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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![peculiar to it; with acids it should evolve abundance of sulphuretted hydrogen ; the evolution of gas may be attended by the sejoaration of a pure white precipitate, but no other precipitate should be formed. It should leave no residue when evaporated and heated to redness in a platinum dish. It should not precipitate or render turbid solution of magnesia or solution of lime even on heating (carbonate of ammonia or free ammonia). Uses.—Sulphide of ammonium is one of the reagents most frequently employed. It is vised (a) to precipitate those heavy metals which sulphuretted hydrogen fails to throw down from acid solutions, such as iron, cobalt, etc., NH^S + FeO,S03 = FeS + NHp,S03 [(NH,),S + FeSO, = FeS + (NH,),SOJ ; (6) to separate the metallic sulphides thrown down from acid solutions by sulphuretted hydrogen into two groups, as it dissolves some of them to sulphur salts, as, for instance, the sulphides of arsenic and antimony, ifec, whOst others remain undissolved, such as sulphide of lead, sulphide of cadmium, &c. The sulphide of ammonium used for this purpose must contain an excess of sulphur if the metallic sulphide to be dis- solved will dissolve only as a higher sulphide, as, for instance, SnS [SnS]^ which dissolves with ease only as SnS^ [SnSJ. From solutions of salts of alumina and sesquioxide of chromium, sulphide of ammonium precipitates hydrates of these oxides, with escape of sulphuretted hydrogen, as the sulphur compounds corresponding with these oxides cannot be formed in the wet way: A1,03,3S03 + 3NH^S + 6H0 = Al,03,3HO + 3(NHp,S03) + 3HS [Al2(SO,)3 + 3(N H J^S + 6H2O = AU(OH), + 3(N H J^SO^ + SH^SJ. Salts insoluble in water are thrown down unaltered by sulphide of am- monium from their solutions in acids ; for example, phosphate of lima is precipitated unaltered from its solution in hydrochloric acid. §41. 2. Sulphide of Sodium, NaS [Na^S]. Prejoaration.—The same as sulphide of ammonium, except that solu- tion of soda is substitvited for solution of ammonia. It is filtered, if ne- cessary, and the solution kept in well-stoppered bottles. If requii-ed to contain some higher sulphide of sodium it must be digested with powdered sulphur. t/ses.—Sulphide of sodium must be substituted for sulphide of am- monium in the separation of sulj)hide of copper from sulphur compounds soluble in alkaline sulphides {e.g., from stannous sulphide), as sulphide of copper is not quite insoluble in sulphide of ammonium. IV. Salts. Of the many salts employed as reagents, those of potassa, soda, and ammonia are used principally on account of their acids; a salt of soda may therefore often be substituted for the corresponding potassa salt. Thus it is almost always a matter of indifference whether carbonate of soda or carbonate of potassa is used, ferrocyanide of potassium or ferro- cyanide of sodium, &c. On this account, the salts of the alkalies are](https://iiif.wellcomecollection.org/image/b21966953_0081.jp2/full/800%2C/0/default.jpg)
