Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: THE ' MERCUROUS NITRATE ' PRECIPITATION. The higher oxides of tungsten, chromium, molybdenum and vanadium are acidic in character, and are quantitatively precipitated from solutions containing them by a soluble mercurous salt. As the conditions of precipitation are nearly the same in every case, a description of them may fairly claim a place under the heading of ' general methods.' Ores and rich ferro-alloys of these metals are frequently ' opened out' by a fusion with carbonates of sodium and potassium together with an oxidant such as potassium nitrate or sodium peroxide. An aqueous extract of the fusion yields a solution of the sodium and potassium salts of the acids, from which the precipitation is made by the following procedure. To the solution is added dilute nitric acid until neutrality, or the faintest degree of acidity, is indicated by methyl orange, and the solution is then boiled in order to expel carbon dioxide. A freshly prepared dilute aqueous solution of pure mercurous nitrate crystals is then added with stirring, until the precipitation is apparently complete. A small quantity of an aqueous emulsion of precipitated mercuric oxide may then be added in order to neutralise the slight excess of nitric acid. The mixture is digested over the corner of the hot plate for an hour or so, the precipitate collected on paper pulp, washed with water containing a small quantity of mercurous nitrate, dried and ignited. The ignition should be conducted cautiously at first in order to prevent mechanical loss in the escaping mercury vapours, and finished at a red heat except in the case of molybdenum. The residues frequently contain small amounts of silica, which should be eliminated by adding hydrofluoric and a drop or two of sulphuric acid, evaporating to dryness and ignit...