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Tin

This metal has been known from very early times, but its ores have been found in a few places only; the metallic tin is not found in nature. Chief among the European sources of tin are the mines in Cornwall, where it is found as tinstone. The Phoenicians and Romans obtained from these mines all the tin employed by them in the manufacture of bronze. Malacca, Borneo, and Mexico also yield tinstone. In the preparation of this metal the tinstone is crushed and washed, and the clean ore is then put into the reverberatory furnace along with fuel and a small portion of lime. By this means the oxide is reduced, and the liquid metal, together with the slag, consisting of calcic silicate, falls to the lower part of the furnace. The blocks of tin thus obtained are still impure, and require further refining by gradually melting out the pure tin, leaving an impure alloy behind. The refined tin thus obtained is principally used for tin-plate, the remainder being the block-tin of commerce. The manner of producing grain-tin is to plunge blocks of the metal into a tin bath, where they are caused to assume a crystallized nature, after which they are either broken up with the hammer, or allowed to fall from a great height. The long grains are caused by the latter process.

Tin is a brilliant, silver-white metal, softer than gold, slightly ductile, and very malleable, as evidenced by the common tin-foil, which is no more than 1/1000 of an inch thick. It melts at 442 deg. The peculiar cracking sound emitted when tin is bent is owing to the disturbance of its crystalline structure. Owing to its weak affinity for oxygen, it tarnishes but slightly on exposure to air or moisture, and is therefore valuable for domestic utensils. It is this property that renders it so useful as a coating to prevent other metals from oxidizing. The common tin-ware is simply thin sheets of iron coated with this metal. Tin dissolves in hydrochloric acid. If this metal be heated beyond its melting-point, with access of air, it becomes converted into the binoxide, and burns with a brilliant white light. It is certainly one of the earliest known metals, as it enters into the composition of bronze, of which alloy many of the ancient statues, weapons, and tools were made. Most metals are made harder, whiter, and more fusible by tin. It forms the principal ingredient of Britannia metal, pewter, and many solders. The finest pewter is mainly composed of tin, with some temper. See PEWTER. Tin forms an amalgam with mercury, with which to silver mirrors and other objects. Tin-foil is placed on a flat slab, then covered with mercury, and the glass placed over it, when, weights being applied, the superfluous mercury escapes, leaving a film of the silvery amalgam adhering to the glass. See MERCURY.

Tin is hardened and made more silvery by alloying with antimony; zinc has the effect of cleansing it. See ANTIMONY; ZINC.

Melted pewter is prevented from oxidizing by letting a piece of zinc float upon the surface of the alloy while casting.

One ninth of tin added to copper makes gun-metal or bronze, which is tough and rigid, but can neither be rolled nor drawn--a wonderful change from the original qualities of either metal when unalloyed; and what is perhaps more remarkable, if further additions, up to about one fourth, of the soft tin be employed, the alloy is made hard and elastic. A further increase up to tin 1, copper 2, and the alloy becomes so brittle that steel tools fail to make any impression upon it, except to crumble it; its malleability is completely destroyed, a brilliant white alloy, highly crystalline, having taken its place, with no trace of the red copper in its texture. Such an alloy is susceptible of a brilliant polish owing to its extremely close and hard nature, and for this reason it is used for speculums; but special means must be employed for grinding the surfaces, as they cannot be cut. See SPECULUM-METAL; ROSSE'S TELESCOPE; COPPER; BRONZE.