ZINC, a metallic chemical element (symbol Zn, atomic num ber 3o, atomic weight 65.38). Zinc as a component of brass had currency in metallurgy long before it became known as an indi vidual metal. The word zinc (in the form zinken) was first used by Paracelsus, who regarded it as a bastard or semi-metal; but the word was subsequently used for both the metal and its ores. Moreover, zinc and bismuth were confused, and the word spiauter (the modern spelter) was indiscriminately given to both these metals. In 1597 Libavius described a "peculiar kind of tin" which was prepared in India, and of which a friend had given him a quantity. From his account it is quite clear that this metal was zinc, but he did not recognize it as the metal of calamine. It is not known to whom the discovery of isolated zinc is due; but we do know that the art of zinc-smelting was practised in England from about 173o. The first continental zinc-works were erected at Liege in 1807.
Occurrence.—Zinc does not occur free in nature, but in com bination it is widely diffused. The chief ore is zinc blende, or sphalerite (see BLENDE), which generally contains, in addition to zinc sulphide, small amounts of the sulphides of iron, silver and cadmium. It may also be accompanied by pyrites, galena, arsen ides and antimonides, quartz, calcite, dolomite, etc. It is widely distributed, and is particularly abundant in Germany (the Harz, Silesia), Austro-Hungary, Belgium, the United States and in England (Cumberland, Derbyshire, Cornwall, North Wales). Second in importance is the carbonate, calamine (q.v.) or zinc spar, which at one time was the principal ore ; it almost invariably contains the carbonates of cadmium, iron, manganese, magnesium and calcium, and may be contaminated with clay, oxides of iron, galena and calcite ; "white calamine" owes its colour to much clay; "red calamine" to admixed iron and manganese oxides. Calamine chiefly occurs in Spain, Silesia and in the United States. Of less importance is the silicate, named electric calamine or hemimorphite ; this occurs in quantity in Altenburg near Aix la-Chapelle, Sardinia, Spain and the United States (New Jersey, Pennsylvania, Missouri, Wisconsin). Other zinc minerals are willemite (q.v.), hydrozincite or zinc bloom, zincite (q.v.) or red zinc ore, ZnO, and franklinite, 3 Production.—Until about 1833 the supply of zinc was almost entirely obtained from Germany, but in this year Russia began to contribute about 2,000 tons annually to the 6,000 to 7,00o de rived from Germany. Belgium entered in 1837 with an output of about 2,000 tons; England in 1855 with 3,000 ; and the United States in 1873 with 6,000 tons. The last country now produces
about one-third of the world's supply. The present state and gen eral trend of the industry is shown by the following statistics for output of smelter and electrolytic zinc (in metric tons) for the chief producing countries and for the world's production.
*Some secondary metal included. "Minerals Yearbook 1938," U.S. Bureau of Mines.
Properties.—Zinc is bluish white, with a high lustre when fractured. It fuses at 419° C and under ordinary atmospheric pressure boils at 918° C. Its vapour density shows that it is mon atomic. The molten metal on cooling deposits crystals belonging to the hexagonal system, and freezes into a compact crystalline solid, which may be brittle or ductile according to circumstances. If zinc be cast into a mould at a red heat, the ingot produced is laminar and brittle ; if cast at just the fusing-point, it is granular and sufficiently ductile to be rolled into sheet at the ordinary temperature. According to some authorities, pure zinc always yields ductile ingots. Commercial "spelter" always breaks under the hammer; but at Ioo° to 15o° C it is susceptible of being rolled out into a very thin sheet. Such a sheet, if once produced, remains flexible when cold. At about C, the metal becomes so brittle that it can be pounded in a mortar. The specific gravity of zinc cannot be expected to be perfectly constant ; according to Karsten, that of pure ingot is 6.915, and rises to 7.191 after rolling. The coefficient of linear expansion is 17X between 20° and me". The specific heat is 0.0929 from 18° to oo°. Compact zinc does not tarnish much in the air. It is fairly soft, and clogs the file. If zinc be heated to near its boiling-point, it catches fire and burns with a brilliant light into its powdery white oxide, which forms a reek in the air (lana philosophica, "philosopher's wool"). Boiling water attacks it appreciably, but slightly, with evolution of hydrogen and formation of the hydroxide, A rod of perfectly pure zinc, when immersed in dilute sulphuric acid, is so very slowly attacked that there is no visible evolution of gas; but, if a piece of platinum, copper or other more electronegative metal be brought into contact with the zinc, it dissolves readily, with evolution of hydrogen and formation of the sulphate. The ordinary impure metal dissolves at once, the more readily the less pure it is. Cold dilute nitric acid dissolves zinc as nitrate, with evolution of nitrous oxide. At higher temperatures, or with stronger acid, nitric oxide, NO, is produced besides or instead of nitrous oxide. Zinc is also soluble in soda and potash solutions, but not in ammonia.