PREFACE. IT is only proper to say that much of the matter con- tained in the following pages has appeared at intervals dur- ing the past two years in the columns of the American Machinist. The publication of the articles referred to and the remarks which they have elicited have served to em- phasize to me the too evident fact of the general scarcity of practical information about air-compression and the uses of compressed air, and the wide diffusion of misinfor- mation and prejudice upon this subject. In spite of it all the use of compressed air is rapidly spreading, and everywhere with satisfaction to the users. I would gladly do what I can to extend the field of its usefulness, and I have so much faith in its powers that I believe that the best of all ways to advertise it is simply to tell the straight truth about it, and that I have tried to do. NEW YORK, May, 1895. FRANK RICHARDS. CONTENTS. CHAP. PAGE I. MECHANICAL versus COMMERCIAL ECONOMY i II. DEFINITIONS AND GENERAL INFORMATION , 9 III. A TABLE FOR AIR-COMPRESSION COMPUTATIONS 20 IV. THE COMPRESSED-AIR PROBLEM 27 V. THE INDICATOR ON THE AIR-COMPRESSOR 38 VI. THE BEGINNING OF ECONOMICAL AIR-COMPRESSION... 53 VII. OF COMPRESSION IN A SINGLE CYLINDER 61 VIII. TWO-STAGE AIR-COMPRESSION 70 IX. TWO-STAGE COMPRESSION, SINGLE-ACTING TANDEM, ETC 8 1 X. THE POWER COST OF COMPRESSED AIR 90 XI. THE POWER VALUE OF COMPRESSED AIR 98 XII. COMPRESSED-AIR TRANSMISSION no XIII. THE UP-TO-DATE AIR-COMPRESSOR 126 XIV. COMPRESSED AIR versus ELECTRICITY 135 XV. THE THERMAL RELATIONS OF AIR AND WATER 141 XVI. THE FREEZING-UP OF COMPRESSED AIR - 147 XVII. REHEATING COMPRESSED AIR 157 XVIII. COMPRESSED AIR FOR PUMPING 167 XIX. THE VARIOUS APPLICATIONS OF COMPRESSED AIR 176 v COMPRESSED AIR. CHAPTER I. MECHANICAL VERSUS COMMERCIAL ECONOMY. BEFORE considering the conditions under which air may be most economically compressed, having regard to the power cost alone, and the conditions relating to the transmission and application of the air, so that the most power may be realized, it seems proper to say something of the many applications of compressed air where the question of the actual power cost of the air, or of the actual amount of power realized from the air, seems to have little to do with the case. This is like asking a suspension of judg- ment, or a reservation of final decision upon the claims of compressed air, until the whole case has been presented and it seems to be rather necessary, because so many have fallen into the habit of thinking only of the losses of power in the use of compressed air, and of arguing that because certain losses are proven, that therefore the employment of compressed air is not to be considered for any purpose. There are many men even in these days, and many intelli- gent engineers among them, who, to their own loss, will not