ZINC

A metal, first mentioned by Para cels us; but its ores were known at a much earlier period. In commerce it is often called spelter; and is obtained either from the native carbonate of zinc, called calamine, or from the native sulphuret or blende of mineralogists. These ores are roasted and mixed with charcoal or carbonaceous flux • the mixture is put into a kind of crucible closed at top, and perforated at bottom by an iron tube, which pa es through the grate of the furnace into water; the vapour of the zinc distils downwards through this tube, and is condensed in the water. The first portions are impure, containing arsenic, and often cadmium, in which case the vapour burns with what the workmen call a brown blaze; when the blue blaze appears the zinc is collected. The zinc of commerce (which is not quite pure) has a peculiar blueish colour and lustre, a lamellar and crystalline texture, and its specific gravity is about 7. At common temperatures it is tough and intractable under the hammer; and when heated to above 500° it becomes brittle, and fuses at about 770°. But at temperatures between 220° and 320o it becomes malleable and ductile; so that it may be beaten out under the hammer, and rolled into sheets and leaves, and drawn into wire, in a manner extremely remarkable when its highly crystalline texture is considered. Being a cheap and light metal, and one which, after having been superficially oxidized, long resists the further action of air and water, it has lately^been much employed as a substitute for lead in lining water cisterns and covering buildings; it has also been lately employed in the curious operation of transferring printing (under the name of zincography). It is a very inflammable metal, burning in the flame of a spirit lamp with a brilliant white light; but the oxide which forms interferes with its continuous combustion, [s. 1352]