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Zinc

Zinc (Zn=65). The preparation of zinc on a manufacturing scale was started at Bristol in 1743, and for many years little competition existed. The chief ores of zinc are the sulphide and the carbonate, known respectively as blende (q.v.) and calamine. The former occurs largely in Cornwall, Derbyshire, the Isle of Man, Cumberland, and North Wales, the latter chiefly in Spain and the United States. For the preparation of the metal from either of these sources, the ore is first roasted in furnaces or kilns, by which means it is converted into oxide with the loss of sulphur dioxide or of carbonic acid. This oxide is then well mixed with coal-dust and heated in clay retorts, and the reduced metal distilled over into attached clay receivers. The metal is usually remelted, skimmed, and cast in ingots; it is never pure, containing usually, quantities of lead, iron, tin, and arsenic associated with it. Zinc is a bluish-white metal which melts at about 430 C. and distills a little over 1,000. It may be rolled or beaten into leaves, but impurities impair this power. It may, by slowly cooling the molten metal, be obtained crystalline, and a bar of zinc emits when bent a slight crackling sound. It has a specific gravity of about 7, and though if strongly heated it burns with the formation of a green flame and thick white fumes, yet at ordinary temperatures it is unalterable in moist air. Pure zinc is hardly attacked by acids, but the commercial metal is readily dissolved with the evolution of hydrogen and the formation of zinc salts. It forms one oxide, ZnO, which occurs native as red zinc-ore and, combined with other oxides, as franklinite. The chloride is obtained as the hydrate, by the evaporation of the solution formed by dissolving zinc in hydrochloric acid.

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