Page:The American Cyclopædia (1879) Volume V.djvu/322

 318 COPPER naturally suggest the possibility of these people having^iad the art of giving to the metal hard- ness adapted to its use for quarry tools. Prescott points out other resemblances in their works to those of the Egyptians. The Peru- vians, too, used copper for the ^ame purposes ; and Humboldt gives the composition of a chis- el found in a silver mine opened by the incas near Cuzco, viz., 94 per cent, copper and 6 per cent. tin. This is almost identical with the composition of the chisel found by Wilkinson at Thebes, which was 94 per cent, copper, 5*9 per cent, tin, and O'l per cent. iron. The Scandinavian tumuli, in Denmark, have af- forded similar collections of copper utensils of very remote antiquity, many of which are pre- served in the museum of Copenhagen ; among them are knives, daggers, chisels, hammers, wedges, axes, &c. There are swords and knives with blades of gold and cutting edges of iron ; some are of copper, also similarly faced, the iron appearing to be the rare and choice metal. In the work of J. Arthur Phil- lips and John Darlington, " Records of Mining and Metallurgy," are given many analyses made by Mr. Phillips of coins and sword blades, some of the former dating back as far as 500 B. C. In the most ancient coins the alloy is, copper 62 to 72 per cent., tin about 7, and lead from 19 to 29'32 per cent. Tin is almost invariably present. Zinc first appears in specimens about the commencement of the Christian era. The cutting instruments are uniformly composed of copper and tin, gener- ally about one part of the latter in ten, and sometimes lead forms a small part of the alloy. Daring the middle ages there is little recorded concerning the working of copper mines and the use of the metal. Copper has been ob- tained in recent times from the mine of Ram- melsberg, near Goslar, in the Hartz mountains, which was worked in the 10th century. The Swedish mine of Fahlun competed with the above in the production of copper in the 12th century; and in the next century the mines of Thuringia were worked. In Great Britain, the Parys mine in Anglesea, it is believed, was worked by the Romans. This was very pro- ductive in the latter part of the 18th century, causing by the abundance of its ores the price of the metal .to be considerably reduced. In 1799, when it was nearly exhausted, the price of copper rose again to 128 per ton. The rich veins at Newlands near Keswick were worked in 1250 ; and in 1470, as appears by a charter granted by Edward IV., the business was extensively carried on. The metal was obtained at Ecton hill in Staffordshire pre- vious to its discovery in Cornwall. The mines of Cornwall, worked for tin at very early pe- riods, appear to have been little regarded for the copper ores they contained before the mid- dle of the 18th century. Copper is a metal remarkable for its fine red color bordering upon yellow, and for its peculiar and disagree- able taste and smell when rubbed. Obtained in very thin films on the surface of glass, by precipitation from its solution in ammonia by the aid of a ferrous salt, it is transparent, and by the light transmitted through it appears green, but by reflected light red. Its specific gravity is from 8-8 to 8'96, varying according to the method of its manufacture. Its hardness is from 2-5 to 3, being about the same as that of gold and silver. It is so ductile that it is hammered into very thin sheets and drawn out into fine wire. In tenacity it ranks next to iron, a wire T V inch in diameter sustaining a weight of 300 Ibs. Its power of conducting heat is 2 times that of iron. It expands, when heated from 32 to 212 F., -^ of its length. It is a ready conductor of heat, and one of the best conductors of electricity. It melts at a full red heat, estimated at from 2,200 to 2,500 F., and at a white heat the vapors passing from it burn with a green flame. The equivalent weight of copper is 31 '7, and its symbol is Cu. It crystallizes in forms of the isometric or tesseral system. Copper under- goes no change in dry air, but when exposed to moist air it becomes slowly covered with a greenish coating, which is a hydrous carbon- ated oxide of the metal. When heated to red- ness in contact with the air, it becomes covered with a reddish scale, which is a peculiar oxide, to be noticed further on. Copper is readily attacked and dissolved by nitric acid, with the evolution of nitric oxide gas, and the formation of a blue solution of nitrate of copper. Hydro- chloric acid does not attack the metal unless the air has access, when it dissolves, forming a chloride. Dilute sulphuric acid has no action on copper, but it decomposes the concentrated acid with the aid of heat, with the evolution of sulphurous acid and the production of sul- phate of copper. Copper forms two principal compounds with oxygen, the black or cupric oxide, often called protoxide, CuO, and the red or cuprous oxide, called also suboxide or dinoxide, Cu 2 O. Both of these are found in nature constituting ores of copper, and may also be obtained artificially. The protoxide dissolves readily in acids, giving rise to salts white and blue or green in color ; and the oxide itself, though black when anhydrous, is blue when combined with water. The red or suboxide, which is ruby or vermilion red in color, yields a yellow hydrate, which readily absorbs oxygen from the air and passes to the state of protoxide. By most acids it is con- verted into a salt of the protoxide with the separation of one half its copper in the metallic state, but by the action of hydrochloric acid is changed into a white subchloride or dichloride, Cu 2 Cl, which is insoluble in water, though soluble in strong solutions of common salt and other chlorides. The black oxide, on the con- trary, yields with hydrochloric acid a very soluble protochloride, CuCl, which is green in solution, but brown when deprived of water. Certain salts of copper are of use in the arts, and may here be briefly noticed. .Sulphate of