of low heat-conducting and radiatingpowers, is very hot, and if the burner comprises a tube of sensiblelength, the gas that actually arrives at the orifice may no longer bepure acetylene, but acetylene diluted with inferior illuminating agents, and accompanied by a certain proportion of carbon. Neglecting the effectof this carbon, which will be considered in the following paragraph, itis manifest that the acetylene issuing from a hot burner--assuming itstemperature to exceed the minimum capable of determining polymerisation--may emit less light per unit of volume than the acetylene escaping from acold burner. Proof of this statement is to be found in some experimentsdescribed by Bullier, who observed that when a small "Manchester" orfish-tail burner was allowed to become naturally hot, the quantity of gasneeded to give the light of one candle (uncorrected) was 1. 32 litres, butwhen the burner was kept cool by providing it with a jacket in whichwater was constantly circulating, only 1. 13 litres of acetylene werenecessary to obtain the same illuminating value, this being an economy of16 per cent. EARLY BURNERS. --One of the chief difficulties encountered in the earlydays of the acetylene industry was the design of a satisfactory burnerwhich should possess a life of reasonable length. The first burners triedwere ordinary oil-gas jets, which resemble the fish-tails used with coal-gas, but made smaller in every part to allow for the higher illuminatingpower of the oil-gas or acetylene per unit of volume. Although the flamesthey gave were very brilliant, and indeed have never been surpassed, thelight quickly fell off in intensity owing to the distortion of theirorifices caused by the deposition of solid matter at the edges. Variousexplanations have been offered to account for the precipitation of solidmatter at the jets. If the acetylene passes directly to the burner from agenerator having carbide in excess without being washed or filtered inany way, the gas may carry with it particles of lime dust, which willcollect in the pipes mainly at the points where they are constricted; andas the pipes will be of comparatively large bore until the actual burneris readied, it will be chiefly at the orifices where the depositionoccurs. This cause, though trivial, is often overlooked. It will beobviated whenever the plant is intelligently designed. As the phosphoricanhydride, or pentoxide, which is produced when a gas containingphosphorus burns, is a solid body, it may be deposited at the burnerjets. This cause may be removed, or at least minimised, by properpurification of the acetylene, which means the removal of phosphoruscompounds. Should the gas contain hydrogen silicide siliciurettedhydrogen), solid silica will be produced similarly, and will play itspart in causing obstruction. According to Lewes the main factor in theblocking of the burners is the presence of liquid polymerised products inthe acetylene, benzene in particular; for he considers that these bodieswill be absorbed by the porous steatite, and will be decomposed under theinfluence of heat in that substance, saturating the steatite with carbonwhich, by a "catalytic" action presumably, assists in the deposition offurther quantities of carbon in the burner tube until distortion of theflame results. Some action of this character possibly occurs; but were itthe sole cause of blockage, the trouble would disappear entirely if thegas were washed with some suitable heavy oil before entering the burners, or if the latter were constructed of a non-porous material. It iscertainly true that the purer is the acetylene burnt, both as regardsfreedom from phosphorus and absence of products of polymerisation, thelonger do the burners last; and it has been claimed that a burnerconstructed at its jets of some non-porous substance, e. G. , "ruby, " doesnot choke as quickly as do steatite ones. Nevertheless, stoppages at theburners cannot be wholly avoided by these refinements. Gaud has shownthat when pure acetylene is burnt at the normal rate in 1-foot Bray jets, growths of carbon soon appear, but do not obstruct the orifices during100 hours' use; if, however, the gas-supply is checked till the flamebecomes thick, the growths appear more quickly, and become obstructiveafter some 60 hours' burning. On the assumption that acetylene begins topolymerise at a temperature of 100° C. , Gaud calculates thatpolymerisation cannot cause blocking of the burners unless the speed ofthe passing gas is so far reduced that the burner is only delivering one-sixth of its proper volume. But during 1902 Javal demonstrated that onheating in a gas-flame one arm of a twin, non-injector burner which hadbeen and still was behaving quite satisfactorily with highly purifiedacetylene, growths were formed at the jet of that arm almostinstantaneously. There is thus little doubt that the principal cause ofthis phenomenon is the partial dissociation of the acetylene (i. E. , decomposition into its elements) as it passes through the burner itself;and the extent of such dissociation will depend, not at all upon thepurity of the gas, but upon the temperature of the burner, upon thereadiness with which the heat of the burner is communicated to the gas, and upon the speed at which the acetylene travels through the burner. Some experiments reported by R. Granjon and P. Mauricheau-Beaupré in 1906indicate, however, that phosphine in the gas is the primary cause of thegrowths upon non-injector burners. According to these investigators thecombustion of the phosphine causes a deposit at the burner orifices ofphosphoric acid, which is raised by the flame to a temperature higherthan that of the burner. This hot deposit then decomposes some acetylene, and the carbon deposited therefrom is rendered incombustible by thephosphoric acid which continues to be produced from the combustion of thephosphine in the gas. The incombustible deposit of carbon and phosphoricacid thus produced ultimately chokes the burner. It will appear in Chapter XI. That some of the first endeavours to avoidburner troubles were based on the dilution of the acetylene with carbondioxide or air before the gas reached the place of combustion; while thesubsequent paragraphs will show that the same result is arrived at moresatisfactorily by diluting the acetylene with air during its actualpassage through the burner. It seems highly probable that the beneficialeffect of the earliest methods was due simply or primarily to thedilution, the molecules of the acetylene being partially protected fromthe heat of the burner by the molecules of a gas which was not injured bythe high temperature, and which attracted to itself part of the heat thatwould otherwise have been communicated to the hydrocarbon. The moderninjector burner exhibits the same phenomenon of dilution, and is to thesame extent efficacious in preventing polymerisation; but inasmuch as itpermits a larger proportion of air to be introduced, and as the additionis made roughly half-way along the burner passage, the cold air is moreeffectual in keeping the former part of the tip cool, and in jacketingthe acetylene during its travel through the latter part, the bore ofwhich is larger than it otherwise would be. INJECTOR AND TWIN-FLAME BURNERS. --In practice it is neither possible tocool an acetylene burner systematically, nor is it desirable to constructit of such a large mass of some good heat conductor that its temperaturealways remains below the dissociation point of the gas. The earliestdirect attempts to keep the burner cool were directed to an avoidance ofcontact between the flame of the burning acetylene and the body of thejet, this being effected by causing the current of acetylene to inject asmall proportion of air through lateral apertures in the burner below thepoint of ignition. Such air naturally carries along with it some of theheat which, in spite of all precautions, still reaches the burner; but italso apparently forms a temporary annular jacket round the stream of gas, preventing it from catching fire until it has arrived at an appreciabledistance from the jet. Other attempts were made by placing two non-injector jets in such mutual positions that the two streams of gas met atan angle, there to spread fan-fashion into a flat flame. This is reallynothing but the old fish-tail coal-gas burner--which yields its flatflame by identical impingement of two gas streams--modified in detail sothat the bulk of the flame should be at a considerable distance from theburner instead of resting directly upon it. In the fish-tail the twoorifices are bored in the one piece of steatite, and virtually join attheir external ends; in the acetylene burner, two separate pieces ofsteatite, three-quarters of an inch or more apart, carried by completelyseparate supports, are each drilled with one hole, and the flame standsvertically midway between them. The two streams of gas are in onevertical plane, to which the vertical plane of the flame is at rightangles. Neither of these devices singly gave a solution of thedifficulty; but by combining the two--the injector and the twin-flameprinciple--the modern flat-flame acetylene burner has been evolved, andis now met with in two slightly different forms known as the Billwillerand the Naphey respectively. The latter apparently ought to be called theDolan. [Illustration: FIG. 8. --TYPICAL ACETYLENE BURNERS. ] The essential feature of the Naphey burner is the tip, which is shown inlongitudinal section at A in Fig. 8. It consists of a mushroom headedcylinder of steatite, drilled centrally with a gas passage, which at itspoint is of a diameter suited to pass half the quantity of acetylene thatthe entire burner is intended to consume. The cap is provided with fourradial air passages, only two of which are represented in the drawing;these unite in the centre of the head, where they enter into thelongitudinal channel, virtually a continuation of the gas-way, leading tothe point of combustion by a tube wide enough to pass the introduced airas well as the gas. Being under some pressure, the acetylene issuing fromthe jet at the end of the cylindrical portion of the tip injects airthrough the four air passages, and the mixture is finally burnt at thetop orifice. As pointed out in Chapter VII. , the injector jet is so smallin diameter that even if the service-pipes leading to the tip contain anexplosive mixture of acetylene and air, the explosion produced locally ifa light is applied to the burner cannot pass backwards through that jet, and all danger is obviated. One tip only of this description evidentlyproduces a long, jet-like flame, or a "rat-tail, " in which the latentilluminating power of the acetylene is not developed economically. Inpractice, therefore, two of these tips are employed in unison, one of thecommonest methods of holding them being shown at B. From each tip issuesa stream of acetylene mixed with air, and to some extent also surroundedby a jacket of air; and at a certain point, which forms the apex of anisosceles right-angled triangle having its other angles at the orificesof the tips, the gas streams impinge, yielding a flat flame, at right-angles, as mentioned before, to the plane of the triangle. If the twotips are three-quarters of an inch apart, and if the angle of impingementis exactly 90°, the distance of each tip from the base of the flameproper will be a trifle over half an inch; and although each stream ofgas does take fire and burn somewhat before meeting its neighbour, comparatively little heat is generated near the body of the steatite. Nevertheless, sufficient heat is occasionally communicated to the metalstems of these burners to cause warping, followed by a want of alignmentin the gas streams, and this produces distortion of the flame, andpossibly smoking. Three methods of overcoming this defect have been used:in one the arms are constructed entirely of steatite, in another they aremade of such soft metal as easily to be bent back again into positionwith the fingers or pliers, in the third each arm is in two portions, screwing the one into the other. The second type is represented by theoriginal Phôs burner, in which the curved arms of B are replaced by apair of straight divergent arms of thin, soft tubing, joined to a pair ofconvergent wider tubes carrying the two tips. The third type is met within the Drake burner, where the divergent arms are wide and have aninternal thread into which screws an external thread cut upon lateralprolongations of the convergent tubes. Thus both the Phôs and the Drakeburner exhibit a pair of exposed elbows between the gas inlet and the twotips; and these elbows are utilised to carry a screwed wire fastened toan external milled head by means of which any deposit of carbon in theburner tubes can be pushed out. The present pattern of the Phôs burner isshown in Fig. 9, in which _A_ is the burner tip, _B_ the wireor needle, and _C_ the milled head by which the wire is screwed inand out of the burner tube. [Illustration: FIG. 9. --IMPROVED PHÔS BURNER. ] [Illustration: FIG. 10. --"WONDER" SINGLE AND TWO-FLAME BURNERS. ] [Illustration: FIG. 11. --"SUPREMA" NO. 266651, TWO-FLAME BURNER. ] [Illustration: FIG. 12. --BRAY'S MODIFIED NAPHEY INJECTOR BURNER TIP. ] [Illustration: FIG. 13. --BRAY'S "ELTA" BURNER. ] [Illustration: FIG. 14. --BRAY'S "LUTA" BURNER. ] [Illustration: FIG. 15. --BRAY'S "SANSAIR" BURNER. ] [Illustration: FIG. 16. --ADJUSTABLE "KONA" BURNER. ] In the original Billwiller burner, the injector gas orifice was broughtcentrally under a somewhat larger hole drilled in a separate sheet ofplatinum, the metal being so carried as to permit entry of air. In orderto avoid the expense of the platinum, the same principle was afterwardsused in the design of an all-steatite head, which is represented at D inFig. 8. The two holes there visible are the orifices for the emission ofthe mixture of acetylene with indrawn air, the proper acetylene jetslying concentrically below these in the thicker portions of the heads. These two types of burner have been modified in a large number of ways, some of which are shown at C, E, and F; the air entering through saw-cuts, lateral holes, or an annular channel. Burners resembling F inoutward form are made with a pair of injector jets and corresponding airorifices on each head, so as to produce a pair of names lying in the sameplane, "end-on" to one another, and projecting at either sideconsiderably beyond the body of the burner; these have the advantage ofyielding no shadow directly underneath. A burner of this pattern, viz. , the "Wonder, " which is sold in this country by Hannam's, Ltd. , is shownin Fig. 10, alongside the single-flame "Wonder" burner, which is largelyused, especially in the United States. Another two-flame burner, made ofsteatite, by J. Von Schwarz of Nuremberg, and sold by L. Wiener ofLondon, is shown in Fig. 11. Burners of the Argand type have also beenmanufactured, but have been unsuccessful. There are, of course, endlessmodifications of flat-flame burners to be found on the markets, but onlya few need be described. A device, which should prove useful where it maybe convenient to be able to turn one or more burners up or down from thesame common distant spot, has been patented by Forbes. It consists of theusual twin-injector burner fitted with a small central pinhole jet; andinside the casing is a receptacle containing a little mercury, the levelof which is moved by the gas pressure by an adaptation of thedisplacement principle. When the main is carrying full pressure, both ofthe jets proper are alight, and the burner behaves normally, but if thepressure is reduced to a certain point, the movement of the mercury sealsthe tubes leading to the main jets, and opens that of the pilot flame, which alone remains alight till the pressure is increased again. Bray haspatented a modification of the Naphey injector tip, which is shown inFig. 12. It will be observed that the four air inlets are at right-anglesto the gas-way; but the essential feature of the device is the conicalorifice. By this arrangement it is claimed that firing back never occurs, and that the burner can be turned down and left to give a small flame forconsiderable periods of time without fear of the apertures becomingchoked or distorted. As a rule burners of the ordinary type do not wellbear being turned down; they should either be run at full power orextinguished completely. The "Elta" burner, made by Geo. Bray and Co. , Ltd. , which is shown in Fig. 13, is an injector or atmospheric burnerwhich may be turned low without any deposition of carbon occurring on thetips. A burner of simple construction but which cannot be turned low isthe "Luta, " made by the same firm and shown in Fig. 14. Of the non-atmospheric type the "Sansair, " also made by Geo. Bray and Co. , Ltd. , isextensively used. It is shown in Fig. 15. In order to avoid the warping, through the heat of the flame, of the arms of burners which sometimesoccurs when they are made of metal, a number of burners are now made withthe arms wholly of steatite. One of the best-known of these, of theinjector type, is the "Kona, " made by Falk, Stadelmann and Co. , ofLondon. It is shown in Fig. 16, fitted with a screw device for adjustingthe flow of gas, so that when this adjuster has been set to give a flameof the proper size, no further adjustment by means of the gas-tap isnecessary. This saves the trouble of manipulating the tap after the gasis lighted. The same adjusting device may also be had fitted to the Phôsburner (Fig. 9) or to the "Orka" burner (Fig. 17), which is a steatite-tip injector burner with metal arms made by Falk, Stadelmann and Co. , Ltd. A burner with steatite arms, made by J. Von Schwarz of Nuremberg, and sold in this country by L. Wiener of London, is shown in Fig. 18. [Illustration: FIG. 17. --"ORKA" BURNER. ] [Illustration: FIG. 18. --"SUPREMA" NO. 216469 BURNER. ] ILLUMINATING DUTY. --The illuminating value of ordinary self-luminousacetylene burners in different sizes has been examined by variousphotometrists. For burners of the Naphey type Lewes gives the followingtable: ___________________________________________________________| | | | | || | | Gas | | Candles || Burner. | Pressure, | Consumed, | Light in | per || | Inches | Cubic Feet | Candles. | Cubic Foot. || | | per Hour. | | ||_________|___________|____________|__________|_____________|| | | | | || No. 6 | 2. 0 | 0. 155 | 0. 794 | 5. 3 || " 8 | 2. 0 | 0. 27 | 3. 2 | 11. 6 || " 15 | 2. 0 | 0. 40 | 8. 0 | 20. 0 || " 25 | 2. 0 | 0. 65 | 17. 0 | 26. 6 || " 30 | 2. 0 | 0. 70 | 23. 0 | 32. 85 || " 42 | 2. 0 | 1. 00 | 34. 0 | 34. 0 ||_________|___________|____________|__________|_____________| From burners of the Billwiller type Lewes obtained in 1899 the values: ___________________________________________________________| | | | | || | | Gas | | Candles || Burner. | Pressure, | Consumed, | Light in | per || | Inches | Cubic Feet | Candles. | Cubic Foot. || | | per Hour. | | ||_________|___________|____________|__________|_____________|| | | | | || No. 1 | 2. 0 | 0. 5 | 7. 0 | 11. 0 || " 2 | 2. 0 | 0. 75 | 21. 0 | 32. 0 || " 3 | 2. 0 | 0. 75 | 28. 0 | 37. 3 || " 4 | 3. 0 | 1. 2 | 48. 0 | 40. 0 || " 5 | 3. 5 | 2. 0 | 76. 0 | 38. 0 ||_________|___________|____________|__________|_____________| Neuberg gives these figures for different burners (1900) as supplied byPintsch: ______________________________________________________________________| | | | | || | Gas | | Candles | |"w| Burner. | Pressure, | Consumed, | Light in | per || | Inches | Cubic Feet | Candles. | Cubic Foot. || | | per Hour. | | ||____________________|___________|____________|__________|_____________|| | | | | || No. 0, slit burner | 3. 9 | 1. 59 | 59. 2 | 37. 3 || " 00000 fishtail | 1. 6 | 0. 81 | 31. 2 | 38. 5 || Twin burner No. 1 | 3. 2 | 0. 32 | 13. 1 | 40. 8 || " " " 2 | 3. 2 | 0. 53 | 21. 9 | 41. 3 || " " " 3 | 3. 2 | 0. 74 | 31. 0 | 41. 9 || " " " 4 | 3. 2 | 0. 95 | 39. 8 | 41. 9 ||____________________|___________|____________|__________|_____________| The actual candle-power developed by each burner was not quoted byNeuberg, and has accordingly been calculated from his efficiency values. It is noteworthy, and in opposition to what has been found by otherinvestigators as well as to strict theory, that Neuberg represents theefficiencies to be almost identical in all sizes of the same descriptionof burner, irrespective of the rate at which it consumes gas. Writing in 1902, Capelle gave for Stadelmann's twin injector burners thefollowing figures; but as he examined each burner at several differentpressures, the values recorded in the second, third, and fourth columnsare maxima, showing the highest candle-power which could be procured fromeach burner when the pressure was adjusted so as to cause consumption toproceed at the most economical rate. The efficiency values in the fifthcolumn, however, are the mean values calculated so as to include all thedata referring to each burner. Capelle's results have been reproducedfrom the original on the basis that 1 _bougie décimale_ equals 0. 98standard English candle, which is the value he himself ascribes to it (1_bougie décimale_ equals 1. 02 candles is the value now accepted). _____________________________________________________________________| | | | | || Nominal | Best | Actual Consumption | Maximum | Average || Consumption, | Pressure| at Stated Pressure. | Light in | Candles per|| Litres. | Inches. | Cubic Feet per Hour. | Candles. | Cubic Foot. ||_____________|_________|_____________________|__________|____________|| | | | | || 10 | 3. 5 | 0. 40 | 8. 4 | 21. 1 || 15 | 2. 8 | 0. 46 | 16. 6 | 33. 3 || 20 | 3. 9 | 0. 64 | 25. 1 | 40. 0 || 25 | 3. 5 | 0. 84 | 37. 8 | 46. 1 || 30 | 3. 5 | 0. 97 | 48. 2 | 49. 4 ||_____________|_________|_____________________|__________|____________| Some testings of various self-luminous burners of which the results werereported by R. Granjon in 1907, gave the following results for the dutyof each burner, when the pressure was regulated for each burner to thatwhich afforded the maximum illuminating duty. The duty in the originalpaper is given in litres per Carcel-hour. The candle has been taken asequal to 0. 102 Carcel for the conversion to candles per cubic foot. ___________________________________________________________________| | | | || | Nominal | Best | Duty. Candles || Burner. | Consumption. | Pressure. | per cubic foot. ||_______________________|_____________|__________ |_________________|| | | | || | Litres. | Inches. | || Twin . . . . | 10 | 2. 76 | 21. 2 || " . . . . | 20 | 2. 76 | 23. 5 || " . . . . | 25 | 3. 94 | 30. 2 || " . . . . | 30 | 3. 94-4. 33 | 44. 8 || ", (pair of flames) | 35 | 3. 55-3. 94 | 45. 6 || Bray's "Manchester" | 6 | 1. 97 | 18. 8 || " | 20 | 1. 97 | 35. 6 || " | 40 | 2. 36 | 42. 1 || Rat-tail . . . | 5 | 5. 5 | 21. 9 || " . . . | 8 | 4. 73 | 25. 0 || Slit or batswing . | 30 | 1. 97-2. 36 | 37. 0 ||_______________________|_____________|___________|_________________| Granjon has concluded from his investigations that the Manchester orfish-tail burners are economical when they consume 0. 7 cubic foot perhour and when the pressure is between 2 and 2. 4 inches. When theseburners are used at the pressure most suitable for twin burners theirconsumption is about one-third greater than that of the latter percandle-hour. The 25 to 35 litres-per-hour twin burners should be used ata pressure higher by about 1 inch than the 10 to 20 litres-per-hour twinburners. At the present time, when the average burner has a smaller hourlyconsumption than 1 foot per hour, it is customary in Germany to quote themean illuminating value of acetylene in self-luminous burners as being 1Hefner unit per 0. 70 litre, which, taking 1 Hefner unit = 0. 913 English candle 1 English candle = 1. 095 Hefner units, works out to an efficiency of 37 candles per foot in burners probablyconsuming between 0. 5 and 0. 7 foot per hour. Even when allowance is made for the difficulties in determiningilluminating power, especially when different photometers, differentstandards of light, and different observers are concerned, it will beseen that these results are too irregular to be altogether trustworthy, and that much more work must be done on this subject before the economyof the acetylene flame can be appraised with exactitude. However, ascertain fixed data are necessary, the authors have studied those andother determinations, rejecting some extreme figures, and averaging theremainder; whence it appears that on an average twin-injector burners ofdifferent sizes should yield light somewhat as follows: _______________________________________________________| | | || Size of Burner in | Candle-power | Candles || Cubic Feet per Hour. | Developed. | per Cubic Foot. ||______________________|______________|_________________|| | | || 0. 5 | 18. 0 | 35. 9 || 0. 7 | 27. 0 | 38. 5 || 1. 0 | 45. 6 | 45. 6 ||______________________|______________|_________________| In the tabular statement in Chapter I. The 0. 7-foot burner was taken asthe standard, because, considering all things, it seems the best, toadopt for domestic purposes. The 1-foot burner is more economical when inthe best condition, but requires a higher gas pressure, and is rather toopowerful a unit light for good illuminating effect; the 0. 5 burnernaturally gives a better illuminating effect, but its economy issurpassed by the 0. 7-foot burner, which is not too powerful for the humaneye. For convenience of comparison, the illuminating powers and duties of the0. 5- and 0. 7-foot acetylene burners may be given in different ways: ILLUMINATING POWER OF SELF-LUMINOUS ACETYLENE. _0. 7-foot Burner. _ | _Half-foot Burner. _ |1 litre = 1. 36 candles. | 1 litre = 1. 27 candles. 1 cubic foot = 38. 5 candles. | 1 cubic foot = 35. 9 candles. 1 candle = 0. 736 litre. | 1 candle = 0. 79 litre. 1 candle = 0. 026 cubic foot. | 1 candle = 0. 028 cubic foot. If the two streams of gas impinge at an angle of 90°, twin-injectorburners for acetylene appear to work best when the gas enters them at apressure of 2 to 2. 5 inches; for a higher pressure the angle should bemade a little acute. Large burners require to have a wider distancebetween the jets, to be supplied with acetylene at a higher pressure, andto be constructed with a smaller angle of impingement. Every burner, ofwhatever construction and size, must always be supplied with gas at itsproper pressure; a pressure varying from time to time is fatal. It is worth observing that although injector burners are satisfactory inpractice, and are in fact almost the only jets yet found to giveprolonged satisfaction, the method of injecting air below the point ofcombustion in a self-luminous burner is in some respects wrong inprinciple. If acetylene can be consumed without polymerisation in burnersof the simple fish-tail or bat's-wing type, it should show a higherilluminating efficiency. In 1902 Javal stated that it was possible toburn thoroughly purified acetylene in twin non-injector burners, providedthe two jets, made of steatite as usual, were arranged horizontallyinstead of obliquely, the two streams of gas then meeting at an angle of180°, so as to yield an almost circular flame. According to Javal, whereas carbonaceous growths were always produced in non-injectoracetylene burners with either oblique or horizontal jets, in the formercase the growths eventually distorted the gas orifices, but in the latterthe carbon was deposited in the form of a tube, and fell off from theburner by its own weight directly it had grown to a length of 1. 2 or 1. 5millimetres, leaving the jets perfectly clear and smooth. Javal has hadsuch a burner running for 10 or 12 hours per day for a total of 2071hours; it did not need cleaning out on any occasion, and its consumptionat the end of the period was the same as at first. He found that it wasnecessary that the tips should be of steatite, and not of metal or glass;that the orifices should be drilled in a flat surface rather than at theapex of a cone, and that the acetylene should be purified to the utmostpossible extent. Subsequent experience has demonstrated the possibilityof constructing non-injector burners such as that shown in Fig. 13, whichbehave satisfactorily even though the jets are oblique. But with suchburners trouble will inevitably ensue unless the gas is always purifiedto a high degree and is tolerably dry and well filtered. Non-injectorburners should not be used unless special care is taken to insure thatthe installation is consistently operated in an efficient manner in theserespects. GLOBES, &C. --It does not fall within the province of the present volumeto treat at length of chimneys, globes, or the various glassware whichmay be placed round a source of light to modify its appearance. It shouldbe remarked, however, that obedience to two rules is necessary forcomplete satisfaction in all forms of artificial illumination. First, nolight much stronger in intensity than a single candle ought ever to beplaced in such a position in an occupied room that its direct rays canreach the eye, or the vision will be temporarily, and may be permanently, injured. Secondly, unless economy is to be wholly ignored, no coloured ortinted globe or shade should ever be put round a source of artificiallight. The best material for the construction of globes is that whichpossesses the maximum of translucency coupled with non-transparency, _i. E. _, a material which passes the highest proportion of the lightfalling upon it, and yet disperses that light in such differentdirections that the glowing body cannot be seen through the globe. Veryroughly speaking, plain white glass, such as that of which the chimneysof oil-lamps and incandescent gas-burners are composed, is quitetransparent, and therefore affords no protection to the eyesight; aprotective globe should be rather of ground or opal glass, or of plainglass to which a dispersive effect has been given by forming small prismson its inner or outer surface, or both. Such opal, ground, or dispersiveshades waste much light in terms of illuminating power, but wastecomparatively little in illuminating effect well designed, they mayactually increase the illuminating effect in certain positions; a tintedglobe, even if quite plain in figure, wastes both illuminating power andeffect, and is only to be tolerated for so-believed aesthetic reasons. Naturally no globe must be of such figure, or so narrow at eitherorifice, as to distort the shape of the unshaded acetylene flame--it ishardly necessary to say this now, but some years ago coal-gas globes wereconstructed with an apparent total disregard of this fundamental point. CHAPTER IX INCANDESCENT BURNERS--HEATING APPARATUS--MOTORS--AUTOGENOUS SOLDERING MERITS OF LIGHTING BY INCANDESCENT MANTLES. --It has already been shownthat acetylene bases its chief claim for adoption as an illuminant incountry districts upon the fact that, when consumed in simple self-luminous burners, it gives a light comparable in all respects save thatof cost to the light of incandescent coal-gas. The employment of a mantleis still accompanied by several objections which appear serious to theaverage householder, who is not always disposed either to devotesufficient attention to his burners to keep them in a high state ofefficiency or to contract for their maintenance by the gas company orothers. Coal-gas cannot be burnt satisfactorily on the incandescentsystem unless the glass chimneys and shades are kept clean, unless themantles are renewed as soon as they show signs of deterioration, and, perhaps most important of all, unless the burners are frequently clearedof the dust which collects round the jets. For this reason luminousacetylene ranks with luminous coal-gas in convenience and simplicity, while ranking with incandescent coal-gas in hygienic value. Very similarremarks apply to paraffin, and, in certain countries, to denaturedalcohol. Since those latter illuminants are also available in ruralplaces where coal-gas is not laid on, luminous acetylene is a lessadvantageous means of procuring artificial light than paraffin (and onoccasion than coal-gas and alcohol when the latter fuels are burnt underthe mantle), if the pecuniary aspect of the question is the only oneconsidered. Such a comparison, however, is by no means fair; for if coal-gas, paraffin, and alcohol can be consumed on the incandescent system, socan acetylene; and if acetylene is hygienically equal to incandescentcoal-gas, it is superior thereto when also burnt under the mantle. Nevertheless there should be one minor but perfectly irremediable defectin incandescent acetylene, viz. , a sacrifice of that characteristicproperty of the luminous gas to emit a light closely resembling that ofthe sun in tint, which was mentioned in Chapter 1. Self-luminousacetylene gives the whitest light hitherto procurable without specialcorrection of the rays, because its light is derived from glowingparticles of carbon which happen to be heated (because of the high flametemperature) to the best possible temperature for the emission of purewhite light. The light of any combustible consumed on the "incandescent"system is derived from glowing particles of ceria, thoria, or similarmetallic oxides; and the character or shade of the light they emit is afunction, apart from the temperature to which they are raised, of theirspecific chemical nature. Still, the light of incandescent acetylene issufficiently pleasant, and according to Caro is purer white than that ofincandescent coal-gas; but lengthy tests carried out by one of theauthors actually show it to be appreciably inferior to luminous acetylenefor colour-matching, in which the latter is known almost to equal fulldaylight, and to excel every form of artificial light except that of theelectric arc specially corrected by means of glass tinted with coppersalts. CONDITIONS FOR INCANDESCENT ACETYLENE LIGHTING. --For success in thecombustion of acetylene on the incandescent system, however, severalpoints have to be observed. First, the gas must be delivered at astrictly constant pressure to the burner, and at one which exceeds acertain limit, ranging with different types and different sizes of burnerfrom 2 to 4 or 5 inches of water. (The authors examined, as long ago as1903, an incandescent burner of German construction claimed to work at apressure of 1. 5 inches, which it was almost impossible to induce to fireback to the jets however slowly the cock was manipulated, provided thepressure of the gas was maintained well above the point specified. Butordinarily a pressure of about 4 inches is used with incandescentacetylene burners. ) Secondly, it is necessary that the acetylene shall atall times be free from appreciable admixture with air, even 0. 5 per cent, being highly objectionable according to Caro; so that generatorsintroducing any noteworthy amount of air into the holder each time theirdecomposing chambers are opened for recharging are not suitable foremployment when incandescent burners are contemplated. The reason forthis will be more apparent later on, but it depends on the obvious factthat if the acetylene already contains an appreciable proportion of air, when a further quantity is admitted at the burner inlets, the gaseousmixture contains a higher percentage of oxygen than is suited to the sizeand design of the burner, so that flashing back to the injector jets isimminent at any moment, and may be determined by the slightestfluctuation in pressure--if, indeed, the flame will remain at the properspot for combustion at all. Thirdly, the fact that the acetylene which isto be consumed under the mantle must be most rigorously purified fromphosphorus compounds has been mentioned in Chapter V. Impure acetylenewill often destroy a mantle in two or three hours; but with highlypurified gas the average life of a mantle may be taken, according toGiro, at 500 or 600 hours. It is safer, however, to assume a rathershorter average life, say 300 to 400 burning hours. Fourthly, owing tothe higher pressure at which acetylene must be delivered to anincandescent burner and to the higher temperature of the acetylene flamein comparison with coal-gas, a mantle good enough to give satisfactoryresults with the latter does not of necessity answer with acetylene; infact, the authors have found that English Welsbach coal-gas mantles ofthe small sizes required by incandescent acetylene burners are notcompetent to last for more than a very few hours, although, in identicalconditions, mantles prepared specially for use with acetylene have proveddurable. The atmospheric acetylene flame, too, differs in shape from anatmospheric flame of coal-gas, and it does not always happen that a coal-gas mantle contracts to fit the former; although it usually emits abetter light (because it fits better) after some 20 hours use than atfirst. Caro has stated that to derive the best results a mantle needs tocontain a larger proportion of ceria than the 1 per cent. Present inmantles made according to the Welsbach formula, that it should besomewhat coarser in mesh, and have a large orifice at the head. Otherauthorities hold that mantles for acetylene, should contain other rareearths besides the thoria and ceria of which the coal-gas mantles almostwholly consist. It seems probable, however, that the composition of theordinary impregnating fluid need not be varied for acetylene mantlesprovided it is of the proper strength and the mantles are raised to ahigher temperature in manufacture than coal-gas mantles by the use ofeither coal-gas at very high pressure or an acetylene flame. Thethickness of the substance of the mantle cannot be greatly increased witha view to attaining greater stability without causing a reduction in thelight afforded. But the shape should be such that the mantle conforms asclosely as possible to the acetylene Bunsen flame, which differs slightlywith different patterns of incandescent burner heads. According to L. Cadenel, the acetylene mantle should be cylindrical for the lower two-thirds of its length, and slightly conical above, with an opening ofmoderate size at the top. The head of the mantle should be of slighterconstruction than that of coal-gas mantles. Fifthly, generators belongingto the automatic variety, which in most forms inevitably add more or lessair to the acetylene every time they are cleaned or charged, appear tohave achieved most popularity in Great Britain; and these frequently donot yield a gas fit for use with the mantle. This state of affairs, addedto what has just been said, makes it difficult to speak in veryfavourable terms of the incandescent acetylene light for use in GreatBritain. But as the advantages of an acetylene not contaminated with airare becoming more generally recognised, and mantles of several differentmakes are procurable more cheaply, incandescent acetylene is now morepracticable than hitherto. Carburetted acetylene or "carburylene, " whichis discussed later, is especially suitable for use with mantle burners. ATMOSPHERIC ACETYLENE BURNERS. --The satisfactory employment of acetylenein incandescent burners, for boiling, warming, and cooking purposes, andalso to some extent as a motive power in small engines, demands theproduction of a good atmospheric or non-luminous flame, _i. E. _, theconstruction of a trustworthy burner of the Bunsen type. This has been exceedingly difficult to achieve for two reasons: first, the wide range over which mixtures of acetylene and air are explosive;secondly, the high speed at which the explosive wave travels through sucha mixture. It has been pointed out in Chapter VIII. That a Bunsen burneris one in which a certain proportion of air is mixed with the gas beforeit arrives at the actual point of ignition; and as that proportion mustbe such that the mixture falls between the upper and lower limits ofexplosibility, there is a gaseous mixture in the burner tube between theair inlets and the outlet which, if the conditions are suitable, willburn with explosive force: that is to say, will fire back to the air jetswhen a light is applied to the proper place for combustion. Such anexplosion, of course, is far too small in extent to constitute any dangerto person or property; the objection to it is simply that the shock ofthe explosion is liable to fracture the fragile incandescent mantle, while the gas, continuing to burn within the burner tube (in the case ofa warming or cooking stove), blocks up that tube with carbon, andexhibits the other well-known troubles of a coal-gas stove which has"fired back. " It has been shown, however, in Chapter VI. That the range over whichmixtures of acetylene and air are explosive depends on the size of thevessel, or more particularly on the diameter of the tube, in which theyare stored; so that if the burner tube between the air inlets and thepoint of ignition can be made small enough in diameter, a normallyexplosive mixture will cease to exhibit explosive properties. Manifestly, if a tube is made very small in diameter, it will only pass a smallvolume of gas, and it may be useless for the supply of an atmosphericburner; but Le Chatelier's researches have proved that a tube may benarrowed at one spot only, in such fashion that the explosive waverefuses to pass the constriction, while the virtual diameter of the tube, as far as passage of gas is concerned, remains considerably larger thanthe size of the constriction itself. Moreover, inasmuch as the speed ofpropagation of the explosion is strictly fixed by the conditionsprevailing, if the speed at which the mixture, of acetylene and airtravels from the air inlets to the point of ignition is more rapid thanthe speed at which the explosion tends to travel from the point ofignition to the air inlets, the said mixture of acetylene and air willburn quietly at the orifice without attempting to fire backwards into thetube. By combining together these two devices: by delivering theacetylene to the injector jet at a pressure sufficient to drive themixture of gas and air forward rapidly enough, and by narrowing theleading tube either wholly or at one spot to a diameter small enough, itis easy to make an atmospheric burner for acetylene which behavesperfectly as long as it is fairly alight, and the supply of gas is notchecked; but further difficulties still remain, because at the instant oflighting and extinguishing, i. E. , while the tap is being turned on oroff, the pressure of the gas is too small to determine a flow ofacetylene and air within the tube at a speed exceeding that of theexplosive wave; and therefore the act of lighting or extinguishing isvery likely to be accompanied by a smart explosion severe enough to splitthe mantle, or at least to cause the burner to fire back. Nevertheless, after several early attempts, which were comparative failures, atmospheric acetylene burners have been constructed that work quitesatisfactorily, so that the gas has become readily available for useunder the mantle, or in heating stoves. Sometimes success has beenobtained by the employment of more than one small tube leading to acommon place of ignition, sometimes by the use of two or more fine wire-gauze screens in the tube, sometimes by the addition of an enlarged headto the burner in which head alone thorough mixing of the gas and airoccurs, and sometimes by the employment of a travelling sleeve whichserves more or less completely to block the air inlets. DUTY OF INCANDESCENT ACETYLENE BURNERS. --Granting that the petty troublesand expenses incidental to incandescent lighting are not consideredprohibitive--and in careful hands they are not really serious--and that mantles suitable for acetylene are employed, the gas may berendered considerably cheaper to use per unit of light evolved byconsuming it in incandescent burners. In Chapter VIII. It was shown thatthe modern self-luminous, l/2-foot acetylene burner emits a light ofabout 1. 27 standard English candles per litre-hour. A large number ofincandescent burners, of German and French construction, consuming from7. 0 to 22. 2 litres per hour at pressures ranging between 60 and 120millimetres have been examined by Caro, who has found them to give lightsof from 10. 8 to 104. 5 Hefner units, and efficiencies of from 2. 40 to 5. 50units per litre-hour. Averaging his results, it may be said thatincandescent burners consuming from 10 to 20 litres per hour at pressuresof 80 or 100 millimetres yield a light of 4. 0 Hefner units per litre-hour. Expressed in English terms, incandescent acetylene burnersconsuming 0. 5 cubic foot per hour at a pressure of 3 or 4 inches give theduties shown in the following table, which may advantageously be comparedwith that printed in Chapter VIII. , page 239, for the self-luminous gas: ILLUMINATING POWER OF INCANDESCENT ACETYLENE. HALF-FOOT BURNERS. 1 litre = 3. 65 candles | 1 candle = 0. 274 litre. 1 cubic foot = 103. 40 candles. | 1 candle = 0. 0097 cubic foot. A number of tests of the Güntner or Schimek incandescent burners of the10 and 15 litres-per-hour sizes, made by one of the authors in 1906, gavethe following average results when tested at a pressure of 4 inches: _________________________________________________________________| | | | || Nominal size | Rate of Consumption per | Light in | Duty || of Burner. | Hour | Candles | Candles per || | | | Cubic Foot ||______________|_________________________|__________|_____________|| | | | | || Litres. | Cubic Foot | Litres | | || 10 | 0. 472 | 13. 35 | 46. 0 | 97. 4 || 15 | 0. 663 | 18. 80 | 70. 0 | 105. 5 ||______________|____________|____________|__________|_____________| These figures indicate that the duty increases slightly with the size ofthe burner. Other tests showed that the duty increased more considerablywith an increase of pressure, so that mantles used, or which had beenpreviously used, at a pressure of 5 inches gave duties of 115 to 125candles per cubic foot. It should be noted that the burners so far considered are small, beingintended for domestic purposes only; larger burners exhibit higherefficiencies. For instance, a set of French incandescent acetyleneburners examined by Fouché showed: _________________________________________________________________| | | | | || Size of Burner | Pressure | Cubic Feet | Light in | Candles per || in Litres. | Inches. | per Hour. | Candles. | Cubic Feet. ||________________|__________|____________|__________|_____________|| | | | | || 20 | 5. 9 | 0. 71 | 70 | 98. 6 || 40 | 5. 9 | 1. 41 | 150 | 106. 4 || 70 | 5. 9 | 2. 47 | 280 | 113. 4 || 120 | 5. 9 | 4. 23 | 500 | 118. 2 ||________________|__________|____________|__________|_____________| By increasing the pressure at which acetylene is introduced into burnersof this type, still larger duties may be obtained from them: _________________________________________________________________| | | | | || Size of Burner | Pressure | Cubic Feet | Light in | Candles per || in Litres. | Inches. | per Hour. | Candles. | Cubic Feet. ||________________|__________|____________|__________|_____________|| | | | | || 55 | 39. 4 | 1. 94 | 220 | 113. 4 || 100 | 39. 4 | 3. 53 | 430 | 121. 8 || 180 | 39. 4 | 6. 35 | 820 | 129. 1 || 260 | 27. 6 | 9. 18 | 1300 | 141. 6 ||________________|__________|____________|__________|_____________| High-power burners such as these are only fit for special purposes, suchas lighthouse illumination, or optical lantern work, &c. ; and theynaturally require mantles of considerably greater tenacity than thoseintended for employment with coal-gas. Nevertheless, suitable mantles canbe, and are being, made, and by their aid the illuminating duty ofacetylene can be raised from the 30 odd candles per foot of the common0. 5-foot self-luminous jet to 140 candles or more per foot, which is again in efficiency of 367 per cent. , or, neglecting upkeep and sundriesand considering only the gas consumed, an economy of nearly 79 per cent. In 1902, working apparently with acetylene dissolved under pressure inacetone (_cf. _ Chapter XI. ), Lewes obtained the annexed results withthe incandescent gas: ________________________________________________________| | | | || Pressure. | Cubic Feet | Candle Power | Candles per || Inches. | per Hour. | Developed. | Cubic Foot. ||___________|_____________|______________|______________|| | | | || 8 | 0. 883 | 65 | 73. 6 || 9 | 0. 94 | 72 | 76. 0 || 10 | 1. 00 | 146 | 146. 0 || 12 | 1. 06 | 150 | 141. 2 || 15 | 1. 25 | 150 | 120. 0 || 20 | 1. 33 | 166 | 124. 8 || 25 | 1. 50 | 186 | 123. 3 || 40 | 2. 12 | 257 | 121. 2 ||___________|_____________|______________|______________| It will be seen that although the total candle-power developed increaseswith the pressure, the duty of the burner attained a maximum at apressure of 10 inches. This is presumably due to the fact either that thesame burner was used throughout the tests, and was only intended to workat a pressure of 10 inches or thereabouts, or that the larger burnerswere not so well constructed as the smaller ones. Other investigatorshave not given this maximum of duty with a medium-sized or medium-drivenburner; but Lewes has observed a similar phenomenon in the case of 0. 7 to0. 8 cubic foot self-luminous jets. Figures, however, which seem to show that the duty of incandescentacetylene does not always rise with the size of the burner or with thepressure at which the gas is delivered to it, have been published inconnexion with the installation at the French lighthouse at Chassiron, the northern point of the Island of Oléron. Here the acetylene isgenerated in hand-fed carbide-to-water generators so constructed as togive any pressure up to nearly 200 inches of water column; purified bymeans of heratol, and finally delivered to a burner composed of thirty-seven small tubes, which raises to incandescence a mantle 55 millimetresin diameter at its base. At a pressure of 7. 77 inches of water, theburner passes 3. 9 cubic feet of acetylene per hour, and at a pressure of49. 2 inches (the head actually used) it consumes 20. 06 cubic feet perhour. As shown by the following table, such increment of gas pressureraises the specific intensity of the light, _i. E. _, the illuminatingpower per unit of incandescent surface, but it does not appreciably raisethe duty or economy of the gas. Manifestly, in terms of duty alone, apressure of 23. 6 inches of water-column is as advantageous as the higherChassiron figures; but since intensity of light is an important matter ina lighthouse, it is found better on the whole to work the generators at apressure of 49. 2 inches. In studying these figures referring to theFrench lighthouse, it is interesting to bear in mind that when ordinarysix-wick petroleum oil burners wore used in the same place, the specificintensity of the light developed was 75 candle-power per square inch, andwhen that plant was abandoned in favour of an oil-gas apparatus, theincandescent burner yielded 161 candle-power per square inch;substitution of incandescent acetylene under pressure has doubled thebrilliancy of the light. ___________________________________________________________| | | || | Duty. | Intensity. || Pressure in Inches. | Candle-power per | Candle-power per || | Cubic Foot. | Square Inch. ||_____________________|__________________|__________________|| | | || 7. 77 | 105. 5 | 126. 0 || 23. 60 | 106. 0 | 226. 0 || 31. 50 | 110. 0 | 277. 0 || 39. 40 | 110. 0 | 301. 0 || 47. 30 | 106. 0 | 317. 0 || 49. 20 | 104. 0 | 324. 9 || 196. 80 | 110. 0 | 383. 0 ||_____________________|__________________|__________________| When tested in modern burners consuming between 12 and 18 litres per hourat a pressure of 100 millimetres (4 inches), some special forms ofincandescent mantles constructed of ramie fibre, which in certainrespects appears to be better suited than cotton for use with acetylene, have shown the following degree of loss in illuminating power afterprolonged employment (Caro): _Luminosity in Hefner Units. _ ________________________________________________________| | | | | || Mantle. | New. | After | After | After || | | 100 Hours. | 200 Hours. | 400 Hours. ||_________|_______|____________|____________|____________|| | | | | || No. 1. | 53. 2 | 51. 8 | 50. 6 | 49. 8 || No. 2. | 76. 3 | 75. 8 | 73. 4 | 72. 2 || No. 3. | 73. 1 | 72. 5 | 70. 1 | 68. 6 ||_________|_______|____________|____________|____________| It will be seen that the maximum loss of illuminating power in 400 hourswas 6. 4 per cent. , the average loss being 6. 0 per cent. TYPICAL INCANDESCENT BURNERS. --Of the many burners for lighting by theuse of incandescent mantles which have been devised, a few of the morewidely used types may be briefly referred to. There is no doubt thatfinality in the design of these burners has not yet been reached, andthat improvements in the direction of simplification of construction andin efficiency and durability will continue to be made. Among the early incandescent burners, one made by the Allgemeine Carbidund Acetylen Gesellschaft of Berlin in 1900 depended on the narrowness ofthe mixing tube and the proportioning of the gas nipple and air inlets toprevent lighting-back. There was a wider concentric tube round the upperpart of the mixing tube, and the lower part of the mantle fitted roundthis. The mouth of the mixing tube of this 10-litres-per-hour burner was0. 11 inch in diameter, and the external diameter of the middlecylindrical part of the mixing tube was 0. 28 inch. There was no gauzediaphragm or stuffing, and firing-back did not occur until the pressurewas reduced to about 1. 5 inches. The same company later introduced aburner differing in several important particulars from the one justdescribed. The comparatively narrow stem of the mixing tube and theproportions of the gas nipple and air inlets were retained, but themixing tube was surmounted by a wide chamber or burner head, in whichnaturally there was a considerable reduction in the rate of flow of thegas. Consequently it was found necessary to introduce a gauze screen intothe burner head to prevent firing back. The alterations have resulted inthe lighting duty of the burner being considerably improved. Among otherburners designed about 1900 may be mentioned the Ackermann, the head ofwhich consisted of a series of tubes from each of which a jet of flamewas produced, the Fouché, the Weber, and the Trendel. Subsequently atubular-headed burner known as the Sirius has been produced for theconsumption of acetylene at high pressure (20 inches and upwards). The more recent burners which have been somewhat extensively used includethe "Schimek, " made by W. Güntner of Vienna, which is shown in Fig. 19. It consists of a tapering narrow injecting nozzle within a conicalchamber C which is open below, and is surmounted by the mixing tube overwhich telescopes a tube which carries the enlarged burner head G, and thechimney gallery D. There are two diaphragms of gauze in the burner headto prevent firing back, and one in the nozzle portion of the burner. Theconical chamber has a perforated base-plate below which is a circularplate B which rotates on a screw cut on the lower part of the nozzleportion A of the burner. This plate serves as a damper to control theamount of air admitted through the base of the conical chamber to themixing tube. There are six small notches in the lower edge of the conicalchamber to prevent the inflow of air being cut of entirely by the damper. The mixing tube in both the 10-litre and the 15-litre burner is about0. 24 inch in internal diameter but the burner head is nearly 0. 42 inch inthe 10-litre and 0. 48 inch in the 15-litre burner. The opening in thehead of the burner through which the mixture of gas and air escapes tothe flame is 0. 15 and 0. 17 inch in diameter in these two sizesrespectively. The results of some testings made with Schimek burners havebeen already given. [Illustration: FIG. 19. --"SCHIMEK" BURNER. ] The "Knappich" burner, made by the firm of Keller and Knappich ofAugsburg, somewhat resembles the later pattern of the Allgemeine Carbidund Acetylen Gesellschaft. It has a narrow mixing tube, viz. , 0. 2 inch ininternal diameter, and a wide burner head, viz. , 0. 63 inch in internaldiameter for the 25-litre size. The only gauze diaphragm is in the upperpart of the burner head. The opening in the cap of the burner head, atwhich the gas burns, is 0. 22 inch in diameter. The gas nipple extendsinto a domed chamber at the base of the mixing tube, and the internal airis supplied through four holes in the base-plate of that chamber. Nomeans of regulating the effective area of the air inlet holes areprovided. The "Zenith" burner, made by the firm of Gebrüder Jacob of Zwickau, moreclosely resembles the Schimek, but the air inlets are in the side of thelower widened portion of the mixing tube, and are more or less closed bymeans of an outside loose collar which may be screwed up and down on athread on a collar fixed to the mixing tube. The mixing tube is 0. 24inch, and the burner head 0. 475 inch in internal diameter. The opening inthe cap of the burner is 0. 16 inch in diameter. There is a diaphragm ofdouble gauze in the cap, and this is the only gauze used in the burner. All the incandescent burners hitherto mentioned ordinarily have the gasnipple made in brass or other metal, which is liable to corrosion, andthe orifice to distortion by heat or if it becomes necessary to removeany obstruction from it. The orifice in the nipple is extremely small--usually less than 0. 015 inch--and any slight obstruction or distortionwould alter to a serious extent the rate of flow of gas through it, andso affect the working of the burner. In order to overcome this defect, inherent to metal nipples, burners are now constructed for acetylene inwhich the nipple is of hard incorrodible material. One of these burnershas been made on behalf of the Office Central de l'Acétylène of Paris, and is commonly known as the "O. C. A. " burner. In it the nipple is ofsteatite. On the inner mixing tube of this burner is mounted an elongatedcone of wire wound spirally, which serves both to ensure proper admixtureof the gas and air, and to prevent firing-back. There is no gauze in thisburner, and the parts are readily detachable for cleaning when required. Another burner, in which metal is abolished for the nipple, is made byGeo. Bray and Co. , Ltd. , of Leeds, and is shown in Fig. 20. In thisburner the injecting nipple is of porcelain. [Illustration: FIG. 20. --BRAY'S INCANDESCENT BURNER. ] ACETYLENE FOR HEATING AND COOKING. --Since the problem of constructing atrustworthy atmospheric burner has been solved, acetylene is not onlyavailable for use in incandescent lighting, but it can also be employedfor heating or cooking purposes, because all boiling, most warming, andsome roasting stoves are simply arrangements for utilising the heat of anon-luminous flame in one particular way. With suitable alterations inthe dimensions of the burners, apparatus for consuming coal-gas may beimitated and made fit to burn acetylene; and as a matter of fact severalfirms are now constructing such appliances, which leave little or nothingto be desired. It may perhaps be well to insist upon the elementary pointwhich is so frequently ignored in practice, viz. , that no stove, exceptperhaps a small portable boiling ring, ought ever to be used in anoccupied room unless it is connected with a chimney, free from down-draughts, for the products of combustion to escape into the outer air;and also that no chimney, however tall, can cause an up-draught in allstates of the weather unless there is free admission of fresh air intothe room at the base of the chimney. Still, at the prices for coal, paraffin oil, and calcium carbide which exist in Great Britain, acetyleneis not an economical means of providing artificial heat. If a 0. 7 cubicfoot luminous acetylene burner gives a light of 27 candles, and ifordinary country coal-gas gives light of 12 to 13 candles in a 5-footburner, one volume of acetylene is equally valuable with 15 or 16 volumesof coal-gas when both are consumed in self-luminous jets; and if, withthe mantle, acetylene develops 99 candles per cubic foot, while coal-gasgives in common practice 15 to 20 candles, one volume of acetylene isequally valuable with 5 to 6-1/2 volumes of coal-gas when both areconsumed on the incandescent system; whereas, if the acetylene is burntin a flat flame, and the coal-gas under the mantle, 1 volume of theformer is equally efficient with 2 volumes of coal-gas as an artificialilluminant. This last method of comparison being manifestly unfair, acetylene may be said to be at least five times as efficient per unit ofvolume as coal-gas for the production of light. But from the table givenon a later page it appears that as a source of artificial heat, acetyleneis only equal to about 2-3 times its volume of ordinary coal-gas. Nevertheless, the domestic advantages of gas firing are very marked; andwhen a properly constructed stove is properly installed, the hygienicadvantages of gas-firing are alone equally conspicuous--for the disfavorwith which gas-firing is regarded by many physicians is due to experiencegained with apparatus warming principally by convection [Footnote:Radiant heat is high-temperature heat, like the heat emitted by a mass ofred-hot coke; convected heat is low-temperature heat, invisible to theeye. Radiant heat heats objects first, and leaves them to warm the air;convected heat is heat applied directly to air, and leaves the air towarm objects afterwards. On all hygienic grounds radiant heat is betterthan convected heat, but the latter is more economical. By an absurd andconfusing custom, that particular warming apparatus (gas, steam, or hotwater) which yields practically no radiant heat, and does all its work byconvection, is known to the trade as a "radiator. "] instead of radiation;or to acquaintance with intrinsically better stoves either not connectedto any flues or connected to one deficient in exhausting power. In thesecircumstances, whenever an installation of acetylene has been laid downfor the illumination of a house or district, the merit of convenience mayoutweigh the defect of extravagance, and the gas may be judiciouslyemployed in a boiling ring, or for warming a bedroom; while, if pecuniaryconsiderations are not paramount, the acetylene may be used for everypurpose to which the townsman would apply his cheaper coal-gas. The difficulty of constructing atmospheric acetylene burners in which theflame would not be likely to strike back to the nipple has already beenreferred to in connexion with the construction atmospheric burners forincandescent lighting. Owing, however, to the large proportions of theatmospheric burners of boiling rings and stove and in particular to thelarger bore of their mixing tube, the risk of the flame striking back isgreater with them, than with incandescent lighting burners. The greatesttrouble is presented at lighting, and when the pressure of the gas-supplyis low. The risk of firing-back when the burner is lighted is avoided insome forms of boiling rings, &c. , by providing a loose collar which canbe slipped over the air inlets of the Bunsen tube before applying a lightto the burner, and slipped clear of them as soon as the burner is alight. Thus at the moment of lighting, the burner is converted temporarily intoone of the non-atmospheric type, and after the flame has thus beenestablished at the head or ring of the burner, the internal air-supply isstarted by removing the loose collar from the air inlets, and the flameis thus made atmospheric. In these conditions it does not travelbackwards to the nipple. In other heating burners it is generallynecessary to turn on the gas tap a few seconds before applying a light tothe burner or ring or stove; the gas streaming through the mixing tubethen fills it with acetylene and air mixed in the proper workingproportions, and when the light is applied, there is no explosion in themixing tube, or striking-back of the flame to the nipple. Single or two-burner gas rings for boiling purposes, or for heatingcooking ovens, known as the "La Belle, " made by Falk Stadelmann and Co. , Ltd. , of London, may be used at as low a gas pressure as 2 inches, thoughthey give better results at 3 inches, which is their normal workingpressure. The gas-inlet nozzle or nipple of the burner is set within aspherical bulb in which are four air inlets. The mixing tube which isplaced at a proper distance in front of the nipple, is proportioned tothe rate of flow of the gas and air, and contains a mixing chamber with abaffling pillar to further their admixture. A fine wire gauze insertionserves to prevent striking-back of the flame. A "La Belle" boiling ringconsumes at 3 inches pressure about 48 litres or 1. 7 cubic feet ofacetylene per hour. ACETYLENE MOTORS. --The question as to the feasibility of developing"power" from acetylene, _i. E. _, of running an engine by means of thegas, may be answered in essentially identical terms. Specially designedgas-engines of 1, 3, 6, or even 10 h. P. Work perfectly with acetylene, and such motors are in regular employment in numerous situations, moreparticularly for pumping water to feed the generators of a large villageacetylene installation. Acetylene is not an economical source of power, partly for the theoretical reason that it is a richer fuel even thancoal-gas, and gas-engines would appear usually to be more efficient asthe fuel they burn is poorer in calorific intensity, _i. E. _, inheating power (which is explosive power) per unit of volume. The richer, or more concentrated, any fuel in, the more rapidly does the explosion ina mixture of that fuel with air proceed, because a rich fuel contains asmaller proportion of non-inflammable gases which tend to retardexplosion than a poor one; and, in reason, a gas-engine works better themore slowly the mixture of gas and air with which it is fed explodes. Still, by properly designing the ports of a gas-engine cylinder, so thatthe normal amount of compression of the charge and of expansion of theexploded mixture which best suit coal-gas are modified to suit acetylene, satisfactory engines can be constructed; and wherever an acetyleneinstallation for light exists, it becomes a mere question of expediencywhether the same fuel shall not be used to develop power, say, forpumping up the water required in a large country house, instead ofemploying hand labour, or the cheaper hot-air or petroleum motor. Takingthe mean of the results obtained by numerous investigators, it appearsthat 1 h. P. -hour can be obtained for a consumption of 200 litres ofacetylene; whence it may be calculated that that amount of energy costsabout 3d. For gas only, neglecting upkeep, lubricating material(which would be relatively expensive) and interest, &c. Acetylene Blowpipes--The design of a satisfactory blowpipe for use withacetylene had at first proved a matter of some difficulty, since the jet, like that of an ordinary self-luminous burner, usually exhibited atendency to become choked with carbonaceous growths. But when acetylenehad become available for various purposes at considerable pressure, aftercompression into porous matter as described in Chapter XI, the troubleswere soon overcome; and a new form of blowpipe was constructed in whichacetylene was consumed under pressure in conjunction with oxygen. Thetemperature given by this apparatus exceeds that of the familiar oxy-hydrogen blowpipe, because the actual combustible material is carboninstead of hydrogen. When 2 atoms of hydrogen unite with 1 of oxygen toform 1 molecule of gaseous water, about 59 large calories are evolved, and when 1 atom of solid amorphous carbon unites with 2 atoms of oxygento form 1 molecule of carbon dioxide, 97. 3 calories are evolved. In bothcases, however, the heat attainable is limited by the fact that atcertain temperatures hydrogen and oxygen refuse to combine to form water, and carbon and oxygen refuse to form carbon dioxide--in other words, water vapour and carbon dioxide dissociate and absorb heat in the processat certain moderately elevated temperatures. But when 1 atom of solidamorphous carbon unites with 1 atom of oxygen to form carbon monoxide, 29. 1 [Footnote: Cf. Chapter VI. , page 185. ] large calories are produced, and carbon monoxide is capable of existence at much higher temperaturesthan either carbon dioxide or water vapour. In any gaseous hydrocarbon, again, the carbon exists in the gaseous state, and when 1 atom of thehypothetical gaseous carbon combines with 1 atom of oxygen to produce 1molecule of carbon monoxide, 68. 2 large calories are evolved. Thus whilesolid amorphous carbon emits more heat than a chemically equivalentquantity of hydrogen provided it is enabled to combine with its higherproportion of oxygen, it emits less if only carbon monoxide is formed;but a higher temperature can be attained in the latter case, because thecarbon monoxide is more permanent or stable. Gaseous carbon, on the otherhand, emits more heat than an equivalent quantity of hydrogen, [Footnote:In a blowpipe flame hydrogen can only burn to gaseous, not liquid, water. ] even when it is only converted into the monoxide. In other words, a gaseous fuel which consists of hydrogen alone can only yield thattemperature as a maximum at which the speed of the dissociation of thewater vapour reaches that of the oxidation of the hydrogen; and werecarbon dioxide the only oxide of carbon, a similar state of affairs wouldbe ultimately reached in the flame of a carbonaceous gas. But since inthe latter case the carbon dioxide does not tend to dissociatecompletely, but only to lose one atom of oxygen, above the limitingtemperature for the formation of carbon dioxide, carbon monoxide is stillproduced, because there is less dissociating force opposed to itsformation. Thus at ordinary temperatures the heat of combustion ofacetylene is 315. 7 calories; but at temperatures where water vapour andcarbon dioxide no longer exist, there is lost to that quantity of 315. 7calories the heat of combustion of hydrogen (69. 0) and twice that ofcarbon monoxide (68. 2 x 2 = 136. 4); so that above those criticaltemperatures, the heat of combustion of acetylene is only 315. 7 - (69. 0 +136. 4) = 110. 3. [Footnote: When the heat of combustion of acetylene isquoted as 315. 7 calories, it is understood that the water formed iscondensed into the liquid state. If the water remains gaseous, as it mustdo in a flame, the heat of formation is reduced by about 10 calories. This does not affect the above calculation, because the heat ofcombustion of hydrogen when the water remains gaseous is similarly 10calories less than 69, _i. E. _, 59, as mentioned above in the text. Deleting the heat of liquefaction of water, the calculation referred tobecomes 305. 7 - (59. 0 + l36. 4) = 110. 3 as before. ] This value of 110. 3calories is clearly made up of the heat of formation of acetylene itself, and twice the heat of conversion of carbon into carbon monoxide, _i. E. _, for diamond carbon, 58. 1 + 26. 1 x 2 = 110. 3; or foramorphous carbon, 52. 1 + 29. 1 x 2 = 110. 3. From the foregoingconsiderations, it may be inferred that the acetylene-oxygen blowpipe canbe regarded as a device for burning gaseous carbon in oxygen; but were itpossible to obtain carbon in the state of gas and so to lead it into ablowpipe, the acetylene apparatus should still be more powerful, becausein it the temperature would be raised, not only by the heat of formationof carbon monoxide, but also by the heat attendant upon the dissociationof the acetylene which yields the carbon. Acetylene requires 2. 5 volumes of oxygen to burn it completely; but inthe construction of an acetylene-oxygen blowpipe the proportion of oxygenis kept below this figure, viz. , at 1. 1 to 1. 8 volumes, so that thedeficiency is left to be made up from the surrounding air. Thus at thejet of the blowpipe the acetylene dissociates and its carbon is oxidised, at first no doubt to carbon monoxide only, but afterwards to carbondioxide; and round the flame of the gaseous carbon is a comparativelycool, though absolutely very hot jacket of hydrogen burning to watervapour in a mixture of oxygen and air, which protects the inner zone fromloss of heat. As just explained, theoretical grounds support theconclusions at which Fouché has arrived, viz. , that the temperature ofthe acetylene-oxygen blowpipe flame is above that at which hydrogen willcombine with oxygen to form water, and that it can only be exceeded bythose found in a powerful electric furnace. As the hydrogen dissociatedfrom the acetylene remains temporarily in the free state, the flame ofthe acetylene blowpipe, possesses strong reducing powers; and this, coupled probably with an intensity of heat which is practically otherwiseunattainable, except by the aid of a high-tension electric current, should make the acetylene-oxygen blowpipe a most useful piece ofapparatus for a large variety of metallurgical, chemical, and physicaloperations. In Fouché's earliest attempts to design an acetyleneblowpipe, the gas was first saturated with a combustible vapour, such asthat of petroleum spirit or ether, and the mixture was consumed with ablast of oxygen in an ordinary coal-gas blow-pipe. The apparatus workedfairly well, but gave a flame of varying character; it was capable offusing iron, raised a pencil of lime to a more brilliant degree ofincandescence than the eth-oxygen burner, and did not deposit carbon atthe jet. The matter, however, was not pursued, as the blowpipe fed withundiluted acetylene took its place. The second apparatus constructed byFouché was the high-pressure blowpipe, the theoretical aspect of whichhas already been studied. In this, acetylene passing through a water-sealfrom a cylinder where it is stored as a solution in acetone (_cf. _Chapter XI. ), and oxygen coming from another cylinder, are each allowedto enter the blowpipe at a pressure of 118 to 157 inches of water column(_i. E. _, 8. 7 to 11. 6 inches of mercury; 4. 2 to 5. 7 lb. Per squareinch, or 0. 3 to 0. 4 atmosphere). The gases mix in a chamber tightlypacked with porous matter such as that which is employed in the originalacetylene reservoir, and finally issue from a jet having a diameter of 1millimetre at the necessary speed of 100 to 150 metres per second. Finding, however, that the need for having the acetylene under pressuresomewhat limited the sphere of usefulness of his apparatus, Fouchéfinally designed a low-pressure blowpipe, in which only the oxygenrequires to be in a state of compression, while the acetylene is drawndirectly from any generator of the ordinary pattern that does not yield agas contaminated with air. The oxygen passes through a reducing valve tolower the pressure under which it stands in the cylinder to that of 1 or1. 5 effective atmosphere, this amount being necessary to inject theacetylene and to give the previously mentioned speed of escape from theblowpipe orifice. The acetylene is led through a system of long narrowtubes to prevent it firing-back. AUTOGENOUS SOLDERING AND WELDING. --The blowpipe is suitable for thewelding and for the autogenous soldering or "burning" of wrought or castiron, steel, or copper. An apparatus consuming from 600 to 1000 litres ofacetylene per hour yields a flame whose inner zone is 10 to 15millimetres long, and 3 to 4 millimetres in diameter; it is sufficientlypowerful to burn iron sheets 8 to 9 millimetres thick. By increasing thesupply of acetylene in proportion to that of the oxygen, the tip of theinner zone becomes strongly luminous, and the flame then tends tocarburise iron; when the gases are so adjusted that this tip justdisappears, the flame is at its best for heating iron and steel. Theconsumption of acetylene is about 75 litres per hour for each millimetreof thickness in the sheet treated, and the normal consumption of oxygenis 1. 7 times as much; a joint 6 metres long can be burnt in 1 millimetreplate per hour, and one of 1. 5 metres in 10 millimetre plate. In certaincases it is found economical to raise the metal to dull redness by othermeans, say with a portable forge of the usual description, or with ablowpipe consuming coal-gas and air. There are other forms of low-pressure blowpipe besides the Fouché, in some of which the oxygen also issupplied at low pressure. Apart from the use of cylinders of dissolvedacetylene, which are extremely convenient and practically indispensablewhen the blowpipe has to be applied in confined spaces (as in repairingpropeller shafts on ships _in situ_), acetylene generators are nowmade by several firms in a convenient transportable form for providingthe gas for use in welding or autogenous soldering. It is generallysupposed that the metal used as solder in soldering iron or steel by thismethod must be iron containing only a trifling proportion of carbon (suchas Swedish iron), because the carbon of the acetylene carburises themetal, which is heated in the oxy-acetylene flame, and would thereby makeordinary steel too rich in carbon. But the extent to which the metal usedis carburised in the flame depends, as has already been indicated, on theproper adjustment of the proportion of oxygen to acetylene. Oxy-acetyleneautogenous soldering or welding is applicable to a great variety of work, among which may be mentioned repairs to shafts, locomotive frames, cylinders, and to joints in ships' frames, pipes, boilers, and rails. Theuse of the process is rapidly extending in engineering works generally. Generators for acetylene soldering or welding must be of ample size tomeet the quickly fluctuating demands on them and must be provided withwater-seals, and a washer or scrubber and filter capable of arresting allimpurities held mechanically in the crude gas, and with a safety vent-pipe terminating in the open at a distance from the work in hand. Thegenerator must be of a type which affords as little after-generation aspossible, and should not need recharging while the blowpipe is in use. There should be a main tap on the pipe between the generator and theblowpipe. It does not appear conclusively established that the gasconsumed should have been chemically purified, but a purifier of amplesize and charged with efficient material is undoubtedly beneficial. Theblowpipe must be designed so that it remains sufficiently cool to preventpolymerisation of the acetylene and deposition of the resultant particlesof carbon or soot within it. It is important to remember that if a diluent gas, such as nitrogen, ispresent, the superior calorific power of acetylene over nearly all gasesshould avail to keep the temperature of the flame more nearly up to thetemperature at which hydrogen and oxygen cease to combine. Hence ablowpipe fed with air and acetylene would give a higher temperature thanany ordinary (atmospheric) coal-gas blowpipe, just as, as has beenexplained in Chapter VI. , an ordinary acetylene flame has a highertemperature than a coal-gas flame. It is likely that a blowpipe fed with"Lindé-air" (oxygen diluted with less nitrogen than in the atmosphere)and acetylene would give as high a limelight effect as the oxy-hydrogenor oxy-coal-gas blowpipe. CHAPTER X CARBURETTED ACETYLENE Now that atmospheric or Bunsen burners for the consumption of acetylenefor use in lighting by the incandescent system and in heating have beenso much improved that they seem to be within measurable reach of a stateof perfection, there appears to be but little use at the present time fora modified or diluted acetylene which formerly seemed likely to bevaluable for heating and certain other purposes. Nevertheless, the factsrelating to this so-called carburetted acetylene are in no way traversedby its failure to establish itself as an active competitor with simpleacetylene for heating purposes, and since it is conceivable that theadvantages which from the theoretical standpoint the carburetted gasundoubtedly possesses in certain directions may ultimately lead to itspractical utilisation for special purposes, it has been deemed expedientto continue to give in this work an account of the principles underlyingthe production and application of carburetted acetylene. It has already been explained that acetylene is comparatively a lessefficient heating agent than it is an illuminating material, because, perunit of volume, its calorific power is not so much greater than that ofcoal-gas as is its illuminating capacity. It has also been shown that thehigh upper explosive limit of mixtures of acetylene and air--a limit somuch higher than the corresponding figure with coal-gas and other gaseousfuels--renders its employment in atmospheric burners (either for lightingor for heating) somewhat troublesome, or dependent upon considerableskill in the design of the apparatus. If, therefore, either the upperexplosive limit of acetylene could be reduced, or its calorific valueincreased (or both), by mixing with it some other gas or vapour whichshould not seriously affect its price and convenience as a self-luminousilluminant, acetylene would compare more favourably with coal-gas in itsready applicability to the most various purposes. Such a method has beensuggested by Heil, and has been found successful on the Continent. Itconsists in adding to the acetylene a certain proportion of the vapour ofa volatile hydrocarbon, so as to prepare what is called "carburettedacetylene. " In all respects the method of making carburetted acetylene isidentical with that of making "air-gas, " which was outlined in ChapterI. , viz. , the acetylene coming from an ordinary generating plant is ledover or through a mass of petroleum spirit, or other similar product, ina vessel which exposes the proper amount of superficial area to thepassing gas. In all respects save one the character of the product issimilar to that of air-gas, _i. E. _, it is a mixture of a permanentgas with a vapour; the vapour may possibly condense in part within themains if they are exposed to a falling temperature, and if the product isto be led any considerable distance, deposition of liquid may occur(conceivably followed by blockage of the mains) unless the proportion ofvapour added to the gas is kept below a point governed by local climaticand similar conditions. But in one most important respect carburettedacetylene is totally different from air-gas: partial precipitation ofspirit from air-gas removes more or less of the solitary usefulconstituent of the material, reducing its practical value, and causingthe residue to approach or overpass its lower explosive limit (_cf. _Chapter I. ); partial removal of spirit from carburetted acetylene onlymeans a partial reconversion of the material into ordinary acetylene, increasing its natural illuminating power, lowering its calorificintensity somewhat, and causing the residue to have almost its primaryhigh upper explosive limit, but essentially leaving its lower explosivelimit unchanged. Thus while air-gas may conceivably become inefficientfor every purpose if supplied from any distance in very cold weather, andmay even pass into a dangerous explosive within the mains; carburettedacetylene can never become explosive, can only lose part of its specialheating value, and will actually increase in illuminating power. It is manifest that, like air-gas, carburetted acetylene is of somewhatindefinite composition, for the proportion of vapour, and the chemicalnature of that vapour, may vary. 100 litres of acetylene will take up 40grammes of petroleum spirit to yield 110 litres of carburetted acetyleneevidently containing 9 per cent. Of vapour, or 100 litres of acetylenemay be made to absorb as much as 250 grammes of spirit yielding 200litres of carburetted acetylene containing 50 per cent. Of vapour; whilethe petroleum spirit may be replaced, if prices are suitable, by benzolor denatured alcohol. The illuminating power of acetylene carburetted with petroleum spirit hasbeen examined by Caro, whose average figures, worked out in Britishunits, are: ILLUMINATING POWER OF CARBURETTED ACETYLENE. HALF-FOOT BURNERS. _Self-luminous. _ | _Incandescent_1 litre = 1. 00 candle. | 1 litre = 3. 04 candles. 1 cubic foot = 28. 4 candles. | 1 cubic foot = 86. 2 candles. 1 candle = 1. 00 litre. | 1 candle = 0. 33 litre. 1 candle = 0. 035 cubic foot. | 1 candle = 0. 012 cubic foot. Those results may be compared with those referring to air-gas, whichemits in incandescent burners from 3. 0 to 12. 4 candles per cubic footaccording to the amount of spirit added to the air and the temperature towhich the gas is exposed. The calorific values of carburetted acetylene (Caro), and those of othergaseous fuels are: Large Calories per _ Cubic Foot. | (Lewes) . 320 | (Gand) . 403 Ordinary acetylene . . | (Heil) . 365 | ___ |_Mean . . 363 | Maximum . 680 Carburetted acetylene . . | Minimum . 467 (petroleum spirit) | ___ |_Mean . . 573 Carburetted acetylene (50 per cent. Benzol by volume) 685 Carburetted acetylene (50 per cent. Alcohol by volume) 364 Coal-gas (common, unenriched) . . . . . 150 _ | Maximum . 178 Air-gas, self-luminous flame | Minimum . 57 | ___ |_Mean . . . 114 _ | Maximum . 26 Air-gas, non-luminous flame | Minimum . 18 | ___ |_Mean . . . 22 Water-gas (Strache) from coke . . . . . 71 Mond gas (from bituminous coal) . . . . . 38 Semi-water-gas from coke or anthracite . . . 36 Generator (producer) gas . . . . . . 29 Besides its relatively low upper explosive limit, carburetted acetyleneexhibits a higher temperature of ignition than ordinary acetylene, whichmakes it appreciably safer in presence of a naked light. It alsopossesses a somewhat lower flame temperature and a slower speed ofpropagation of the explosive wave when mixed with air. These data are: ______________________________________________________________________| | | | || | Explosive | Temperature. | || | Limits. | Degrees C. | Explosive || |19 mm. Tube. | | Explosive || |_____________|__________________| Wave. || | | | | | Metres per || | | |Of Igni-| | Second. || |Lower. |Upper. | tion. |Of Flame. | ||________________________|______|______|________|_________|____________|| | | | | | || Acetylene (theoretical)| --- | --- | --- |1850-2420| --- || " (observed) | 3. 35 | 52. 3 | 480 |1630-2020| 0. 18-100 || Carburetted \ from | 2. 5 | 10. 2 | 582 | 1620 | 3. 2 || acetylene / . . To | 5. 4 | 30. 0 | 720 | 1730 | 5. 3 || Carburetted acetylene\ | 3. 4 | 22. 0 | --- | 1820 | 1. 3 || (benzol) . . . / | | | | | || Carburetted acetylene\ | 3. 1 | 12. 0 | --- | 1610 | 1. 1 || (alcohol) . . . / | | | | | || Air-gas, self-luminous\|15. 0 | 50. 0 | --- |1510-1520| --- || flame . . . . /| | | | | || Coal-gas . . . | 7. 9 | 19. 1 | 600 | --- | --- ||________________________|______|______|________|_________|____________| In making carburetted acetylene, the pressure given by the ordinaryacetylene generator will be sufficient to drive the gas through thecarburettor, and therefore there will be no expense involved beyond thecost of the spirit vaporised. Thus comparisons may fairly be made betweenordinary and carburetted acetylene on the basis of material only, theexpense of generating the original acetylene being also ignored. In GreatBritain the prices of calcium carbide, petroleum spirit, and 90s benzoldelivered in bulk in country places may be taken at 15£ per ton, and1s. Per gallon respectively, petroleum spirit having a specificgravity of 0. 700 and benzol of 0. 88. On this basis, a unit volume (100cubic metres) of plain acetylene costs 1135d. , of "petrolised"acetylene containing 66 per cent. Of acetylene costs 1277d. , andof "benzolised" acetylene costs 1180d. In other words, 100 volumesof plain acetylene, 90 volumes of petrolised acetylene, and 96 volumes ofbenzolised acetylene are of equal pecuniary value. Employing the datagiven in previous tables, it appears that 38. 5 candles can be won fromplain acetylene in a self-luminous burner, and 103 candles therefrom inan incandescent burner at the same price as 25. 5-29. 1 and 78-87 candlescan be obtained from carburetted acetylene; whence it follows that atEnglish prices petrolised acetylene is more expensive as an illuminant ineither system of combustion than the simple gas, while benzolisedacetylene, burnt under the mantle only, is more nearly equal to thesimple gas from a pecuniary aspect. But considering the calorific value, it appears that for a given sum of money only 363 calories can beobtained from plain acetylene, while petrolised acetylene yields 516, andbenzolised acetylene 658; so that for all heating or cooking purposes(and also for driving small motors) carburetted acetylene exhibits anotable economy. Inasmuch as the partial saturation of acetylene with anycombustible vapour is an operation of extreme simplicity, requiring nopower or supervision beyond the occasional recharging of the carburettor, it is manifest that the original main coming from the generator supplyingany large establishment where much warming, cooking (or motor driving)might conveniently be done with the gas could be divided within theplant-house, one branch supplying all, or nearly all, the lightingburners with plain acetylene, and the other branch communicating with acarburettor, so that all, or nearly all, the warming and cooking stoves(and the motor) should be supplied with the more economical carburettedacetylene. Since any water pump or similar apparatus would be in anouthouse or basement, and the most important heating stove (the cooker)be in the kitchen, such an arrangement would be neither complicated norinvolve a costly duplication of pipes. It follows from the fact that even a trifling proportion of vapourreduces the upper limit of explosibility of mixtures of acetylene withair, that the gas may be so lightly carburetted as not appreciably tosuffer in illuminating power when consumed in self-luminous jets, and yetto burn satisfactorily in incandescent burners, even if it has beengenerated in an apparatus which introduces some air every time theoperation of recharging is performed. To carry out this idea, Caro hassuggested that 5 kilos. Of petroleum spirit should be added to thegenerator water for every 50 cubic metres of gas evolved, _i. E. _, 1lb. Per 160 cubic feet, or, say, 1 gallon per 1000 cubic feet, or per 200lb. Of carbide decomposed. Caro proposed this addition in the case ofcentral installations supplying a district where the majority of theconsumers burnt the gas in self-luminous jets, but where a few preferredthe incandescent system; but it is clearly equally suitable foremployment in all private plants of sufficient magnitude. A lowering of the upper limit of explosibility is also produced by thepresence of the acetone which remains in acetylene when obtained from acylinder holding the compressed gas (_cf. _ Chapter XI. ). Accordingto Wolff and Caro such gas usually carries with it from 30 to 60 grammesof acetone vapour per cubic metre, _i. E. _, 1. 27 grammes per cubicfoot on an average; and this amount reduces the upper limit ofexplosibility by about 16 per cent. , so that to this extent the gasbehaves more smoothly in an incandescent burner of imperfect design. Lépinay has described some experiments on the comparative technical valueof ordinary acetylene, carburetted acetylene, denatured alcohol andpetroleum spirit as fuels for small explosion engines. One particularmotor of 3 (French) h. P. Consumed 1150 grammes of petroleum spirit perhour at full load; but when it was supplied with carburetted acetyleneits consumption fell to 150 litres of acetylene and 700 grammes of spirit(specific gravity 0. 680). A 1-1/4 h. P. Engine running light required 48grammes of 90 per cent. Alcohol per horse-power-hour and 66 litres ofacetylene; at full load it took 220 grammes of alcohol and 110 litres ofacetylene. A 6 h. P. Engine at full load required 62 litres of acetylenecarburetted with 197 grammes of petroleum spirit per horse-power-hour(uncorrected); while a similar motor fed with low-grade Taylor fuel-gastook 1260 litres per horse-power-hour, but on an average developed thesame amount of power from 73 litres when 10 per cent. Of acetylene wasadded to the gas. Lépinay found that with pure acetylene ignition of thecharge was apt to be premature; and that while the consumption ofcarburetted acetylene in small motors still materially exceeded thetheoretical, further economics could be attained, which, coupled with thesmooth and regular running of an engine fed with the carburetted gas, made carburetted acetylene distinctly the better power-gas of the two. CHAPTER XI COMPRESSED AND DISSOLVED ACETYLENE--MIXTURES WITH OTHER GASES In all that was said in Chapters II. , III. , IV. , and V. Respecting thegeneration and employment of acetylene, it was assumed that the gas wouldbe produced by the interaction of calcium carbide and water, either bythe consumer himself, or in some central station delivering the acetylenethroughout a neighbourhood in mains. But there are other methods of usingthe gas, which have now to be considered. COMPRESSED ACETYLENE. --In the first place, like all other gases, acetylene is capable of compression, or even of conversion into theliquid state; for as a gas, the volume occupied by any given weight of itis not fixed, but varies inversely with the pressure under which it isstored. A steel cylinder, for instance, which is of such size as to holda cubic foot of water, also holds a cubic foot of acetylene atatmospheric pressure, but holds 2 cubic feet if the gas is pumped into itto a pressure of 2 atmospheres, or 30 lb. Per square inch; while byincreasing the pressure to 21. 53 atmospheres at 0° C. (Ansdell, Willsonand Suckert) the gas is liquefied, and the vessel may then contain 1cubic foot of liquid acetylene, which is equal to some 400 cubic feet ofgaseous acetylene at normal pressure. It is clear that for many purposesacetylene so compressed or liquefied would be convenient, for if thecylinders could be procured ready charged, all troubles incidental togeneration would be avoided. The method, however, is not practicallypermissible; because, as pointed out in Chapters II. And VI. , acetylenedoes not safely bear compression to a point exceeding 2 atmospheres; andthe liability to spontaneous dissociation or explosion in presence ofspark or severe blow, which is characteristic of compressed gaseousacetylene, is greatly enhanced if compression has been pushed to thepoint of liquefaction. However, two methods of retaining the portability and convenience ofcompressed acetylene with complete safety have been discovered. In one, due to the researches of Claude and Hess, the gas is pumped underpressure into acetone, a combustible organic liquid of high solventpower, which boils at 56° C. As the solvent capacity of most liquids formost gases rises with the pressure, a bottle partly filled with acetonemay be charged with acetylene at considerable effective pressure untilthe vessel contains much more than its normal quantity of gas; and whenthe valve is opened the surplus escapes, ready for employment, leavingthe acetone practically unaltered in composition or quantity, and fit toreceive a fresh charge of gas. In comparison with liquefied acetylene, its solution in acetone under pressure is much safer; but since theacetone expands during absorption of gas, the bottle cannot be entirelyfilled with liquid, and therefore either at first, or during consumption(or both), above the level of the relatively safe solution, the cylindercontains a certain quantity of gaseous acetylene, which is compressedabove its limit of safety. The other method consists in pumping acetyleneunder pressure into a cylinder apparently quite full of some highlyporous solid matter, like charcoal, kieselguhr, unglazed brick, &c. Thishas the practical result that the gas is held under a high state ofcompression, or possibly as a liquid, in the minute crevices of thematerial, which are almost of insensible magnitude; or it may be regardedas stored in vessels whose diameter is less than that in which anexplosive wave can be propagated (_cf. _ Chapter VI. ). DISSOLVED ACETYLENE. --According to Fouché, the simple solution ofacetylene in acetone has the same coefficient of expansion by heat asthat of pure acetone, viz. , 0. 0015; the corresponding coefficient ofliquefied acetylene is 0. 007 (Fouché), or 0. 00489 (Ansdell) _i. E. _, three or five times as much. The specific gravity of liquid acetylene is0. 420 at 16. 4° C. (Ansdell), or 0. 528 at 20. 6° C. (Willson and Suckert);while the density of acetylene dissolved in acetone is 0. 71 at 15° C. (Claude). The tension of liquefied acetylene is 21. 53 atmospheres at 0°C. , and 39. 76 atmospheres at 20. 15° C. (Ansdell); 21. 53 at 0° C. , and39. 76 at 19. 5° C. (Willson and Suckert); or 26. 5 at 0° C. , and 42. 8 at20. 0° C. (Villard). Averaging those results, it may be said that thetension rises from 23. 2 atmospheres at 0° C. To 40. 77 at 20° C. , which isan increment of 1/26 or 0. 88 atmosphere, per 1° Centigrade; while, ofcourse, liquefied acetylene cannot be kept at all at a temperature of 0°unless the pressure is 21 atmospheres or upwards. The solution ofacetylene in acetone can be stored at any pressure above or below that ofthe atmosphere, and the extent to which the pressure will rise as thetemperature increases depends on the original pressure. Berthelot andVieille have shown that when (_a_) 301 grammes of acetone arecharged with 69 grammes of acetylene, a pressure of 6. 74 atmospheres at14. 0° C. Rises to 10. 55 atmospheres at 35. 7° C. ; (_b_) 315 grammesof acetone are charged with 118 grammes of acetylene, a pressure of 12. 25atmospheres at 14. 0° C. Rises to 19. 46 at 36. 0° C. ; (_c_) 315grammes of acetone are charged with 203 grammes of acetylene, a pressureof 19. 98 atmospheres at 13. 0° C. Rises to 30. 49 at 36. 0° C. Therefore in(_a_) the increase in pressure is 0. 18 atmosphere, in (_b_)O. 33 atmosphere, and in (_c_) 0. 46 atmosphere per 1° Centigradewithin the temperature limits quoted. Taking case (_b_) as thenormal, it follows that the increment in pressure per 1° C. Is 1/37(usually quoted as 1/30); so that, measured as a proportion of theexisting pressure, the pressure in a closed vessel containing a solutionof acetylene in acetone increases nearly as much (though distinctly less)for a given rise in temperature as does the pressure in a similar vesselfilled with liquefied acetylene, but the absolute increase is roughlyonly one-third with the solution as with the liquid, because the initialpressure under which the solution is stored is only one-half, or less, that at which the liquefied gas must exist. Supposing, now, that acetylene contained in a closed vessel, either ascompressed gas, as a solution in acetone, or as a liquid, were brought toexplosion by spark or shock, the effects capable of production have to beconsidered. Berthelot and Vieille have shown that if gaseous acetylene isstored at a pressure of 11. 23 kilogrammes per square centimetre, [Footnote: 1 kilo. Per sq. Cm. Is almost identical with 1 atmosphere, or15 lb. Per sq. Inch. ] the pressure after explosion reaches 92. 33atmospheres on an average, which is an increase of 8. 37 times theoriginal figure; if the gas is stored at 21. 13 atmospheres, the meanpressure after explosion is 213. 15 atmospheres, or 10. 13 times theoriginal amount. If liquid acetylene is tested similarly, the originalpressure, which must clearly be more than 21. 53 atmospheres (Ansdell) at0° C. , may rise to 5564 kilos, per square centimetre, as Berthelot andVieille observed when a steel bomb having a capacity of 49 c. C. Wascharged with 18 grammes of liquefied acetylene. In the case of thesolution in acetone, the magnitudes of the pressures set up are of twoentirely different orders according as the original pressure 20atmospheres or somewhat less; but apart from this, they vary considerablywith the extent to which the vessel is filled with the liquid, and theyalso depend on whether the explosion is produced in the solution or inthe gas space above. Taking the lower original pressure first, viz. , 10atmospheres, when a vessel was filled with solution to 33 per cent. Ofits capacity, the pressure after explosion reached about 95 atmospheresif the spark was applied to the gas space; but attained 117. 4 atmosphereswhen the spark was applied to the acetone. When the vessel was filled 56per cent. Full, the pressures after explosion reached about 89, or 155atmospheres, according as the gas or the liquid was treated with thespark. But when the original pressure was 20 atmospheres, and the vesselwas filled to 35 per cent. Of its actual capacity with solution, thefinal pressures ranged from 303 to 568 atmospheres when the gas wasfired, and from 2000 to 5100 when the spark was applied to the acetone. Examining these figures carefully, it will be seen that the phenomenaaccompanying the explosion of a solution of acetylene in acetone resemblethose of the explosion of compressed gaseous acetylene when the originalpressure under which the solution is stored is about 10 atmospheres; butresemble those of the explosion of liquefied acetylene when the originalpressure of the solution reaches 20 atmospheres, this being due to thefact that at an original pressure of 10 atmospheres the acetone itselfdoes not explode, but, being exothermic, rather tends to decrease theseverity of the explosion; whereas at an original pressure of 20atmospheres the acetone does explode (or burn), and adds its heat ofcombustion to the heat evolved by the acetylene. Thus at 10 atmospheresthe presence of the acetone is a source of safety; but at 20 atmospheresit becomes an extra danger. Since sound steel cylinders may easily be constructed to boar a pressureof 250 atmospheres, but would be burst by a pressure considerably lessthan 5000 atmospheres, it appears that liquefied acetylene and itssolution in acetone at a pressure of 20 atmospheres are quite unsafe; andit might also seem that both the solution at a pressure of 10 atmospheresand the simple gas compressed to the same limit should be safe. But thereis an important difference here, in degree if not in kind, because, givena cylinder of known capacity containing (1) gaseous acetylene compressedto 10 atmospheres, or (2) containing the solution at the same pressure, if an explosion were to occur, in case (1) the whole contents wouldparticipate in the decomposition, whereas in case (2), as mentionedalready, only the small quantity of gaseous acetylene above the solutionwould be dissociated. It is manifest that of the three varieties of compressed acetylene nowunder consideration, the solution in acetone is the only one fit forgeneral employment; but it exhibits the grave defects (_a_) that thepressure under which it is prepared must be so small that the pressure inthe cylinders can never approach 20 atmospheres in the hottest weather orin the hottest situation to which they may be exposed, (_b_) thatthe gas does not escape smoothly enough to be convenient from largevessels unless those vessels are agitated, and (_c_) that thecylinders must always be used in a certain position with the valve at thetop, lest part of the liquid should run out into the pipes. For thesereasons the simple solution of acetylene in acetone has not become ofindustrial importance; but the processes of absorbing either the gas, orbetter still its solution in acetone, in porous matter have alreadyachieved considerable success. Both methods have proved perfectly safeand trustworthy; but the combination of the acetone process with theporous matter makes the cylinders smaller per unit volume of acetylenethey contain. Several varieties of solid matter appear to worksatisfactorily, the only essential feature in their composition beingthat they shall possess a proper amount of porosity and be perfectly freefrom action upon the acetylene or the acetone (if present). Lime doesattack acetone in time, and therefore it is not a suitable ingredient ofthe solid substance whenever acetylene is to be compressed in conjunctionwith the solvent; so that at present either a light brick earth which hasa specific gravity of 0. 5 is employed, or a mixture of charcoal withcertain inorganic salts which has a density of 0. 3, and can be introducedthrough a small aperture into the cylinder in a semi-fluid condition. Both materials possess a porosity of 80 per cent. , that is to say, when acylinder is apparently filled quite full, only 20 per cent, of the spaceis really occupied by the solid body, the remaining 80 per cent, beingavailable for holding the liquid or the compressed gas. If allcomparisons as to degree of explosibility and effects of explosion areomitted, an analogy may be drawn between liquefied acetylene or itscompressed solution in acetone and nitroglycerin, while the gas orsolution of the gas absorbed in porous matter resembles dynamite. Nitroglycerin is almost too treacherous a material to handle, but as anexplosive (which in reason absorbed or dissolved acetylene is not)dynamite is safe, and even requires special arrangements to explode it. In Paris, where the acetone process first found employment on a largescale, the company supplying portable cylinders to consumers uses largestorage vessels filled, as above mentioned, apparently full of poroussolid matter, and also charged to about 43 per cent, of their capacitywith acetone, thus leaving about 37 per cent. Of the apace for theexpansion which occurs as the liquid takes up the gas. Acetylene isgenerated, purified, and thoroughly dried according to the usual methods;and it is then run through a double-action pump which compresses it firstto a pressure of 3. 5 kilos. , next to a pressure of 3. 5 x 3. 5 = 12 kilos, per square centimetre, and finally drives it into the storage vessels. Compression is effected in two stages, because the process is accompaniedby an evolution of much heat, which might cause the gas to explode duringthe operation; but since the pump is fitted with two cylinders, theacetylene can be cooled after the first compression. The storage vesselsthen contain 100 times their apparent volume of acetylene; for as thesolubility of acetylene in acetone at ordinary temperature and pressureis about 25 volumes of gas in 1 of liquid, a vessel holding 100 volumeswhen empty takes up 25 x 43 = 1000 volumes of acetylene roughly atatmospheric pressure; which, as the pressure is approximately 10atmospheres, becomes 1000 x 10 = 10, 000 volumes per 100 normal capacity, or 100 times the capacity of the vessel in terms of water. From theselarge vessels, portable cylinders of various useful dimensions, similarlyloaded with porous matter and acetone, are charged simply by placing themin mutual contact, thus allowing the pressure and the surplus gas toenter the small one; a process which has the advantage of renewing thesmall quantity of acetone vaporised from the consumers' cylinders as theacetylene is burnt (for acetone is somewhat volatile, cf. Chapter X. ), sothat only the storage vessels ever need to have fresh solvent introduced. Where it is procurable, the use of acetylene compressed in this fashionis simplicity itself; for the cylinders have only to be connected withthe house service-pipes through a reducing valve of ordinaryconstruction, set to give the pressure which the burners require. Whenexhausted, the bottle is simply replaced by another. Manifestly, however, the cost of compression, the interest on the value of the cylinders, andthe carriage, &c. , make the compressed gas more expensive per unit ofvolume (or light) than acetylene locally generated from carbide andwater; and indeed the value of the process does not lie so much in thedirection of domestic illumination as in that of the lighting, andpossibly driving, of vehicles and motor-cars--more especially in theillumination of such vehicles as travel constantly, or for businesspurposes, over rough road surfaces and perform mostly out-and-homejourneys. Nevertheless, absorbed acetylene may claim close attention forone department of household illumination, viz. , the portable table-lamp;for the base of such an apparatus might easily be constructed to imitatethe acetone cylinder, and it could be charged by simple connexion with alarger one at intervals. In this way the size of the lamp for a givennumber of candle-hours would be reduced below that of any type of actualgenerator, and the troubles of after-generation, always more or lessexperienced in holderless generators, would be entirely done away with. Dissolved acetylene is also very useful for acetylene welding orautogenous soldering. The advantages of compressed and absorbed acetylene depend on the smallbulk and weight of the apparatus per unit of light, on the fact that noamount of agitation can affect the evolution of gas (as may happen withan ordinary acetylene generator), on the absence of any liquid which mayfreeze in winter, and on there being no need for skilled attention exceptwhen the cylinders are being changed. These vessels weigh between 2. 5 and3 kilos, per 1 litre capacity (normal) and since they are charged with100 times their apparent volume of acetylene, they may be said to weigh 1kilo, per 33 litres of available acetylene, or roughly 2 lb. Per cubicfoot, or, again, if half-foot burners are used, 2 lb. Per 36 candle-hours. According to Fouché, if electricity obtained from leadaccumulators is compared with acetylene on the basis of the weight ofapparatus needed to evolve a certain quantify of light, 1 kilo, ofacetylene cylinder is equal to 1. 33 kilos, of lead accumulator with arclamps, or to 4 kilos. Of accumulator with glow lamps; and moreover theacetylene cylinder can be charged and discharged, broadly speaking, asquickly or as slowly as may be desired; while, it may be added, the samecylinder will serve one or more self-luminous jets, one or moreincandescent burners, any number and variety of heating apparatus, simultaneously or consecutively, at any pressure which may be required. From the aspect of space occupied, dissolved acetylene is not soconcentrated a source of artificial light as calcium carbide; for 1volume of granulated carbide is capable of omitting as much light as 4volumes of compressed gas; although, in practice, to the 1 volume ofcarbide must be added that of the apparatus in which it is decomposed. LIQUEFIED ACETYLENE. --In most civilised countries the importation, manufacture, storage, and use of liquefied acetylene, or of the gascompressed to more than a fraction of one effective atmosphere, is quiteproperly prohibited by law. In Great Britain this has been done by anOrder in Council dated November 26, 1897, which specifies 100 inches ofwater column as the maximum to which compression may be pushed. Powerbeing retained, however, to exempt from the order any method ofcompressing acetylene that might be proved safe, the Home Secretaryissued a subsequent Order on March 28, 1898, permitting oil-gascontaining not more than 20 per cent, by volume of acetylene (see below)to be compressed to a degree not exceeding 150 lb. Per square inch, _i. E. _, to about 10 atmospheres, provided the gases are mixedtogether before compression; while a third Order, dated April 10, 1901, allows the compression of acetylene into cylinders filled as completelyas possible with porous matter, with or without the presence of acetone, to a pressure not exceeding 150 lb. Per square inch provided thecylinders themselves have been tested by hydraulic pressure for at leastten minutes to a pressure not less than double [Footnote: In France thecylinders are tested to six times and in Russia to five times theirworking pressure. ] that which it is intended to use, provided the solidsubstance is similar in every respect to the samples deposited at theHome Office, provided its porosity does not exceed 80 per cent. , providedair is excluded from every part of the apparatus before the gas iscompressed, provided the quantity of acetone used (if used at all) is notsufficient to fill the porosity of the solid, provided the temperature isnot permitted to rise during compression, and provided compression onlytakes place in premises approved by H. M. 's Inspectors of Explosives. DILUTED ACETYLENE. --Acetylene is naturally capable of admixture ordilution with any other gas or vapour; and the operation may be regardedin either of two ways; (1) as a, means of improving the burning qualitiesof the acetylene itself, or (2) as a means of conferring upon some othergas increased luminosity. In the early days of the acetylene industry, generation was performed in so haphazard a fashion, purification sogenerally omitted, and the burners were so inefficient, that it wasproposed to add to the gas a comparatively small proportion of some othergaseous fluid which should be capable of making it burn withoutdeposition of carbon while not seriously impairing its latentilluminating power. One of the first diluents suggested was carbondioxide (carbonic acid gas), because this gas is very easy and cheap toprepare; and because it was stated that acetylene would bear an additionof 5 or even 8 per cent, of carbon dioxide and yet develop its fulldegree of luminosity. This last assertion requires substantiation; for itis at least a grave theoretical error to add a non-inflammable gas to acombustible one, as is seen in the lower efficiency of all flames whenburning in common air in comparison with that which they exhibit inoxygen; while from the practical aspect, so harmful is carbon dioxide inan illuminating gas, that coal-gas and carburetted water-gas arefrequently most rigorously freed from it, because a certain gain inilluminating power may often thus be achieved more cheaply than by directenrichment of the gas by addition of hydrocarbons. Being prepared fromchalk and any cheap mineral acid, hydrochloric by preference, in thecold, carbon dioxide is so cheap that its price in comparison with thatof acetylene is almost _nil_; and therefore, on the aboveassumption, 105 volumes of diluted acetylene might be made essentiallyfor the same price as 100 volumes of neat acetylene, and according tosupposition emit 5 per cent. More light per unit of volume. It is reported that several railway trains in Austria are regularlylighted with acetylene containing 0. 4 to 1. 0 per cent. Of carbon dioxidein order to prevent deposition of carbon at the burners. The gas isprepared according to a patent process which consists in adding a certainproportion of a "carbonate" to the generator water. In the UnitedKingdom, also, there are several installations supplying an acetylenediluted with carbon dioxide, the gas being produced by putting into thatportion of a water-to-carbide generator which lies nearest to the water-supply some solid carbonate like chalk, and using a dilute acid to attackthe material. Other inventors have proposed placing a solid acid, likeoxalic, in the former part of a generator and decomposing it with acarbonate solution; or they have suggested putting into the generator amixture of a solid acid and a solid soluble carbonate, and decomposing itwith plain water. Clearly, unless the apparatus in which such mixtures as these areintended to be prepared is designed with considerable care, the amount ofcarbon dioxide in the gas will be liable to vary, and may fall to zero. If any quantity of carbide present has been decomposed in the ordinaryway, there will be free calcium hydroxide in the generator; and if thecarbon dioxide comes into contact with this, it will be absorbed, unlesssufficient acid is employed to convert the calcium carbonate (orhydroxide) into the corresponding normal salt of calcium. Similarly, during purification, a material containing any free lime would tend toremove the carbon dioxide, as would any substance which became alkalineby retaining the ammonia of the crude gas. It cannot altogether be granted that the value of a process for dilutingacetylene with carbon dioxide has been established, except in so far asthe mere presence of the diluent may somewhat diminish the tendency ofthe acetylene to polymerise as it passes through a hot burner (_cf. _Chapter VIII. ). Certainly as a fuel-gas the mixture would be lessefficient, and the extra amount of carbon dioxide produced by each flameis not wholly to be ignored. Moreover, since properly generated andpurified acetylene can be consumed in proper burners without trouble, allreason for introducing carbon dioxide has disappeared. MIXTURES OF ACETYLENE AND AIR. --A further proposal for diluting acetylenewas the addition to it of air. Apart from questions of explosibility, this method has the advantage over that of adding carbon dioxide that theair, though not inflammable, is, in virtue of its contained oxygen, asupporter of combustion, and is required in a flame; whereas carbondioxide is not only not a supporter of combustion, but is actually aproduct thereof, and correspondingly more objectionable. According tosome experiments carried out by Dufour, neat acetylene burnt undercertain conditions evolved between 1. 0 and 1. 8 candle-power per litre-hour; a mixture of 1 volume of acetylene with 1 volume of air evolved 1. 4candle-power; a mixture of 1 volume of acetylene with 1. 2 volumes of air, 2. 25 candle-power; and a mixture of 1 volume of acetylene with 1. 3volumes of air, 2. 70 candle-power per litre-hour of acetylene in theseveral mixtures. Averaging the figures, and calculating into terms ofacetylene (only) burnt, Dufour found neat acetylene to develop 1. 29candle-power per litre-hour, and acetylene diluted with air to develop1. 51 candle-power. When, however, allowance is made for the cost andtrouble of preparing such mixtures the advantage of the processdisappears; and moreover it is accompanied by too grave risks, unlessconducted on a largo scale and under most highly skilled supervision, tobe fit for general employment. Fouché, however, has since found the duty, per cubic foot of neatacetylene consumed in a twin injector burner at the most advantageousrate of 3. 2 inches, to be as follows for mixtures with air in theproportions stated: Percentage of air 0 17 27 33. 5Candles per cubic feet 38. 4 36. 0 32. 8 26. 0 At lower pressures, the duty of the acetylene when diluted appears to berelatively somewhat higher. Figures which have been published in regardto a mixture of 30 volumes of air and 70 volumes of acetylene obtained bya particular system of producing such a mixture, known as the "Molet-Boistelle, " indicate that the admixture of air causes a slight increasein the illuminating duty obtained from the acetylene in burners ofvarious sizes. The type of burner and the pressure employed in theseexperiments were not, however, stated. This system has been used atcertain stations on the "Midi" railway in France. Nevertheless even wherethe admixture of air to acetylene is legally permissible, the risk ofobtaining a really dangerous product and the nebulous character of theadvantages attainable should preclude its adoption. In Great Britain the manufacture, importation, storage, and use ofacetylene mixed with air or oxygen, in all proportions and at allpressures, with or without the presence of other substances, isprohibited by an Order in Council dated July 1900; to which prohibitionthe mixture of acetylene and air that takes place in a burner orcontrivance in which the mixture is intended to be burnt, and theadmixture of air with acetylene that may unavoidably occur in the firstuse or recharging of an apparatus (usually a water-to-carbide generator), properly designed and constructed with a view to the production of pureacetylene, are the solitary exceptions. MIXED CARBIDES. --In fact the only processes for diluting acetylene whichpossess real utility are that of adding vaporised petroleum spirit orbenzene to the gas, as was described in Chapter X. Under the name ofcarburetted acetylene, and one other possible method of obtaining adiluted acetylene directly from the gas-generator, to which a few wordswill now be devoted. [Footnote: Mixtures of acetylene with relativelylarge proportions of other illuminating gases, such as are referred to onsubsequent pages, are also, from one aspect, forms of diluted acetylene. ]Calcium carbide is only one particular specimen of a large number ofsimilar metallic compounds, which can be prepared in the electricfurnace, or otherwise. Some of those carbides yield acetylene whentreated with water, some are not attacked, some give liquid products, andsome yield methane, or mixtures of methane and hydrogen. Among the latteris manganese carbide. If, then, a mixture of manganese carbide andcalcium carbide is put into an ordinary acetylene generator, the gasevolved will be a mixture of acetylene with methane and hydrogen inproportions depending upon the composition of the carbide mixture. It isclear that a suitable mixture of the carbides might be made by preparingthem separately and bulking the whole in the desired proportions; whilesince manganese carbide can be won in the electric furnace, it might befeasible to charge into such a furnace a mixture of lime, coke, andmanganese oxide calculated to yield a simple mixture of the carbides or akind of double carbide. Following the lines which have been adopted inwriting the present book, it is not proposed to discuss the possibilityof making mixed carbides; but it may be said in brief that Brame andLewes have carried out several experiments in this direction, usingcharges of lime and coke containing (_a_) up to 20 per cent. Ofmanganese oxide, and (_b_) more than 60 per cent. Of manganeseoxide. In neither case did they succeed in obtaining a material whichgave a mixture of acetylene and methane when treated with water; in case(_a_) they found the gas to be practically pure acetylene, so thatthe carbide must have been calcium carbide only; in case (_b_) thegas was mainly methane and hydrogen, so that the carbide must have beenessentially that of manganese alone. Mixed charges containing between 20and 60 per cent. Of manganese oxide remain to be studied; but whetherthey would give mixed carbides or no, it would be perfectly simple to mixready-made carbides of calcium and manganese together, if any demand fora diluted acetylene should arise on a sufficiently large scale. It is, however, somewhat difficult to appreciate the benefits to be obtainedfrom forms of diluted acetylene other than those to which reference ismade later in this chapter. There is, nevertheless, one modification of calcium carbide which, in asmall but important sphere, finds a useful _rôle_. It has beenpointed out that a carbide containing much calcium phosphide is usuallyobjectionable, because the gas evolved from it requires extrapurification, and because there is the (somewhat unlikely) possibilitythat the acetylene obtained from such material before purification may bespontaneously inflammable. If, now, to the usual furnace charge of limeand coke a sufficient quantity of calcium phosphate is purposely added, it is possible to win a mixture of calcium phosphide and carbide, or, asBradley, Read, and Jacobs call it, a "carbophosphide of calcium, " havingthe formula Ca_5C_6P_2, which yields a spontaneously inflammable mixtureof acetylene, gaseous phosphine, and liquid phosphine when treated withwater, and which, therefore, automatically gives a flame when broughtinto contact with the liquid. The value of this material will bedescribed in Chapter XIII. GAS-ENRICHING. --Other methods of diluting acetylene consist in adding acomparatively small proportion of it to some other gas, and may beconsidered rather as processes for enriching that other gas withacetylene. Provided the second gas is well chosen, such mixtures exhibitproperties which render them peculiarly valuable for special purposes. They have, usually, a far lower upper limit of explosibility than that ofneat acetylene, and they admit of safe compression to an extent greatlyexceeding that of acetylene itself, while they do not lose illuminatingpower on compression. The second characteristic is most important, anddepends on the phenomena of "partial pressure, " which have been referredto in Chapter VI. When a single gas is stored at atmospheric pressure, itis insensibly withstanding on all sides and in all directions a pressureof roughly 15 lb. Per square inch, which is the weight of the atmosphereat sea-level; and when a mixture of two gases, X and Y, in equal volumesis similarly stored it, regarded as an entity, is also supporting apressure of 15 lb. Per square inch. But in every 1 volume of that mixturethere is only half a volume of X and Y each; and, ignoring the presenceof its partner, each half-volume is evenly distributed throughout a spaceof 1 volume. But since the volume of a gas stands in inverse ratio to thepressure under which it is stored, the half-volume of X in the 1 volumeof X + Y apparently stands at a pressure of half an atmosphere, for ithas expanded till it fills, from a chemical and physical aspect, thespace of 1 volume: suitable tests proving that it exhibits the propertieswhich a gas stored at a pressure of half an atmosphere should do. Therefore, in the mixture under consideration, X and Y are both said tobe at a "partial pressure" of half an atmosphere, which is manifestly 7. 5lb. Per square inch. Clearly, when a gas is an entity (either an elementor one single chemical compound) partial and total pressure areidentical. Now, it has been shown that acetylene ceases to be a safe gasto handle when it is stored at a pressure of 2 atmospheres; but the limitof safety really occurs when the gas is stored at a _partial_pressure of 2 atmospheres. Neat acetylene, accordingly, cannot becompressed above the mark 30 lb. Shown on a pressure gauge; but dilutedacetylene (if the diluent is suitable) may be compressed in safety tillthe partial pressure of the acetylene itself reaches 2 atmospheres. Forinstance, a mixture of equal volumes of X and Y (X being acetylene)contains X at a partial pressure of half the total pressure, and maytherefore be compressed to (2 / 1/2 =) 4 atmospheres before X reaches thepartial pressure of 2 atmospheres; and therewith the mixture is broughtjust to the limit of safety, any effect of Y one way or the other beingneglected. Similarly, a mixture of 1 volume of acetylene with 4 volumesof Y may be safely compressed to a pressure of (2 / 1/5 =) 10atmospheres, or, broadly, a mixture in which the percentage of acetyleneis _x_ may be safely compressed to a pressure not exceeding (2 /_x_/100) atmospheres. This fact permits acetylene after properdilution to be compressed in the same fashion as is allowable in the caseof the dissolved and absorbed gas described above. If the latent illuminating power of acetylene is not to be wasted, thediluent must not be selected without thought. Acetylene burns with a veryhot flame, the luminosity of which is seriously decreased if thetemperature is lowered. As mentioned in Chapter VIII. , this may be doneby allowing too much air to enter the flame; but it may also be effectedto a certain extent by mixing with the acetylene before combustion somecombustible gas or vapour which burns at a lower temperature thanacetylene itself. Manifestly, therefore, the ideal diluent for acetyleneis a substance which possesses as high a flame temperature as acetyleneand a certain degree of intrinsic illuminating power, while the lower theflame temperature of the diluent and the less its intrinsic illuminatingpower, the less efficiently will the acetylene act as an enrichingmaterial. According to Love, Hempel, Wedding, and others, if acetylene ismixed with coal-gas in amounts up to 8 per cent. Or thereabouts, theilluminating power of the mixture increases about 1 candle for every 1per cent. Of acetylene present: a fact which is usually expressed bysaying that with coal-gas the enrichment value of acetylene is 1 candleper 1 per cent. Above 8 per cent. , the enrichment value of acetylenerises, Love having found an increase in illuminating power, for each 1per cent. Of acetylene in the mixture, of 1. 42 candles with 11. 28 percent. Of acetylene; and of 1. 54 candles with 17. 62 per cent. Ofacetylene. Theoretically, if the illuminating power of acetylene is takenat 240 candles, its enrichment value should be (240 / 100 =) 2. 4 candlesper 1 per cent. ; and since, in the case of coal-gas, its actualenrichment value falls seriously below this figure, it is clear thatcoal-gas is not an economical diluent for it. Moreover, coal-gas can beenriched by other methods much more cheaply than with acetylene. Simple("blue") water-gas, according to Love, requires more than 10 per cent. Ofacetylene to be added to it before a luminous flame is produced; while amixture of 20. 3 per cent. Of acetylene and 79. 7 per cent. Of water-gashad an illuminating power of 15. 47 candles. Every addition to theproportion of acetylene when it amounted to 20 per cent. And upwards ofthe mixture had a very appreciable effect on the illuminating power ofthe latter. Thus with 27. 84 per cent. Of acetylene, the illuminatingpower of the mixture was 40. 87 candles; with 38. 00 per cent. Of acetyleneit was 73. 96 candles. Acetylene would not be an economical agent toemploy in order to render water-gas an illuminating gas of about thequality of coal-gas, but the economy of enrichment of water-gas byacetylene increases rapidly with the degree of enrichment demanded of it. Carburetted water-gas which, after compression under 16 atmospherespressure, had an illuminating power of about 17. 5 candles, was enrichedby additions of acetylene. 4. 5 per cent. Of acetylene in the mixture gavean illuminating power of 22. 69 candles; 8. 4 per cent. , 29. 54 candles;11. 21 per cent. , 35. 05 candles; 15. 06 per cent. , 42. 19 candles; and 21. 44per cent. , 52. 61 candles. It is therefore evident that the effect ofadditions of acetylene on the illuminating power of carburetted water-gasis of the same order as its effect on coal-gas. The enrichment value ofthe acetylene increases with its proportion in the mixture; but only whenthe proportion becomes quite considerable, and, therefore, the gas ofhigh illuminating power, does enrichment by acetylene become economical. Methane (marsh-gas), owing to its comparatively high flame temperature, and to the fact that it has an intrinsic, if small, illuminating power, is a better diluent of acetylene than carbon monoxide or hydrogen, inthat it preserves to a greater extent the illuminative value of theacetylene. Actually comparisons of the effect of additions of various proportions ofa richly illuminating gas, such as acetylene, on the illuminative valueof a gas which has little or no inherent illuminating power, are largelyvitiated by the want of any systematic method for arriving at therepresentative illuminative value of any illuminating gas. A statementthat the illuminating power of a gas is _x_ candles is, strictlyspeaking, incomplete, unless it is supplemented by the information thatthe gas during testing was burnt (1) in a specified type of burner, and(2) either at a specified fixed rate of consumption or so as to afford alight of a certain specified intensity. There is no general agreement, even in respect of the statutory testing of the illuminating power ofcoal-gas supplies, as to the observance of uniform conditions of burningof the gas under test, and in regard to more highly illuminating gasesthere is even greater diversity of conditions. Hence figures such asthose quoted above for the enrichment value of acetylene inevitably showa certain want of harmony which is in reality due to the imperfection orincompleteness of the modes of testing employed. Relatively to another, one gas appears advantageously merely in virtue of the conditions ofassessing illuminating power having been more favourable to it. Thereforeenrichment values, such as those given, must always be regarded as onlyapproximately trustworthy in instituting comparisons between eitherdifferent diluent gases or different enriching agents. ACETYLENE MIXTURES FOR RAILWAY-CARRIAGE LIGHTING. --In modern practice, the gases which are most commonly employed for diluents of acetylene, under the conditions now being considered, are cannel-coal gas (inFrance) and oil-gas (elsewhere). Fowler has made a series of observationson the illuminating value of mixtures of oil-gas and acetylene. 13. 41 percent. Of acetylene improved the illuminating power of oil-gas from 43 to49 candles. Thirty-nine-candle-power oil-gas had its illuminating powerraised to about 60 candles by an admixture of 20 per cent. Of acetylene, to about 80 candles by 40 per cent. Of acetylene, and to about 110candles by 60 per cent. Of acetylene. The difficulty of employingmixtures fairly rich in acetylene, or pure acetylene, for railway-carriage lighting, lies in the poor efficiency of the small burners whichyield from such rich gas a light of 15 to 20 candle-power, such as issuitable for the purpose. For the lighting of railway carriages it isseldom deemed necessary to have a flame of more than 20 candle-power, andit is somewhat difficult to obtain such a flame from oil-gas mixturesrich in acetylene, unless the illuminative value of the gas is wasted toa considerable extent. According to Bunte, 15 volumes of coal-gas, 8volumes of German oil-gas, and 1. 5 volumes of acetylene all yield anequal amount of light; from which it follows that 1 volume of acetyleneis equivalent to 5. 3 volumes of German oil-gas. A lengthy series of experiments upon the illuminating power of mixturesof oil-gas and acetylene in proportions ranging between 10 and 50 percent. Of the latter, consumed in different burners and at differentpressures, has been carried out by Borck, of the German State RailwayDepartment. The figures show that per unit of volume such mixtures maygive anything up to 6. 75 times the light evolved by pure oil-gas; butthat the latent illuminating power of the acetylene is lessadvantageously developed if too much of it is employed. As 20 per cent. Of acetylene is the highest proportion which may be legally added to oil-gas in this country, Borck's results for that mixture may be studied: ______________________________________________________________________| | | | | | | || | | | | | | Propor- || | | | Consump- | | Consump- | tionate || Kind of | No. Of | Pres- | tion per | Candle- | tion per | Illum- || Burner. | Burner | sure. | Hour. | Power. | Candle- | inating || | | mm. | Litres. | | Hour. | Power || | | | | | Litres. | to Pure || | | | | | | Oil-Gas. ||___________|________|_______|__________|_________|__________|_________|| | | | | | | || Bray | 00 | 42 | 82 | 56. 2 | 1. 15 | 3. 38 || " | 000 | 35 | 54 | 28. 3 | 1. 91 | 4. 92 || " | 0000 | 35 | 43. 3 | 16 | 2. 71 | 4. 90 || Oil-gas | | | | | | || burner | 15 | 24 | 21 | 7. 25 | 2. 89 | 4. 53 || " " | 30 | 15 | 22 | 10. 5 | 2. 09 | 3. 57 || " " | 40 | 16 | 33. 5 | 20. 2 | 1. 65 | 3. 01 || " " | 60 | 33 | 73 | 45. 2 | 1. 62 | 3. 37 || || The oil-gas from which this mixture was prepared showing: || || Bray | 00 | 34 | 73. 5 | 16. 6 | 4. 42 | . . . || " | 000 | 30 | 48 | 6. 89 | 6. 96 | . . . || " | 0000 | 28 | 39 | 3. 26 | 11. 6 | . . . || Oil-gas | | | | | | || burner | 15 | 21 | 19 | 1. 6 | 11. 8 | . . . || " " | 30 | 14 | 21. 5 | 2. 94 | 7. 31 | . . . || " " | 40 | 15 | 33 | 6. 7 | 4. 92 | . . . || " " | 60 | 25 | 60 | 13. 4 | 4. 40 | . . . ||___________|________|_______|__________|_________|__________|_________| It will be seen that the original oil-gas, when compressed to 10atmospheres, gave a light of 1 candle-hour for an average consumption of7. 66 litres in the Bray burners, and for a consumption of 7. 11 litres inthe ordinary German oil-gas jets; while the mixture containing 20 percent. Of acetylene evolved the same amount of light for a consumption of2. 02 litres in Bray burners, or of 2. 06 litres in the oil-gas jets. Again, taking No. 40 as the most popular and useful size of burner, 1volume of acetylene oil-gas may be said to be equal to 3 volumes ofsimple oil-gas, which is the value assigned to the mixture by the GermanGovernment officials, who, at the prices ruling there, hold the mixtureto be twice as expensive as plain oil-gas per unit of volume, which meansthat for a given outlay 50 per cent. More light may be obtained fromacetylene oil-gas than from oil-gas alone. This comparison of cost is not applicable, as it stands, to compressedoil-gas, with and without enrichment by acetylene, in this country, owingto the oils from which oil-gas is made being much cheaper and of betterquality here than in Germany, where a heavy duty is imposed on importedpetroleum. Oil-gas as made from Scotch and other good quality gas-oil inthis country, usually has, after compression, an illuminating duty ofabout 8 candles per cubic foot, which is about double that of thecompressed German oil-gas as examined by Borck. Hence the following table, containing a summary of results obtained by H. Fowler with compressed oil-gas, as used on English railways, must beaccepted rather than the foregoing, in so far as conditions prevailing inthis country are concerned. It likewise refers to a mixture of oil-gasand acetylene containing 20 per cent. Of acetylene. ______________________________________________________________________| | | | | | || | | | | | Ratio of || | |Consumption| |Candles per| Illuminating || Burner. |Pressure. | per Hour. |Candle| Cubic Foot| Power to that || | Inches. |Cubic Feet. |Power. | per Hour. |of Oil-gas [1] || | | | | | in the same || | | | | | Burner. ||_____________|_________|___________|______|___________|_______________|| | | | | | || Oil-gas . . | 0. 7 | 0. 98 | 12. 5 | 12. 72 | 1. 65 || Bray 000 . | 0. 7 | 1. 17 | 14. 4 | 12. 30 | 1. 57 || " 0000 . | 0. 7 | 0. 97 | 10. 4 | 10. 74 | 1. 41 || " 00000 | 0. 7 | 0. 78 | 5. 6 | 7. 16 | 1. 08 || " 000000 | 0. 7 | 0. 55 | 1. 9 | 3. 52 | 1. 14 ||_____________|_________|___________|______|___________|_______________| [Footnote 1: Data relating to the relative pecuniary values of acetylene(carburetted or not), coal-gas, paraffin, and electricity as heating orilluminating agents, are frequently presented to British readers aftersimple recalculation into English equivalents of the figures which obtainin France and Germany. Such a method of procedure is utterly incorrect, as it ignores the higher prices of coal, coal-gas, and especiallypetroleum products on the Continent of Europe, which arise partly fromgeographical, but mainly from political causes. ] The mixture was tried also at higher pressures in the same burners, butwith less favourable results in regard to the duty realised. The oil-gaswas also tried at various pressures, and the most favourable result istaken for computing the ratio in the last column. It is evident from thistable that 1 volume of this acetylene-oil-gas mixture is equal at themost to 1. 65 volume of the simple oil-gas. Whether the mixture will provecheaper under particular conditions must depend on the relative prices ofgas-oil and calcium carbide at the works where the gas is made andcompressed. At the prevailing prices in most parts of Britain, simpleoil-gas is slightly cheaper, but an appreciable rise in the price of gas-oil would render the mixture with acetylene the cheaper illuminant. Thefact remains, however, that per unit weight or volume of cylinder intowhich the gas is compressed, acetylene oil-gas evolves a higher candle-power, or the same candle-power for a longer period, than simple, unenriched British oil-gas. Latterly, however, the incandescent mantlehas found application for railway-carriage lighting, and poorercompressed gases have thereby been rendered available. Thus coal-gas, towhich a small proportion of acetylene has been added, may advantageouslydisplace the richer oil-gas and acetylene mixtures. Patents have been taken out by Schwander for the preparation of a mixtureof acetylene, air, and vaporised petroleum spirit. A current of naturallydamp, or artificially moistened, air is led over or through a mass ofcalcium carbide, whereby the moisture is replaced by an equivalentquantity of acetylene; and this mixture of acetylene and air iscarburetted by passing it through a vessel of petroleum spirit in themanner adopted with air-gas. No details as to the composition, illuminating power, and calorific values of the gas so made have beenpublished. It would clearly tend to be of highly indefinite constitutionand might range between what would be virtually inferior carburettedacetylene, and a low-grade air-gas. It is also doubtful whether thecombustion of such gas would not be accompanied by too grave risks torender the process useful. CHAPTER XII SUNDRY USES There are sundry uses for acetylene, and to some extent for carbide, which are not included in what has been said in previous chapters of thisbook; and to them a few words may be devoted. In orchards and market gardens enormous damage is frequently done to thecrops by the ravages of caterpillars of numerous species. Thesecaterpillars cannot be caught by hand, and hitherto it has provedexceedingly difficult to cope with them. However, when they have changedinto the perfect state, the corresponding butterflies and moths, likemost other winged insects, are strongly attracted by a bright light. Asacetylene can easily be burnt in a portable apparatus, and as the burnerscan be supplied with gas at such comparatively high pressure that theflames are capable of withstanding sharp gusts of wind even when notprotected by glass, the brilliant light given by acetylene forms anexcellent method of destroying the insects before they have had time tolay their eggs. Two methods of using the light have been tried withastonishing success: in one a naked flame is supported within somereceptacle, such as a barrel with one end knocked out, the interior ofwhich is painted heavily with treacle; in the other the flame issupported over an open dish filled with some cheap heavy oil (or perhapstreacle would do equally well). In the first case the insects areattracted by the light and are caught by the adhesive surfaces; in thesecond they are attracted and singed, and then drowned in, or caught by, the liquid. Either a well-made, powerful, vehicular lamp with its bull's-eye (if any) removed could be used for this purpose, or a portablegenerator of any kind might be connected with the burner through aflexible tube. It is necessary that the lights should be lit just beforedusk when the weather is fine and the nights dark, and for some twentyevenings in June or July, exactly at the period of the year when theperfect insects are coming into existence. In some of the vineyards ofBeaujolais, in France, where great havoc has been wrought by the pyralid, a set of 10-candle-power lamps were put up during July 1901, at distancesof 150 yards apart, using generators containing 6 oz. Of carbide, anddishes filled with water and petroleum 18 or 20 inches in diameter. Ineighteen nights, some twenty lamps being employed, the total catch ofinsects was 170, 000, or an average of 3200 per lamp per night. At Frenchprices, the cost is reported to have been 8 centimes per night, or 32centimes per hectare (2. 5 acres). In Germany, where school children areoccasionally paid for destroying noxious moths, two acetylene lampsburning for twelve evenings succeeded in catching twice as many insectsas the whole juvenile population of a village during August 1902. Asimilar process has been recommended for the destruction of the malarialmosquito, and should prove of great service to mankind in infecteddistricts. The superiority of acetylene in respect of brilliancy andportability will at once suggest its employment as the illuminant in the"light" moth-traps which entomologists use for entrapping moths. In thesetraps, the insects, attracted by the light, flutter down panes of glass, so inclined that ultimate escape is improbable; while they are protectedfrom injury through contact with the flame by moans of an interveningsheet of glass. Methods of spraying with carbide dust have been found useful in treatingmildew in vines; while a process of burying small quantities of carbideat the roots has proved highly efficacious in exterminating phylloxera inthe French and Spanish vineyards. It was originally believed that theimpurities of the slowly formed acetylene, the phosphine in particular, acted as toxic agents upon the phylloxera; and therefore carbidecontaining an extra amount of decomposable phosphides was speciallymanufactured for the vine-growers. But more recently it has been argued, with some show of reason, that the acetylene itself plays a part in theprocess, the effects produced being said to be too great to be ascribedwholly to the phosphine. It is well known that many hydrocarbon vapours, such as the vapour of benzene or of naphthalene, have a highly toxicaction on low organisms, and the destructive effect of acetylene onphylloxera may be akin to this action. As gaseous acetylene will bear a certain amount of pressure in safety--apressure falling somewhat short of one effective atmosphere--and aspressure naturally rises in a generating apparatus where calcium carbidereacts with water, it becomes possible to use this pressure as a sourceof energy for several purposes. The pressure of the gas may, in fact, beemployed either to force a stream of liquid through a pipe, or to propelcertain mechanism. An apparatus has been constructed in France on thelines of some portable fire-extinguishing appliances in which thepressure set up by the evolution of acetylene in a closed space producesa spray of water charged with lime and gas under the pressure obtaining;the liquid being thrown over growing vines or other plants in order todestroy parasitic and other forms of life. The apparatus consists of ametal cylinder fitted with straps so that it can be carried by man orbeast. At one end it has an attachment for a flexible pipe, at the otherend a perforated basket for carbide introduced and withdrawn through a"man-hole" that can be tightly closed. The cylinder is filled with waterto a point just below the bottom of the basket when the basket isuppermost; the carbide charge is then inserted, and the cover fasteneddown. As long as the cylinder is carried in the same position, noreaction between the carbide and the water occurs, and consequently nopressure arises; but on inverting the vessel, the carbide is wetted, andacetylene is liberated in the interior. On opening the cock on the outletpipe, a stream of liquid issues and may be directed as required. Bycharging the cylinder in the first place with a solution of coppersulphate, the liquid ejected becomes a solution and suspension of copperand calcium salts and hydroxides, resembling "Bordeaux mixture, " and maybe employed as such. In addition, it is saturated with acetylene whichadds to its value as a germicide. The effective gas pressure set up in a closed generator has also beenemployed in Italy to drive a gas-turbine, and so to produce motion. Theplant has been designed for use in lighthouses where acetylene is burnt, and where a revolving or flashing light is required. The gas outlet froma suitably arranged generator communicates with the inlet of a gas-turbine, and the outlet of the turbine is connected to a pipe leading tothe acetylene burners. The motion of the turbine is employed to rotatescreens, coloured glasses, or any desired optical arrangements round theflames; or, in other situations, periodically to open and close a cock onthe gas-main leading to the burners. In the latter case, a pilot flamefed separately is always alight, and serves to ignite the gas issuingfrom the main burners when the cock is opened. Another use for acetylene, which is only dependent upon a suitablylowered price for carbide to become of some importance, consists in thepreparation of a black pigment to replace ordinary lampblack. One methodfor this purpose has been elaborated by Hubou. Acetylene is prepared fromcarbide smalls or good carbide, according to price, and the gas is pumpedinto small steel cylinders to a pressure of 2 atmospheres. An electricspark is then passed, and the gas, standing at its limit of safety, immediately dissociates, yielding a quantitative amount of hydrogen andfree carbon. The hydrogen is drawn off, collected in holders, and usedfor any convenient purpose; the carbon is withdrawn from the vessel, andis ready for sale. At present the pigment is much too expensive, at leastin British conditions, to be available in the manufacture of black paint;but its price would justify its employment in the preparation of the bestgrades of printers' ink. One of the authors has examined an averagesample and has found it fully equal in every way to blacks, such as thosetermed "spirit blacks, " which fetch a price considerably above their realvalue. It has a pure black cast of tint, is free from greasy matter, andcan therefore easily be ground into water, or into linseed oil withoutinterfering with the drying properties of the latter. Acetylene black hasalso been tried in calico printing, and has given far better results intone and strength than other blacks per unit weight of pigment. It may beadded that the actual yield of pigment from creosote oils, the commonestraw material for the preparation of lampblack ("vegetable black"), seldomexceeds 20 or 25 per cent. , although the oil itself contains some 80 percent, of carbon. The yield from acetylene is clearly about 90 per cent. , or from calcium carbide nearly 37. 5 per cent, of the original weight. An objection urged against the Hubou process is that only smallquantities of the gas can be treated with the spark at one time; if thecylinders are too large, it is stated, tarry by-products are formed. Asecond method of preparing lampblack (or graphite) from acetylene is thatdevised by Frank, and depends on utilising the reactions between carbonmonoxide or dioxide and acetylene or calcium carbide, which have alreadybeen sketched in Chapter VI. When acetylene is employed, the yield ispure carbon, for the only by-product is water vapour; but if the carbideprocess is adopted, the carbon remains mixed with calcium oxide. Possiblysuch a material as Frank's carbide process would give, viz. , 36 parts byweight of carbon mixed with 56 parts of quicklime or 60 parts of carbonmixed with 112 parts of quicklime, might answer the purpose of a pigmentin some black paints where the amount of ash left on ignition is notsubject to specification. Naturally, however, the lime might be washedaway from the carbon by treatment with hydrochloric acid; but the cost ofsuch a purifying operation would probably render the residual pigment tooexpensive to be of much service except (conceivably) in the manufactureof certain grades of printers' ink, for which purpose it might competewith the carbon obtainable by the Hubou process already referred to. Acetylene tetrachloride, or tetrachlorethane, C_2H_2Cl_4, is now producedfor sale as a solvent for chlorine, sulphur, phosphorus, and organicsubstances such as fats. It may be obtained by the direct combination ofacetylene and chlorine as explained in Chapter VI. , but the liability ofthe reaction to take place with explosive violence would preclude thedirect application of it on a commercial scale. Processes free from suchrisk have now, however, been devised for the production oftetrachlorethane. One patented by the Salzbergwerk Neu-Stassfurt consistsin passing acetylene into a mixture of finely divided iron and chlorideof sulphur. The iron acts as a catalytic. The liquid is kept cool, and assoon as the acetylene passes through unabsorbed, its introduction isstopped and chlorine is passed in. Acetylene and chlorine are then passedin alternately until the liquid finally is saturated with acetylene. Thetetrachlorethane, boiling at 147° C. , is then distilled off, and theresidual sulphur is reconverted to the chloride for use again in theprocess. A similar process in which the chlorine is used in excess isapplicable also to the production of hexachlorethane. Dependent upon price, again, are several uses for calcium carbide as ametallurgical or reducing reagent; but as those are uses for carbide onlyas distinguished from acetylene, they do not fall within the purview ofthe present book. When discussing, in Chapter III. , methods for disposing of the limesludge coming from an acetylene generator, it was stated that on occasiona use could be found for this material. If the carbide has been entirelydecomposed in an apparatus free from overheating, the waste lime isrecovered as a solid mass or as a cream of lime practically pure white incolour. Sometimes, however, as explained in Chapter II. , the lime sludgeis of a bluish grey tint, even in cases where the carbide decomposed wasof good quality and there was no overheating in the generator. Suchdiscoloration is of little moment for most of the uses to which thesludge may be put. The residue withdrawn from a carbide-to-watergenerator is usually quite fluid; but when allowed to rest in a suitablepit or tank, it settles down to a semi-solid or pasty mass which containson a rough average 47 per cent. Of water and 53 per cent. Of solidmatter, the amount of lime present, calculated as calcium oxide, beingabout 40 per cent. Since 64 parts by weight of pure calcium carbide yield74 parts of dry calcium hydroxide, it may be said that 1 part of ordinarycommercial carbide should yield approximately 1. 1 parts of dry residue, or 2. 1 parts of a sludge containing 47 per cent. Of moisture; and sludgeof this character has been stated by Vogel to weigh about 22. 5 cwt. Percubic yard. Experience has shown that those pasty carbide residues can be employedvery satisfactorily, and to the best advantage from the maker's point ofview, by builders and decorators for the preparation of ordinary mortaror lime-wash. The mortar made from acetylene lime has been found equal instrength and other properties to mortar compounded from fresh slakedlime; while the distemper prepared by diluting the sludge has been usedmost successfully in all places where a lime-wash is required, _e. G. _, on fruit-trees, on cattle-pens, farm-buildings, factories, and the "offices" of a residence. Many of the village installationsabroad sell their sludge to builders for the above-mentioned purposes atsuch a price that their revenue accounts are materially benefited by theadditional income. The sludge is also found serviceable for softening thefeed-water of steam boilers by the common liming process; although it hasbeen stated that the material contains certain impurities--notably "fattymatter"--which becomes hydrolysed by the steam, yielding fatty acids thatact corrosively upon the boiler-plates. This assertion would appear torequire substantiation, but a patent has been taken out for a process ofdrying the sludge at a temperature of 150° to 200° C. In order to removethe harmful matter by the action of the steam evolved. So purified, it isclaimed, the lime becomes fit for treating any hard potable or boiler-feed water. It is very doubtful, however, whether the intrinsic value ofacetylene lime is such in comparison with the price of fresh lime that, with whatever object in view, it would bear the cost of any method ofartificial drying if obtained from the generators in a pasty state. When, on the other hand, the residue is naturally dry, or nearly so, itis exactly equal to an equivalent quantity of quick or slaked lime as adressing for soil. In this last connexion, however, it must be rememberedthat only certain soils are improved by an addition of lime in any shape, and therefore carbide residues must not be used blindly; but if analysisindicates that a particular plot of ground would derive benefit from anapplication of lime, acetylene lime is precisely as good as any otherdescription. Naturally a residue containing unspent carbide, orcontaminated with tarry matter, is essentially valueless (except asmentioned below); while it must not be forgotten that a solid residue ifit is exposed to air, or a pasty residue if not kept under water, willlose many of its useful properties, because it will be partiallyconverted into calcium carbonate or chalk. Nevertheless, in some respects, the residue from a good acetylenegenerator is a more valuable material, agriculturally speaking, than purelime. It contains a certain amount of sulphur, &c. , and it thereforesomewhat resembles the spent or gas lime of the coal-gas industry. Thissulphur, together, no doubt, with the traces of acetylene clinging to it, renders the residue a valuable material for killing the worms and verminwhich tend to infest heavily manured and under-cultivated soil. Acetylenelime has been found efficacious in exterminating the "finger-and-toe" ofcarrots, the "peach-curl" of peach-trees, and in preventing cabbages frombeing "clubbed. " It may be applied to the ground alone, or afteradmixture with some soil or stable manure. The residue may also beemployed, either alone or mixed with some agglomerate, in theconstruction of garden paths and the like. If the residues are suitably diluted with water and boiled with (say)twice their original weight of flowers of sulphur, the product consistsof a mixture of various compounds of calcium and sulphur, or calciumsulphides--which remain partly in solution and partly in the solid state. This material, used either as a liquid spray or as a moist dressing, hasbeen said to prove a useful garden insecticide and weed-killer. There are also numerous applications of the acetylene light, each of muchvalue, but involving no new principle which need be noticed. The light isso actinic, or rich in rays acting upon silver salts, that it ispeculiarly useful to the photographer, either for portraiture or for hisvarious positive printing operations. Acetylene is very convenient foroptical lantern work on the small scale, or where the oxy-hydrogen oroxy-coal-gas light cannot be used. Its intensity and small size make itsself-luminous flame preferable on optical grounds to the oil-lamp or thecoal-gas mantle; but the illuminating surface is nevertheless too largeto give the best results behind such condensers as have been carefullyworked to suit a source of light scarcely exceeding the dimensions of apoint. For lantern displays on very large screens, or for the projectionof a powerful beam of light to great distances in one direction (as innight signalling, &c. ), the acetylene blowpipe fed with pure oxygen, orwith air containing more than its normal proportion of oxygen, which isdiscussed in Chapter IX. , is specially valuable, more particularly if theordinary cylinder of lime is replaced by one of magnesia, zirconia, orother highly refractory oxide. CHAPTER XIII PORTABLE ACETYLENE LAMPS AND PLANT It will be apparent from what has been said in past chapters that theconstruction of a satisfactory generator for portable purposes must be aproblem of considerable complexity. A fixed acetylene installation tendsto work the more smoothly, and the gas evolved therefrom to burn the morepleasantly, the more technically perfect the various subsidiary items ofthe plant are; that is to say, the more thoroughly the acetylene ispurified, dried, and delivered at a strictly constant pressure to theburners and stoves. Moreover, the efficient behaviour of the generatoritself will depend more upon the mechanical excellence and solidity ofits construction than (with one or two exceptions) upon the precisesystem to which it belongs. And, lastly, the installation will, broadlyspeaking, work the better, the larger the holder is in proportion to thedemands ever made upon it; while that holder will perform the whole dutyof a gasholder more effectually if it belongs to the rising variety thanif it is a displacement holder. All these requirements of a goodacetylene apparatus have to be sacrificed to a greater or less extent inportable generators; and since the sacrifice becomes more serious as thegenerator is made smaller and lighter in weight, it may be said ingeneral terms that the smaller a portable (or, indeed, other) acetyleneapparatus is, the less complete or permanent satisfaction will it giveits user. Again, small portable apparatus are only needed to developintensities of light insignificant in comparison with those which mayeasily be won from acetylene on a larger scale; they are therefore fittedwith smaller burners, and those burners are not merely small in terms ofconsumption and illuminating power, but not infrequently are very badlyconstructed, and are relatively deficient in economy or duty. Thus anycomparisons which may be made on lines similar to those adopted inChapter I. , or between unit weights, volumes, or monetary equivalents ofcalcium carbide, paraffin, candles, and colza oil, become utterlyincorrect if the carbide is only decomposed in a small portable generatorfitted with an inefficient jet; first, because the latent illuminatingpower of the acetylene evolved is largely wasted; secondly, because anygas produced over and above that capable of instant combustion must beblown off from a vent-pipe; and thirdly, because the carbide itself tendsto be imperfectly decomposed, either through a defect in the constructionof the lamp, or through the brief and interrupted requirements of theconsumer. In several important respects portable acetylene apparatus may be dividedinto two classes from a practical point of view. There is the portabletable or stand lamp intended for use in an occupied room, and there isthe hand or supported lamp intended for the illumination of vehicles oropen-air spaces. Economy apart, no difficulty arises from imperfectcombustion or escape of unburnt gas from an outdoor lamp, but in a roomthe presence of unburnt acetylene must always be offensive even if it isnot dangerous; while the combustion products of the impurities--and in aportable generator acetylene cannot be chemically purified--are highlyobjectionable. It is simply a matter of good design to render any form ofportable apparatus safe against explosion (employment of proper carbidebeing assumed), for one or more vent-pipes can always be inserted in theproper places; but from an indoor lamp those vent-pipes cannot be made todischarge into a place of safety, while, as stated before, a generator inwhich the vent-pipes come into action with any frequency is but anextravagant piece of apparatus for the decomposition of so costly amaterial as calcium carbide. Looked at from one aspect the holder of afixed apparatus is merely an economical substitute for the wasteful vent-pipe, because it is a place in which acetylene can be held in reservewhenever the make exceeds the consumption in speed. It is perhapspossible to conceive of a large table acetylene lamp fitted with a water-sealed rising holder; but for vehicular purposes the displacement holderis practically the only one available, and in small apparatus it becomestoo minute in size to be of much service as a store for the gas producedby after-generation. Other forms of holder have been suggested byinventors, such as a collapsible bag of india-rubber or the like; butrubber is too porous, weak, and perishable a material to be altogethersuitable. If it is possible, by bringing carbide and water into mutualcontact in predetermined quantities, to produce gas at a uniform rate, and at one which corresponds with the requirements of the burner, in asmall apparatus--and experience has shown it to be possible withinmoderately satisfactory limits--it is manifest that the holder is onlyneeded to take up the gas of after-generation; and in Chapters II. AndIII. It was pointed out that after-generation only occurs when water isbrought into contact with an excess of carbide. If, then, the oppositesystem of construction is adopted, and carbide is fed into watermechanically, no after-generation can take place; and provided the makeof gas can be controlled in a small carbide-feed generator as accuratelyas is possible in a small water-to-carbide generator, the carbide-feedprinciple will exhibit even greater advantages in portable apparatus thanit does in plant of domestic size. Naturally almost every variety ofcarbide-feeding gear, especially when small, requires or prefersgranulated (or granulated and "treated") carbide; and granulated carbidemust inevitably be considerably more expensive per unit of light evolvedthan the large material, but probably in the application to which theaverage portable acetylene apparatus is likely to be put, strict economyis not of first consequence. In portable acetylene generators of thecarbide-feed type, the supply is generally governed by the movements of amushroom-headed or conical valve at the mouth of a conical carbidevessel; such movements occurring in sympathy with the alterations inlevel of the water in the decomposing chamber, which is essentially asmall displacement holder also, or being produced by the contraction of aflexible chamber through which the gas passes on its way to the burner. So far as it is safe to speak definitely on a matter of this kind, thecarbide-feed device appears to work satisfactorily in a stationary(_e. G. _, table) lamp; but it is highly questionable whether it couldbe applied to a vehicular apparatus exposed to any sensible amount ofvibration. The device is satisfactory on the table of an occupied room sofar, be it understood, as any small portable generators can be: it has noholder, but since no after-generation occurs, no holder is needed; stillthe combustion products contaminate the room with all the sulphur andphosphorus of the crude acetylene. For vehicular lamps, and probably for hand lanterns, the water-to-carbidesystem has practically no alternative (among actual generators), andsafety and convenience have to be gained at the expense of the carbide. In such apparatus the supply of water is usually controlled ultimately bypressure, though a hand-operated needle-valve is frequently put on thewater tube. The water actually reaches the carbide either by droppingfrom a jet, by passing along, upwards or downwards, a "wick" such as isused in oil-lamps, or by percolating through a mass of porous materiallike felt. The carbide is held in a chamber closed except at the gas exitto the burner and at the inlet from the water reservoir: so that if gasis produced more rapidly than the burner takes it, more water isprevented from entering, or the water already present is driven backwardsout of the decomposing chamber into some adjoining receptacle. It isimpossible to describe in detail all the lamps which have beenconstructed or proposed for vehicular use; and therefore the subject mustbe approached in general terms, discussing simply the principles involvedin the design of a safe portable generator. In all portable apparatus, and indeed in generators of larger dimensions, the decomposing chamber must be so constructed that it can never, even bywrong manipulation, be sealed hermetically against the atmosphere. Ifthere is a cock on the water inlet tube which is capable of beingcompletely shut, there must be no cock between the decomposing chamberand the burner. If there is a cock between the carbide vessel and theburner, the water inlet tube must only be closed by the water, beingwater-sealed, in fact, so that if pressure rises among the carbide thesurplus gas may blow the seal or bubble through the water in thereservoir. If the water-supply is mainly controlled by a needle-valve, itis useful to connect the burner with the carbide vessel through a shortlength of rubber tube; and if this plan is adopted, a cock can, ifdesired, be put close to the burner. The rubber should not be allowed toform a bend hanging down, or water vapour, &c. , may condense andextinguish the flame. In any case there should be a steady fall from theburner to the decomposing chamber, or to some separate catch-pit for theproducts of condensation. Much of the success attainable with smallgenerators will depend on the water used. If it is contaminated withundissolved matter, the dirt will eventually block the fine orifices, especially the needle-valve, or will choke the pores of the wick or thefelt pad. If the water contains an appreciable amount of "temporaryhardness, " and if it becomes heated much in the lamp, fur will bedeposited sooner or later, and will obviously give trouble. Where thewater reservoir is at the upper part of the lamp, and the liquid isexposed to the heat of the flame, fur will appear quickly if the water ishard. Considerable benefit would accrue to the user of a portable lamp bythe employment of rain water filtered, if necessary, through fabric orpaper. The danger of freezing in very severe weather may be prevented bythe use of calcium chloride, or preferably, perhaps, methylated spirit inthe water (_cf. _ Chapter III. , p. 92). The disfavour with whichcycle and motor acetylene lamps are frequently regarded by nocturnaltravellers, other than the users thereof, is due to thoughtless design inthe optical part of such lamps, and is no argument against the employmentof acetylene. By proper shading or deflection of the rays, the eyes ofhuman beings and horses can be sufficiently protected from the glare, andthe whole of the illumination concentrated more perfectly on the roadsurface and the lower part of approaching objects--a beam of light neverreaching a height of 5 feet above the ground is all that is needed tosatisfy all parties. As the size of the generator rises, conditions naturally become moresuited to the construction of a satisfactory apparatus; until generatorsintended to supply light to the whole of (say) a railway carriage, or thehead and cab lamps of a locomotive, or for the outside and insidelighting of an omnibus are essentially generators of domestic dimensionssomewhat altered in internal construction to withstand vibration andagitation. As a rule there is plenty of space at the side of a locomotiveto carry a generator fitted with a displacement holder of sufficientsize, which is made tall rather than wide, to prevent the water movingabout more than necessary. From the boiler, too, steam can be supplied toa coil to keep the liquid from freezing in severe weather. Such apparatusneed not be described at length, for they can be, and are, made on linesresembling those of domestic generators, though more compactly, andhaving always a governor to give a constant pressure. For carriagelighting any ordinary type of generator, preferably, perhaps, fitted witha displacement holder, can be erected either in each corridor carriage, or in a brake van at the end of the train. Purifiers may be added, ifdesired, to save the burners from corrosion; but the consumption ofunpurified gas will seldom be attended by hygienic disadvantages, becausethe burners will be contained in closed lamps, ventilating into theoutside air. The generator, also, may conveniently be so constructed thatit is fed with carbide from above the roof, and emptied of lime sludgefrom below the floor of the vehicle. It can hardly be said that the useof acetylene generated on board adds a sensible risk in case ofcollision. In the event of a subsequent fire, the gas in the generatorwould burn, but not explode; but in view of the greater illuminatingpower per unit volume of carbide than per equal volume of compressed oil-gas, a portable acetylene generator should be somewhat less objectionablethan broken cylinders of oil-gas if a fire should follow a railwayaccident of the usual kind. More particularly by the use of "cartridges"of carbide, a railway carriage generator can be constructed of sufficientcapacity to afford light for a long journey, or even a double journey, sothat attention would be only required (in the ordinary way) at one end ofthe line. Passing on from the generators used for the lighting of vehicles and forportable lamps for indoor lighting to the considerably larger portablegenerators now constructed for the supply of acetylene for weldingpurposes and for "flare" lamps, it will be evident that they may embodymost or all of the points which are essential to the proper working of afixed generator for the supply of a small establishment. The holder willgenerally be of the displacement type, but some of these larger portablegenerators are equipped with a rising holder. The generators are, naturally, automatic in action, but may be either of the water-to-carbideor carbide-to-water type--the latter being preferable in the larger sizesintended for use with the oxy-acetylene blow-pipe for welding, &c. , forwhich use a relatively large though intermittent supply of acetylene iscalled for. The apparatus is either carried by means of handles or polesattached to it, or is mounted on a wheelbarrow or truck for convenienceof transport to the place where it is to be used. The so called "flare"lamps, which are high power burners mounted, with or without a reflector, above a portable generator, are extremely useful for lighting open spaceswhere work has to be carried on temporarily after nightfall, and arerapidly displacing oil-flares of the Lucigen type for such purposes. The use of "cartridges" of calcium carbide has already been brieflyreferred to in Chapters II. And III. These cartridges are usually eitherreceptacles of thin sheet-metal, say tin plate, or packages of carbidewrapped up in grease proof paper or the like. If of metal, they may havea lid which is detached or perforated before they are put into thegenerator, or the generator (when automatic and of domestic size) may beso arranged that a cartridge is punctured in one or more places whenevermore gas is required. If wrapped in paper, the cartridges may be droppedinto water by an automatic generator at the proper times, the liquid thenloosening the gum and so gaining access to the interior; or one spot maybe covered by a drape of porous material (felt) only, through which thewater penetrates slowly. The substance inside the cartridge may beordinary, granulated, or "treated" carbide. Cartridges or "sticks" ofcarbide are also made without wrappings, either by moistening powderedcarbide with oil and compressing the whole into moulds, or by compressingdry carbide dust and immersing the sticks in oil or molten grease. Theformer process is said to cause the carbide to take up too much oil, sothat sticks made by the second method are reputed preferable. All thesecartridges have the advantage over common carbide of being more permanentin damp air, of being symmetrical in shape, of decomposing at a knownspeed, and of liberating acetylene in known quantity; but evidently theyare more expensive, owing to the cost of preparing them, &c. They may bemade more cheaply from the dust produced in the braking of carbide, butin that case the yield of gas will be relatively low. It is manifest that, where space is to spare, purifiers containing thematerials mentioned in Chapter V. Can be added to any portable acetyleneapparatus, provided also that the extra weight is not prohibitive. Cyclelamps and motor lamps must burn an unpurified gas unpurified fromphosphorus and sulphur; but it is always good and advisable to filter theacetylene from dust by a plug of cotton wool or the like, in order tokeep the burners as clear as may be. A burner with a screwed needle forcleaning is always advantageous. Formerly the burners used on portableacetylene lamps were usually of the single jet or rat-tail, or the unionjet or fish tail type, and exhibited in an intensified form, on accountof their small orifices, all the faults of these types of burners for theconsumption of acetylene (see Chapter VIII. ). Now, however, there arenumerous special burners adapted for use in acetylene cycle and motorlamps, &c. , and many of these are of the impinging jet type, and somehave steatite heads to prevent distortion by the heat. One such cycle-lamp burner, as sold in England by L. Wiener, of Fore Street, London, isshown in Fig. 21. A burner constructed like the "Kona" (Chapter VIII. ) ismade in small sizes (6, 8 and 10 litres per hour) for use in vehicularlamps, under the name of the "Konette, " by Falk, Stadelmann and Co. , Ltd. , of London, who also make a number of other small impinging jetburners. A single jet injector burner on the "Phôs" principle is made insmall sizes by the Phôs Co. , of London, specially for use in lamps onvehicles. [Illustration: FIG. 21. --CYCLE-LAMP BURNER NO. 96042A. ] Nevertheless, although satisfactory medium-sized vehicular lamps for thegeneration of acetylene have been constructed, the best way of usingacetylene for all such employments as these is to carry it ready made ina state of compression. For railway purposes, where an oil-gas plant isin existence, and where it is merely desired to obtain a somewhatbrighter light, the oil-gas may be enriched with 20 per cent. Ofacetylene, and the mixed gas pumped into the same cylinders to a pressureof 10 atmospheres, as mentioned in Chapter XI. ; the only alterationnecessary being the substitution of suitable small burners for the commonoil-gas jets. As far as the plant is concerned, all that is required is agood acetylene generator, purifier, and holder from which the acetylenecan be drawn or forced through a meter into a larger storage holder, themeter being connected by gearing with another meter on the pipe leadingfrom the oil-gas holder to the common holder, so that the necessaryproportions of the two gases shall be introduced into the common holdersimultaneously. From this final holder the enriched gas will be pumpedinto the cylinders or into a storage cylinder, by means of a thoroughlycooled pump, so that the heat set free by the compression may be safelydissipated. Whenever still better light is required in railway carriages, as also forthe illumination of large, constantly used vehicles, such as omnibuses, the acetone process (_cf. _ Chapter XI. ) exhibits notable advantages. The light so obtained is the light of neat acetylene, but the gas isacetylene having an upper limit of explosibility much lower than usualbecause of the vapour of acetone in it. In all other respects thepresence of the acetone will be unnoticeable, for it is a fairly pureorganic chemical body, which burns in the flame completely to carbondioxide and water, exactly as acetylene itself does. If the acetylene ismerely compressed into porous matter without acetone, the gas burnt isacetylene simply; but per unit of volume or weight the cylinders will notbe capable of developing so much light. In the United States, at least one railway system (The Great Northern)has a number of its passenger coaches lighted by means of plain acetylenecarried in a state of compression in cylinders without porous matter. Thegas is generated, filtered from dust, and stored in an ordinary risingholder at a factory alongside the line; being drawn from this holderthrough a drier to extract moisture, and through a safety device, by apump which, in three stages, compresses the acetylene into large storagereservoirs. The safety device consists of a heavy steel cylinder filledwith some porous substance which, like the similar material of theacetone cylinders, prevents any danger of the acetylene contained in thewater-sealed holder being implicated in an explosion starting backwardsfrom the compression, by extinguishing any spark which might be producedthere. The plant on the trains comprises a suitable number of cylinders, filled by contact with the large stores of gas to a pressure of 10atmospheres, pipes of fusible metal communicating with the lamps, andordinary half-foot acetylene burners. The cylinders are provided withfusible plugs, so that, in the event of a fire, they and the service-pipes would melt, allowing the gas to escape freely and burn in the air, instead of exploding or dissociating explosively within the cylindersshould the latter be heated by any burning woodwork or the like. It isstated that this plan of using acetylene enables a quantity of gas to becarried under each coach which is sufficient for a run of from 53 to 70hours' duration, or of over 3600 miles; that is to say, enables thetrain, in the conditions obtaining on the line in question, to make acomplete "round trip" without exhaustion of its store of artificiallight. The system has been in operation for some years, and appears tohave been so carefully managed that no accident has arisen; but it isclear that elements of danger are present which are eliminated when thecylinders are loaded with porous matter and acetone. The use of a similarsystem of compressed acetylene train lighting in South America has beenattended with a disastrous explosion, involving loss of life. It may safely be said that the acetone system, or less convenientlyperhaps the mere compression into porous matter, is the best to adopt forthe table-lamp which is to be used in occupied rooms Small cylinders ofsuch shapes as to form an elegant base for a table-lamp on more or lessconventional lines would be easy to make. They would be perfectly safe tohandle. If accidentally or wilfully upset, no harm would arise. Bydeliberate ill-treatment they might be burst, or the gas-pipe fracturedbelow the reducing valve, so that gas would escape under pressure for atime; but short of this they would be as devoid of extra clangor in timesof fire as the candle or the coal-gas burner. Moreover, they would onlycontaminate the air with carbon dioxide and water vapour, for the gas ispurified before compression; and modern investigations have conclusivelydemonstrated that the ill effects produced in the air of an imperfectlyventilated room by the extravagant consumption of coal-gas depend on theaccumulation of the combustion products of the sulphur in the gas ratherthan upon the carbon dioxide set free. One particular application of the portable acetylene apparatus is ofspecial interest. As calcium carbide evolves an inflammable gas when itmerely comes into contact with water, it becomes possible to throw intothe sea or river, by hand or by ejection from a mortar, a species of bombor portable generator which is capable of emitting a powerful beam oflight if only facilities are present for inflaming the acetylenegenerated; and it is quite easy so to arrange the interior of suchapparatus that they can be kept ready for instant use for long periods oftime without sensible deterioration, and that they can be recharged afteremployment. Three methods of firing the gas have been proposed. In onethe shock or contact with the water brings a small electric battery intoplay which produces a spark between two terminals projecting across theburner orifice; in the second, a cap at the head of the generatorcontains a small quantity of metallic potassium, which decomposes waterwith such energy that the hydrogen liberated catches fire; and in thethird a similar cap is filled with the necessary quantity of calciumphosphide, or the "carbophosphide of calcium" mentioned in Chapter XI. , which yields a flame by the immediate ignition of the liquid phosphineproduced on the attack of water. During the two or three seconds consumedin the production of the spark or pilot flame, the water is penetratingthe main charge of calcium carbide in the interior of the apparatus, until the whole is ready to give a bright light for a time limited onlyby the capacity of the generator. It is obvious that such apparatus maybe of much service at sea: they may be thrown overboard to illuminateseparate lifebuoys in case of accident, or be attached to the lifebuoysthey are required to illuminate, or be used as lifebuoys themselves iffitted with suitable chains or ropes; they may be shot ahead toilluminate a difficult channel, or to render an enemy visible in time ofwar. Several such apparatus have already been constructed and severelytested; they appear to give every satisfaction. They are, of course, soweighted that the burner floats vertically, while buoyancy is obtainedpartly by the gas evolved, and partly by a hollow portion of thestructure containing air. Cartridges of carbide and caps yielding a self-inflammable gas can be carried on board ship, by means of which thetorches or lifebuoys may be renewed after service in a few minutes' time. CHAPTER XIV VALUATION AND ANALYSIS OF CARBIDE The sale and purchase of calcium carbide in this country will, underexisting conditions, usually be conducted in conformity with the set ofregulations issued by the British Acetylene Association, of which a copy, revised to date, is given below: "REGULATIONS AS TO CARBIDE OF CALCIUM. " 1. The carbide shall be guaranteed by the seller to yield, when brokento standard size, _i. E. _, in lumps varying from 1 to 2-1/2 inches orlarger, not less than 4. 8 cubic feet per lb. , at a barometric pressure of30 inches and temperature of 60° Fahr. (15. 55° Centigrade). The actualgas yield shall be deemed to be the gas yield ascertained by the analyst, plus 5 per cent. "Carbide yielding less than 4. 8 cubic feet in the sizes given above shallbe paid for in proportion to the gas yield, _i. E. _, the price to bepaid shall bear the same relation to the contract price as the gas yieldbears to 4. 8 cubic feet per lb. "2. The customer shall have the right to refuse to take carbide yieldingin the sizes mentioned above less than 4. 2 cubic foot, per lb. , and itshall lie, in case of refusal and as from the date of the result, of theanalysis being made known to either party, at the risk and expense of theseller. "3. The carbide shall not contain higher figures of impurities than shallfrom time to time be fixed by the Association. "4. No guarantee shall be given for lots of less than 3 cwt. , or forcarbide crushed to smaller than the above sizes. "5. In case of dispute as to quality, either the buyer or the sellershall have the right to have one unopened drum per ton of carbide, orpart of a ton, sent for examination to one of the analysts appointed bythe Association, and the result of the examination shall be held to applyto the whole of the consignment to which the drum belonged. "6. A latitude of 5 per cent, shall be allowed for analysis; consequentlydifferences of 5 per cent. Above or below the yields mentioned in 1 and 2shall not be taken into consideration. "7. Should the yield of gas be less than 4. 8 cubic feet less 5 per cent. , the carriage of the carbide to and from the place of analysis and thecost of the analysis shall be paid for by the seller. Should the yield bemore than 4. 8 cubic feet less 5 per cent. , the carriage and costs ofanalysis shall be borne by the buyer, who, in addition, shall pay anincrease of price for the carbide proportionate to the gas yield above4. 8 cubic feet plus 5 per cent. "8. Carbide of 1 inch mesh and above shall not contain more than 5 percent. Of dust, such dust to be defined as carbide capable of passingthrough a mesh of one-sixteenth of an inch. "9. The seller shall not be responsible for deterioration of qualitycaused by railway carriage in the United Kingdom, unless he has soldincluding carriage to the destination indicated by the buyer. "10. Carbide destined for export shall, in case the buyer desires to haveit tested, be sampled at the port of shipment, and the guarantee shallcease after shipment. "11. The analyst shall take a sample of not less than 1 lb. Each from thetop, centre, and bottom of the drum. The carbide shall be carefullybroken up into small pieces, due care being taken to avoid exposure tothe air as much as possible, carefully screened and tested for gas yieldby decomposing it in water, previously thoroughly saturated by exposureto acetylene for a period of not less than 48 hours. "12. Carbide which, when properly decomposed, yields acetylene containingfrom all phosphorus compounds therein more than . 05 per cent. By volumeof phosphoretted hydrogen, may be refused by the buyer, and any carbidefound to contain more than this figure, with a latitude of . 01 per cent. For the analysis, shall lie at the risk and expense of the seller in themanner described in paragraph 2. "The rules mentioned in paragraph 7 shall apply as regards the carriageand costs of analysis; in other words, the buyer shall pay these costs ifthe figure is below 0. 05 per cent. Plus 0. 01 per cent. , and the seller ifthe figure is above 0. 05 per cent. Plus 0. 01 per cent. "The sampling shall take place in the manner prescribed in paragraphs 5and 11, and the analytical examination shall be effected in the mannerprescribed by the Association and obtainable upon application to theSecretary. " * * * * * The following is a translation of the corresponding rules issued by theGerman Acetylene Association (_Der Deutsche Acetylenverein_) inregard to business dealings in calcium carbide, as put into force onApril 1, 1909: "REGULATIONS OF THE GERMAN ACETYLENE ASSOCIATION FOR TRADE IN CARBIDE. "_Price_. "The price is to be fixed per 100 kilogrammes (= 220 lb. ) net weight ofcarbide in packages containing about 100 kilogrammes. "By packages containing about 100 kilogrammes are meant packagescontaining within 10 per cent. Above or below that weight. "The carbide shall be packed in gas- and water-tight vessels of sheet-iron of the strength indicated in the prescriptions of the carryingcompanies. "The prices for other descriptions of packing must be specially stated. "_Place of Delivery_. "For consignment for export, the last European shipping port shall betaken as the place of delivery. "_Quality_. "Commercial carbide shall be of such quality that in the usual lumps of15 to 80 mm. (about 3/5 to 3 inches) diameter it shall afford a yield ofat least 300 litres at 15° C. And 760 mm. Pressure of crude acetylene perkilogramme for each consignment (= 4. 81 cubic feet at 60° F. And 30inches per lb. ). A margin of 2 per cent. Shall be allowed for theanalysis. Carbide which yields less than 300 litres per kilogramme, butnot less than 270 litres (= 4. 33 cubic feet) of crude acetylene perkilogramme (with the above-stated 2 per cent. Margin for analysis) mustbe accepted by the buyer. The latter, however, is entitled to make aproportionate deduction from the price and also to deduct the increasedfreight charges to the destination or, if the latter is not settled atthe time when the transaction is completed, to the place of delivery. Carbide which yields less than 270 litres of crude acetylene perkilogramme need not be accepted. "Carbide must not contain more than 5 per cent. Of dust. By dust is to beunderstood all which passes through a screen of 1 mm. (0. 04 inch) square, clear size of holes. "Small carbide of from 4 to 15 mm. (= 1/6 to 3/5 inch) in size (andintermediate sizes) must yield on the average for each delivery at least270 litres at 15° C. And 760 mm. Pressure of crude acetylene perkilogramme (= 4. 33 cubic feet at 60° F. And 30 inches per lb. ) A marginof 2 per cent. Shall be allowed for the analysis. Small carbide of from 4to 15 mm. In size (and intermediate sizes) which yields less than 270litres but not less than 250 litres (= 4. 01 cubic feet per lb. ) of crudeacetylene per kilogramme (with the above-stated 2 per cent. Margin foranalysis) must be accepted by the buyer. The latter, however, is entitledto make a proportionate deduction from the price and also to deduct theincreased freight charges to the destination or, if the latter is notsettled at the time when the transaction is completed, to the place ofdelivery. Small carbide of from 4 to 15 mm. In size (and intermediatesizes) which yields less than 250 litres per kilogramme need not beaccepted. "Carbide shall only be considered fit for delivery if the proportion ofphosphoretted hydrogen in the crude acetylene does not amount to morethan 0. 04 volume per cent. A margin of 0. 01 volume per cent. Shall beallowed for the analysis for phosphoretted hydrogen. The whole of thephosphorus compounds contained in the gas are to be calculated asphosphoretted hydrogen. "_Period for Complaints. _ "An interval of four weeks from delivery shall be allowed for complaintsfor consignments of 5000 kilogrammes (= 5 tons) and over, and an intervalof two weeks for smaller consignments. A complaint shall refer only to aquantity of carbide remaining at the time of taking the sample. "_Determination of Quality. _ "1. In case the parties do not agree that the consignee is to send to theanalyst for the determination of the quality one unopened and undamageddrum when the consignment is less than 5000 kilogrammes, and two suchdrums when it is over 5000 kilogrammes, a sample for the purpose oftesting the quality is to be taken in the following manner: "A sample having a total weight of at least 2 kilogrammes (= 4. 4 lb. ) isto be taken. If the delivery to be tested does not comprise more than tendrums, the sample is to be taken from an unopened and undamaged drumselected at random. With deliveries of more than ten drums, the sample isto be drawn from not fewer than 10 per cent, of the lot, and from each ofthe unopened and undamaged drums drawn for the purpose not less than 1kilogramme (= 2. 2 lb. ) is to be taken. "The sampling is to be carried out by a trustworthy person appointed bythe two parties, or by one of the experts regularly recognised by theGerman Acetylene Association, thus: Each selected drum, before opening, is to be turned over twice (to got rid of any local accumulation of dust)and the requisite quantity is to be withdrawn with a shovel (not with thehand) from any part of it. These samples are immediately shot into one ormore vessels which are closed air- and water-tight. The lid is secured bya seal. No other description of package, such as cardboard cases, boxes, &c. , is permissible. "If there is disagreement as to the choice of a trustworthy person, eachof the two parties is to take the required quantity, as specified above. "2. The yield of gas and the proportion of phosphoretted hydrogencontained in it are to be determined by the methods prescribed by theGerman Acetylene Association. If there are different analyses giving non-concordant results, an analysis is to be made by the German AcetyleneAssociation, which shall be accepted as final and binding. "In cases, however, where the first analysis has been made in theLaboratory of the German Acetylene Association and arbitration isrequired, the decisive analysis shall be made by the Austrian AcetyleneAssociation. If one of the parties prevents the arbitrator's analysisbeing carried out, the analysis of the other party shall be absolutelybinding on him. "3. The whole of the cost of sampling and analysis is to be borne by theparty in the wrong. " * * * * * The corresponding regulations issued by the Austrian AcetyleneAssociation (_Der Oesterreichische Acetylenverein_) are almostidentical with those of the German Association. They contain, however, provisions that the price is to include packing, that the carbide mustnot be delivered in lumps larger than the fist, that the sample may besealed in a glass vessel with well-ground glass stopper, that the sampleis to be transmitted to the testing laboratory with particulars of thesize of the lots and the number of drums drawn for sampling, and that thewhole of it is to be gasified in lots of upwards of 1 kilogramme (= 2. 2lb. ) apiece. In Italy, it is enacted by the Board of Agriculture, Commerce andIndustry that by calcium carbide is to be understood for legal purposesalso any other carbide, or carbide-containing mixture, which evolvesacetylene by interaction with water. Also that only calcium carbide, which on admixture with water yields acetylene containing less than 1 percent. Of its volume of sulphuretted hydrogen and phosphoretted hydrogentaken together, may be put on the market. It is evident from the regulations quoted that the determination of thevolume of gas which a particular sample of calcium carbide is capable ofyielding, when a given weight of it is decomposed under the mostfavourable conditions, is a matter of the utmost practical importance toall interested in the trafficking of carbide, _i. E. _, to the makers, vendors, brokers, and purchasers of that material, as well as to allmakers and users of acetylene generating plant. The regulations of theBritish Association do not, however, give details of the method which theanalyst should pursue in determining the yield of acetylene; and whilethis may to a certain extent be advantageously left to the discretion ofthe competent analyst, it is desirable that the results of the experiencealready won by those who have had special opportunities for practisingthis branch of analytical work should be embodied in a set of directionsfor the analysis of carbide, which may be followed in all ordinaryanalyses of that material. By the adoption of such a set of directions asa provisional standard method, disputes as to the quantity of carbidewill be avoided, while it will still be open to the competent analyst tomodify the method of procedure to meet the requirements of special cases. It would certainly be unadvisable in the present state of our analyticalmethods to accept any hard and fast of rules for analysis for determiningthe quality of carbide, but it is nevertheless well to have the best ofexisting methods codified for the guidance of analysts. The substance ofthe directions issued by the German Association (_Der DeutscheAcetylenverein_) is reproduced below. "METHODS FOR THE DETERMINATION OF TILE YIELD OF GAS FROM CALCIUM CARBIDE. "The greatest precision is attained when the whole of the samplesubmitted to the analyst is gasified in a carbide-to-water apparatus, andthe gas evolved is measured in an accurately graduated gasholder. "The apparatus used for this analysis must not only admit of all theprecautionary rules of gas-analytical work being observed, but must alsofulfil certain other experimental conditions incidental to the nature ofthe analysis. "(_a_) The apparatus must be provided with an accurate thermometerto show the temperature of the confining water, and with a pressuregauge, which is in communication with the gasholder. "(_b_) The generator must either be provided with a gasholder whichis capable of receiving the quantity of gas evolved from the whole amountof carbide, or the apparatus must be so constructed that it becomespossible with a gasholder which in not too large (up to 200 litres = say7 cubic feet capacity) to gasify a larger amount of carbide. "(_c_) The generator must be constructed so that escape of theevolved gas from it to the outer air is completely avoided. "(_d_) The gasholder must be graduated in parts up to 1/4 per cent. Of its capacity, must travel easily, and be kept, as far as may be insuspension by counterweighting. "(_e_) The water used for decomposing the carbide and the confiningwater must be saturated, before use, with acetylene, and, further, thegenerator must, before the analysis proper, be put under the pressure ofthe confining (or sealing) liquid. " The following is a description of a typical form of apparatuscorresponding with the foregoing requirements: "The apparatus, shown in the annexed figure, consists of the generator A, the washer B, and the gasholder C. [Illustration: FIG. 22. --LARGE-SCALE APPARATUS FOR DETERMINING YIELD OFGAS FROM CARBIDE. ] "The generator A consists of a cylindrical vessel with sloping bottom, provided with a sludge outlet _a_, a gas exit-pipe _b_, and alid _b'_ fastened by screws. In the upper part ten boxes _c_are installed for the purpose of receiving the carbide. The bottoms ofthose boxes are flaps which rest through their wire projections on arevolvable disc _d_, which is mounted on a shaft _l_. Thisshaft passes through a stuffing-box to the outside of the generator andcan be rotated by moans of the chains _f_, the pulleys _g_ and_h_, and the winch _i_. Its rotation causes rotation of thedisc _d_. The disc _d_, on which the bottoms of the carbide-holders are supported, is provided with a slot _e_. On rotating thedisc, on which the supporting wires of the bottoms of the carbide-holdersrest, the slot is brought beneath these wires in succession; and thebottoms, being thus deprived of their support, drop down. It is possiblein this way to effect the discharge of the several carbide-holders bygradual turning of the winch _i_. "The washer B is provided with a thermometer _m_ passing through asound stuffing-box and extending into the water. "The gasholder C is provided with a scale and pointer, which indicate howmuch gas there is in it. It is connected with the pressure-gauge_n_, and is further provided with a control thermometer _o_. The gas exit-pipe _q_ can be shut off by a cock. There is a cockbetween the gasholder and the washer for isolating one from the other. "The dimensions of the apparatus are such that each carbide-holder cancontain readily about half a kilogramme (say l lb. ) of carbide. Thegasholder is of about 200 litres (say 7 cubic feet) capacity; and if thebell is 850 mm. (= 33-1/2 inches) high, and 550 mm. (= 21-1/2 inches) indiameter it will admit of the position being read off to within half alitre (say 0. 02 cubic foot). " The directions of the German Association for sampling a consignment ofcarbide packed in drums each containing 100 kilogrammes (say 2 cwt. ) havealready been given in the rules of that body. They differ somewhat fromthose issued by the British Association (_vide ante_), and haveevidently been compiled with a view to the systematic and rapid samplingof larger consignments than are commonly dealt with in this country. Drawing a portion of the whole sample from every tenth drum issubstantially the same as the British Association's regulations for casesof dispute, viz. , to have one unopened drum (_i. E. _, one or twocwt. ) per ton of carbide placed at the analyst's disposal for sampling. Actually the mode of drawing a portion of the whole sample from everytenth vessel, or lot, where a large number is concerned, is one whichwould naturally be adopted by analysts accustomed to sampling any otherproducts so packed or stored, and there in no reason why it should bedeparted from in the case of large consignments of carbide. For lots ofless than ten drums, unless there is reason to suspect want ofuniformity, it should usually suffice to draw the sample from one drumselected at random by the sampler. The analyst, or person who undertakesthe sampling, must, however, exercise discretion as to the scheme ofsampling to be followed, especially if want of uniformity of the severallots constituting the consignment in suspected. The size of the lumpsconstituting a sample will be referred to later. The British Association's regulations lead to a sample weighing about 3lb. Being obtained from each drum. If only one drum is sampled, thequantity taken from each position may be increased with advantage so asto give a sample weighing about 10 lb. , while if a large number of drumsis sampled, the several samples should be well mixed, and the ordinarymethod of quartering and re-mixing followed until a representativeportion weighing about 10 lb. Remains. A sample representative of the bulk of the consignment having beenobtained, and hermetically sealed, the procedure of testing by means ofthe apparatus already described may be given from the GermanAssociation's directions: "The first carbide receptacle is filled with 300 to 400 grammes (say 3/4lb. ) of any readily decomposable carbide, and is hung up in the apparatusin such a position with regard to the slot _e_ on the disc _d_that it will be the first receptacle to be discharged when the winch_i_ is turned. The tin or bottle containing the sample for analysisis then opened and weighed on a balance capable of weighing exactly to1/2 gramme (say 10 grains). The carbide in it is then distributedquickly, and as far as may be equally, into the nine remaining carbidereceptacles, which are then shut and hung up quickly in the generator. The lid _b'_ is then screwed on the generator to close it, and theempty tin or bottle, from which the sample of carbide has been removed, is weighed. "The contents of the first carbide receptacle are then discharged byturning the winch _i_. Their decomposition ensures on the one handthat the sealing water and the generating water are saturated withacetylene, and on the other hand that the dead space in the generator isbrought under the pressure of the seal, so that troublesome correctionswhich would otherwise be entailed are avoided. After the carbide iscompletely decomposed, but not before two hours at least have elapsed, the cock _p_ is shut, and the gasholder is run down to the zero markby opening the cock _q_. The cock _q_ is then shut, _p_ isopened, and the analytical examination proper is begun by discharging theseveral carbide receptacles by turning the winch _i_. After thefirst receptacle has been discharged, five or ten minutes are allowed toelapse for the main evolution of gas to occur, and the cock _p_ isthen shut. Weights are added to the gasholder until the manometer_n_ gives the zero reading; the position of the gasholder C is thenread off, and readings of the barometer and of the thermometer _o_are made. The gasholder is then emptied down to the zero mark by closingthe cock _p_ and opening _q_. When this is done _q_ isclosed and _p_ is opened, and the winch _i_ is turned until thecontents of the next carbide receptacle are discharged. This procedure isfollowed until the carbide from the last receptacle has been gasified;then, after waiting until all the carbide has been decomposed, but in anycase not less than two hours, the position of the gasholder is read, andreadings of the barometer and thermometer are again taken. The total ofthe values obtained represents the yield of gas from the sampleexamined. " The following example is quoted: Weight of the tin received, with its contained | carbide . . . . . . _| = 6325 grammes. Weight of the empty tin . . . . = 1485 " _______ Carbide used . . . = 4840 " = 10670 lb. The carbide in question was distributed among the nine receptacles andgasified. The readings were: ________________________________________________| | | | || No. | Litres. | Degrees C. | Millimetres. ||______|__________|______________|_______________|| | | | || 1 | 152. 5 | 13 | 762 || 2 | 136. 6 | " | " || 3 | 138. 5 | " | " || 4 | 161. 0 | " | " || 5 | 131. 0 | " | " || 6 | 182. 5 | 13. 5 | " || 7 | 146. 0 | " | " || 8 | 163. 0 | 14. 0 | " || 9 | 178. 5 | " | " ||______|__________|______________|_______________| After two hours, the total of the readings was 1395. 0 litres at 13. 5° C. And 762 mm. , which is equivalent to 1403. 7 litres (= 49. 57 cubic feet) at15° C. And 760 mm. (or 60° F. And 30 inches; there is no appreciablechange of volume of a gas when the conditions under which it is measuredare altered from 15° C. And 760 mm. To 60° F. And 30 inches, or _viceversâ_). The yield of gas from this sample is therefore 1403. 7/4. 840 = 290 litresat 15° C. And 760 mm. Per kilogramme, or 49. 57/10. 67 = 4. 65 cubic feet at60° F. And 30 inches per pound of carbide. The apparatus described can, of course, be used when smaller samples of carbide only are available forgasification, but the results will be less trustworthy if much smallerquantities than those named are taken for the test. Other forms of carbide-to-water apparatus may of course be devised, whichwill equally well fulfil the requisite conditions for the test, viz. , complete decomposition of the whole of the carbide without excessive riseof temperature, and no loss of gas by solution or otherwise. An experimental wet gas-motor, of which the water-line has beenaccurately set (by means of the Gas Referees' 1/12 cubic foot measure, ora similar meter-proving apparatus), may be used in place of the graduatedgasholder for measuring the volume of the gas evolved, provided the rateof flow of the gas does not exceed 1/6 cubic foot, or say 5 litres perminute. If the generation of gas is irregular, as when an apparatus ofthe type described above is used, it is advisable to insert a smallgasholder or large bell-governor between the washer and the meter. Themeter must be provided with a thermometer, according to the indicationsof which the observed volumes must be corrected to the correspondingvolume at normal temperature. If apparatus such as that described above is not available, fairlytrustworthy results for practical purposes may be obtained by thedecomposition of smaller samples in the manner described below, providedthese samples are representative of the average composition of the largersample or bulk, and a number of tests are made in succession and theresults of individual tests do not differ by more than 10 litres of gasper kilogramme (or 0. 16 cubic foot per pound) of carbide. It is necessary at the outset to reduce large lumps of carbide in thesample to small pieces, and this must be done with as little exposure aspossible to the (moist) air. Failing a good pulverising machine of thecoffee-mill or similar type, which does its work quickly, the lumps mustbe broken as rapidly as possible in a dry iron mortar, which may withadvantage be fitted with a leather or india-rubber cover, through a holein which the pestle passes. As little actual dust as possible should bemade during pulverisation. The decomposition of the carbide is besteffected by dropping it into water and measuring the volume of gasevolved with the precautions usually practised in gas analysis. Anexample of one of the methods of procedure described by the GermanAssociation will show how this test can be satisfactorily carried out: "A Woulff's bottle, _a_ in the annexed figure, of blown glass andholding about 1/4 litre is used as the generating vessel. One neck, about15 mm. In internal diameter, is connected by flexible tubing with aglobular vessel _b_, having two tubulures, and this vessel isfurther connected with a conical flask _c_, holding about 100 c. C. The other neck is provided with tubing _d_, serving to convey thegas to the inlet-tube, with tap _e_, of the 20-litre measuringvessel _f_, which is filled with water saturated with acetylene, andcommunicates through its lower tubulure with a similar large vessel_g_. The generating vessel _a_ is charged with about 150 c. C. Of water saturated with acetylene. The vessel _f_ is filled up tothe zero mark by raising the vessel _g_; the tap _e_ is thenshut, and connexion is made with the tube _d_. Fifty grammes (or say2 oz. ) of the pulverised carbide are then weighed into the flask _c_and this is connected by the flexible tubing with the vessel _b_. The carbide is then decomposed by bringing it in small portions at a timeinto the bulb _b_ by raising the flask _c_, and letting it dropfrom _b_ into the generating vessel _a_, after having openedthe cock _e_ and slightly raised the vessel _f_. After the lastof the carbide has been introduced two hours are allowed to elapse, andthe volume of gas in _f_ is then read while the water stands at thesame level in _f_ and _g_, the temperature and pressure beingnoted simultaneously. " A second, but less commendable method of decomposing the carbide is byputting it in a dry two-necked bottle, one neck of which is connectedwith _e_, and dropping water very slowly from a tap-funnel, whichenters the other neck, on to the carbide. The generating bottle should bestood in water, in order to keep it cool, and the water should be droppedin at the rate of about 50 c. C. In one hour. It will take about threehours completely to gasify the 50 grammes of carbide under theseconditions. The gas is measured as before. [Illustration: FIG. 23. --SMALL-SCALE APPARATUS FOR DETERMINING YIELD OFGAS FROM CARBIDE. ] Cedercreutz has carried out trials to show the difference between theyields found from large and small carbide taken from the same drum. Onesample consisted of the dust and smalls up to about 3/5 inch in size, while the other contained large carbide as well as the small. The lattersample was broken to the same size as the former for the analysis. Testswere made both with a large testing apparatus, such as that shown in Fig. 22, and with a small laboratory apparatus, such as that shown in Fig. 23. The dust was screened off for the tests made in the large apparatus. Twosets of testings were made on different lots of carbide, distinguishedbelow as "A" and "B, " and about 80 grammes wore taken for eachdetermination in the laboratory apparatus, and 500 grammes in the largeapparatus. The results are stated in litres (at normal temperature andpressure) per kilogramme of carbide. ___________________________________________________________________| | | || | "A" | "B" ||_____________________________________________________|______|______|| | | || Lot |Litres|Litres|| Small carbide, unscreened, in laboratory \ (1) | 276 | 267 || apparatus . . . . . / (2) | 273 | 270 || Average sample of carbide, unscreened, in \ (1) | 318 | 321 || laboratory apparatus . . . / (2) | 320 | 321 || Small carbide, dust freed, in large apparatus (1) | 288 | 274 || Average sample of carbide, dust freed, in \ (2) | 320 | 322 || large apparatus . . . . / | | ||_____________________________________________________|______|______| As the result of the foregoing researches Cedercreutz has recommendedthat in order to sample the contents of a drum, they should be tippedout, and about a kilogramme (say 2 to 3 lb. ) taken at once from them witha shovel, put on an iron base and broken with a hammer to pieces of about2/5 inch, mixed, and the 500 grammes required for the analysis in theform of testing plant which he employs taken from this sample. Obviouslya larger sample can be taken in the same manner. On the other hand theBritish and German Associations' directions for sampling the contents ofa drum, which have already been quoted, differ somewhat from the above, and must generally be followed in cases of dispute. Cedercreutz's figures, given in the above table, show that it would bevery unfair to determine the gas-making capacity of a given parcel ofcarbide in which the lumps happened to vary considerably in size byanalysing only the smalls, results so obtained being possibly 15 percent. Too low. This is due to two causes: first, however carefully it bestored, carbide deteriorates somewhat by the attack of atmosphericmoisture; and since the superficies of a lump (where the attack occurs)is larger in proportion to the weight of the lump as the lump itself issmaller, small lumps deteriorate more on keeping than large ones. Thesecond reason, however, is more important. Not being a pure chemicalsubstance, the commercial material calcium carbide varies in hardness;and when it is merely crushed (not reduced altogether to powder) thesofter portions tend to fall into smaller fragments than the hardportions. As the hard portions are different in composition from the softportions, if a parcel is sampled by taking only the smalls, practicallythat sample contains an excess of the softer part of the originalmaterial, and as such is not representative. Originally the GermanAcetylene Association did not lay down any rules as to the crushing ofsamples by the analyst, but subsequently they specified that the materialshould be tested in the size (or sizes) in which it was received. TheBritish Association, on the contrary, requires the sample to be broken insmall pieces. If the original sample is taken in such fashion as toinclude large and small lumps as accurately as possible in the sameproportion as that in which they occur in the main parcel, no error willbe introduced if that sample is crushed to a uniform size, and thensubdivided again; but a small deficiency in gas yield will be produced, which will be in the consumer's favour. It is not altogether easy to seethe advantage of the British idea of crushing the sample over the Germanplan of leaving it alone; because the analytical generator will easilytake, or its parts could be modified to take, the largest lumps met with. If the sample is in very large masses, and is decomposed too quickly, polymerisation of gas may be set up; but on the other hand, the crushingand re-sampling will cause wastage, especially in damp weather, or whenthe sampling has to be done in inconvenient places. The BritishAssociation requires the test to be made on carbide parcels rangingbetween 1 and 2-1/2 inches or larger, because that is the "standard" sizefor this country, and because no guarantee is to be had or expected fromthe makers as to the gas-producing capacity of smaller material. Manifestly, if a consumer employs such a form of generator that he isobliged to use carbide below "standard" size, analyses may be made on hisbehalf in the ordinary way; but he will have no redress if the yield ofacetylene is less than the normal. This may appear a defect or grievance;but since in many ways the use of small carbide (except in portablelamps) is not advantageous--either technically or pecuniarily--the rulesimply amounts to an additional judicious incentive to the adoption ofapparatus capable of decomposing standard-sized lumps. The German andAustrian Associations' regulations, however, provide a standard for thequality of granulated carbide. It has been pointed out that the German Association's direction that thewater used in the testing should be saturated with acetylene by apreliminary decomposition of 1/2 kilogramme of carbide is not whollyadequate, and it has been suggested that the preliminary decompositionshould be carried out twice with charges of carbide, each weighing notless than 1 per cent. Of the weight of water used. A further possiblesource of error lies in the fact that the generating water is saturatedat the prevailing temperature of the room, and liberates some of itsdissolved acetylene when the temperature rises during the subsequentgeneration of gas. This error, of course, makes the yield from the sampleappear higher than it actually is. Its effects may be compensated byallowing time for the water in the generator or gasholder to cool to itsoriginal temperature before the final reading is made. With regard to the measurement of the temperature of the evolved gas inthe bell gasholder, it is usual to assume that the reading of athermometer which passes through the crown of the gasholder suffices. Ifthe thermometer has a very long stem, so that the bulb is at about themid-height of the filled bell, this plan is satisfactory, but if anordinary thermometer is used, it is better to take, as the averagetemperature of the gas in the holder, the mean of the readings of thethermometer in the crown, and of one dipping into the water of the holderseal. The following table gives factors for correcting volumes of gas observedat any temperature and pressure falling within its range to the normaltemperature (60° F. ) and normal barometric height (30 inches). The normalvolume thus found is, as already stated, not appreciably different fromthe volume at 15° C. And 760 mm. (the normal conditions adopted byContinental gas chemists). To use the table, find the observedtemperature and the observed reading of the barometer in the border ofthe table, and in the space where these vertical and horizontal columnsmeet will be found a number by which the observed volume of gas is to bemultiplied in order to find the corresponding volume under normalconditions. For intermediate temperatures, &c. , the factors may bereadily inferred from the table by inspection. This table must only beapplied when the gas is saturated with aqueous vapour, as is ordinarilythe case, and therefore a drier must not be applied to the gas beforemeasurement. Hammerschmidt has calculated a similar table for the correction ofvolumes of gas measured at temperatures ranging from 0° to 30° C. , andunder pressures from 660 to 780 mm. , to 15° C. And 760 mm. It is based onthe coefficient of expansion of acetylene given in Chapter VI. , but, aswas there pointed out, this coefficient differs by so little from that ofthe permanent gases for which the annexed table was compiled, that noappreciable error results from the use of the latter for acetylene also. A table similar to the annexed but of more extended range is given in the"Notification of the Gas Referees, " and in the text-book on "GasManufacture" by one of the authors. The determination of the amounts of other gases in crude or purifiedacetylene is for the most part carried out by the methods in vogue forthe analysis of coal-gas and other illuminating gases, or by slightmodifications of them. For an account of these methods the textbook on"Gas Manufacture" by one of the authors may be consulted. For instance, two of the three principal impurities in acetylene, viz. , ammonia andsulphuretted hydrogen, may be detected and estimated in that gas in thesame manner as in coal gas. The detection and estimation of phosphineare, however, analytical operations peculiar to acetylene among commonilluminating gases, and they must therefore be referred to. _Table to facilitate the Correction of the Volume of Gas at differentTemperatures and under different Atmospheric Pressures. _ _____________________________________________________| | || | THERMOMETER. || BAR. |_______________________________________________|| | | | | | | || | 46° | 48° | 50° | 52° | 54° | 56° ||_____|_______|_______|_______|_______|_______|_______|| | | | | | | ||28. 4 | 0. 979 | 0. 974 | 0. 970 | 0. 965 | 0. 960 | 0. 955 ||28. 5 | 0. 983 | 0. 978 | 0. 973 | 0. 968 | 0. 964 | 0. 959 ||28. 6 | 0. 986 | 0. 981 | 0. 977 | 0. 972 | 0. 967 | 0. 962 ||28. 7 | 0. 990 | 0. 985 | 0. 980 | 0. 975 | 0. 970 | 0. 966 ||28. 8 | 0. 993 | 0. 988 | 0. 984 | 0. 979 | 0. 974 | 0. 969 ||28. 9 | 0. 997 | 0. 992 | 0. 987 | 0. 982 | 0. 977 | 0. 973 ||29. 0 | 1. 000 | 0. 995 | 0. 990 | 0. 986 | 0. 981 | 0. 976 ||29. 1 | 1. 004 | 0. 999 | 0. 994 | 0. 989 | 0. 984 | 0. 979 ||29. 2 | 1. 007 | 1. 002 | 0. 997 | 0. 992 | 0. 988 | 0. 982 ||29. 3 | 1. 011 | 1. 005 | 1. 001 | 0. 996 | 0. 991 | 0. 986 ||29. 4 | 1. 014 | 1. 009 | 1. 004 | 0. 999 | 0. 995 | 0. 990 ||29. 5 | 1. 018 | 1. 013 | 1. 008 | 1. 003 | 0. 998 | 0. 993 ||29. 6 | 1. 021 | 1. 016 | 1. 011 | 1. 006 | 1. 001 | 0. 996 ||29. 7 | 1. 025 | 1. 019 | 1. 015 | 1. 010 | 1. 005 | 1. 000 ||29. 8 | 1. 028 | 1. 023 | 1. 018 | 1. 013 | 1. 008 | 1. 003 ||29. 9 | 1. 031 | 1. 026 | 1. 022 | 1. 017 | 1. 012 | 1. 007 ||30. 0 | 1. 035 | 1. 030 | 1. 025 | 1. 020 | 1. 015 | 1. 010 ||30. 1 | 1. 038 | 1. 033 | 1. 029 | 1. 024 | 1. 019 | 1. 014 ||30. 2 | 1. 042 | 1. 037 | 1. 032 | 1. 027 | 1. 022 | 1. 017 ||30. 3 | 1. 045 | 1. 040 | 1. 036 | 1. 030 | 1. 025 | 1. 020 ||30. 4 | 1. 049 | 1. 044 | 1. 039 | 1. 034 | 1. 029 | 1. 024 ||30. 5 | 1. 052 | 1. 047 | 1. 042 | 1. 037 | 1. 032 | 1. 027 ||_____|_______|_______|_______|_______|_______|_______| _____________________________________________________| | || | THERMOMETER. || BAR. |_______________________________________________|| | | | | | | || | 58° | 60° | 62° | 64° | 66° | 68° ||_____|_______|_______|_______|_______|_______|_______|| | | | | | | ||28. 5 | 0. 954 | 0. 949 | 0. 944 | 0. 939 | 0. 934 | 0. 929 ||28. 6 | 0. 958 | 0. 953 | 0. 947 | 0. 943 | 0. 938 | 0. 932 ||28. 7 | 0. 961 | 0. 956 | 0. 951 | 0. 946 | 0. 941 | 0. 936 ||28. 8 | 0. 964 | 0. 959 | 0. 954 | 0. 949 | 0. 944 | 0. 939 ||28. 9 | 0. 968 | 0. 963 | 0. 958 | 0. 953 | 0. 948 | 0. 942 ||29. 0 | 0. 971 | 0. 966 | 0. 961 | 0. 956 | 0. 951 | 0. 946 ||29. 1 | 0. 975 | 0. 969 | 0. 964 | 0. 959 | 0. 954 | 0. 949 ||29. 2 | 0. 978 | 0. 973 | 0. 968 | 0. 963 | 0. 958 | 0. 952 ||29. 3 | 0. 981 | 0. 976 | 0. 971 | 0. 966 | 0. 961 | 0. 956 ||29. 4 | 0. 985 | 0. 980 | 0. 975 | 0. 969 | 0. 964 | 0. 959 ||29. 5 | 0. 988 | 0. 983 | 0. 978 | 0. 973 | 0. 968 | 0. 962 ||29. 6 | 0. 992 | 0. 986 | 0. 981 | 0. 976 | 0. 971 | 0. 966 ||29. 7 | 0. 995 | 0. 990 | 0. 985 | 0. 980 | 0. 974 | 0. 969 ||29. 8 | 0. 998 | 0. 993 | 0. 988 | 0. 983 | 0. 978 | 0. 972 ||29. 9 | 1. 002 | 0. 997 | 0. 991 | 0. 986 | 0. 981 | 0. 976 ||30. 0 | 1. 005 | 1. 000 | 0. 995 | 0. 990 | 0. 985 | 0. 979 ||30. 1 | 1. 009 | 1. 003 | 0. 998 | 0. 993 | 0. 988 | 0. 983 ||30. 2 | 1. 012 | 1. 007 | 1. 002 | 0. 996 | 0. 991 | 0. 986 ||30. 3 | 1. 015 | 1. 010 | 1. 005 | 1. 000 | 0. 995 | 0. 989 ||30. 4 | 1. 019 | 1. 014 | 1. 008 | 1. 003 | 0. 998 | 0. 993 ||30. 5 | 1. 022 | 1. 017 | 1. 012 | 1. 006 | 1. 001 | 0. 996 ||_____|_______|_______|_______|_______|_______|_______| _____________________________________________| | || | THERMOMETER. || BAR. |_______________________________________|| | | | | | || | 70° | 72° | 74° | 76° | 78° ||_____|_______|_______|_______|_______|_______|| | | | | | ||28. 4 | 0. 921 | 0. 915 | 0. 910 | 0. 905 | 0. 900 ||28. 5 | 0. 924 | 0. 919 | 0. 914 | 0. 908 | 0. 903 ||28. 6 | 0. 927 | 0. 922 | 0. 917 | 0. 912 | 0. 906 ||28. 7 | 0. 931 | 0. 925 | 0. 920 | 0. 915 | 0. 909 ||28. 8 | 0. 934 | 0. 929 | 0. 924 | 0. 918 | 0. 913 ||28. 9 | 0. 937 | 0. 932 | 0. 927 | 0. 921 | 0. 916 ||29. 0 | 0. 941 | 0. 935 | 0. 930 | 0. 925 | 0. 919 ||29. 1 | 0. 944 | 0. 939 | 0. 933 | 0. 928 | 0. 923 ||29. 2 | 0. 947 | 0. 942 | 0. 937 | 0. 931 | 0. 926 ||29. 3 | 0. 950 | 0. 945 | 0. 940 | 0. 935 | 0. 929 ||29. 4 | 0. 954 | 0. 949 | 0. 943 | 0. 938 | 0. 932 ||29. 5 | 0. 957 | 0. 952 | 0. 947 | 0. 941 | 0. 936 ||29. 6 | 0. 960 | 0. 955 | 0. 950 | 0. 944 | 0. 939 ||29. 7 | 0. 964 | 0. 959 | 0. 953 | 0. 948 | 0. 942 ||29. 8 | 0. 967 | 0. 962 | 0. 957 | 0. 951 | 0. 946 ||29. 9 | 0. 970 | 0. 965 | 0. 960 | 0. 954 | 0. 949 ||30. 0 | 0. 974 | 0. 968 | 0. 963 | 0. 958 | 0. 952 ||30. 1 | 0. 977 | 0. 972 | 0. 966 | 0. 961 | 0. 955 ||30. 2 | 0. 980 | 0. 975 | 0. 970 | 0. 964 | 0. 959 ||30. 3 | 0. 984 | 0. 978 | 0. 973 | 0. 968 | 0. 962 ||30. 4 | 0. 987 | 0. 982 | 0. 976 | 0. 971 | 0. 965 ||30. 5 | 0. 990 | 0. 985 | 0. 980 | 0. 974 | 0. 969 ||_____|_______|_______|_______|_______|_______| For the detection of phosphine, Bergé's solution may be used. It is a"solution of 8 to 10 parts of corrosive sublimate in 80 parts of waterand 20 parts of 30 per cent. Hydrochloric acid. " It becomes cloudy whengas containing phosphine is passed into it. It is, however, applied mostconveniently in the form of Keppeler's test-papers, which have beendescribed in Chapter V. Test-papers for phosphine, the active body inwhich has not yet been divulged, have recently been produced for sale byF. B. Gatehouse. The estimation of phosphine will usually require to be carried out either(1) on gas directly evolved from carbide in order to ascertain if thecarbide in question yields an excessive proportion of phosphine, or (2)upon acetylene which is presumably purified, drawn either from the outletof the purifier or from the service-pipes, with the object ofascertaining whether an adequate purification in regard to phosphine hasbeen accomplished. In either case, the method of estimation is the same, but in the first, acetylene should be specially generated from a smallrepresentative sample of the carbide and led directly into the apparatusfor the absorption of the phosphine. If the acetylene passes into theordinary gasholder, the amount of phosphine in gas drawn off from theholder will vary from time to time according to the temperature and thedegree of saturation of the water in the holder-tank with phosphine, aswell as according to the amount of phosphine in the gas generated at thetime. A method frequently employed for the determination of phosphine inacetylene is one devised by Lunge and Cedercreutz. If the acetylene is tobe evolved from a sample of carbide in order to ascertain how muchphosphine the latter yields to the gas, about 50 to 70 grammes of thecarbide, of the size of peas, are brought into a half-litre flask, and atap-funnel, with the mouth of its stem contracted, is passed through arubber plug fitting the mouth of the flask. A glass tube passing throughthe plug serves to convey the gas evolved to an absorption apparatus, which is charged with about 75 c. C. Of a 2 to 3 per cent. Solution ofsodium hypochlorite. The absorption apparatus may be a ten-bulbedabsorption tube or any convenient form of absorption bulbs which subjectthe gas to intimate contact with the solution. If acetylene from aservice-pipe is to be tested, it is led direct from the nozzle of a gas-tap to the absorption tube, the outlet of which is connected with anaspirator or the inlet of an experimental meter, by which the volume ofgas passed through the solution is measured. But if the generating flaskis employed, water is allowed to drop from the tap-funnel on to thecarbide in the flask at the rate of 6 to 7 drops a minute (the tap-funnelbeing filled up from time to time), and all the carbide will thus bedecomposed in 3 to 4 hours. The flask is then filled to the neck withwater, and disconnected from the absorption apparatus, through which alittle air is then drawn. The absorbing liquid is then poured, and washedout, into a beaker; hydrochloric acid is added to it, and it is boiled inorder to expel the liberated chlorine. It is then usual to precipitatethe sulphuric acid by adding solution of barium chloride to the boilingliquid, allowing it to cool and settle, and then filtering. The weight ofbarium sulphate obtained by ignition of the filter and its contents, multiplied by 0. 137, gives the amount of sulphur present in the acetylenein the form of sulphuretted hydrogen. The filtrate and washings from thisprecipitate are rendered slightly ammoniacal, and a small excess of"magnesia mixture" is added; the whole is stirred, left to stand for 12hours, filtered, the precipitate washed with water rendered slightlyammoniacal, dried, ignited, and weighed. The weight so found multipliedby 0. 278 gives the weight of phosphorus in the form of phosphine in thevolume of gas passed through the absorbent liquid. Objection may rightly be raised to the Lunge and Cedercreutz method ofestimating the phosphine in crude acetylene on the ground that explosionsare apt to occur when the gas is being passed into the hypochloritesolution. Also it must be borne in mind that it aims at estimating onlythe phosphorus which is contained in the gas in the form of phosphine, and that there may also be present in the gas organic compounds ofphosphorus which are not decomposed by the hypochlorite. But when theacetylene is evolved from the carbide in proper conditions for theavoidance of appreciable heating it appears fairly well established thatphosphorus compounds other than phosphine exist in the gas only inpractically negligible amount, unless the carbide decomposed is of anabnormal character. Various methods of burning the acetylene andestimating the phosphorus in the products of combustion have, howeverbeen proposed for the purpose of determining the total amount ofphosphorus in acetylene. Some of them are applicable to the simultaneousdetermination of the total sulphur in the acetylene, and in this respectbecome akin to the Gas Referees' method for the determination of thesulphur compounds in coal-gas. Eitner and Keppeler have proposed to burn the acetylene on which theestimation is to be made in a current of neat oxygen. But this procedureis rather inconvenient, and by no means essential. Lidholm liberatedacetylene slowly from 10 grammes of carbide by immersing the carbide inabsolute alcohol and gradually adding water, while the gas mixed with astream of hydrogen leading to a burner within a flask. The flow ofhydrogen was reduced or cut off entirely while the acetylene was comingoff freely, but hydrogen was kept burning for ten minutes after the flamehad ceased to be luminous in order to ensure the burning of the lasttraces of acetylene. The products of combustion were aspirated through acondenser and a washing bottle, which at the close were rinsed out withwarm solution of ammonia. The whole of the liquid so obtained wasconcentrated by evaporation, filtered in order to remove particles ofsoot or other extraneous matter, and acidified with nitric acid. Thephosphoric acid was then precipitated by addition of ammonium molybdate. J. W. Gatehouse burns the acetylene in an ordinary acetylene burner offrom 10 to 30 litres per hour capacity, and passes the products ofcombustion through a spiral condensing tube through which water isdropped at the rate of about 75 c. C. Per hour, and collected in a beaker. The burner is placed in a glass bell-shaped combustion chamber connectedat the top through a right-angled tube with the condenser, and closedbelow by a metal base through which the burner is passed. The amount ofgas burnt for one determination is from 50 to 100 litres. When the gas isextinguished, the volume consumed is noted, and after cooling, thecombustion chamber and condenser are washed out with the liquid collectedin the beaker and finally with distilled water, and the whole, amountingto about 400 c. C. , is neutralised with solution of caustic alkali (ifdecinormal alkali is used, the total acidity of the liquid thusascertained may be taken as a convenient expression of the aggregateamount of the sulphuric, phosphoric and silicic acids resulting from thecombustion of the total corresponding impurities in the gas), acidifiedwith hydrochloric acid, and evaporated to dryness with the additiontowards the end of a few drops of nitric acid. The residue is taken up indilute hydrochloric acid; and silica filtered off and estimated ifdesired. To the filtrate, ammonia and magnesia mixture are added, and themagnesium pyrophosphate separated and weighed with the usual precautions. Sulphuric acid may, if desired, be estimated in the filtrate, but in thatcase care must be taken that the magnesia mixture used was free from it. Mauricheau-Beaupré has elaborated a volumetric method for the estimationof the phosphine in crude acetylene depending on its decomposition by aknown volume of excess of centinormal solution of iodine, addition ofexcess of standard solution of sodium thiosulphate, and titrating backwith decinormal solution of iodine with a few drops of starch solution asan indicator. One c. C. Of centinormal solution of iodine is equivalent to0. 0035 c. C. Of phosphine. This method of estimation is quickly carriedout and is sufficiently accurate for most technical purposes. In carrying out these analytical operations many precautions have to betaken with which the competent analyst is familiar, and they cannot begiven in detail in this work, which is primarily intended for ordinaryusers of acetylene, and not for the guidance of analysts. It may, however, be pointed out that many useful tests in connexion withacetylene supply can be conducted by a trained analyst, which are not ofa character to be serviceable to the untrained experimentalist. Amongsuch may be named the detection of traces of phosphine in acetylene whichhas passed through a purifier with a view to ascertaining if thepurifying material is exhausted, and the estimation of the amount of airor other diluents in stored acetylene or acetylene generated in aparticular manner. Advice on these points should be sought from competentanalysts, who will already have the requisite information for thecarrying out of any such tests, or know where it is to be found. Theanalyses in question are not such as can be undertaken by untrainedpersons. The text-book on "Gas Manufacture" by one of the authors givesmuch information on the operations of gas analysis, and may be consulted, along with Hempel's "Gas Analysis" and Winkler and Lunge's "Technical GasAnalysis. " APPENDIX DESCRIPTIONS OF A NUMBER OF ACETYLENE GENERATORS AS MADE IN THE YEAR 1909 (_The purpose of this Appendix is explained in Chapter IV. , page 111, and a special index to it follows the general index at the end of thisbook. _) AMERICA--CANADA. _Maker_: SICHE GAS CO. , LTD. , GEORGETOWN, ONTARIO. _Type_: Automatic; carbide-to-water. The "Siche" generator made by this firm consists of a water-tank_A_, having at the bottom a sludge agitator _N_ and draw-offfaucet _O_, and rigidly secured within it a bell-shaped generatingchamber _B_, above which rises a barrel containing the feed chamber_C_, surmounted by the carbide chamber _D_. The carbide used isgranulated or of uniform size. In the generating chamber _B_ is anannular float _E_, nearly filling the area of the chamber, andconnected, by two rods passing, with some lateral play, through aperturesin the conical bottom of the feed chamber _C_, to the T-shapedtubular valve _F_. Consequently when the float shifts vertically orlaterally the rods and valves at once move with it. The angle of the coneof the feed chamber and the curve of the tubular valve are based on theangle of rest of the size of carbide used, with the object of securingsensitiveness of the feed. The feed is thus operated by a very smallmovement of the float, and consequently there is but very slight rise andfall of the water in the generating chamber. Owing to the lateral play, the feed valve rarely becomes concentric with its seat. There is a cover_G_ over the feed valve _F_, designed to distribute the carbideevenly about the feed aperture and to prevent it passing down the hollowof the valve and the holes through which the connecting-rods pass. Italso directs the course of the evolved gas on its way to the service-pipethrough the carbide in the feed chamber _C_, whereby the gas isdried. The carbide chamber _D_ has at its bottom a conical valve, normally open, but closed by means of the spindle _H_, which isengaged at its upper end by the closing screw-cap _J_, which isfurnished with a safelocking device to prevent its removal until theconical valve is closed and the hopper chamber _D_ thereby cut offfrom the gas-supply. The cap _J_, in addition to a leather washer tomake a gas-tight joint when down, has a lower part fitting to make analmost gas-tight joint. Thus when the cap is off; the conical valve fitsgas-tight; when it is on and screwed down it is gas-tight; and when onbut not screwed down, it is almost gas-tight. Escape of gas is thusavoided. A special charging funnel _K_, shown in half-scale, isprovided for inserting in place of the screw cap. The carbide falls fromthe funnel into the chamber _D_ when the chain is pulled. A freshcharge of carbide may be put in while the apparatus is in action. Theevolved gas goes into the chamber _C_ through a pipe, with cock, toa dust-arrester _L_, which contains a knitted stocking lightlyfilled with raw sheep's wool through which the gas passes to the service-pipe. The dust-arrester needs its contents renewing once in one, two, orthree years, according to the make of gas. The pressure of the gas isvaried as desired by altering the height of water in the tank _A_. When cleaning the machine, the water must never be run below the top ofthe generating chamber. [Illustration: FIG. 24. --"SICHE" GENERATOR. ] AMERICA--UNITED STATES. _Maker:_ J. B. COLT CO. , 21 BARCLAY STREET, NEW YORK. _Type:_ Automatic; carbide-to-water. The "Colt" generator made by this firm comprises a carbide hopper mountedabove a generating tank containing water, and an equalising bellgasholder mounted above a seal-pot having a vent-pipe _C_communicating with the outer air. The carbide hopper is charged with 1/4x 1/12 inch carbide, which is delivered from it into the water in thegenerating tank in small portions at a time through a double valve, whichis actuated through levers connected to the crown of the equalisinggasholder. As the bell of the gasholder falls the lever rotates a rockshaft, which enters the carbide hopper, and through a rigidly attachedlever raises the inner plunger of the feed-valve. The inner plunger inturn raises the concentric outer stopper, thereby leaving an annularspace at the base of the carbide hopper, through which a small deliveryof carbide to the water in the generating tank then ensues. The gasevolved follows the course shown by the arrows in the figure into thegasholder, and raises the bell, thereby reversing the action of thelevers and allowing the valve to fall of its own weight and so cut offthe delivery of carbide. The outer stopper of the valve descends beforethe inner plunger and so leaves the conical delivery mouth of the hopperfree from carbide. The inner plunger, which is capped at its lower endwith rubber, then falls and seats itself moisture-tight on the cleardelivery mouth of the hopper. The weight of the carbide in the hopper istaken by its sides and a projecting flange of the valve casing, so thatthe pressure of the carbide at the delivery point is slight and uniform. The outside of the delivery mouth is finished by a drip collar withdouble lip to prevent condensed moisture creeping upwards to the carbidein the hopper. A float in the generating tank, by its descent when thewater falls below a certain level, automatically draws a cut off acrossthe delivery mouth of the carbide hopper and so prevents the delivery ofcarbide either automatically or by hand until the water in the generatingtank has been restored to its proper level. Interlocking levers, (11) and(12) in the figure, prevent the opening of the feed valve while the cap(10) of the carbide hopper is open for recharging the hopper. There is astirrer actuated by a handle (9) for preventing the sludge choking thesludge cock. The gas passes into the gasholder through a floating seal, which serves the dual purpose of washing it in the water of the gasholdertank and of preventing the return of gas from the holder to thegenerating tank. From the gasholder the gas passes to the filter (6)where it traverses a strainer of closely woven cotton felt for thepurpose of the removal of any lime. [Illustration: FIG. 25. --"COLT" GENERATING PLANT. ] Drip pipes (30) and (31) connected to the inlet- and outlet-pipes of thegasholder are sealed in water to a depth of 6 inches, so that in theevent of the pressure in the generator or gasholder rising above thatlimit the surplus gas blows through the seal and escapes through thevent-pipe _C_. There is also a telescopic blow-off (32) and (33), which automatically comes into play if the gasholder bell rises above acertain height. _Maker:_ DAVIS ACETYLENE CO. , ELKHARDT, INDIANA. _Type:_ Automatic; carbide-to-water. The "Davis" generator made by this firm comprises an equalising bellgasholder with double walls, the inner wall surrounding a central tuberising from the top of the generating chamber, in which is placed awater-sealed carbide chamber with a rotatory feeding mechanism which isdriven by a weight motor. The carbide falls from the chamber on to a widedisc from which it is pushed off a lump at a time by a swingingdisplacer, so arranged that it will yield in every direction and preventclogging of the feeding mechanism. Carbide falls from the disk into thewater of the generating chamber, and the evolved gas raises the bell andso allows a weighted lever to interrupt the action of the clockwork, until the bell again descends. The gas passes through a washer in thegasholder tank, and then through an outside scrubber to the service-pipe. There is an outside chamber connected by a pipe with the generatingchamber, which automatically prevents over-filling with water, and alsoacts as a drainage chamber for the service- and blow-off-pipes. There isan agitator for the residuum and a sludge-cock through which to removesame. The feeding mechanism permits the discharge of lump carbide, andthe weight motor affords independent power for feeding the carbide, atthe same time indicating the amount of unconsumed carbide and securinguniform gas pressure. [Illustration: FIG. 26. --"DAVIS" GENERATOR. ] _Maker:_ SUNLIGHT GAS MACHINE CO. , 49 WARREN STREET, NEW YORK. _Type:_ Automatic; carbide-to-water. The "Omega" apparatus made by this firm consists of a generating tankcontaining water, and surmounted by a hopper which is filled with carbideof 1/4-inch size. The carbide is fed from the hopper into the generatingtank through a mechanism consisting of a double oscillating cup soweighted that normally the feed is closed. The fall of the bell of theequalising gasholder, into which the gas evolved passes, operates a lever_B_, which rotates the weighted cup in the neck of the hopper and socauses a portion of carbide to fall into the water in the generatingtank. The feed-cup consists of an upper cup into which the carbide isfirst delivered. It is then tipped from the upper cup into the lower cupwhile, at the same time, further delivery from the hopper is prevented. Thus only the portion of carbide which has been delivered into the lowercup is emptied at one discharge into the generator. There is a safetylock to the hopper cap which prevents the feeding mechanism coming intooperation until the hopper cap is screwed down tightly. Provision is madefor a limited hand-feed of carbide to start the apparatus. The gasholderis fitted with a telescoping vent-pipe, by which gas escapes to the openin the event of the bell being raised above a certain height. There isalso an automatic cut-off of the carbide feed, which comes into operationit the gas is withdrawn too rapidly whether through leakage in the pipesor generating plant, or through the consumption being increased above thenormal generating capacity of the apparatus. The gas evolved passes intoa condensing or washing chamber placed beneath the gasholder tank andthence it travels to the gasholder. From the gasholder it goes through apurifier containing "chemically treated coke and cotton" to the supply-pipe. [Illustration: FIG. 27. --"OMEGA" GENERATOR. ] 1 Vent-cock handle. 2 Residuum-cock handle. 3 Agitator handle. 4 Filling funnel. 5 Water overflow. 6 Hopper cap and lever. 7 Starting feed. 8 Rocker arm. 9 Feed connecting-rod. A Pawl. B Lever for working feed mechanism. C Guide frame. D Residuum draw-off cock. G Chain from hopper cap to feed mechanism. H Blow-off and vent-pipe connexion. I Gas outlet from generator. J Gas service-cock. K Filling funnel for gasholder tank. L Funnel for condensing chamber. M Gas outlet at top of purifier. N Guides on gas-bell. O Crosshead on swinging pawl. P Crane carrying pawl. Q Shaft connecting feed mechanism. R Plug in gas outlet-pipe. S Guide-frame supports. U Removable plate to clean purifier. Z Removable plate to expose feed-cups for cleaning same. AUSTRIA-HUNGARY _Maker:_ RICH. KLINGER, GUMPOLDSKIRCHEN, NEAR VIENNA. _Type:_ Non-automatic; carbide-to-water. The generating plant made by this firm consists of the generator _A_which is supported in a concrete water and sludge tank _B_, astorage gasholder _J_, and purifiers _K_. In the top of thegenerator are guide-ways _F_, through each of which is passed aplunger _C_ containing a perforated cage charged with about 8 lb. Oflump carbide. The plungers are supported by ropes passing over pulleys_D_, and when charged they are lowered through the guide-ways_F_ into the water in the tank _B_. The charge of carbide isthus plunged at once into the large body of water in the tank, and thegas evolved passes through perforations in the washer _G_ to thecondenser _H_ and thence to the storage gasholder _J_. Afterexhaustion of the charge the plungers are withdrawn and a freshly chargedcage of carbide inserted ready for lowering into the generating tank. There is a relief seal _f_ through which gas will blow and escape bya pipe _g_ to the open should the pressure within the apparatusexceed the depth of the seal, viz. , about 9 inches. There is a syphon pot_N_ for the collection and withdrawal of condensed water. The sludgeis allowed to accumulate in the bottom of the concrete tank _B_until it becomes necessary to remove it at intervals of about threemonths. Water is added to the tank daily to replace that used up in thegeneration of the gas. The gas passes from the storage holder through oneof the pair of purifiers _K_, with water-sealed lids, which arecharged with a chemical preparation for the removal of phosphorettedhydrogen. This purifying material also acts as a desiccating agent. Fromthe purifiers the gas passes through the meter _L_ to the service-pipes. [Illustration: FIG. 28. --KLINGER'S GENERATING PLANT. ] BELGIUM. _Maker_: SOC. AN. DE L'ACÉTYLITHE, 65 RUE DU MARCHE, BRUSSELS. _Type_: Automatic; contact. The generating apparatus made by this firm uses, instead of ordinarycarbide, a preparation known as "acétylithe, " which is carbide treatedspecially with mineral oil, glucose and sugar. The object of using thistreated carbide is to avoid the effects of the attack of atmospherichumidity or water vapour, which, with ordinary carbide, give rise to thephenomena of after-generation. The generator comprises a water-tank_A_ with conical base, a basket _C_ containing the treatedcarbide inserted within a cylindrical case _B_ which is open at thebottom and is surmounted by a cylindrical filter _D_. At starting, the tank _A_ is filled with water to the level _N N'_. Thewater rises within the cylindrical case until it comes in contact withthe treated carbide, which thereupon begins to evolve gas. The gas passesthrough the filter _D_, which is packed with dry cotton-wool, andescapes through the tap _M_. As soon as the contained air has beendisplaced by gas the outlet of the tap _M_ is connected by aflexible tube to the pipe leading to a purifier and the service-pipe. When the tap _M_ is closed, or when the rate of evolution of the gasexceeds the rate of consumption, the evolved gas accumulates within thecylindrical case _B_ and begins to displace the water, the level ofwhich within the case is lowered from _S S'_, first to _S1 S'1_and ultimately to, say, _S2 S'2_. The evolution of gas is therebygradually curtailed or stopped until more is required for consumption. The water displacement causes the water-level in the outer tank to riseto _N1 N'1_ and ultimately to, say _N2 N'2_. The lime formed bythe decomposition of the carbide is loosened from the unattacked portionand taken more or less into solution as sucrate of lime, which is asoluble salt which the glucose or sugar in the treated carbide forms withlime. The solution is eventually run off through the cock _R_. Thecover _T_ of the filter is screwed down on rubber packing until gas-tight. The purifier is charged with puratylene or other purifyingmaterial. [Illustration: FIG. 29. --ACÉTYLITHE GENERATOR. ] _Maker_: L. DEBRUYNE, 22 PLACE MASUI, BRUSSELS. _Type_: (1) Automatic; carbide-to-water. The generating plant made by this firm, using granulated carbide, comprises an equalising gasholder _E_ alongside a generating tank_B_, which is surmounted by a closed carbide receptacle _A_ anda distributing appliance. The carbide receptacle is filled withgranulated carbide and the lid _N_ screwed down; the carbide is thenwithdrawn from the base of the receptacle by the distributing applianceand discharged in measured quantities as required into the water in thegenerating tank. The distributing appliance is actuated by a weightedcord _H_ attached to the bell _I_ of the gasholder anddischarges at each time a quantity of carbide only sufficient nearly tofill the gasholder with acetylene. The gas passes from the generatorthrough the pipe _J_ and seal-pot _D_, or bypass _F_, tothe gasholder. The generating tank is provided with a funnel _G_ forreplacing the water consumed, a sludge-stirrer and a draw-off cock_L_, and a water-level cock _C_. The gas passes from thegasholder through a purifier _K_, charged with heratol, to theservice-pipe. [Illustration: FIG. 30. --L. DEBRUYNE'S GENERATING PLANT FOR GRANULATEDCARBIDE. ] (2) Automatic; carbide-to-water. The "Debruyne" generator comprises an equalising bell gasholder _A_placed alongside a generating tank _B_ containing water into whichlump carbide is discharged as necessary from each in turn of a series ofchambers mounted in a ring above the generating tank. The chambers areremovable for refilling, and when charged are hermetically sealed untilopened in turn above the shoot _C_, through which their contents aredischarged into the generating tank. The carbide contained in eachchamber yields sufficient gas nearly to fill the gasholder. Thedischarging mechanism is operated through an arm _E_ attached to thebell _G_ of the gasholder, which sets the mechanism in motion whenthe bell has fallen nearly to its lowest position. The lip _L_serves for renewing the water in the generator, and the gas evolved goesthrough the pipe _K_ with tap _F_ to the gasholder. There is aneccentric stirrer for the sludge and a large-bore cock for dischargingit. The gas passes from the gasholder through the pipe _J_ to thepurifier _H_, charged with heratol, and thence to the service-pipe. [Illustration: FIG. 3l. --THE "DEBRUYNE" GENERATING PLANT FOR LUMPCARBIDE. ] _Maker_: DE SMET VAN OVERBERGE, ALOST. _Type_: (1) Automatic; carbide-to-water. This generating apparatus comprises an equalising gasholder _A_placed alongside a generating tank _B_, above which is mounted on arotating spindle a series of chambers _C_, arranged in a circle, which are filled with carbide. The generating tank is closed at the top, but on one side there is a shoot _D_ through which the carbide isdischarged from the chambers in turn into the water in the tank. Theseries of chambers are rotated by means of a cord passing round a pulley_E_ and having a weight _F_ at one end, and being attached tothe bell of the gasholder at the other. When the bell falls, owing to theconsumption of gas, to a certain low position, the carbide chamber, whichhas been brought by the rotation of the pulley over the shoot, is openedat the bottom by the automatic liberation of a catch, and its contentsare discharged into the generating tank. The contents of one carbidechamber suffice to fill the gasholder to two-thirds of its totalcapacity. The carbide chambers after filling remain hermetically closeduntil the bottom is opened for the discharge of the carbide. There is asludge-cock _G_ at the bottom of the generating tank. The gas passesfrom the gasholder through a purifier _H_, which is ordinarilycharged with puratylene. [Illustration: FIG. 32. --AUTOMATIC GENERATING PLANT OF DE SMET VANOVERBERGE. ] (2) Non-automatic; carbide-to-water. This apparatus comprises a storage bell gasholder _J_ placedalongside a generating tank in the top of which is a funnel _E_ witha counter-weighted lever pivoted on the arm _B_. The base of thefunnel is closed by a flap valve _C_ hinged at _D_. When it isdesired to generate gas the counter-weight _A_ of the lever israised and the valve at the bottom of the funnel is thereby opened. Acharge of carbide is then tipped into the funnel and drops into the waterin the generating tank. The valve is then closed and the gas evolved goesthrough the pipe _G_ to the gasholder, whence it passes through apurifier to the service-pipe. There is a sludge-cock on the generatingtank. [Illustration: FIG. 33. --NON-AUTOMATIC GENERATING PLANT OF DE SMET VANOVERBERGE. ] _Maker_: SOC. AN. BELGE DE LA PHOTOLITHE, 2 RUE DE HUY, LIÉGE. _Type_: Automatic; carbide-to-water. The "Photolithe" generating plant made by this firm comprises anequalising bell gasholder _A_ in the tank _O_, alongside agenerating tank _B_ which is surmounted by a carbide storagereceptacle divided into a number of compartments. These compartments arefitted with flap bottoms secured by catches, and are charged withcarbide. Through the middle of the storage receptacle passes a spindle, to the upper end of which is attached a pulley _b_. Round the pulleypasses a chain, one end of which carries a weight _n_, while in theother direction it traverses guide pulleys and is attached to a loop onthe crown of the gasholder bell. When the bell falls below a certainpoint owing to the consumption of gas, it pulls the chain and rotates thepulley _b_ and therewith an arm _d_, which liberates the catchsupporting the flap-bottom of the next in order of the carbidecompartments. The contents of this compartment are thereby dischargedthrough the shoot _C_ into the generating tank _B_. The gasevolved passes through the cock _R_ and the pipe _T_ into thegasholder, the rise of the bell of which takes the pull off the chain andallows the weight at its other end to draw it up until it is arrested bythe stop _f_. The arm _d_ is thereby brought into position toliberate the catch of the next carbide receptacle. The generating tank isenlarged at its base to form a sludge receptacle _E_, which isprovided with a sludge draw-off cock _S_ and a hand-hole _P_. Between the generating tank proper and the sludge receptacle is a grid, which is cleaned by means of a rake with handle _L_. The gas passesfrom the gasholder through a purifier _H_ charged with puratylene, to the service-pipe. [Illustration: FIG. 34. --"PHOTOLITHE" GENERATING PLANT. ] The same firm also makes a portable generating apparatus in which thecarbide is placed in a basket in the crown of the bell of the gasholder. This apparatus is supplied on a trolley for use in autogenous solderingor welding. FRANCE. _Maker_: LA SOC. DES APPLICATIONS DE L'ACÉTYLÈNE, 26 RUE CADET, PARIS. _Type_: Automatic; carbide-to-water. The "Javal" generating plant made by this firm consists of an equalisingbell gasholder _A_ in the tank _B_ with a series of buckets_D_, with removable bottoms _h_, mounted on a frame _F_round the guide framing of the holder. Alongside the gasholder stands thegenerating tank _H_ with shoot _K_, into which the carbidedischarged from the buckets falls. On top of the generator is a tippingwater-bucket _I_ supplied with water through a ball cock. The bellof the gasholder is connected by chains _a_ and _c_, and levers_b_ and _d_ with an arm which, when the bell descends to acertain point, comes in contact with the catch by which the bottom of thecarbide bucket is held in place, and, liberating the same, allows thecarbide to fall into the shoot. When the bell rises, in consequence ofthe evolved gas, the ring of carbide buckets is rotated sufficiently tobring the next bucket over the shoot. Thus the buckets are discharged inturn as required through the rise and fall of the gasholder bell. [Illustration: FIG. 35. --"JAVAL" GENERATOR. ] The carbide falling from the opened bucket strikes the end _i_ ofthe lever _k_, and thereby tips the water-bucket _I_ anddischarges its contents into the shoot of the generator. The rise in thelevel of the water in the generator, due to the discharge of the waterfrom the bucket _I_, lifts the float _L_ and therewith, throughthe attached rod and chain _u_, the ball _s_ of the valve_t_. The sludge, which has accumulated in the base _N_ of thegenerator from the decomposition of the previous portion of carbide, isthereby discharged automatically into a special drain. The discharge-valve closes automatically when the float _L_ has sunk to itsoriginal level. The gas evolved passes from the generator through theseal-pot _M_ and the pipe _r_ with cock _q_ into thegasholder, from which it passes through the pipe _x_; withcondensation chamber and discharge tap _y_ into the purifier_R_, which is charged with heratol. _Maker_: L'HERMITE, LOUVIERS, EURE. _Type_: (1) Automatic; carbide-to-water. The generating plant known as "L'Éclair, " by this firm comprises anequalising bell gasholder _A_ floating in an annular water-seal_N_, formed in the upper part of a generating tank _B_ intowhich carbide enters through the shoot _K_. Mounted at the side ofthe tank is the carbide delivery device, which consists of the carbidecontainers _J_ supported on an axis beneath the water-sealed cover_H_. The containers are filled with ordinary lump carbide when thecover _H_ is removed. The tappet _O_ attached to the bell ofthe gasholder come in contact with a pawl when the gasholder belldescends to a certain level and thereby rotates a pinion on theprotruding end of the axis which carries the carbide containers _J_. Each time the bell falls and the tappet strikes the pawl, one compartmentof the carbide containers discharges its contents down the shoot _K_into the generating tank _B_. The gas evolved passes upwards andcauses the bell _A_ to rise. The gas is prevented from rising intothe shoot by the deflecting plates _G_. The natural level of thewater in the generating tank, when the apparatus is in use, is shown bythe dotted lines _L_. The lime sludge is discharged from time totime through the cock _E_, being stirred up by means of the agitator_C_ with handle _D_. When the sludge is discharged water isadded through _M_ to the proper level. The gas evolved passes fromthe holder through the pipe with tap _F_ to the service-pipe. Apurifier is supplied if desired. [Illustration: FIG. 36. --"L'ÉCLAIR, " GENERATOR. ] _References_ A Gasholder. B Generator. C Agitator. D Handle of agitator. E Sludge-cock. F Gas outlet. G Deflecting plates. H Cover. I Carbide. J Automatic distributor. K Shoot. L Water-level. M Water-inlet. N Water-seal. O Tappet. (2) Automatic; water-to-carbide; contact. A generating plant known as "L'Étoile" made by this firm. A tappet on thebell of an equalising gasholder depresses a lever which causes water toflow into a funnel, the outlet of which leads to a generating chambercontaining carbide. _Maker_: MAISON SIRIUS, FR. MANGIAMELI & CO. , 34 RUE DES PETITS-HÔTELS, PARIS. _Type_: (1) Automatic; carbide-to-water. The generating plant made by this firm comprises a drum-shaped carbideholder mounted above a generating tank, a condenser, a washer, anequalising gasholder, and a purifier. The drum _A_ is divided intoeight chambers _a_ each closed by a fastening on the periphery ofthe drum. These chambers are packed with lump carbide, which isdischarged from them in turn through the funnel _B_ into thegenerating tank, which is filled with water to the level of the overflowcock _b_. A deflecting plate _d_ in the tank distributes thecarbide and prevents the evolved gas passing out by way of the funnel_B_. The gas evolved passes through the pipe _O_ into thecondenser, which is packed with coke, through which the gas goes to thepipe _E_ and so to the washer _P_ through the water, in whichit bubbles and issues by the pipe _G_ into the gasholder. The bell_L_ of the gasholder is connected by a chain _C_ to the axis ofthe drum _A_, on which is a pinion with pawl so arranged that thepull on the chain caused by the fall of the bell of the gasholder rotatesthe drum by 1/8 of a turn. The catch on the outside of the carbidechamber, which has thereby been brought to the lowest position, is at thesame time freed, so that the contents of the chamber are dischargedthrough the funnel _B_. The evolved gas causes the bell to rise andthe drum remains at rest until, owing to the consumption of gas, the bellagain falls and rotates the drum by another 1/8 of a turn. Each chamberof the drum holds sufficient carbide to make a volume of gas nearly equalto the capacity of the gasholder. Thus each discharge of carbide verynearly fills the gasholder, but cannot over-fill it. The bell is providedwith a vent-pipe _i_, which comes into operation should the bellrise so high that it is on the point of becoming unsealed. From thegasholder the gas passes through the pipe _J_, with cock _e_, to the purifier, which is charged with frankoline, puratylene, or otherpurifying material, whence it passes to the pipe _N_ leading to theplace of combustion. The generating tank is provided with a sludge-cock_g_, and a cleaning opening with lid _f_. This generating planthas been primarily designed for the use of acetylene for autogenouswelding, and is made also mounted on a suitable trolley for transport forthis purpose. [Illustration: FIG. 37. --"SIRIUS" GENERATOR. ] (2) Automatic; carbide-to-water. A later design of generating plant, known as the Type G, also primarilyintended for the supply of acetylene for welding, has the carbide storemounted in the crown of the bell of the equalising gasholder, to theframing of the tank of which are attached a purifier, charged withfrankoline, and a safety water-seal or valve. The whole plant is mountedon a four-legged stand, and is provided with handles for carrying as awhole without dismounting. It is made in two sizes, for charges of 5-1/2and 11 lb. Of carbide respectively. GERMANY. _Maker_: KELLER AND KNAPPICH, G. M. B. H. , AUGSBURG. _Type_: Non-automatic; carbide-to-water. The "Knappich" generating plant made by this firm embodies a generatingtank, one-half of which is closed, and the other half of which is open atthe top, containing water. A small drum containing carbide is attached bya clamp to the end of a lever which projects above the open half of thetank. The lever is fastened to a horizontal spindle which is turnedthrough 180° by means of a counter-weighted lever handle. The carbidecontainer is thus carried into the water within the closed half of thetank, and is opened automatically in transit. The carbide is thus exposedto the water and the evolved gas passes through a pipe from the top ofthe generating tank to a washer acting on the Livesey principle, andthence to a storage gasholder. The use of closed carbide containers incharging is intended to preclude the introduction of air into thegenerator, and the evolution and escape of gas to the air while thecarbide is being introduced. Natural circulation of the water in thegenerating tank is encouraged with a view to the dissipation of heat andwashing of the evolved gas. From the gasholder the gas passes in adownward direction through two purifiers arranged in series, charged witha material supplied under the proprietary name of "Carburylen. " Thismaterial is stated to act as a desiccating as well as a purifying agent. The general arrangement of the plant is shown in the illustration. (Fig. 38). [Illustration: FIG. 38. --"KNAPPICH" GENERATING PLANT. ] _Maker_: NORDISCHE AZETYLEN-INDUSTRIE; ALTONA-OTTENSEN. _Type_: Automatic; water-to-carbide; "drawer. " The apparatus made by this firm consists of an equalising gasholder withbell _D_ and tank _E_, a water-tank _O_, and two drawergenerators _C_ situated in the base of the gasholder tank. Thewater-supply from the tank _O_ through the pipe _P_ with valve_Q_ is controlled by the rise and fall of the bell through themedium of the weight _J_ attached to the bell. When the belldescends this weight rests on _K_ and so moves a counter-weightedlever, which opens the valve _Q_. The water then flows through thenozzle _B_ into one division of the funnel _A_ and down thecorresponding pipe to one of the generators. The generators contain trayswith compartments intended to be half filled with carbide. The gasevolved passes up the pipe _T_ and through the seal _U_ intothe bell of the gasholder. There is a safety pipe _F_, the upper endof which is carried outside the generator house. From the gasholder thegas is delivered through the cock _M_ to a purifier charged with aspecial purifying material mixed with cork waste and covered withwadding. There is a drainage cock _N_ at the base of the purifier. The nozzle _B_ of the water-supply pipe is shifted to discharge intoeither compartment of the funnel _A_, according to which of the twogenerators is required to be in action. The other generator may then berecharged without interfering with the continuous working of the plant. [Illustration: FIG. 39. --GENERATING PLANT OF THE NORDISCHE AZETYLEN-INDUSTRIE. ] GREAT BRITAIN AND IRELAND. _Maker:_ THE ACETYLENE CORPORATION OF GREAT BRITAIN LTD. , 49VICTORIA STREET, LONDON, S. W. _Type:_ (1) Automatic; water-to-carbide; contact, superposed pans. The "A1" generating plant made by this firm comprises a bell gasholder, with central guide, standing alongside the generator. The generatorconsists of a rectangular tank in which is a generating chamber having awater-sealed lid with pressure test-cock _I_. Into the generatingchamber fit a number of pans _J_, which are charged with carbide. Water is supplied to the generating chamber from an overhead tank_B_ through the starting tap _D_ and the funnel _E_. Itflows out of the supply-pipe near the top of the generating chamberthrough a slot in the side of the pipe facing the corner of the chamber, so that it runs down the latter without splashing the carbide in theupper pans. It enters first the lowest carbide pan through theperforations, which are at different levels in the side of the pan. Itthus attacks the carbide from the bottom upwards. The evolved gas passesfrom the generating chamber through a pipe opening near the top of thesame to the washer _A_, which forms the base of the generating tank. It bubbles through the water in the washer, which therefore also servesas a water-seal, and passes thence to the gasholder. On the bell of thegasholder is an arm _C_ which, when the holder descends nearly toits lowest point, depresses the rod _C_, which is connected by achain to a piston in the outlet-pipe from the water-tank _B_. Thefall of the gasholder thereby raises the piston and allows water to flowout of the tank _B_ through the tap _D_ to the funnel _E_. The generating tank is connected by a pipe, with tap _G_, with thewasher _A_, and the water in the generating tank is run off throughthis pipe each time the generating chamber is opened for recharging, thereby flushing out the washer _A_ and renewing the water in thesame. There is a sludge discharging tap _F_. With a view to theready dissipation of the heat of generation the generating chamber ismade rectangular and is placed in a water-tank as described. Some of theheat of generation is also communicated to the underlying washer andwarms the water in it, so that the washing of the gas is effected by warmwater. Water condensing in the gasholder inlet-pipe falls downwards tothe washer. There is a water lip _H_ by which the level of the waterin the washer is automatically kept constant. The gasholder is providedwith a safety-pipe _K_, which allows gas to escape through it to theopen before the sides of the holder become unsealed, should the holderfor any reason become over-filled. The holder is of a capacity to takethe whole of the gas evolved from the carbide in one pan, and the water-tank _B_ holds just sufficient water for the decomposition of onecharge of the generator. From the gasholder the gas passes through apurifier, which is ordinarily charged with "Klenzal, " and a baffle-boxfor abstraction of dust, to the service-pipe. With plants intended tosupply more than forty lights for six hours, two or more generatingchambers are employed, placed in separate compartments of one rectangulargenerating tank. The water delivery from the water-tank _B_ thentakes place into a trough with outlets at different levels for eachgenerating chamber. By inspection of this trough it may be seen at oncewhether the charge in any generating chamber is unattacked, in course ofattack, or exhausted. [Illustration: FIG. 40. --THE "A1" GENERATING PLANT OF THE ACETYLENECORPORATION OF GREAT BRITAIN, LTD. ] (2) Automatic; water-to-carbide; contact. The same firm also makes the "Corporation Flexible-Tube Generator, " whichis less costly than the "A1" (_vide supra_). The supply of water tothe generating vessels takes place from the tank of the equalising bellgasholder and is controlled by a projection on the bell which depresses aflexible tube delivering into the generating vessels below the level ofthe water inlet to the tube. (3) Automatic; water-to-carbide; "drawer. " The same firm also makes a generator known as the "A-to-Z, " which is lesscostly than either of the above. In it water is supplied from the tank ofa bell gasholder to a drawer type of generator placed in the base of thegasholder tank. The supply of water is controlled by an external piston-valve actuated through the rise and fall of the bell of the gasholder. The flow of water to the generator is visible. _Maker_: THE ACETYLENE GAS AND CARBIDE OF CALCIUM CO. , PONTARDAWE, R. S. O. , GLAM. _Type_: Automatic; water-to-carbide; flooded compartment. The "Owens" generator made by this firm comprises an equalising bellgasholder alongside which are placed two or more inclined generatingcylinders. The front lower end of each cylinder is fitted with a lidwhich is closed by a screw clamp. There is inserted in each cylinder acylindrical trough, divided into ten compartments, each of which containscarbide. Water is supplied to the upper ends of the cylinders from ahigh-level tank placed at the back of the gasholder. In the larger sizesthe tank is automatically refilled from a water service through aball-cock. The outlet-valve of this tank is operated through a counter-weighted lever, the unweighted end of which is depressed by a loop, attached to the crown of the gasholder bell, when the bell has nearlyreached its lowest position. This action of the bell on the lever opensthe outlet-valve of the tank and allows water to flow thence into one ofthe generating cylinders. It is discharged into the uppermost of thecompartments of the carbide trough, and when the carbide in thatcompartment is exhausted it flows over the partition into the nextcompartment, and so on until the whole trough is flooded. The gas passesfrom the generating cylinders through a water-seal and a baffle platecondenser placed within the water link of the gasholder to the bell ofthe latter. There is a water seal on the water supply-pipe from the tankto the generators, which would be forced should the pressure within thegenerators for any reason become excessive. There is also a sealed vent-pipe which allows of the escape of gas from the holder to the open shouldthe holder for any reason be over filled. The gas passes from the holderthrough a purifier charged with "Owens" purifying material to the servicepipe. The plant is shown in Fig 41. [Illustration: FIG. 41. --"OWENS" GENERATOR. ] _Maker_ ACETYLENE ILLUMINATING CO, LTD, 268-270 SOUTH LAMBETH ROAD, LONDON, SW _Type_ (1) Non automatic, carbide to water The generator _A_ of this type made by this firm is provided with aloading box _B_, with gas tight lid, into which the carbide is put. It is then discharged by moving a lever which tilts the hinged bottom_D_ of the box _B_, and so tips the carbide through the shoot_E_ on to the conical distributor _F_ and into the water in thegenerating chamber. There is a sludge cock _G_ at the base of thegenerator. Gas passes as usual from the generator to a washer and storagegasholder. Heratol is the purifying material supplied. [Illustration: FIG. 42. --CARBIDE-TO-WATER GENERATOR OF THE ACETYLENEILLUMINATING CO. , LTD. ] (2) Non-automatic; water-to-carbide; contact. The generator _A_ is provided with a carbide container withperforated base, and water is supplied to it from a delivery-pipe througha scaled overflow. The gas evolved passes through the pipe _E_ tothe washer _B_, which contains a distributor, and thence to thestorage gasholder _G_. There is a sludge-cock _F_ at the baseof the generator. From the gasholder the gas passes through the purifier_D_, charged with heratol, to the service-pipe. [Illustration: FIG. 43. --WATER-TO-CARBIDE GENERATING PLANT OF THEACETYLENE ILLUMINATING CO. , LTD. ] _Maker_: THE ALLEN CO. , 106 VICTORIA STREET, LONDON, S. W. _Type_: Automatic; water-to-carbide; contact, superposed trays. The generating plant made by this firm comprises an equalising bellgasholder, from the tank of which water is supplied through a flexibletube to the top of a water-scaled generating chamber in which is avertical cylinder containing a cage packed with carbide. The open end ofthe flexible tube is supported by a projection from the bell of thegasholder, so that as the bell rises it is raised above the level of thewater in the tank and so ceases to deliver water to the generator untilthe bell again falls. The water supplied flows by way of the water-sealof the cover of the generating chamber to the cylinder containing thecarbide cage. Larger sizes have two generating chambers, and the nozzleof the water delivery-pipe may be switched over from one to the other. There is an overflow connexion which brings the second chamberautomatically into action when the first is exhausted. One chamber may berecharged while the other is in action. Spare cylinders and cages areprovided for use when recharging. There is a cock for drawing off watercondensing in the outlet-pipe from the gasholder. The gas passes from theholder to the lower part of a purifier with water-scaled cover, throughthe purifying material in which it rises to the outlet leading to theservice-pipe. Purifying material under the proprietary name of the"Allen" compound is supplied. The plant is shown in Fig. 44. [Illustration: FIG. 44. --"ALLEN" FLEXIBLE-TUBE GENERATOR. ] Maker: THE BON-ACCORD ACETYLENE GAS CO. , 285 KING STREET, ABERDEEN. Type: Automatic; water-to-carbide; contact, superposed trays. The "Bon Accord" generating plant made by this firm comprises anequalising displacement gasholder _B_ immersed in a water-tank_A_. Alongside the tank are placed two water-jacketed generatingchambers _G1_ and _G2_ containing cages _K_ charged withcarbide. Water passes from within the gasholder through the water inlet-pipes _L1 L2_, the cock _H_, and the pipes _F1 F2_ to thegenerating chambers, from which the gas evolved travels to the holder_B_, in which it displaces water until the water-level falls belowthe mouths of the pipes _L1_ and _L2_, and so cuts off thesupply of water to the generating chambers. The gas passes from theholder _B_ through the pipe with outlet-cock _T_ to a washercontaining an acid solution for the neutralisation of ammonia, thenthrough a purifier containing a "special mixture of chloride of lime. "After that through a tower packed with lime, and finally through apressure regulator, the outlet of which is connected to the service-pipe. There is an indicator _I_ to show the amount of gas in the holder. One generator may be charged while the other is in action. [Illustration: FIG. 45. --"BON-ACCORD" GENERATOR. ] _Maker_: FREDK. BRABY AND CO. , LTD. , ASHTON GATE WORKS, BRISTOL; AND352-364 EUSTON ROAD, LONDON. _Type:_ (I) Automatic; carbide-to-water. The "A" type of generator made by this firm comprises an equalising bellgasholder, round the bell of which are arranged a series of buckets whichare charged with carbide. Those buckets are discharged in turn as thebell falls from time to time through a mechanism operated by a weightsuspended from a wire cord on a revolving spindle. The carbide isdischarged on to a different spot in the generating tank from eachbucket. There is a cock for the periodical removal of sludge. Gas passesthrough a purifier charged with puratylene to the service-pipe. Thedisposition of the parts of the plant and the operating mechanism arcshown in the accompanying figure, which represents the generatingapparatus partly in elevation and partly in section. The carbide buckets(1) are loosely hooked on the flat ring (2) bolted to the gasholder tank(3). The buckets discharge through the annular water-space (4) betweenthe tank and the generator (5). The rollers (6), fitted on the generator, support a ring (7) carrying radial pins (8) projecting outwards, one pinfor each bucket. The ring can travel round on the rollers. Superposed onthe ring is a tray (9) closed at the bottom except for an aperturebeneath the throat (11), on which is mounted an inclined striker (12), which strikes the projecting tongues (1_a_) of the lids of thebuckets in turn. There is fixed to the sides of the generator a funnel(13) with open bottom (13_a_) to direct the carbide, on to therocking grid (14) which is farther below the funnel than appears from thefigure. Gas passing up behind the funnel escapes through a duct (15) tothe gasholder. The ring (7) is rotated through the action of the weight(16) suspended by the chain or rope (17) which passes round the shaft(18), which is supported by the bracket (19) and has a handle for windingup. An escapement, with upper limb (20_a_) and lower limb(20_b_), is pivotally centred at (21) in the bracket (19) andnormally restrains the turning of the shaft by the weight. There is afixed spindle (24) supported on the bracket (23)--which is fixed to thetank or one of the guide-rods--having centred on it a curved bar orquadrant (25) running loose on the spindle (24) and having a crank arm(26) to which is connected one end of a rod (27) which, at the other end, is connected to the arm (28) of the escapement. The quadrant bears atboth extremities against the flat bar (29) when the bell (22) issufficiently raised. The bar (29) extends above the bell and carries anarm (30) on which is a finger (30_a_). There is fixed on the shaft(18) a wheel (31), with diagonal divisions or ways extending from side toside of its rim, and stop-pins (32) on one side at each division. Aclutch prevents the rotation of the wheel during winding up. [Illustration: FIG. 46. --THE "A" GENERATOR OF FRED K. BRABY AND CO. , LTD. ] (2) Automatic; water-to-carbide; contact, superposed trays. The type "B" generator made by this firm comprises an equalising bellgasholder, a crescent-shaped feed water-tank placed on one side of thegasholder, and mechanism for controlling a tap on the pipe by which thefeed water passes to a washer whence it overflows through a seal into ahorizontal generating chamber containing cells packed with carbide. Themechanism controlling the water feed embodies the curved bar (25), connecting-rod (27) and flat guide-bar (29) as used for controlling thecarbide feed in the "A" type of generator (Fig. 46). When the belldescends water is fed into the washer, and the water-level of the seal isthus automatically maintained. The gas evolved passes through a pipe, connecting the seal on the top of the generating chamber with the washer, into the gasholder. Plants of large size have two generating chamberswith connexions to a single washer. _Maker:_ THE DARGUE ACETYLENE GAS CO. , 57 GREY STREET, NEWCASTLE-ON-TYNE. _Type:_ Automatic; water-to-carbide; "drawer. " The "Dargue" acetylene generator made by this firm comprises anequalising bell gasholder _B_ floating in a water-tank _A_, which is deeper than is necessary to submerge the bell of the gasholder. In the lower part of this tank are placed two or more horizontalgenerating chambers which receive carbide-containing trays divided bypartitions into a number of compartments which are half filled withcarbide. Water is supplied from the gasholder tank through the tap_E_ and pipe _F_ to the generating chambers in turn. It risesin the latter and floods the first compartment containing carbide beforegaining access to the second, and so on throughout the series ofcompartments. As soon as the carbide in the first generating chamber isexhausted, the water overflows from it through the pipe with by-pass tap_J_ to the second generating chamber. The taps _G_ and _H_serve to disconnect one of the generating chambers from the water-supplyduring recharging or while another chamber is in action. The gas evolvedpasses from each generating chamber through a pipe _L_, terminatingin the dip-pipe _M_, which is provided with a baffle-plate havingvery small perforations by which the stream of gas is broken up, therebysubjecting it to thorough washing by the upper layers of water in thegasholder tank. The washed gas, which thus enters the gasholder, passesfrom it through the pipe _N_ with main cock _R_ to the service-pipes. The water-supply to the generator is controlled through the tap_E_, which is operated by a chain connected to an arm attached tothe bell of the gasholder. The water in the gasholder tank is accordingly made to serve for thesupply of the generating chambers, for the washing of the gas, and as ajacket to the generating chambers. The heat evolved by the decompositionof the carbide in the latter creates a circulation of the water, ensuringthereby thorough mixing of the fresh water, which is added from time totime to replace that removed for the decomposition of the carbide, withthe water already in the tank. Thus the impurities acquired by the waterfrom the washing of the gas do not accumulate in it to such an extent asto render it necessary to run off the whole of the water and refill, except at long intervals. A purifier, ordinarily charged with puratylene, is inserted in many cases after the main cock _R_. The same firmmakes an automatic generator on somewhat similar lines, speciallydesigned for use in autogenous welding, the smaller sizes of which arereadily portable. [Illustration: FIG. 47. --"DARGUE" GENERATOR. ] _Maker_: J. AND J. DRUMMOND, 162 MARKET STREET, ABERDEEN. _Type_: Automatic; water-to-carbide; contact. The generating plant made by this firm comprises two or more generatingvessels _B_ in which carbide is contained in removable casesperforated at different levels. Water is supplied to these generatingvessels, entering them at the bottom, from an elevated tank _A_through a pipe _C_, in which is a tap _F_ connected by a leverand chain _L_ with the bell _G_ of the equalising gasholder_H_, into which the evolved gas passes. The lever of the tap_F_ is counter-weighted so that when the bell _G_ descends thetap is opened, and when the bell rises the tap is closed. The gas passesfrom the generating chambers _B_ through the pipe _D_ to thewasher-cooler _E_ and thence to the gasholder. From the latter itpasses through the dry purifier _J_ to the service-pipe. Thegasholder bell is sealed in oil contained in an annular tank instead ofin the usual single-walled tank containing water. The purifying materialordinarily supplied is puratylene. The apparatus is also made to a largeextent in a compact form specially for use on board ships. [Illustration: FIG. 48. --J. AND J. DRUMMOND'S GENERATING PLANT. ] _Agents_: FITTINGS, LTD. , 112 VICTORIA STREET, S. W. _Type_: Automatic; carbide-to-water. The "Westminster" generator supplied by this firm is the "Davis"generator described in the section of the United States. The rights forthe sale of this generator in Great Britain are held by this firm. _Maker_: LOCKERBIE AND WILKINSON, TIPTON, STAFFS. _Type_: (1) Automatic; water-to-carbide; contact, superposed trays. The "Thorscar" generator of this firm comprises an equalising gasholder, the gas-space of the bell _B_ of which is reduced by conical upperwalls. When the bell descends and this lining enters the water in thetank _A_ the displacement of water is increased and its level raiseduntil it comes above the mouths of the pipes _E_, through which aportion then flows to the generators _D_. The evolution of the gasin the latter causes the bell to rise and the conical lining to be liftedout of the water, the level of which thereupon falls below the mouths ofthe pipes _E_ in consequence of the reduced displacement of thebell. The supply of water to the generators is thus cut off until thebell again falls and the level of the water in the tank is raised abovethe mouths of the pipes _E_. The generating chambers _D_ areprovided with movable cages _F_ in which the carbide is arranged ontrays. The gas evolved travels through a scrubbing-box _G_containing charcoal, and the pipe _J_ with drainage-pipe _P_ tothe water-seal or washer _K_ inside the holder, into which it thenpasses. The outlet-pipe for gas from the holder leads through thecondensing coil _L_ immersed in the water in the tank to thecondensed water-trap _N_, and thence by the tap _Q_ to thesupply-pipe. The generating chambers are water-jacketed and provided withgauge-glasses _H_ to indicate when recharging is necessary, and alsowith sludge-cocks _M_. The object of the displacement cone in theupper part of the bell is to obtain automatic feed of water to thecarbide without the use of cocks or movable parts. There is a funnel-shaped indicator in front of the tank for regulating the height of waterto a fixed level, and also an independent purifier, the purifyingmaterial or which is supplied under the proprietary name of "Thorlite. " [Illustration: FIG. 49. --"THORSCAR" GENERATOR. ] (2) Non-automatic; water-to-carbide; "drawer. " This generating plant, the "Thorlite, " comprises a water-tank _A_from which water is admitted to the drawer generating chambers _B_, one of which may be recharged while the other is in operation. The gasevolved passes through a seal _C_ to the gasholder _D_, whenceit issues as required for use through the purifier _E_ to thesupply-pipe. For the larger sixes a vertical generating chamber is used. The purifier and purifying material are the same as for the automaticplant of the same firm. [Illustration: FIG. 50. --"THORLITE" GENERATING PLANT. ] _Maker_: THE MANCHESTER ACETYLENE GAS CO. , LTD. , ACRE WORKS, CLAYTON, MANCHESTER. _Type_: Automatic; water-to-carbide; "drawer. " The plant made by this firm comprises an equalising gasholder _A_from the tank of which water is supplied to generating cylinders _B_placed at the side of the tank, the number of which varies with thecapacity of the plant. The cylinders receive tray carbide-containersdivided into compartments perforated at different levels so that they areflooded in turn by the inflowing water. A weight _C_ carried by achain _D_ from one end of a lever _E_ pivoted to the framing ofthe gasholder is supported by the bell of the gasholder when the latterrises; but when the holder falls the weight _C_, coming upon thelever _E_, raises the rod _F_, which thereupon opens the valve_G_, which then allows water to flow from the gasholder tank throughthe pipe _H_ to one of the generating cylinders. When the carbide inthe first cylinder is exhausted, the water passes on to a second. Onegenerating cylinder may be recharged while another is in action. Therising of the holder, due to the evolved gas, causes the bell to supportthe weight _C_ and thus closes the water supply-valve _G_. Thegas evolved passes through vertical condensers _J_ into washing-boxes _K_, which are placed within the tank. The gas issues from thewashing-boxes into the gasholder bell, whence it is withdrawn through thepipe _L_ which leads to the purifier. Puratylene is the purifyingmaterial ordinarily supplied by this firm. [Illustration: FIG. 51. --GENERATING PLANT OF THE MANCHESTER ACETYLENE GASCO. , LTD. ] _Maker:_ R, . J. MOSS AND SONS, 98 SNOW HILL, BIRMINGHAM. _Type:_ (1) Automatic; water-to-carbide; superposed trays. The "Moss" generator, "Type A, " made by this firm comprises an equalisinggasholder, four, three, or two generating chambers, and an intermediatewater-controlling chamber. Each generating chamber consists of a frame inwhich are arranged about a central tube trays half filled with carbide, having water inlet-holes at several different levels, and each dividedinto two compartments. Over this frame is put a bell-shaped cover or cap, and the whole is placed in an outer tank or bucket, in the upper part ofwhich is a water inlet-orifice. The water entering by this orifice passesdown the outside of the bell, forming a water-seal, and rises within thebell to the perforations in the carbide trays from the lowest upwards, and so reaches the carbide in successive layers until the whole has beenexhausted. The gas evolved passes through the central tube to a water-seal and condensing tank, through which it escapes to the controllingchamber, which consists of a small water displacement chamber, the gasoutlet of which is connected to the equalising gasholder. The bell of theequalising gasholder is weighted or balanced so that when it rises to acertain point the pressure is increased to a slight extent andconsequently the level of the water in the displacement controllingchamber is lowered. In this chamber is a pipe perforated at about thewater-level, so that when the level is lowered through the increasedpressure thrown by the rising gasholder the water is below theperforations and cannot enter the pipe. The pipe leads to the waterinlet-orifices of the generating tanks and when the equalising gasholderfalls, and so reduces the pressure within the controlling chamber, thewater in the latter rises and flows through the pipe to the generatingtanks. The water supplied to the carbide is thus under the dual controlof the controlling chamber and of the differential pressure within thegenerating tank. The four generators are coupled so that they come intoaction in succession automatically, and their order of operation isnaturally reversed after each recharging. An air-cock is provided in thecrown of the bell of each generator and, in case there should be need ofexamination when charged, cocks are provided in other parts of theapparatus for withdrawing water. There is a sludge-cock on eachgenerator. The gas passes from the equalising gasholder through apurifier, for which the material ordinarily supplied is puratylene. [Illustration: FIG. 52. --"MOSS TYPE A" GENERATOR. ] The "Moss Type B" generator is smaller and more compact than "Type A. " Ithas ordinarily only two generating chambers, and the displacement watercontrolling chamber is replaced by a bell governor, the bell of which isbalanced through a lever and chains by a weight suspended over the bellof the equalising gasholder, which on rising supports this counter-weightand so allows the governor bell to fall, thereby cutting off the flow ofwater to the generating chambers. [Illustration: FIG 53. --"MOSS TYPE B" GENERATOR. ] The "Moss Type C" generator is smaller than either "Type A" or "B, " andcontains only one generating chamber, which is suspended in a pocket inthe crown of the equalising gasholder. Water enters through a hole nearthe top of the bucket of the generating chamber, when it descends withthe holder through the withdrawal of gas from the latter. [Illustration: FIG 54. --"MOSS TYPE C" GENERATOR. ] (2) Semi-automatic; water-to-carbide; superposed trays. The "Moss Semi-Non-Auto" generating plant resembles the automatic plantdescribed above, but a storage gasholder capable of holding the gasevolved from one charging of the whole of the generating chambers isprovided in place of the equalising gasholder, and the generation of gasproceeds continuously at a slow rate. The original form of the "Acetylite" generator (_vide infra_)adapted for lantern use is also obtainable of R. J. Moss and Sons. _Maker:_ WM. MOYES AND SONS, 115 BOTHWELL STREET, GLASGOW. _Type:_ Automatic; carbide-to-water. The "Acetylite" generator made by this firm consists of an equalisinggasholder and one or more generating tanks placed alongside it. On thetop of each generating tank is mounted a chamber, with conical base, charged with granulated carbide 1/8 to 1/2 inch in size. There is anopening at the bottom of the conical base through which passes a rod withconical head, which, when the rod is lowered, closes the opening. The rodis raised and lowered through levers by the rise and fall of the bell ofthe equalising gasholder, which, when it has risen above a certain point, supports a counter-weight, the pull of which on the lever keeps theconical feed-valve open. The gas evolved in the generating tanks passesthrough a condensing chamber situated at the base of the tank into theequalising gasholder and so automatically controls the feed of carbideand the evolution of gas according to the rate of withdrawal of the gasfrom the holder to the service-pipes. The water in the gasholder tankacts as a scrubbing medium to the gas. The generating tanks are providedwith sludge-cocks and a tap for drawing off condensed water. The gaspasses from the equalising gasholder, through a purifier and dryercharged with heratol or other purifying material to the service-pipes. The original form of the "Acetylite" generator is shown in elevation andvertical section in Fig. 55. Wm. Moyes and Sons now make it also with adetached equalising gasholder connected with the generator by a pipe inwhich is inserted a lever cock actuated automatically through a lever andcords by a weight above the bell of the gasholder. Some other changeshave been made with a view to securing constancy of action over longperiods and uniformity of pressure. In this form the apparatus is alsomade provided with a clock-work mechanism for the supply of lighthouses, in which the light is flashed on periodically. The flasher is operatedthrough a pilot jet, which serves to ignite the gas at the burners whenthe supply is turned on to them at the prescribed intervals by the clock-work mechanism. [Illustration: FIG. 55. --"ACETYLITE" GENERATOR. ] _Maker_: THE PHÔS CO. , 205 AND 207 BALLS POND ROAD, LONDON, N. _Type_: Non-automatic; water-to-carbide; drip. The type "E" generator made by this firm consists of a generating chamberplaced below a water chamber having an opening with cap _E_ forrefilling. The generating chamber in closed by a door _B_, withrubber washer _C_, held in position by the rod _A_, the ends ofwhich pass into slots, and the screw _A'_. The movable carbidechamber _D_ has its upper perforated part half filled with carbide, which is pressed upwards by a spring _D'_. The carbide chamber whenfilled is placed in the generating chamber, which is closed, and thelever _F_ of one of the taps _F'_ is turned from "off" to "on, "whereupon water drips from the tank on to the carbide. The evolution ofgas is stopped by reversing the lever of the tap. The second tap isprovided for use when the evolution of gas, through the water-supply fromthe first tap, has been stopped and it is desired to start the apparatuswithout waiting for water from the first tap to soak through a layer ofspent carbide. The two taps are not intended for concurrent use. Theevolved gas passes through a purifier containing any suitable purifyingmaterial to the pipes leading to the burners. [Illustration: FIG. 56. --"PHÔS TYPE E" GENERATOR. ] _Maker:_ ROSCO ACETYLENE COMPANY, BELFAST. _Type:_ Non-automatic; carbide-to-water The "Rosco" generating plant made by this firm comprises a generatingtank _A_ which is filled with water to a given level by means of thefunnel-mouthed pipe _B_ and the overflow _O_. On the top of thewater-sealed lid of the generating tank is mounted the carbide feed-valve_L_, which consists of a hollow plug-tap with handle _M_. Whenthe handle _M_ is turned upwards the hollow of the tap can be filledfrom the top of the barrel with carbide. On giving the tap a third of aturn the hollow of the plug is cut off from the outer air and is openedto the generating tank so that the carbide contained in it is dischargedover a distributor _E_ on to the tray _N_ in the water in thegenerating tank. The gas evolved passes through the scrubber and seal-pot_J_ to the storage gasholder _Q_. From the latter the gaspasses through the dry purifier _T_ to the service-pipe. A sludge-cock _P_ is provided at the bottom of the generating tank and isstated to be available for use while generation of gas is proceeding. Thepurifying material ordinarily supplied is "Roscoline. " [Illustration: FIG. 57. --"ROSCO" GENERATING PLANT. ] _Maker_: THE RURAL DISTRICTS GAS LIGHT CO. , 28 VICTORIA STREET, S. W. _Type_: Automatic; water-to-carbide; contact, superposed trays. The "Signal-Arm" generating apparatus made by this firm comprises a bellgasholder _A_, from the tank _B_ of which water is suppliedthrough a swivelled pipe _C_ to a generating chamber _D_. Oneend of the swivelled pipe is provided with a delivery nozzle, the otherend is closed and counter-weighted, so that normally the open end of thepipe is raised above the level of the water in the tank. A tappet_E_ on the bell of the gasholder comes into contact with, anddepresses, the open end of the swivelled pipe when the bell falls below acertain point. As soon as the open end of the swivelled pipe has thusbeen lowered below the level of the water in the tank, water flowsthrough it into the funnel-shaped mouth _F_ of a pipe leading to thebottom of the generating chamber. The latter is filled with cagescontaining carbide, which is attacked by the water rising in the chamber. The gas evolved passing into and raising the bell of the gasholder causesthe open end of the swivelled pipe to rise, through the weight of thecounterpoise _G_, above the level of the water in the tank and socuts off the supply of water to the generating chamber until the bellagain descends and depresses the swivelled pipe. The tappet on the bellalso displaces a cap _H_ which covers the funnel-shaped mouth of thepipe leading to the generating chamber, which cap, except when theswivelled supply-pipe is being brought into play, prevents any extraneousmoisture or other matter entering the mouth of the funnel. Between thegenerating chamber and the gasholder is a three-way cock _J_ in thegas connexion, which, when the gasholder is shut off from the generator, brings the latter into communication with a vent-pipe _K_ leading tothe open. The gas passes from the holder to a chamber _L_ undergrids packed with purifying material, through which it passes to theoutlet of the purifier and thence to the service-pipe. Either heratol orchloride of lime is used in the purifier, the lid of which, like thecover of the generator, is water-sealed. [Illustration: FIG. 58. --"SIGNAL-ARM" GENERATING PLANT. ] _Maker_: ST. JAMES' ILLUMINATING CO. , LTD. , 3 VICTORIA STREET, LONDON, S. W. _Type_: (1) Automatic; water-to-carbide; contact, superposed trays. This plant consists of the generators _A_, the washer _B_, theequalising gasholder _C_, the purifier _D_, and the water-tank_E_. The carbide is arranged in baskets in the generators to whichwater is supplied from the cistern _E_ through the pipe _F_. The supply is controlled by means of the valve _H_, which isactuated through the rod _G_ by the rise and fall of the gasholder_C_. Gas travels from the gasholder through the purifier _D_ tothe service-pipe. The purifier is packed with heratol resting on a layerof pumice. The washer _B_ contains a grid, the object of which is todistribute the stream of gas through the water. There is a syphon-pot_J_ for the reception of condensed moisture. Taps _K_ areprovided for shutting off the supply of water from the generators during;recharging, and there is an overflow connexion _L_ for conveying thewater to the second generator as soon as the first is exhausted. There isa sludge-cock _M_ at the base of each generator. (2) Non-automatic; water-to-carbide; contact, superposed trays. This resembles the preceding plant except that the supply of water fromthe cistern to the generators takes place directly through the pipe_N_ (shown in dotted lines in the diagram) and is controlled by handthrough the taps _K_. The automatic control-valve _H_ and therod _G_ are omitted. The gasholder _C_ is increased in size sothat it becomes a storage holder capable of containing the whole of thegas evolved from one charging. [Illustration: FIG. 59. --GENERATING PLANT OF THE ST. JAMES' ILLUMINATINGCO. , LTD. (SECTIONAL ELEVATION AND PLAN. )] _Maker_: THE STANDARD ACETYLENE CO. , 123 VICTORIA STREET, LONDON, S. W. _Type_: (1) Non-automatic; carbide-to-water. This plant comprises the generator _A_, the washer _B_, thestorage gasholder _C_, and the purifier _D_. The generator isfirst filled with water to the crown of the cover, and carbide is thenthrown into the water by hand through the gas-tight lock, which is openedand closed as required by the horizontal handle _P_. A cast-irongrid prevents the lumps of carbide falling into the sludge in the conicalbase of the generator. At the base of the cone is a sludge-valve_G_. The gas passes from the generator through the pipe _H_into the washer _B_, and after bubbling through the water thereingoes by way of the pipe _K_ into the gasholder _C_. The syphon-pot _E_ is provided for the reception of condensed moisture, whichis removed from time to time by the pump _M_. From the gasholder thegas flows through the valve _R_ to the purifier _D_, whence itpasses to the service-pipes. The purifier is charged with materialsupplied under the proprietary name of "Standard. " [Illustration: FIG. 60. --CARBIDE-TO-WATER GENERATING PLANT OF THE STANDARDACETYLENE CO. ] (2) Automatic; water-to-carbide; contact, superposed trays. This plant comprises the generators _A_, the washer _B_, theequalising gasholder _C_, the purifier _D_, and the water-tank_E_. The carbide is arranged on a series of wire trays in eachgenerator, to which water is supplied from the water-tank _E_through the pipe _Y_ and the control-tap _U_. The gas passesthrough the pipes _H_ to the washer _B_ and thence to theholder _C_. The supply of water to the generators is controlled bythe tap _U_ which is actuated by the rise and fall of the gasholderbell through the rod _F_. The gas passes, as in the non-automaticplant, through a purifier _D_ to the service-pipes. Taps _W_are provided for cutting off the flow of water to either of thegenerators during recharging and an overflow pipe _h_ serves toconvey the water to the second generator as soon as the carbide in thefirst is exhausted. A sludge-cook _G_ is put at the base of eachgenerator. [Illustration: FIG. 61. --AUTOMATIC, WATER-TO-CARBIDE GENERATING PLANT OFTHE STANDARD ACETYLENE CO. ] (3) Non-automatic; water-to-carbide; contact, superposed-trays. This apparatus resembles the preceding except that the supply of water tothe generators is controlled by hand through the taps _W_, thecontrol valve _U_ being omitted, and the gasholder _C_ being astorage holder of sufficient dimensions to contain the whole of theacetylene evolved from one charging. _Maker_: THORN AND HODDLE ACETYLENE CO. , 151 VICTORIA STREET, S. W. _Type_: Automatic; water-to-carbide; "drawer. " The "Incanto" generating plant made by this firm consists of a risingbell gasholder which acts mainly on an equaliser. The fall of the belldepresses a ball valve immersed in the tank, and so allows water to flowfrom the tank past an outside tap, which is closed only duringrecharging, to a generating chamber. The generating chamber is horizontaland is fixed in the base of the tank, so that its outer case issurrounded by the water in the tank, with the object of keeping it cool. The charge of carbide is placed in a partitioned container, and isgradually attacked on the flooding principle by the water which entersfrom the gasholder tank when the ball valve is depressed. The gas evolvedpasses from the generating chamber by a pipe which extends above thelevel of the water in the tank, and is then bent down so that its enddips several inches below the level of the water. The gas issuing fromthe end of the pipe is thus washed by the water in the gasholder tank. From the gasholder the gas is taken off as required for use by a pipe, the mouth of which is just below the crown of the holder. There is a lipin the upper edge of the gasholder tank into which water is poured fromtime to time to replace that consumed in the generation of the gas. Thereare from one to three generating chambers in each apparatus according toits size. The purifier is independent, and a purifying mixture under theproprietary name of "Curazo" is supplied for use in it. [Illustration: FIG. 62. --"INCANTO" GENERATOR. ] _Maker:_ WELDREN AND BLERIOT, 54 LONG ACRE, LONDON, W. C. _Type:_ Automatic; contact. This firm supplies the "Acétylithe" apparatus (_see_ Belgium). INDEX Absorbed acetylene, Acagine, Accidents, responsibility for, Acetone, effect of, on acetylene, solution of acetylene in, Acetylene-copper, Acetylene-oil-gas, Acetylene Association (Austrian)--regulations as to carbide, Acetylene Association (British)--analysis of carbide, generator rules, pressure gauges, purification rules, Acetylene Association (German)--analysis of carbide, holders, generator rules, standard carbide, Acetylene tetrachloride, production of, Ackermann burner, Advantages of acetylene, general, hygienic, intrinsic, pecuniary, "After generation, "Air, admission of, to burners, and acetylene, ignition temperature of, composition of, dilution of acetylene with, before combustion, effect of acetylene lighting on, coal-gas lighting on, on illuminating power of acetylene, paraffin lighting on, in acetylene, in flames, effect of, in generators, danger of, objections to, in incandescent acetylene, in service-pipes, proportion of, rendering acetylene explosive, removing, from pipes, specific gravity of, sterilised by flames, Air-gas, and acetylene, comparison between, and carburetted acetylene, comparison between, effect of cold on, illuminating power of, Alcohol, action of, on carbide, for carburetting acetylene, holder seals, from acetylene, production of, Allgemeine Carbid und Acetylen Gesellschaft burner, Alloys, fusible, for testing generators, Alloys of copper. See _Copper (alloyed)_Aluminium sulphide, in carbideAmerica (U. S. ), regulations of the National Board of Fire Underwriters, American gallon, value of, Ammonia, in acetylene, in coal-gas, removal of, solubility of, in water, Analysis of carbide, Ansdell, compressed and liquid acetylene, Anthracene, formation of, from acetylene, Anti-freezing agents, Area of purifiers, Argand burners, Aromatic hydrocarbons, Arrangement of generating plant, Arsenious oxide purifier, Atkins, dry process of generation, Atmospheric moisture and carbide, Atomic weights, Attention needed by generators, Austrian Acetylene Association, regulations as to carbide, Austrian Government Regulations, Autogenous soldering and welding, Automatic generators. See _Generators (automatic)_ B Baking of carbideBall-sockets for acetylene, Barium peroxide purifier, sulphate in bleaching-powder, Barrel, gas, for acetylene, quality ofBell gasholders. See _Holders (rising)_Benz purifying material, Benzene, for carburetting acetylene, production of, from acetylene, Benzine. See _Petroleum spirit_Bergé, detection of phosphorus, and Reychler, purification of acetylene, and Reychler's reagent, solubility of acetylene in, Bernat, formula for mains and pipes, Berthelot, addition of chlorine to acetylene, sodium acetate, sulphuric acid and acetylene, Berthelot and Matignon, thermochemical data, and Vieille, dissolved acetylene, Billwiller burners, Black, acetylene, Blagden, sodium hypochlorite, Bleaching-powder purifier (simple), Blochmann, copper acetylide, Blow-off pipes. See _Vent-pipes_Blowpipe, acetylene, Boiling-ring, Boistelle. See _Molet_Borek, enrichment of oil-gas, _Bougie décimale_, Brackets for acetylene, Bradley, Read, and Jacobs, calcium carbophosphide, Brame and Lewes, manganese carbide, Bray burners, British Acetylene Association. See _Acetylene Association(British)_, Fire Offices Committee Regulations, regulations. See _Acetylene Association (British); Home Office; Orders in Council_Bromine-water purifier, Bullier, effect of heat on burners, phosphorus in acetylene, and Maquenne purifier, Bunsen burner, principle of, Bunte, enrichment of oil-gas, Burner orifices and gas density, Burners, atmospheric, principle of, design of, glassware for, heating, incandescent, Ackermann, Allgemeine Carbid und Acetylen Gesellschaft, Bray, firing back in, Fouché, Günther's, illuminating power of, Jacob, Gebrüder, Keller and Knappich, Knappich, O. C. A. , pressure for, principles of construction of, Schimek, Sirius, Trendel, typical, Weber, Zenith, self-luminous, Argand, as standard of light, Billwiller, Bray, choking of, corrosion of, cycle, Falk, Stadelmann and Co. 's, Konette, Phôs, Wiener's, Dolan, Drake, effect of heat on, Elta, Falk, Stadelmann and Co. 's, firing back in, fish-tail, Forbes, Hannam's, illuminating power of, self-luminous injector, Javal, Kona, Luta, Naphey, Orka, Phôs, Pintsch, pressure for, rat-tail, Sansair, Schwarz's, Stadelmann, Suprema, twin, angle of impingement in, injector, non-injector, warping of, Wiener's, Wonder, By-products, See also _Residues_ C Cadenel, shape of incandescent acetylene mantle, "Calcidum, "Calcium carbide, action of heat on, action of non-aqueous liquids on, analysis of, and carbon bisulphide, reaction between, and hydroxide, reaction between, and ice, reaction between, and steam, reaction between, and water, reaction between, as drying material, baking of, balls and cartridges. See _Cartridges_ bulk of, chemical properties of, crushing of, decomposition of, by solids containing water, heat evolved during, imperfect, speed of, temperature attained during, deterioration of, on storage, drums of, dust in, explosibility of, fire, risk of, formula for, granulated, heat-conducting power of, of formation of, impurities in, inertness of, in residues, physical properties of, purity of, quality, regulations as to, sale and purchase of, regulations as to, scented, shape of lumps of, sizes of, small, yield of gas from, specific gravity of, heat of, standard, British, German, "sticks, " storage regulations for, subdivided charges of, sundry uses of, swelling of, during decomposition, "treated, " yield of acetylene from, Calcium carbophosphide, Calcium chloride, cause of frothing in generators, for seals, purifier, solubility of acetylene in, Calcium hydroxide, adhesion of, to carbide, and carbide, reaction between, milk of, solubility of acetylene in, physical properties of, space occupied by, Calcium hypochlorite, Calcium oxide, and water, reaction between, hydration of, hygroscopic nature of, physical properties of, Calcium phosphide, Calcium sulphide, Calorie, definition of, Calorific power of acetylene, various gases, Candle-power. See _Illuminating power_Capelle, illuminating power of acetylene, Carbide. See _Calcium carbide_Carbide-containers, air in, filling of, partitions in, water-jacketing, Carbide-feed generators. See _Generators (carbide-to-water)_Carbide impurities in acetylene, Carbide-to-water generators. See _Generators (carbide-to-water)_Carbides, mixed, Carbolic acid, production of, from acetylene, Carbon, combustion of, in flames, deposition of, in burners, gaseous, heat of combustion of, heat of combustion of, vaporisation of, pigment, production of, Carbon bisulphide and acetylene, reaction between, and calcium carbide, reaction between, in coal-gas, Carbon dioxide, addition of, to acetylene, dissociation of, effect of, on explosibility of acetylene, for removing air from pipes, heat of formation of, produced by respiration, benzene, coal-gas, in flame of acetylene, Carbon monoxide, in acetylene, heat of combustion of, formation of, temperature of ignition of, Carbonic acid. See _Carbon dioxide_Carburetted acetylene, composition of, effect of cold on, illuminating power of, manufacture of, pecuniary value of, Carburetted water-gas, enrichment of, Carburine. See _Petroleum spirit_Carlson, specific heat of carbide, Caro, acetone vapour in acetylene, addition of petroleum spirit to generator water, air in incandescent acetylene, calorific power of gases, colour of incandescent acetylene, composition of mantles, durability of mantles, heat production in generators, illuminating power of carburetted acetylene, of incandescent acetylene, oil of mustard, silicon in crude acetylene, Caro and Saulmann, "Calcidum, "Carriage, cost of, and artificial lighting, Cartridges of carbide, Cast-iron pipe for acetylene, Castor oil for acetylene joints, Catani, temperature of acetylene flame, Caustic potash purifier, Cedercreutz, yield of gas from carbide, and Lunge, purification, Ceilings, blackening of, Ceria, proportion of, in mantles, Cesspools for residues, Chandeliers, hydraulic, for acetylene, Charcoal and chlorine purifier, Charging generators after dark, at irregular intervals, Chassiron lighthouse, Chemical formulæ, meaning of, Chemical reactions and heat, of acetylene, Chimneys for stoves, &c. , glass, for burners, Chloride of lime. See _Bleaching-powder_Chlorine and acetylene, compounds of, and charcoal purifier, in acetylene, Chromic acid purifier, Cigars, lighted, danger of, Claude and Hess, dissolved acetylene, Coal-gas, enrichment of, with acetylene, illuminating power of, impurities in, vitiation of air by, Cocks, hand-worked, in generators, Coefficient of expansion of acetone, air, dissolved acetylene, gaseous acetylene, liquid acetylene, simple gases, Coefficient of friction of acetylene, of coal-gas, Coke filters for acetylene, Cold, effect of, on acetylene, on air-gas, on carburetted acetylene, on generation, Colour judging by acetylene, of acetylene flame, of air-gas flame, Colour of atmospheric acetylene flame, of coal-gas flame, of electric light, of incandescent acetylene flame, of spent carbide, Combustion of acetylene, deposit from, Composition pipe for acetylene, Compounds, endo- and exo-thermic, explosive, of acetylene and copper, "Compounds, " of phosphorus and sulphur, silicon, Compressed acetylene, Condensed matter in pipes, removal of, Condensers, Connexions, flexible, for acetylene, Construction of generators, principles of, regulations as to, Contact generators, Convection of heat, Cooking-stoves, Copper acetylide, (alloyed) in acetylene apparatus, (unalloyed) in acetylene apparatus, and acetylene, reactions between, carbides, chloride purifierCorrosion in apparatus, avoidance of, Corrosive sublimate purifier, as test for phosphorusCost of acetylene lighting, Cotton-wool filters for acetylene, Council, Orders in. See _Orders in Council_Counterpoises for rising holders, Couples, galvanic, Coward. See _Dixon_Critical pressure and temperature of acetylene, Crushing of carbide, "Cuprene, "Cuprous chloride purifier, Cycle lamps, burners for, dilute alcohol for, Cylinders for absorbed acetylene, D Davy, addition of chlorine to acetylene, Davy's lamp for generator sheds, Decomposing vessels. See _Carbide containers_Decomposition of acetylene, of carbide, See _Calcium carbide (decomposition of)_De Forcrand, heat of formation of carbide, Density. See _Specific gravity_Deposit at burner orifices, on reflectors from combustion of acetylene, Deterioration of carbide in air, Diameter of pipes and explosive limits, Diaphragms, flexible, in generators, Diffusion through gasholder seals, Diluted acetylene, Dimensions of mains and pipes, Dipping generators, Displacement gasholders. See _Holders (displacement)_Dissociation of acetylene, carbon dioxide, water vapour, Dissolution of acetylene, depression of freezing-point by, of gas in generators, Dissolved acetylene, Dixon and Coward, ignition temperature of acetylene, of various gases, Dolan burners, Doors of generator sheds, Drainage of mains, Drake burners, Driers, chemical, Dripping generators, Drums of carbide, Dry process of generation, Dufour, addition of air to acetylene, "Dummies" in gasholder tanks, Dust and incandescent lighting, in acetylene, carbide, E Effusion of gases, Eitner, explosive limits of acetylene, and Keppeler, estimation of phosphine, phosphorus in crude acetylene, Electric lamps in generator sheds, lighting, cost, and efficiency of, Elta burner, Endothermic compounds, nature of acetylene, Engines, use of acetylene in, Enrichment, value of acetylene for, with acetylene, épurène purifying material, Equations, chemical, meaning of, Erdmann, acetylene as a standard of light, colour of acetylene flame, production of alcohol, Ethylene, formation of from acetylene, heats of formation and combustion of, ignition temperature of, Exhaustion of air by flames, Exothermic compounds, Expansion of gaseous acetylene, coefficient of, of liquid acetylene coefficient of, various coefficients of, Explosibility of carbide, Explosion of chlorine and acetylene, of compressed acetylene, Explosive compounds of acetylene and copper, effects of acetylene dissociation, limits, meaning of term, of acetylene, of various gases, nature of acetylene, wave, speed of, in gases, Expulsion of air from mains, F Faced joints for acetylene, Falk, Stadelmann and Co. , boiling-ring, burners, cycle-lamp burner, Ferric hydroxide purifier, Fery, temperature of flames, and Violle, acetylene as standard of light, Filters for acetylene, Filtration, Fire Offices Committee Regulations (British), risks of acetylene apparatus, carbide, flame illuminants, Underwriters, United States, Regulations, "Firing back" in incandescent burners, self-luminous burners, Fish, action of lime on, Fittings for acetylene, quality of, Flame, colour of, air-gas, atmospheric acetylene, coal-gas, incandescent, acetylene, self-luminous acetylene, Flame illuminants, risk of fire with, of acetylene containing air, steadiness of acetylene, Flame temperature of acetylene, temperature of various gases, Flames, distortion of, by solid matter, effect of air on, nitrogen on, evolution of heat in, light in, jumping of, liberation of carbon from, loss of heat from, shading of acetylene, size of, Flare lamps, Flash-point of paraffin, Flexible connexions for acetylene, Floats in holder seals, Flooded-compartment generators, Flow of gases in pipes, Flues for heating burners, Fog, transmission of light through, Forbes burner, Foreign regulations, Formulæ, meaning of chemical, Fouché, absorbed acetylene, burner, dissolved acetylene, illuminating power of acetylene air mixtures, incandescent acetylene, liquid acetylene, oxy-acetylene blowpipe, Fournier. See _Maneuvrier_Fowler, enrichment of oil-gas, Fraenkel, deposit on reflectors from combustion of acetylene, silicon in acetylene, France, regulations of the Conseil d'Hygiène de la Seine, village acetylene mains in, Frank, freezing-point of calcium chloride solutions, preparation of black pigment, purifier, Frankoline, Freezing of generators, of holder seals, Freezing of portable lamps, of pressure-gauges, Freezing-point, depression of by dissolution of acetylene, of calcium chloride solutions, of dilute alcohol, of dilute glycerin, Freund and Mai, copper acetylide, Friction of acetylene, coefficient of, coal-gas, coefficient of, gas in pipes, Frost, effect of, on air-gas, on carburetted acetylene, Froth, lime, in acetylene, Frothing in generators, Fuchs and Schiff, olive oil, Furnace gases for removing air from pipes, G Gallon, American, value of, Galvanic action, Garelli and Falciola, depression of freezing-point by dissolution of acetylene, Gas barrel for acetylene, objection to, drying of, engines, acetylene for, escape of, from generators, firing, effects of, volumes, correction of, for temperature and pressure, yield of, from carbide, determining, standard, Gases, calorific value of, effusion of, explosive limits of, flame temperature of, illuminating power of, inflammable properties of, speed of explosive wave in, temperature of ignition of, Gasfitters' paint, Gasholders. See _Holders_Gatehouse, F. B. , test-papers, J. W. , estimation of phosphine, Gaud, blocking of burners, polymerisation of acetylene, Generation, dry process of, Generating plant, regulations as to construction of, Generator impurities in acetylene, pressure, utilisation of, sheds, lighting of, smoking in, water, addition of bleaching-powder to, of petroleum spirit to, Generators and holders, isolation of, attention needed by, Generators, charging after dark, chemical reactions in, construction of, copper in, corrosion in, dissolution of gas in, effect of tarry matter in, escape of gas from, failure of, for analytical purposes, for welding, frothing in, frozen, thawing of, gauge of sheet-metal for, heat dissipation in, economy in, produced in, high temperatures and impurities in, instructions for using, joints in, making, "lagging" for, lead solder in, materials for construction of, maximum pressure in, output of gas from, overheating in, polymerisation in, pressure in, protection of, from frost, purchase of, regulations as to, American (National Board of Fire Underwriters), Austrian Government, British Acetylene Association, Fire Offices Committee, Home Office Committee(1901), French (Council d' Hygiene de la Seine), German Acetylene Association, Hungarian Government, Italian Government, responsibility for accidents with, selection of, temperatures in, typical, vent-pipes for, waste-pipes for, water-jackets for, water-scale in, Generators (automatic), advantages of, carbide-to-water, definition of, flexible diaphragms for, holders of, interlocking in, mechanism for, pressure thrown by, speed of reaction in, store of gas in, supply of water to, use of oil in, water-to-carbide, worked by holder bell, by pressure, Generators (carbide-to-water), advantages of, frothing of, grids for, loss of gas in, maximum temperature in, pressure in, quantity of water required by, Generators (contact), (dipping), temperatures in, (dripping), temperatures in, (flooded compartment), (non-automatic), advantages of, carbide-to-water, hand-charging of, water required for, definition of, speed of reaction in, water-to-carbide, (portable), (shoot), (water-to-carbide), overheating in, with carbide in excess, with water in excess, Gerard, silicon in crude acetylene, Gerdes, acetylene copper, German Acetylene Association. (See _Acetylene Association, German_)Gin, heat of formation of carbide, Glassware, for burners, Glow-lamps, electric, in generator sheds, Glucose for treatment of carbide, Glycerin for holder-seals, for wet meters, Governor, displacement holder as, Governors, Graham, effusion of gases, Gramme-molecules, Granjon, illuminating power of self-luminous burners, phosphine in acetylene, pressure, purifier, Granulated carbide. See _Calcium carbide, (granulated)_Graphite, artificial, production of, Grease for treatment of carbide, Grids for carbide-to-water generators, in purifiers, Grittner, acetylene, and copper, Guides for rising holders, Güntner burner, H Haber, effect of heat on acetylene, Haldane, toxicity of sulphuretted hydrogen, Hammcrschmidt, correction of gas volumes, and Sandmann, milk of lime, Hannam's Ltd. , burners, Hartmann, acetylene flame, Haze, on combustion of acetylene, Heat absorbed during change of physical state, action on acetylene. See _Overheating_ carbide, and temperature, difference between, conducting power of carbide iron and steel, water, convected, developed by acetylene lighting, coal-gas lighting, electric lighting, paraffin lighting, dissipation of, in generators, economy in generators, effect of, on acetylene. (See _Overheating_) on burners, evolution of, in flames, expansion of gaseous acetylene by, liquid acetylene by, from acetylene, production of, latent. See _Latent heat_ loss of, from flames, of chemical reactions, of combustion of acetylene, carbon, carbon monoxide, ethylene, of formation of acetylene, calcium carbide, hydroxide, oxide, carbon dioxide, monoxide, ethylene, water, of hydration of calcium oxide, of reaction between carbide and calcium hydroxide, between carbide and water, of solution of calcium hydroxide, of vaporisation of carbon, water, radiant, specific. See _Specific heat_Heating apparatus for generator sheds, Hefner unit, Heil, atmospheric acetylene flame, carburetted acetylene, Heise, acetylene flame, Hempel, enrichment of coal-gas, Heratol, Hess. See _Claude_Hexachlorethane, production of, High houses, supply of acetylene to, Holder-bells, for testing mains, supplying water to automatic generators, weighting of, Holder-seals, freezing of, level of liquid in, liquids in, and pressure, solubility of acetylene in, use of floats in, liquids in, for decomposing carbide, oil in, water in, for washing the gas, Holders (gas) and generators, isolation of, and pressure, relationship between, and purifiers, relative position of, exposed, roofs over, false interiors for, freezing of, gauge of sheet-metal for, loss of pressure in, moistening of gas in, of automatic generators, preservation of, from corrosion, situation of, size of, vent-pipes for, value of, Holders (displacement), action of, pressure given by, (rising), guides and counterpoises for, pressure thrown by, equalisation of, tanks for, Home Office, maximum pressure permitted by, prohibition of air in acetylene by, Committee, 1901, recommendations, report, Home Secretary's Orders. See _Orders in Council_Hoxie. See _Stewart_, Hubou, acetylene black, Hungarian rules for apparatus, Hydraulic pendants for acetylene, Hydrocarbons formed by polymerisation, illuminating power of, volatile, names of, Hydrochloric acid in purified acetylene, Hydrogen and acetylene, reactions between, effect of, on acetylene flame, ignition temperature of, in acetylene, liberated by heat from acetylene, silicide in crude acetylene, Hygienic advantages of acetylene, I Ice, reaction between carbide and, Ignition temperature of acetylene, various gases, Illuminating power and illuminating effect, definition of, of acetylene, after storage, carburetted, effect of air on, incandescent, nominal, self-luminous, of acetylene-oil-gas, of air-gas, of polymerised acetylene, of candles, of coal-gas, of electric lamps, of hydrocarbons, various, of paraffin, Illumination, amount of, required in rooms, of lighthouses, of optical lanterns, Impurities in acetylene, carbide, detection and estimation of, effect of, on air, generator, harmfullness of, water soluble, See also _Ammonia_ and _Sulphuretted hydrogen_ in coal-gas, in purified acetylene, maximum limits of, Incandescent acetylene, burners. See _Burners (incandescent)_ mantles, Inertness of carbide, Inflaming-point of acetylene, Inflammability, spontaneous, Installations, new, removal of air from, Interlocking of automatic generators, Iron and acetylene, reactions between, and steel, heat-conducting power of, silicide in carbide, Insecticide, carbide residues as, Isolation of apparatus parts, Intensity, specific, of acetylene light, of oil light, Italian Government rules, J Jackets for generators, Jacob, Gebrüder, burner, Jacobs. See _Bradley_Jaubert, arsenious oxide purifier, Javal burners, blocking of, purifier, Jet photometer of acetylene, Joint-making in generators, pipes, K Keller and Knappich burner, Keppeler, lead chromate in acagine, Keppeler, purification, silicon in acetylene, test-papers, See also _Eitner_Kerosene. See _Paraffin oil_Klinger, vent-pipes, Knappich burner, Kona burner, Konette cycle-lamp burner, L La Belle boiling ring, Labour required in acetylene lighting, Lagging for generators, Lamps for generator sheds paraffin, portable, acetone process for, Landolt-Börnstein, solubility of acetylene in water, Landriset. See _Rossel_Lantern, optical, illumination of, Latent heat, Lead chromate in bleaching-powder, objection to, in generators, pipes for acetylene, salts in bleaching-powder, wire, &c. , for faced joints, Leakage of acetylene, Leaks, search for, Le Chatelier, explosive limits, temperature of acetylene flame, thermo-coupleLeduc, specific gravity of acetylene, Lépinay, acetylene for engines, Level alteration and pressure in mains, Lewes, ammonia in crude acetylene, blocking of burners, haze, heat of decomposition of carbide, production in generators, illuminating power of acetylene, phosphorus in crude acetylene, polymerisation of acetylene, presence of hydrogen and carbon monoxide in acetylene, reaction between carbide and calcium hydroxide, silicon in crude acetylene, temperature of acetylene flame, Lewes and Brame, manganese carbide, Lidholm, estimation of phosphine, Lifebuoys, acetylene for, Lifetime of burners, mantles, Lifting power of acetylene in holders, Light, acetylene as a standard of, colour of acetylene, incandescent, self-luminous, evolution of, in flames, from acetylene, production of, transmission of through fog, Lights, single, disadvantages of, strong and weak, comparison between, Lighthouse illumination, Lighting by acetylene, scope of, of generator sheds, Lime dust in acetylene, reaction with sodium carbonate, sludge. See _Residues_ solubility of, in sugar solutions, water, solubility of gas in, Lime-light, acetylene for the, Limits, explosive, of acetylene, Lindé-air, Linseed oil for acetylene joints, Liquid acetylene, properties of, condensation in pipes, in holder-seals and pressure, in pressure-gauge, Liquids, corrosive action of, on metals, for seals, purification by, solubility of acetylene in, Locomotive lighting, Loss of gas in generators, of pressure in holders, in mains, in purifiers, on distribution, Love, enrichment by acetylene, Lubricating oil for seals, Luminous burners. See _Burners, self-luminous_Lunge and Cedercreutz, determination of phosphorus in acetylene, purification, Luta burner, Lutes for holders. See _Seals_ M Mahler, temperature of flames, Mai and Freund, copper acetylide, Mains, deposition of liquid in, diameter of, and explosive limits, dimensions of, escapes from, friction in, laying of, lead, quality of, removing air from, testing of, Make of acetylene from carbide, in generators, Manchester burners, Maneuvrier and Fournier, specific heat of acetylene, Manganese carbide, Mantles for acetylene, Manure for generator protection, Manurial value of generator residue, Maquenne. See _Bullier_Marsh gas, enrichment with acetylene, formed from acetylene, Matignon. See _Berthelot_, Mauricheau-Beaupré, épurène, estimation of phosphine, frothing in generators, phosphine in acetylene, silicon in acetylene, Mechanism for automatic generators, Mercaptans in acetylene, Mercuric chloride purifier, test for phosphorus, Merck test-papers, Metals for generators, gauge of, Meters for acetylene, Methane, enrichment with acetylene, formed from acetylene, ignition temperature of, Methylated spirit for generators, for holder seals, Meyer and Münch, ignition temperatures, Mildew in vines, use of acetylene in, Milk of lime, solubility of acetylene in, Mineral oil for lighting. (See _Paraffin oil_) for seals, Miner's lamp for generator sheds, Mist, transmission of light through, Mixter, thermo-chemical data, Mixtures of acetylene and air, illuminating duty of, Moisture, effect of, on carbide, in acetylene, Molecular volume of acetylene, weight of acetylene, weights, various, Molet-Boistelle acetylene-air mixture, Morel, formula for acetylene pipes, sodium plumbate purifier, specific heat of acetylene, of carbide, Mosquitoes, destruction of, Moths, catching of, Motion of fluids in pipes, Motors, acetylene for, Münch. See _Meyer_Münsterberg, acetylene flame, Mustard, oil of, N Naphey burners, Naphthalene, formation of, from acetylene, Neuberg, illuminating power of acetylene, radiant efficiency of acetylene, Nieuwland, mixtures of acetylene and chlorine, Nichols, illuminating power of acetylene after storage, temperature of acetylene flame, Nickel and acetylene, reactions between, Nipples, burner, materials for, Nitrides in carbide, Nitrogen in flames, effect of, Non-automatic generators. See _Generators (non-automatic)_Non-luminous acetylene flame, appearance of, burners. See _Burners (atmospheric)_Non-return valves, O O. C. A. Burner, Odour of acetylene, Oil, action of, on carbide, castor, for acetylene joints, in generators, in residues, in seals, linseed, for acetylene joints, mustard, olive, for seals, (See also _Paraffin oil_)Olive oil for seals, Oil-gas, enrichment of, Optical efficiency of acetylene, Orders in Council, air in acetylene, compression of absorbed acetylene, acetylene-oil-gas, neat acetylene, Origin of petroleum, Orka burner, Ortloff, friction of acetylene, Overheating in generators, See also _Polymerisation_Oxide of iron purifier, Oxy-acetylene blowpipe, Oxygen required for combustion of acetylene, of benzene, combustion of acetylene with, flames burning in, P Paint, cause of frothing in generators, gas-fitters', Paraffin oil, action of, on carbide, flash-point of, illuminating power of, in residues, lamps, lighting, effect of on air, heat developed by, quality of different grades of, use of in automatic generators, seals, Paraffin wax, treatment of carbide with, Partial pressure, Pendants, water-slide for acetylene, Petroleum oil. See _Paraffin oil_ spirit, addition of, to generator water, composition of, for carburetted acetylene, spirits, nomenclature of, theory of origin of, Pfeiffer, purifier, Pfleger, puratylene, Phenol, production of, from acetylene, Phôs burners, Phosphine, cause of deposit at burner orifices, composition of, in crude acetylene, amount of, toxicity of, Phosphoretted hydrogen. See _Phosphine_Phosphorus and incandescent mantles, "compounds, " in crude acetylene, in purified acetylene, detection and determination of, removal of, "Phossy-jaw, "Photometer, jet of acetylene, Phylloxera, use of acetylene for, Physical properties of acetylene, Pickering, freezing-points of calcium chloride solutions, Pictet, freezing-points of dilute alcohol, purification of acetylene, Pintsch burners, Pipes, blow-off. See _Vent-pipes_ diameter of, and explosive limits, vent. See _Vent-pipes_ (See also _Mains_)Plant, acetylene, fire risks of, order of items in, Platinum in burners, Poisonous nature of acetylene, Pole, motion of fluids in pipes, pressure thrown by holders, Polymerisation, definition of, of acetylene, See also _Overheating_Porous matter, absorption of acetylene in, Portable lamps, acetone process for, temperature in, Potassium bichromate purifier, hydroxide purifier, permanganate purifier, Power from acetylene, production of, Precautions with generators, with new installations, Presence of moisture in acetylene, Pressure and leakage, after explosions of acetylene, atmospheric, automatic generators working by, correction of gas volumes for, critical, of acetylene, definition of (gas), for incandescent burners, self-luminous burners, gauge, liquid for, given by displacement holders, rising holders, in generators, utilisation of, in mains and pipes, in purifiers, loss of, irregular, caused by vent-pipes, maximum safe, for acetylene, necessity for regular, partial, regulators. See _Governors_Protection of generators from frost, holders from frost, Puratylene, Purchase of a generator, carbide, regulations as to, Purification by liquids and solids, in portable lamps, necessary extent of, reasons for, regulations as to, speed of, Purified acetylene, chlorine in, hydrochloric acid in, phosphorus in, sulphur in, Purifiers and holder, relative positions of, construction of, duplication of, exhaustion of, foul, emptying of, loss of pressure in, mechanical, for acetylene, Purifying materials, density of, efficiency of, quantity required, Pyralid, destruction of the, Q Quality of carbide, regulations as to, Quicklime. See _Calcium oxide_ R Radiant efficiency of acetylene, heat, Railway lighting by acetylene, Ramie mantles for acetylene, Range of explosibility, meaning of term, of acetylene, Rat-tail burner, Reactions between copper and acetylene, chemical, of acetylene, physical, of acetylene, Reaction grids in generators, Read and Jacobs. See _Bradley_Rod lead for acetylene joints, Regulations, American (National Board of Fire Underwriters of U. S. A. ), Austrian Acetylene Association, Government, British Acetylene Association, Fire Offices Committee, Home Office Committee (1901), for analysis of carbide, for construction of generating plant, for generators, for purification, for sale and purchase of carbide, for sampling carbide, for storing carbide, French (Conseil d'Hygiène de la Seine), German Acetylene Association, Hungarian Government, Italian Government, Residue from dry process of generation, Residues, carbide in, colour of, composition of, consistency of, disposal of, containing oil, manurial value of, utilisation of, Respiration of acetylene, Reversibility of reaction between calcium oxide and water, Reychler. See _Bergé_Rising holders. See _Holders (rising)_Rossel and Landriset, ammonia in crude acetylene, purifier, sulphur in crude acetylene, Roofs over exposed holders, Rooms, amount of illumination required in, Rubber tubes for acetylene, Ruby for burners, Rules. See _Regulations_ S Safety lamp, Davy's, for generator sheds, valves. See _Vent-pipes_Sale of carbide, regulations as to, Salt, common, in holder-seals, Salzbergwerk Neu Stassfurt, production of tetrachlorethane, Sampling carbide, Sandmann. See _Hammerschmidt_Sansair burner, Saulmann. See _Caro_Sawdust in bleaching-powder, Scale, water, in generators, Scented carbide, Schiff. See _Fuchs_Schimek burner, Schwander, carburetted acetylene, Schwarz burners, Seal-pots, Seals (holder). See _Holder-seals_Seams in generator-making, Self-luminous burners. See _Burners (self-luminous)_Sensible heat, Separation of holder from generator, Service-pipes. See _Mains_Shoot generators, Silicon compounds, in acetylene, in carbide, Sirius burner, Slaked lime. See _Calcium hydroxide_Sludge. See _Residues_Sludge-cocks, automatic locking of, Sludge-pipes, blocked, clearance of, Smell of crude and purified acetylene, Smith, purification, Smoke, production of, by flames, Smoking, danger of, in generator sheds, Soap, use of, in testing pipes, Soda, washing, for decomposing carbide, Sodium acetate solution for generator jackets, Sodium carbonate and lime, reaction between, crystallised, for decomposing carbide, chloride for holder-seals, solubility of acetylene in, hypochlorite purifier, plumbate purifier, sulphate in bleaching-powder, Soil, carbide residues as dressing for, Solder in generators, Soldering, autogenous, Solids containing water, decomposition of carbide by, purification by, Solubility of acetylene, in generators, in holders, in liquids, Soot, production by, of flames, Space occupied by purifying materials, Sparks from steel tools, danger of, Specific gravity and holder pressure, leakage, of acetylene, dissolved, gaseous, liquid, of air, of carbide, of gases, and burner construction, of water, heat of acetylene, of carbide, heats, various, intensity. See _Intensity, specific_Speed of reactions between carbide, water, and calcium hydroxide, of purification, Spent lime. See _Residues_Spontaneous inflammability, Spraying apparatus, Stable manure for warming generators, Stadelmann burners, Standard of illumination in rooms, of light, acetylene as, Steam, latent heat of, use of, specific heat of, reaction between carbide and, Steam-barrel for acetylene mains, Steatite for burners, Steel, heat-conducting power of, tools, danger ofSterilisation of air by flames, Stewart and Hoxie, radiant efficiency of acetylene, Storage regulations for carbide, vessels for carbide, temporary, Styrolene. Formation of, from acetylene, Suckert. See _Willson_Suffocation by acetylene, Sugar solutions, solubility of lime in, Sulphur "compounds, " in coal-gas, in crude acetylene, in purified acetylene, removal of, Sulphuretted hydrogen, solubility of, in water, toxicity of, Sulphuric acid and acetylene, reactions between as purifying material, Superficial area in purifiers, Supply of water to automatic generators, Suprenia burners, Swelling of carbide during decomposition, Symbols, chemical, meaning of, Syphons for removing water, T Table-lamps, acetone process for, Tabular numbers, Tanks for rising holders, construction of, "Tantalus Cup, "Taps for acetylene pipes, Tar, cause of frothing in generators, Tarry matter in generators, Telescopic gasholders. _See Holder (rising)_Temperature and heat, difference between, correction of volumes for, critical, of acetylene, high, effect of, on acetylene. See _Polymerization_ of acetylene blowpipe, flame, of dissociation of acetylene, of ignition of acetylene, various gases, of reaction between carbide and calcium hydroxide, between carbide and water, Temperatures in generators, calculation of, determination of, Tension of liquid acetylene, Test-papers, Tetrachlorethane, production of, Tetrachloride, acetylene, production of, Thawing of frozen apparatus, Thermo-chemical data, Thermo-couple, Le Chatelier's, Thomson, radiant efficiency of acetylene, thermo-chemical data, Tools, steel or iron, danger of, Town supplies, Toxicity of acetylene, of sulphur and phosphorus compounds, Train-lighting by acetylene, Treated carbide. See _Calcium carbide (treated)_Trondol burner, Tubes, diameter of, and explosive limits, Tubes for acetylene. See _Mains_Tubing, flexible, for acetylene, Typical generators, U Ullmax purifier, Unaccounted-for gas, Underwriters, United States Fire, United States. See _America_Uses, sundry, for acetylene, V Valuation of carbide, Value of acetylene, hygienic, enriching, pecuniary, of purifying materials, Valves, screw-down, for generators, Vapour, water, in acetylene, objections to, removal of, value of, Vehicular lamps, Ventilation of generator sheds, Vent-pipes, economy of, for carbide vessels, generators, holders, noise in, position of mouths of, size of, Vibration and incandescent lighting, Vieille, dissolved acetylene, Vigouroux, silicon in acetylene, Village installations, mains for, leakage in, supplies, Villard, liquid acetylene, Vines, treatment by acetylene of, for mildew and phylloxera, Violle and Féry, acetylene as standard of light, Vitiation of air by flames, Volume, alteration of, on dissociation, and weight of acetylene, molecular, of acetylene, Volume of acetylene passing through pipes, Volumes, gas, correction for temperature and pressure, W Washers, oil, water, Waste-pipes of generators, Water and calcium oxide, reaction between, and carbide, heat of reaction between, boiling-point, evolution of gas at, condensation of, in pipes, consumption of, in generators, convection currents in, freezing-point, evolution of gas at, heat absorbed in warming, conducting power of, of formation of, in excess, generators with, in holders, freezing of, use for decomposition, use for washing, jackets for generators, quality of, for portable generators, quantity required in carbide-to-water generators, scale in generators, solubility of acetylene in, of impurities in, of load in, specific gravity of, supply for automatic generators, non-automatic generators, yield of gas per unit of, Water-gas, enrichment with acetylene, Water-seals, as not-return valves, setting water-level in, Water-slide pendants for acetylene, Water-soluble impurities in acetylene, See also _Ammonia and Sulphuretted hydrogen_Water-to-carbide generators. See _Generators (water-to-carbide)_Water-vapour, dissociation of, existence of, at low temperatures, in acetylene, objections to, removal of, value of, reaction between carbide and, Weber burner, Wedding, enrichment of coal-gas, Weed-killer, carbide residues as, Weight and volume of acetylene, Weights, atomic, molecular, Welding, acetylene, White lead, for acetylene joints, Wiener burners, Willgerodt, purification, Willson and Suckert, liquid acetylene, Windows in generator sheds, Winter, manipulation of generators during, Wöhler, addition of chlorine to acetylene, Wolff, acetone in acetylene, illuminating power of acetylene, purifier, silicon in acetylene, Wonder burner, Work done in actuating automatic generators, Y Yield of gas, deficient, cause of, from carbide, determining, (British standard), (German standard), from water, Z Zenith burner, INDEX TO APPENDIX A "A" Generator (of Braby and Co. , Ltd. ), "A1" generator (of Acetylene Corporation of Great Britain), "A-to-Z" generator (of Acetylene Corporation of Great Britain), Acetylene Corporation of Great Britain, Acetylene Gas and Carbide of Calcium Co. , Acetylene Illuminating Co. , Ltd. , "Acetylite" generator, "Acétylithe" generator, Acétylithe, Soc. An. De l', Allen Co. , "Allen" Flexible-tube generator, "Allen" purifying material, American generators, Applications de l'Acétylène, La Soc. Des. , Austrian generator, Automatic generators, B "B" generator (of Braby and Co. , Ltd. ), Belgian generators, Bon Accord Acetylene Gas Co. , "Bon Accord" generator, Braby, Frederick and Co. , Ltd. , British generators, C Canadian generators, Carbide-to-water generators, "Carburlen" purifying material, Chloride of lime purifying material, Colt Co. , J. G. , "Colt" generator, Compartment, flooded, generator, Contact generators, Cork waste and wadding purifying material, "Corporation Flexible Tube Generator, ""Curaze" purifying material, D "Dargue" generator, Dargue Acetylene Gas Co. , Davis Acetylene Co. , "Davis" generator, Debruyne, L. , Debruyne's generators, Drawer generators, Drip generator, Drummond, J. And J. , E English generators, F Flooded compartment generator, Fittings, Ltd. , Frankoline purifying material, French generators, G German generators, H Heratol, purifying material, I "Incanto" generator, Irish generator, J "Javal" generator, K Keller and Knappich, G. M. B. H. , "Klenzal" purifying material, Klinger, Rich. , Klinger's generator, "Knappich" generator, L "L'Éclair" generator, "L'Étoile" generator, L'Hermite, Lockerbie and Wilkinson, M Manchester Acetylene Gas Col. , Ltd. , Mangiameli, Fr. And Co. , Moss, R. J. And Sons, "Semi-Non-Auto" generator, "Type A" generator, "Type B" generator, "Type C" generator, Moyes Wm. , and Sons, N Non-automatic generators, Nordische Azetylen Industrie, O "Omega" generator, Overberge, De Smet van, "Owens" generator, "Owens" purifying material, P Phôs Co. , "Phôs Type E" generator, "Photolithe" generator, Photolithe, Soc. An. Belg de la, Pumice purifying material, Puratylene purifying material, Purifying material, "Allen, " "Carburylen, " chloride of lime, coke and cotton, chemically treated, cork waste and wadding, "Curaze, " frankoline, heratol, "Klenzal, " "Owens, " pumice, puratylene, "Roscoline, " "Standard, " "Thorlite, " R Rosco Acetylene Co. , "Rosco" generator, "Roscoline" purifying material, Rural Districts Gas Light Co. , S St. James' Illuminating Co. , Ltd. , Scotch generators, Semi-automatic generator, Siche Gas Co. , Ltd. , "Siche" generator, "Signal-Arm" generator, "Sirius" generator, Sirius, Maison, Standard Acetylene Co. , "Standard" purifying material, Sunlight Gas Machine Co. , Superposed pans or trays, T "Thorlite" generator, purifying material, Thorn and Hoddle Co. , "Thorscar" generator, Trays, superposed, U United States generators, W Wadding and cork waste purifying material, Water-to-carbide generators, Weldhen and Bleriot, Welsh generator, "Westminster" generator,