Page:Collier's New Encyclopedia v. 10.djvu/578

LEFT ZINC 498 ZINC ter. This was effected in large crucibles, which were exposed to a long-continued heat in furnaces constructed for the purpose. The zinc immediately on its liberation from the calamine of course united with the copper without giving any notice of its presence. The only use to which zinc was applied for many years after its discovery was for mix- ing with copper to form brass; and it was comparatively of late years that the fact of its becoming ductile and malleable when heated was made known. A patent was granted to the discoverers of this property, Sylvester and Hobson, in 1805, since which period the zinc manufacture has made steady progress. Zinc has a considerable power of dis- solving iron; in consequence of which the iron pots in which it is melted soon become corroded and unfit for use. Its specific gravity varies, according to the closeness of texture oi the sample, from 7.03 to 7.2, or even 7.3. Zinc is abun- dantly distributed in the form of various ores throughout the whole world. Its principal ores are: Red zinc ore, which is found and worked in New Jersey. It consists of oxide of zinc, colored vnth binoxide of manganese. Carbonate of zinc, or calamine, found extensively in the Devonian and Carboniferous forma- tions of most countries, especially near Lancaster, Columbia co.. Pa., where mines were opened in 1853. Hydrated silicate of zinc, which is worked exten- sively in the United States. Sulphide of zinc, blende, or black jack^ which is met with in large quantities in various parts of England and Europe. In the extrac- tion of zinc from its ores, the blende or calamine is first crushed between rollers and roasted. In the case of the blende this is a tedious process, and requires great care. The result in either case is oxide of zinc, which is mixed with half its weight of powdered coke or anthra- cite, and introduced into crucibles of peculiar constructon. A circular fur- nace is employed, within which the cru- cibles are ranged. In the bottom of each crucible is an opening, to which a short iron pipe is attached, passing through the bottom of the furnace. To the end of this is affixed a removable tube com- municating with a sheet-iron vessel. The hole in the bottom of the crucible having been partially plugged with coke, a charge of ore and coal is introduced, and the op of the crucible luted down. The tube connected with the iron vessel is lowered so as to leave the crucible tube open, and the heat is raised. So soon as the flame at the mouth of the short iron tube begins to turn from white to blue, connection is madp with the tube leading to the iron pan, and the zinc gradually distils downward, partly in powder and partly in stalactitic masses. The crude metal is remelted, skimmed, and cast into ingots. In Silesia and Bel- gium retorts are used instead of cru- cibles, or per ascensum instead of per descensum. Zinc is often known in com- merce as spelter, the derivation of which term is unknown. The equivalent of zinc, as determined by Erdmann, is 52.53. Zinc only forms one oxide ZnO, which occurs in nature as red zinc ore. The anhydrous oxide is formed when zinc is burnt in air, and has been occasionally found in four and six-sided prisms in the flues of zinc furnaces. It is best prepared in the laboratory by calcining the precipitate produced by mixing solu- tions of sesquicarbonate of ammonia and sulphate of zinc. On the large scale, when it is required as a pigment, it is made by distilling zinc in clay re- torts, passing into chambers through which a current of air is maintained. The volatilized metal bums at the high temperature to which it is exposed, and the oxide is deposited in the condensing chambers. As a pigment, it has not met with great success, as it does not wear so well as white lead, from its lesser specific gravity. In situations where it is exposed to sulphurous fumes, it stands perfectly; and being harmless in its nature, it is not open to the ob- jections raised against its poisonous congener. Oxide of zinc forms a light white powder, which becomes yellow when heated, regaining its whiteness when it cools. It is a permanent oxide, even at the greatest heat. When ex- posed to the air, it becomes converted into a carbonate. It dissolves readily in acids, and its salts have the same form as those of magnesia and oxide of iron, with which it is isomorphous. Its salts, though neutral in composition, have an acid reaction. It is not easily dissolved in solutions of potash and soda, but if fused with them in a silver crucible, it forms compounds soluble in water in which the oxide of zinc appears to play the part of an acid. The hy- drated oxide is formed by adding a solu- tion of potash to the sulphate of zinc. It is readily soluble in excess of alkaline solution. In medicine, oxide of zinc is used in ointments as an astringent and desiccant, and by itself as a tonic, espe- cially in cases of nervous debility brought on by drinking. Zinc is said to be a binoxide, but it requires confirma- tion. Nitrate of zinc is prepared by dis- solving zinc in dilute nitric acid. K forms deliquescent four-sided prisms,