Production.—During the 18th century the world's supply of tin was mainly from England, Saxony and Bohemia; in 18or England produced about 2,500 tons, while the supplies of Saxony and Bohemia had been greatly diminished. The English supply then gradually increased to about ro,000 tons in 1860, and this figure was fairly well sustained until about 1890, when a period of depression to about 4,00o tons set in. In the opening decades of the 19th century supplies began to be drawn from the island of Banka. Billiton became of note in 1853. The Straits Settle ments ranked as an important producer in 187o and now produce a large part of the world's supply. Australian deposits were worked in 1872, and those of Bolivia somewhat later. The pro duction of Siam, though relatively small, shows the greatest pro portional increase in the ten years 1928-37. The following table shows the output (in metric tons) of the largest producers and also the total world's output for certain recent years.
An ingot of tin is pure white (except for a slight tinge of blue) ; the colour depends, however, upon the temperature at which it is poured—if too low, the surface is dull, if too high, iridescent. It exhibits considerable lustre and is not subject to tarnishing on exposure to normal air. The metal is fairly soft and easily flattened out under the hammer, but almost devoid of tenacity. That it is elastic, with narrow limits, is proved by its clear ring when struck with a hard body in circumstances permit ting of free vibration. The specific gravity of cast tin is 7.29, of rolled tin 7.299 and of electrically deposited tin 7.143 to 7.178. A tin ingot is distinctly crystalline; hence the characteristic crackling noise, or "cry" of tin, which a bar of tin gives out when being bent. This structure can be rendered visible by superficial etching with dilute acid; and as the minuter crystals dissolve more quickly than the larger ones, the surface assumes a frosted appearance (moirde metallique). The metal is bimorphous: by cooling molten tin at ordinary air temperature tetragonal crystals are obtained, while by cooling at a temperature just below the melting point rhombic forms are produced. When exposed for a sufficient time to very low temperatures (to —39° C for 14 hours), tin becomes so brittle that it falls into a grey powder, termed the grey modi fication, under a pestle; indeed, when kept in cold climates for several years, it sometimes crumbles into powder spontaneously (see ALLOTROPY). At ordinary temperatures tin proves fairly ductile under the hammer, and its ductility seems to increase as the temperature rises up to about oo° C. At some temperature near its fusing point it becomes brittle, and still more brittle from —14° C downwards. Iron renders the metal hard and brittle; arsenic, antimony and bismuth (up to 0.5%) reduce its tenacity; copper and lead (I to 2%) make it harder and stronger but impair its malleability; and stannous oxide reduces its tenacity. Tin fuses at about 23o° C; at about 1,600° C it begins to volatilize slowly; at about 2,270° C it boils. The hot vapour
produced combines with the oxygen of the air into white oxide,
Its coefficient of linear expansion between o° and oo° is 0.002717; its specific heat 0.0562; its thermal and electrical conductivities are 145 to 152 and 114.5 to 140.1 respectively, compared to silver as 1,000. The metal is scarcely affected by dilute hydrochloric or sulphuric acids; very dilute nitric acid slowly dissolves it, but strong acid converts it to (3-stannic acid (see below) ; concentrated hydrochloric acid attacks it fairly readily, and concentrated sulphuric acid when hot.
Commercially pure tin is used for making such apparatus as evaporating basins, infusion pots, stills, etc. It is also employed for making two varieties of tin foil—one for the silvering of mirrors (now superseded) the other for wrapping up chocolate, toilet soap, tobacco, etc. The mirror foil must contain some copper to prevent it from being too readily amalgamated by the mercury. For making tin-foil the metal is rolled into thin sheets, pieces of which are beaten out with a wooden mallet. As pure tin does not tarnish in the air and is proof against acid liquids, such as vinegar, lime juice, etc., it is utilized for culinary and domestic vessels. But it is expensive, and tin vessels have to be made very heavy to give them sufficient stability of form; hence it is generally employed merely as a protecting coating for utensils made of iron usually. (See TIN-PLATE.) Rolled plates of mild steel are "pickled" in dilute hydrochloric or sulphuric acid, annealed, cold rolled, re annealed at a lower temperature, again pickled in weaker acid, and washed with water. They are then tinned by passing through a bath of the molten metal which is divided into two sections and so arranged that the plate passes through a flux of molten zinc chloride floating on the metal in the first section, and emerges through a coating of grease floating on the metal in the second section ; they are then rolled in order to remove excess of tin and to impart polish to the surface.
By far the greater part of the tin produced metallurgically is used for making alloys. Ordinary solder is a mixture of equal parts of tin and lead; pewter (q.v.) is 3 parts of tin to 1 part of lead. Locomotive bearings are a, lead-copper alloy containing about 8% of tin. Bronze (q.v.) is an alloy of tin with copper, and the properties differ greatly from those of either metal separately. Coinage bronze contains 5% of tin (with the addition of about 1% of zinc) ; bronzes containing 9-10% of tin are used as gun-metal, those having 10-12% are used as engineers' brasses, those with 2-1 % for bearings and those with 16-24% for bells, the precise proportion depending upon the type of bell required. Speculum metal contains 33% of tin and 67% of copper. All the properties of these alloys are, however, considerably modified by the rate of cooling, and processes such as hammering and cold working.