Zinc
A brilliant bluish-white metal, found in nature in combination with sulphur as zinc blende, and with oxygen and carbonic acid as calamine. Great quantities of red oxide are found in New Jersey. It is a brittle metal at common temperatures, but when heated from 212 deg. to 300 deg. it may be rolled out into thin sheets, and retains its malleability when cold. It again becomes brittle at 400 deg., and melts at 741 deg.; taking fire if exposed to the air, and emitting a whitish-green flame as it burns, forming the oxide of zinc. This metal tarnishes readily in a moist atmosphere, and forms a film of oxide which resists further change. This property is what makes this metal so valuable for gas-pipes, roofing, and for galvanizing iron. It prevents oxidation of the metals on which it is applied. See GALVANIZED IRON. The native carbonate, or calamine, is the most valuable of the zinc ores. It is first roasted to expel water and carbonic acid, then mixed with fragments of coke or charcoal, and distilled at a full red heat in an earthen retort; carbonic acid escapes, while the reduced metal volatilizes, and is condensed, generally mixed with minute portions of arsenic.
When zinc forms a component part of any alloy, a better mixture is obtained by melting the zinc separately, and pouring it into a ladle containing the melted copper, through a hole in the cover. This is done to prevent the rapid oxidation of the zinc; for if this is done without excluding the air, the zinc volatilizes very quickly and with violence, throwing off vapors which burn and produce an immense quantity of oxide, which falls down in flakes. When zinc is not more than from 35 to 40 per cent of a mixture with copper, the alloy retains its malleability and ductility. Beyond this proportion it assumes the crystalline state, until at zinc 2, copper 1 the alloy may be crumbled in a mortar.
Bronze alloys are improved by the addition of a small proportion of zinc: their malleability is increased, with little or no diminution in the hardness; besides which it assists materially in the mixing.
It is certain that zinc and copper alloys form a more perfect chemical union than the alloys of lead with copper or tin with copper. Zinc is caused to combine with lead by the admixture of a third alloy, arsenic; but, like other alloys with arsenic, it becomes very brittle, and almost useless.
Zinc combines with tin to form a hard brittle alloy, not of much use commercially.
Old zinc plate, etc., assumes the crystalline state again when remelted. A small proportion of zinc will render gold brittle; zinc vapors alone sensibly affect gold in fusion. Gold 10, zinc 1 makes a brittle alloy, the color of brass; and gold 10, zinc 5 makes a white, hard alloy, susceptible of a high degree of polish.
Very few of the zinc alloys, except those with copper to form brass alloys, are of much service; and the maximum of strength in the latter is obtained when the alloy contains about 44 per cent of zinc. See COPPER; FONTAINE-MOREAU'S BRONZES.