the precipitate thrown down by hydrate of potassium is white, and soluble in excess of the precipitant. If it contain arsenic, brownish-black flocks will be separated during the solution, and arseniuretted hydrogen evolved, which may be inflamed and tested in the usual manner. The presence of other metals in tin may be detected by treating the hydrochloric solution with nitric acid, sp. gr. 1·16, first in the cold, and afterwards with heat, until all the tin is thrown down in the state of insoluble stannic oxide. The decanted acid solution from pure tin leaves no residuum on evaporation. If, after all the acid has been dissipated by heat, dilution with water occasion a heavy white precipitate, the sample contained bismuth; if, after dilution, a solution of sulphate of ammonium or of sodium produce a similar white precipitate (sulphate of lead), it contained lead; if ammonia, added in excess, occasion reddish-brown flocks, or if ferricyanide of potassium give a blue precipitate, it contained iron; and, if the clear supernatant liquid leave a residuum on evaporation, copper.
Tests. The stannous salts are characterised as follows:—1. Hydrate of potassium gives a bulky white precipitate, readily soluble in excess of the precipitant; on concentrating the solution, the precipitate is changed from stannous hydrate into stannic hydrate, which remains in solution, and metallic tin, which separates in brown flakes.—2. Ammonia, and the carbonates of potassium, sodium, and ammonium, give white precipitates, insoluble in excess.—3. Sulphuretted hydrogen gives, in neutral and acid solutions, a dark brown precipitate, which is soluble in hydrate of potassium, in the alkaline sulphides (especially when they contain an excess of sulphur), and in strong hot hydrochloric acid; and insoluble in nitric acid, even when boiling.—4. Sulphide of ammonium produces a like brown precipitate, soluble in excess of the precipitant, provided the latter contains an excess of sulphur.—5. Terchloride of gold gives, in the cold, on the addition of a little nitric acid, a precipitate of the purple of Cassius.—6. Mercuric chloride gives a black precipitate, but in excess it produces a white one.
Stannous Chloride. SnCl2. Syn. Protochloride of tin. Prep. (Anhydrous.) Distil a mixture of tin and mercuric chloride. Grey, resin-like, solid, fusible, and volatile.
(Hydrated; Tin salt.) Boil an excess of tin in hydrochloric acid. A powerful deoxidising agent. It is somewhat extensively used as a mordant in dyeing.
Stannous Hydrate. Sn(HO)2. Syn. Hydrated oxide of tin. Prep. Precipitate stannous chloride with carbonate of potassium, well wash, and dry under 196°. Greyish-white powder, soluble in acids and alkaline hydrates, except ammonia.
Stannous Iodide. SnI2. Syn. Protiodide of tin. Heat tin and iodine together. A
fusible brownish-red, translucent substance, soluble in water.
Stannous Oxide. SnO. Syn. Protoxide of tin. Prep. Ignite the hydrate in an atmosphere of carbonic anhydride. Black powder, inflammable in air, and insoluble in acids.
Stannous Sulphide. SnS. Syn. Protosulphide of tin. A brittle bluish-grey substance, obtained by heating tin and sulphur.
The stannous salts behave with reagents as follows:—1. Hydrate of potassium, ammonia and alkaline carbonates, give a white precipitate, which is freely soluble in an excess of hydrate of potassium and in acids, sparingly soluble in excess of ammonia, only very slightly soluble in excess of carbonate of potassium, and insoluble in excess of carbonate of ammonium.—2. Sulphuretted hydrogen gives, in acid neutral solutions, a golden-yellow precipitate, either at once or on heating the liquid, which is readily soluble in pure hydrate of potassium, the alkaline sulphides, and boiling hydrochloric acid; less soluble in ammonia, and insoluble in nitric acid.—3. A plate of metallic zinc throws down metallic tin, under the form of grey scales or a spongy mass, from solutions free from nitric acid; and from those containing free nitric acid, white stannic hydrate.—4. Mercuric chloride gives a white precipitate.—5. Ferrocyanide of potassium gives no precipitate at first, but after a time the whole forms a thick jelly.