ZINC. A metal, first mentioned by Paracelsus ; but its ores were known at a much earlier period. In commerce it is often called svelter ; and is obtained either from the native carbonate of zinc, called calamine, or from the native sulphuret or blends of mineralogists. These ores are roasted and mixed with charcoal or carboniferous flux : the mixture is put into a kind of crucible closed at top, and perforated at bottom by an iron tube, which passes through the grate of the furnace into water ; the vapor 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 vapor 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 bluish color and a lamellar and crystalline texture, and its specific gravity is about 7. At common temperatures it is tough and intractable under the haminer; and when heated to above 500° it becomes brittle, and fuses at about 770°. But at tempera tures between 220° and 320° 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 con sidered. Being a cheap and light metal, and one which, after having been super ficially 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 employ ed in the curious operation of transfer ring printing (under the name of xinco graphy). 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 continu ous combustion, which can only be car ried on at a high red heat, when the va por of the metal burns with an intensely bright flame, and yields at the same time a quantity of flocculent oxide, which floats about in the surrounding air, and was formerly called philosophers' wool, pom pholix, and nihal album. The equivalent
of zinc is 82 and that of its oxide 40.
Though zinc is apparently without action upon water, yet it is a most oxidable me tal ; but the insolubility of its oxide pro tects it from farther action, so that when a film is once formed upon it, it resists fur ther change ; but when a little acid is present in the water, and the zinc not quite pure, it is rapidly acted upon, and oxidized at the expense of the water, which evolves abundance of hydrogen (when dilute sulphuric acid is used), and the oxide of zinc is removed and dis solved by the acid. It is this action which renders zinc so powerful a genera tor of electricity in the voltaic pile.. The salts of zinc are mostly soluble, and have a nauseous astringent and metallic taste. The sulphate of zinc, or white vi triol, is employed in medicine as an emetic and tonic, and the oxide and car bonate are externally used in the form of ointment. The chloride of zinc is a co lorless compound, fusible at a heat a lit tle above 212°, and known to the older chemists the name of butter of zinc. It is much used for soldering. Brass is an alloy of zinc and copper.
Franklinite, which is a carbonate of zinc mixed with silicates, is found abun dantly in Sussex and Morris counties, N. J. ; almost all the American zinc (which is of great purity) is manufactured from it. (See FaAxxxxxrrn.) Zinc, rolled into large plates, is employ ed as a substitute for lead and slates, in the roofing of buildings. The great ad vantage of these plates of zinc is their lightness, being only about one-sixth part of the weight of lead. They do not rust, which is another great advantage, and has led to the employment of zinc pipes both for cold and hot water. No cover ing is better adapted for verandas and summer houses.