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 of 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 with 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 blend° 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 made with the tube leading to the iron pan, and the zinc gradually distils downward, partly in powder and partly in stalactite 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 burns 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. If forms deliquescent four-sided prisms, soluble in water and alcohol. Sulphate of zinc, or white vitriol, is manufactured on a large scale by roasting native sul phide of zinc (blende), extracting the mass with water, and evaporating to the crystallizing point. It is generally sent into commerce in white fused masses. Generally speaking, it contains six atoms of water of crystallization; but com pounds containing less have been formed. It crystallizes ordinarily in four-sided prisms. It is used in medicine as an emetic, and very largely by calico print ers_ It is soluble in parts of water, but insoluble in alcohol. Several basic sulphates are said to exist. It combines directly with ammonia, forming a defi nite compound. It also forms double sul phates with those of potassa, ammonia, magnesia, and protoxide of iron. Car bonate of zinc, or calamine, occurs in nature in large amorphous masses, and occasionally in crystals of the same form as those of carbonate of lime. It is the chief ore of zinc, and is employed in its impure state in medicine as an exsiccant, and in healing cerates. The anhydrous carbonate may be prepared in the labora tory by placing a tube containing carbon ate of soda in a strong tube containing sulphate of zinc, sealing the outer tube hermetically, heating it to 320° F., and inverting it so that the solution may mix; crystalline grains of the anhydrous carbonate are gradually deposited. No neutral carbonate of zinc can be obtained from its salts by double decomposition. Chloride of zinc is prepared by dissolv ing granulated zinc in hydrochloric acid, and evaporating, when it is obtained in a semi-solid hydrated mass, known as butter of zinc. If this be further heated, it fuses, becomes anhydrous and solid. It is deliquescent, fuses easily, and may be distilled. It is remarkably soluble in water, and its strong affinity for that substance renders it of great use as a desiccating agent in organic research. In solution it forms Burnett's disinfect ing fluid. It is a powerful escharotic when applied to the skin, and is used in surgery for that purpose. It fuses above 700° F., but does not decompose unless more strongly heated; hence a bath of it is sometimes used for maintaining ob jects at a high temperature. Its solution absorbs ammoniacal gas with avidity. It forms double salts with the chlorides of the alkaline metals. Its solution is also much used in soldering zinc, iron, and copper. Its solution is also much used for preserving objects for dissec tion, as it does not corrode the instru ments in the same way as corrosive sub limate. Several oxychlorides are said to exist. Sulphide of zinc, or blende, is found native contaminated with a large number of the other metals. It may be prepared by the direct combination of its elements. The hydrated sulphide is ob tained as a white precipitate, by adding an alkaline sulphide to a solution of some zinc salt. There are several oxy sulphides of zinc. The trisilicate of zinc, or electric calamine, is found native in several parts of the world. Heat de velops electricity in it; hence its name. Valerianate of zinc is used in medicine in combating nervous disorders.
The production of spelter in the United States in the calendar year 1900 was 123,886 short tons, the largest on record. Illinois, Indiana, Kansas, and Missouri were the chief producing States. For the first time the United States be came the exporter of both metal and ore in that year.
The production of primary zinc in the United States in 1919 was 452,272 short tons valued at $66,032,000. Okla homa ranked first in the production of zinc, with 121,988 tons; Illinois was second, and Kansas third. In 1919 the United States produced practically all the zinc smelted. Zinc imports in that year amounted to 48,649 tons of ore. 17,009 tons of zinc content, with a total value of $529,660. The exports of zinc in 1919 were valued at $50,530,132.