TIN. A metal of a white colour, intermediate between silver and lead. It is considerably harder than lead ; scarcely at all sonorous ; very malleable, being capable of extension, under the hammer, to about a two-thousandth part of an inch in thickness. The ordinary tinfoil is about a one-thousandth part of an inch thick. Tin has a slight unpleasant taste, and emits a peculiar smell when rubbed. Specific gravity, 7.291. It is very flexible, producing a remarkable crack ling noise when bended, the loudness of which is a common, though not very ac curate test of its purity. Tin melts at 442e Fahr. ; when fresh cast, or fresh scraped, it is very brilliant, but it gradually loses its lustre by exposure to the air, and acquires a greyish-white tint, which does not sensibly change. Like lead, when heated nearly to fusion, it is brittle, and may be easily broken up by a hammer, when it exhibits a grained or fibrous texture. It may also be reduced to powder by agitation, at the period of its transition from the solid to the fluid state.
There are several kipds or qualities of tin. The Cornish block tin is usually In blocks of about three cwt. each ; which are, however, run into smaller masses, of 30 or 40 lbs. each, for the convenience of trade. The common block tin is contaminated with a minute quantity of other metals, generally copper, to the extent of about a thousandth part. " Refined block-tin " is in blocks of tin melted into long narrow sticks, of a few ounces each. The "grain tin" is the purest of the several English kinds, being obtained from the pure oxide of tin of the steam-works of Cornwall. It is first cast into blocks of about 120 lbs. each, and afterwards melted, so as to separate it into fragments resembling rocks; which is produced by letting the metal fall, when barely fluid, from a great height. The tin imported from the East Indies, particularly Malacca, is es teemed very pure, and considered the best for organ pipes, and some other uses.
The tin ore of Cornwall, obtained from the mines, is stamped to reduce it into fragments, then washed, to separate the earthy matter, and afterwards roasted in a reverberating furnace ; • which process is repeated until the assay shows it to contain at least half of its weight of metal, when it is sold to the smelters. In this state it is mixed with cam and slaked lime, well moistened,
and then smelted in a reverberating furnace, capable of reducing about 7 cwt. at a time. A given weight of tin, produced from Cornish ore, consumes about double its weight of coal in the operations of roasting and smelting. Between three and four thousand tons of tin are produced annually from the mines of Corn wall. Chaptal says, that if tin be kept in fusion in a lined crucible, and the surface be covered with a quantity of charcoal, to prevent its calcination, the metal becomes whiter, more sonorous. and harder. provided the fire be kept up for eight or ten hours.
Mercury dissolves tin with great facility, and in all proportions. To make this combination, heated mercury is poured on melted tin ; the consistence of the amalgam differs according to the relative proportions of the two metals.
Nickel, united to tin, forms a white and brilliant mass. Half a part of tin, melted with two parts of cobalt, and the same quantity of muriate of soda, fur nished Beaume with an alloy in small close grams of a light violet colour. Equal parts of tin and bismuth form a brittle alloy, of a medium colour between the two metals, and the fracture of which presents cubical facets.
Zinc unites perfectly with tin, and produces a hard metal, of a close-grained fracture; its ductility increases with the proportion of tin.
Antimony and tin form a white and brilliant alloy, which is distinguished from other alloys of tin by its possessing a less specific gravity than either of the two metals by which it is formed.
In combining arsenic with tin, precautions must be taken to prevent the arsenic from escaping by volatilization. Three parts of tin may be put into a retort, with one-eighth part of arsenic in powder ; fit on n receiver, and make the retort red hot; very little arsenic rises, and a metallic lump is found at the bottom, containing about one-fifteenth part of arsenic ; it crystallizes in large facets, is very brittle, and hard to melt.