ZINC

A metal, first mentioned by Para cels us; but its ores were known at a much earlier period. In commerce a called miter; and is obtained either from the rbonate Of zinc, called calamine, or from the native sulphuret or blende of mineralogists. These ares are roasted and mixed with charcoal or carbonaceous flux; the mixture is put into a kind of crucible closed at top, and peril bottom by an iron tube, which pa es through the i ice into water; the vapour of the zinc distils downwards through this tube, and is condensed in the rite 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 epiiie pure) has a peculiar bluish colour and lustre, a lamellar and crystalline texture, and its specific gravity,. At common temperatures it is tough and ine under the hammer: and when heated to above becomes brittle, and fu-es at about 770°. But at ires between 220° and 330° 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 wiien its highly crystal line texture is considered. Being a cheap and light metal. w Ich, after having been Superficially oxidized, long resists the farther action of air and water, it has latouch employed as a substitute for lead in lining ivtter:is ten is 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 inlammable netal, burning in the flame of a spirit lamp with v brilliant white light: but the oxide which forms interferes with its continuous combustion, which can only be [s. 1363]