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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![may also be used if it is free from arsenic and antimony) dissolved in dilute nitric acid is precipitated with sulphu}-otted hydrogen, and a part of the precipitated sulphide is treated with ammonia and filtered, the remainder is treated with sulphide of ammonium and filtered. The filtrates are then mixed with hydrochloric acid in excess; the first should give no precipitate, the second only a white precipitate of sulphur. Uses.—When teroxide of bismuth is boiled with alkaline solutions of metallic sulphides, it reacts with them forming metalhc oxides and sul- phide of bismuth. It is also used to convert tersulphide and penta- sulphide of arsenic into arsenious and arsenic acids. h. Sulphur Bases. § 40. 1. Sulphide of Ammonium, NH,S [(NHj.S]. l a. Colourless protosulphide of ammonium, and h. Yellow polysulphide of ammonium, are employed. Preparation.—a. Sulphuretted hydrogen gas is passed through Sparts of solution of ammonia until no further absorption takes place; 2 parts more of the same solution of ammonia are then added. The action of sulphuretted hydrogen on ammonia gives rise to the formation, firsl^ of NH^S [(NH,),SJ, then of NH^S,HS [NH„HS]; on adding to the procuct solution of ammonia equal in volume to that which has been saturated, the ammonia reacts with the hydrosulphide of sulphide of ammonium, and protosulphide of ammonium is formed. Only two-thirds of this quantity of solution of ammonia should be added, however, as it is better that the reagent should contain a little hydrosulphide of sulpMde- of ammonium than that free ammonia should be present. Hydro- sulphide of sulphide of ammonium has usually been employed hitherto, instead of the simple protosulphide; this is unnecessary, and tends to increase the smell of sulphuretted hydrogen in the laboratory, as the hydrosulphide gives ofi that gas in contact with metallic sulphur acids. Sulphide of ammonium should be kept in well-corked bottles. It is colourless at first, and deposits no sulphur on the addition of an acid. On exposure to the air, however, it acquires a yellow tint, due to the formation of bisulphide of ammonium, ammonia and water, thus : 2NH4S + 0=NH^S, + NH3-I- HO [4(NH,),S + O,=2(N H,),S, + 4N H3-^ 2H,0]. By the continued action of the oxygen of the air, still higher sulphides are formed at first, but afterwards sulphur is deposited, and nothing I'emains in solution but ammonia and hyposulphite of ammonia. The hyposulphite is formed in the manner shown in the equation : NH^S, + 03 = EH,0,SA [2(NHJA + 30,=2(NH,),S^03].. h. Sulphide of ammonium which has turned yellow by moderate ex- posui'e to the air may be used for all the purposes requiring the employ- ment of yellow sulphide of ammonium. The yellow sulphide may also be expeditiously prepared by digesting the protosulphide with suljohur. All kinds of yellow sulphide of ammonium deposit sulphur and become turbid and milky on being mixed with acids. Tests.—Sulphide of ammonium should strongly emit the odour](https://iiif.wellcomecollection.org/image/b21966953_0080.jp2/full/800%2C/0/default.jpg)
