Licence: Public Domain Mark
Credit: Qualitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![§ 53.] CHLOEIDE OF AMMONIUM. G3' it is then digested for several days with nitric acid in the water bath,, in order to convert the phosphoric acid which is almost invariably pre- sent in the ore to the tribasic state. When the nitric acid is evapo- rated, the residue (or commercial pure molybdic acid) is dissolved in 4 parts'of solution of ammonia, filtered rapidly, and the filtrate poured into 15 parts by weight of nitric acid of sp. gr, 1-20. The mixture is allowed to remain several days in a moderately warm place, which will cause the separation of any remaining traces of phosphoric acid as- phospho-molybdate of ammonia. The colourless solution is decanted from the precipitate, and kept for use. If heated to 40°, no white pre- cipitate (molybdic acid or an acid salt of the same) will separate; but if the temperature is raised beyond that point this will at once take place unless more nitric acid be added (Eggertz). l^ses.—Phosphoric acid and arsenic acid form with molybdic acid and ammonia peculiar yellow compounds which are almost absolutely insoluble in the nitric acid solution of molybdate of ammonia. The phosphoric acid compound is formed in the cold, the arsenic acid com- pound requires heat. Molybdate of ammonia afibrds therefore an excellent means for detecting these acids, and more especially very minute quantities of phosphoric acid in acid solutions containing ferric oxide, alumina, and alkaline earths. § 53. 12. Chloride of Ammonium, NH^Cl [NH.ci]. Preparation.-—The white sublimed sal ammoniac of commerce is selected; if it contains iron, it must be purified. For this purpose, some chlorine water is added to the boiling solution, to convert the feiTous to ferric chloride, and then ammonia to alkaline reaction, the boiling being- continued until the alkaline reaction has almost disappeared ; the preci- pitate is then allowed to subside, and the solution filtered and evaporated until it crystallizes. For use, 1 part of the salt is dissolved in 8 parts of water. Tests.—Solution of chloride of ammonium should leave no fixed residue when evaporated on a platinum spatula. Sulphide of ammo- nium should have no action on it, and it must be perfectly neutral to test paper. Uses.—Chloride of ammonium serves principally to retain in solution certain oxides (such as protoxide of manganese, magnesia) or salts (such as tartrate of lime) when other oxides or salts are to be precipitated by ammonia or some other reagent. This application of chloride of ammonium is based upon the tendency of ammonia salts to form double compounds with other salts. Chloride of ammonium serves also to distinguish between precipitates possessed of similar properties; for instance, to distinguish the basic phosphate of magnesia and ammonia, which is insoluble in chloride of ammonium, from other precipitates of magnesia. It is used also to precipitate from their solutions in potassa various substances which are soluble in that alkali, but insoluble in ammonia; such as alumina, sesquioxide of chromium, &c. In this process, the elements of the chloride of ammonium react with those of the potassa, chloride of potassium, water, and ammonia being formed. Chloride of ammonium is used also as a special reagent in the precipi- tation of platinum as platinochloride of ammonium.](https://iiif.wellcomecollection.org/image/b21966953_0087.jp2/full/800%2C/0/default.jpg)
