Tin. This metal approaches silver in whiteness and lustre. "When pure, it is very malleable; is harder, than lead; melts at 442° Fahr., and volatilizes at a white heat. Its specific gravity is 7.29 to 7.31. This metal is decomposed by nitric, sulphuric, and muriatic acids; and may be combined and alloyed with most of the useful metals. Tin occurs in nature in the state of the oxide, and sometimes as sulphuret (tin pyrites.) In Cornwall, England, it is found under the name of tin-stone, associated with copper ore, in the slate or granite rocks; and as an alluvial deposit (stream tin) in the beds of rivers. A pure article of tin comes from Banca. The metal is obtained from the ore, first reduced to powder in stamping mills, washed to remove earthy matter, and then roasted to expel arsenic and sulphur; it is then deoxidized or reduced by smelting with about 1/6 its weight of powdered culm (a kind of coal found in Wales), and a little slacked lime; it is next refined by liquation (see No. 21 (Liquation)), followed by a second smelting of the purer portion ; it is then, while in a state of fusion, stirred with billets of green wood, allowed to settle, and cast into moulds. The product is termed refined or block-tin. Tin produces a peculiar crackling noise when bent; in this manner pure tin foil may be distinguished from the so-called tin foil in general use, which consists of lead with a tin surface only.

3315. Tests for the Purity of Tin

3315.      Tests for the Purity of Tin. It is almost entirely dissolved by hydrochloric acid, yielding a colorless solution of muriate (chloride) of tin. If it contains arsenic, brownish-black flocks will be separated during the solution, and arseniuretted hydrogen evolved. The presence of other metals in tin may be detected by treating the muriate of tin solution with nitric acid, specific gravity 1.16, first in the cold, and afterwards with heat, until all the tin is precipitated in an insoluble peroxide; the decanted acid solution from pure tin leaves no residuum on evaporation. If there be a residuum, and dilution with water occasions a heavy white precipitate, the tin contained bismuth. If, after dilution, the addition of a solution of sulphate of ammonia or of soda produces a white precipitate, the tin contained lead. If red prussiate of potash gives a blue precipitate, it contained iron; and if the clear liquid leaves a residuum on evaporation, it contained copper.

3316. Grain Tin

3316.     Grain Tin. This is made from block tin. The blocks are heated until they become brittle, and then allowed to fall from a considerable height, by which they are broken into small fragments, which constitute grain tin, or tin in tears.

3317. Tin Powder or Filings

3317.     Tin Powder or Filings. Melt grain tin (see No. 3316 (Grain Tin)) in an iron vessel, pour it in an earthen-ware mortar heated a little above its melting point, and triturate briskly as the metal cools; lastly, sift the product, and repeat the process with what remains in the sieve. Powdered tin is also prepared by filing and rasping.