Page:The American Cyclopædia (1879) Volume V.djvu/323

 COPPER 319 copper, or blue vitriol, is best prepared by dis- solving the oxide in dilute sulphuric acid, or by oxidizing at a low red heat the native com- pounds of sulphur and copper, as is done in the roasting of copper ores, which after this pro- cess give to water a solution of sulphate. This salt crystallizes in large blue prismatic crystals, which have the composition CuO, S0 8 + eHO, and contain almost exactly one fourth their weight of metallic copper. Besides its use in medicine, noticed hereafter, considerable quan- tities of sulphate of copper are consumed as an application to seed wheat to destroy the germs of the fungus known as smut. For this pur- pose the grain is soaked in a solution of the salt. It is also largely consumed in dyeing, and in the preparation of various pigments, among which are Scheele's green and Schwein- furt green, both very beautiful but poisonous colors, in which oxide of copper is combined with arsenic ; Brunswick green, which is an oxy chloride of copper ; and verditer, a carbon- ate of copper. Verdigris is the name given to various acetates of copper. A pure crystallized acetate is prepared by dissolving oxide of cop- per in acetic acid; but the pigment known under that name is a mixture of several basic acetates or compounds of acetate and hydrous oxide of copper, prepared by parting sheets of copper in layers with the refuse of the grape from which the juice has been expressed, when a greenish layer of verdigris forms, and after some weeks is scraped off. The sources of cop- per are the native metal and the oxidized and the sulphuretted ores. Mention will be made of the latter in treating of copper mines. The ores in which the metal occurs in an oxidized form are as follows : red oxide, or ruby cop- per, which is the suboxide already noticed, and occurs both massive and crystallized in isometric forms ; in its pure state it consists of 88-8 parts of copper and 11-2 of oxygen. The black oxide is less abundant in nature, and generally occurs in an earthy uncrystalline form, but in 1846 a vein of massive and crystalline black oxide was found at Copper Harbor, Lake Superior, which yielded about 20 tons of the ore. The native carbonates of copper are two in number. The one is called azurite, and occurs in beautiful transparent blue crystals in certain copper mines, but is rarely abundant. The other, known as malachite, is sometimes crystallized, but more often occurs in concre- tionary masses of various shades of green, which are generally banded or arranged in such a manner that the mineral, which takes a fine polish, is much prized as an ornamental stone. Great quantities of it are found in the Siberian mines, and many beautiful objects are manufactured from it. Both of these carbon- ates contain water and an excess of oxide, con- stituting what are called basic carbonates. Malachite, from the large quantities in which it is sometimes found, is a valuable ore of cop- per. Chrysocolla is the name given to a green hydrated silicate of copper which sometimes 226 VOL. v. 21 accompanies the other oxidized ores of this metal, while atacamite is a green oxychloride of copper which occurs in considerable quanti- ties in some South American mines. The white dichloride of copper has also been met with in a Chilian copper mine. All of these ores probably result from the oxidation of the native metal, or of the sulphuretted compounds of copper from which by far the greater part of the supplies of this metal are derived. Sul- phur combines with copper in two proportions, corresponding to the two oxides already no- ticed. The protosulphide, CuS, is known as indigo copper, and is comparatively rare ; but the disulphide, called also copper glance or vitreous copper ore, is more abundant, and constitutes a very rich ore. It is soft, leaden gray in color, and contains about 80 per cent, of copper. These ores are, however, less frequent than the double sulphides of copper and iron, one of which is known by the names of bornite, erubescite, variegated copper ore, purple, peacock, or horse-flesh ore, epithets suggested by the various shades of color which it presents upon its fresh or partially tarnished surfaces. Its composition varies slightly, the analyses of different varieties yielding from 56 to 63 per cent, of copper, 21 to 28 of sulphur, and 7 to 14 of iron. A less common ore is the so-called tetrahedrite, fahlerz, or gray copper, which is a complex sulphide, contain- ing, besides copper, portions of arsenic or anti- mony, and more or less zinc and iron, often with silver or mercury. The most abundant ore of copper is the so-called yellow copper ore, pyritous copper, copper pyrites, or chal- copyrite, which is of a brass-yellow color, brittle, and, like the other sulphuretted copper ores, so soft as to be cut by a knife. It con- tains in its purest form 34- 6 per cent, of cop- per, 34-9 of sulphur, and 30'5 of iron, but very generally occurs mechanically intermixed with more or less iron pyrites. Arsenides of copper are met with in nature, but have no impor- tance as ores of the metal. The uses of copper in the arts are very various, from its tough- ness, malleability, ductility, and resistance to oxidation ; and moreover, from its great power of conducting both heat and electricity, it is adapted to very many useful purposes. Among these are the construction of boilers and vessels for distilling, and various chemical and culinary purposes; for submerged electric cables; for coinage ; and for the engraver's art. In the construction of ships it is largely used for sheathing ; and from the poisonous quality of the products of its slow oxidation in sea water it prevents the adhesion of barnacles and other shell fish, which would otherwise fix themselves upon the surface of the vessel and greatly im- pede its movements. Unlike iron, the results of its oxidation do not exert a corrosive and destroying action on wood, and for this reason copper replaces iron for the construction of the nails, bolts, and fastenings of ships. For many of these and other purposes, it is found