Compounds of Tin

Stannic chloride,

named by Andreas Libavius in 1605 Spiritus argenti vivi sublimati from its preparation by distilling tin or its amalgam with corrosive sublimate, and afterwards termed Spiritus fumans Libavii, is obtained by passing dry chlorine over granulated tin contained in a retort ; the tetrachloride distils over as a heavy liquid, from which the excess of chlorine is easily removed by shaking with a small quantity of tin filings and re distilling. It is a colourless fuming liquid of specific gravity 2.2 79 at o° C; it freezes at —33°, and boils at 113.9°. The chloride unites energetically with water to form crystalline hydrates (e.g., SnC14.3H20), easily soluble in water. With one-third its weight of water it forms the so-called "butter of tin." It combines readily with alkaline and other chlorides to form double salts, e.g., M2SnC16, analogous to the chloroplatinates; the salt (NH4)2SnC16 is known industrially as "pink salt" on account of its use as a mordant to produce a pink colour. The oxymuriate of tin used by dyers is The plain chloride solution is similarly used. It is usually prepared by dissolving the metal in aqua regia (q.v.).

Stannous fluoride, SnF2, is obtained as small, white mono clinic tables by evaporating a solution of stannous oxide in hydro fluoric acid in a vacuum. Stannic fluoride, SnF4, is obtained as white hygroscopic crystals from stannic chloride and anhydrous hydrofluoric acid at a high temperature ; it forms a characteristic series of salts, the stannifluorides, M2SnF6, isomorphous with the silici-, titani-, germani- and zirconi-fluorides. Stannous bromide, SnBr2, is a light yellow substance formed from tin and hydro bromic acid. Stannic bromide, SnBr4, is a white crystalline mass, melting at 33° and boiling at 201°, obtained by the combination of tin and bromine, preferably in carbon bisulphide solution. Stannous iodide, SnI2, forms yellow red needles, and is obtained from potassium iodide and stannous chloride. Stannic iodide, forms red octahedra and is prepared similarly to stannic bromide. Both iodides combine with ammonia.

Stannous sulphide, SnS, is obtained as a lead-grey mass by heating tin with sulphur, and as a brown precipitate by adding sulphuretted hydrogen to a stannous solution; this is soluble in ammonium polysulphide, and dries to a black powder. Stannic sulphide, is obtained by heating a mixture of tin, mercury, sulphur and sal-ammoniac (in the proportions 12, 6, 7 and 6 re spectively) in the beautiful form of aurum musivum (mosaic gold)—a solid consisting of golden yellow, metallic lustrous scales, and used chiefly as a yellow "bronze" for plaster-of-Paris statuettes, etc. The yellow precipitate of stannic sulphide ob tained by adding sulphuretted hydrogen to a stannic solution readily dissolves in solutions of the alkaline sulphides to form thiostannates of the formula the free acid, H2SnS3, may be obtained as an almost black powder by drying the yellow precipitate formed when hydrochloric acid is added to a solution of a thiostannate.

Organic Compounds of Tin.—Numerous organic compounds of tin are known, such as tin tetraethyl, Sn(C2H5)4. Where the four radicals are different, the compound can exist in enantio • morphous forms (see STEREOCHEMISTRY ) ; thus W. J. Pope and his collaborators (1900-1902) resolved methylethylpropyl tin iodide, Sn(CH3) into dextro- and laevo-modi fications. Compounds of tin with 0-diketones (see KETONES) are also known. The simplest is stannic bisacetylacetone dichloride, (\V. Dilthey, 1902), and G. T. Morgan and H. D. K. Drew (1920) showed that in all such compounds with univalent 0-diketones tin has a co-ordination number of 6, i.e., the constitution is [R2SnX2], X being a halogen atom, and the same co-ordination number is found in "pink salt" (see above), A co-ordination number of 8 is, however, in dicated in tetra-aquabisacetylacetone stannibromide 02)2, 4H2O] Methyl stannic iodide (stanniform), a yellow crys talline substance melting at 87° C, has been applied in therapeutics (1929) as antiphlogistic, analgesic and antiseptic ; it combines the usefulness of tin in staphylococcic infections with the powerful germicidal properties of iodine.

Hydrides.—A hydride, of melting point —150° C, has been obtained by electrolysis of a stannous sulphate solution between lead electrodes, a trace of colloids (e.g., 0.5% of dextrin) being used as a stabilizer; it forms only about o.or% of the re sulting gas and is separated from this hydrogen by condensation in liquid air. A second hydride, Sn2H2, is said to be produced as a grey powder by immersing aluminium foil in an alkaline solution of potassium stannite.

Analysis.—Tin compounds when heated on charcoal with sodium carbonate or potassium cyanide in the reducing blowpipe flame yield the metal and a scanty ring of white Sn02. Stannous salt solutions yield a brown precipitate of SnS with sulphuretted hydrogen, which is insoluble in cold dilute acids and in real sul phide of ammonium (NH4)2S ; but the yellow, or the colourless reagent on addition of sulphur, dissolves the precipitate as a salt of The solution on acidification yields a yellow precipitate of this sulphide. Stannic salt solutions give a yellow precipitate of with sulphuretted hydrogen, which is insoluble in cold dilute acids but readily soluble in sulphide of ammonium, and is re-precipitated therefrom as on acidification. Only stannous salts (not stannic) give a precipitate of calomel in mercuric chloride solution. A mixture of stannous and stannic chloride, when added to a sufficient quantity of solution of chloride of gold, gives an intensely purple precipitate of gold purple (purple of Cassius). The test is very delicate, although the colour is not in all cases a pure purple. Tin is generally quantitatively esti mated as the dioxide or electrolytically.