Copper
This useful metal has been known from the earliest times. With tin it no doubt formed the first metallic compound, and was extensively employed by the ancients in the production of ornaments, statuary, domestic utensils, and implements of war. Pliny informs us that the Roman supply was drawn from Cyprus, the metal being called cyprium for that reason. The latter word was corrupted to cuprum, from whence is derived the English, copper. The color of copper is a brilliant red, its specific gravity 8.788, its tenacity only somewhat below that of iron, and higher than either silver or gold. Copper melts at 2550 deg.; its malleability and ductility is high, takes a remarkable degree of polish, ranks next to silver as a conductor of electricity, is hardly affected by dry air, but, on exposure to a damp atmosphere, a green carbonate gathers on its surface. This metal is widely distributed throughout nature, occurring in ores, soils, and waters--in fact, it is almost as universal as iron. In Lake Superior the metal occurs native, and in some instances irregular masses exceeding 100 tons in weight are found.
Out of nearly a dozen different ores cuprite, or red oxide, contains the most metal--about 80 per cent when pure--the rest yielding smaller quantities. Chrysolica, a hydrated silicate of copper found in Chili, Missouri, and Wisconsin, yields only 30 per cent. The Cornish ores consist of copper pyrites, a sulphide of copper and iron.
There are three ways of obtaining copper from its ores, the dry, or pyro-metallurgical, the wet, or hydro-metallurgical, and the electro-metallurgical; but the two former are the methods generally employed. The dry method, or smelting, is invariably pursued when the ores contain over 5 per cent of copper; for a lower grade than this the wet process only is profitable. Swansea and Lancashire are the chief copper-smelting centres in Great Britain. The ores are selected with a view to special treatment, according to their character. The first operation is calcining in reverberatory furnaces, where the ore is spread 8 inches deep on the bottom and subjected to the action of air and fire at a dull-red heat, being frequently turned over to expose every part to their combined influence for from 12 to 24 hours, according to the proportion of sulphide of iron, silica, etc., contained in the charge. The sulphur by this action is partly burned off and forms sulphurous and sulphuric acids; partially volatilized in the pure state; arsenic volatilizes and is oxidized; and some sulphur from the copper and iron forms oxides by combining with the oxygen. The calcined ore is then fused in the reverberatory ore-fusing furnace, which is provided with a hopper through which to effect the charging, the charge usually consisting of calcined ore 2600, metal-slag from previous operations 800, cobbing 250. About five hours' hard firing reduces this to a fluid mass, which, after being well skimmed, is tapped into perforated iron boxes, which are suspended in cisterns 50 inches square and 80 inches deep, full of water. At this stage the compound analyzes at: copper 33, sulphur 29, iron 33, and is termed granulated or coarse metal. It is subsequently recalcined, in a similar manner as for the ore, in 4-ton charges. About 24 hours, at a gradually increasing heat, up to a bright red, prepares the metal for running off into cubs, where it is treated to another bath of water, after which it is again fused, and by this treatment the silica and oxide of iron combine to form slags, which are skimmed off and the metal again tapped, but in this case it is run into sand-moulds. The resulting compound is now called blue metal, and consists of copper 58, sulphur 20, iron 12.
It is now ready for a further treatment by roasting, in charges of 3 tones. The roasting furnace is provided with side charging arrangements and additional air-holes in the bridge, through which a free current of air is admitted, passing over the fused mass, which is kept in a semi-fluid state for about 24 hours, during which time much more of the sulphur has been driven off, and the iron turned into slag by its union with silica, the latter being constantly skimmed off as it is formed.
At this stage, when other impurities have been driven off, it has become a sulphide of copper, and must receive still another 24 hours' roasting to eliminate the sulphur, after which it is again tapped into sand-moulds, forming, according to quality, the several kinds of copper known as blister, coarse, pimpled, and bed copper. Ingots showing a smooth, hollow surface indicate the presence of tin, and are called bed; a pimply surface indicates sulphur; scales of oxide on the surface indicate the blister quality, which is esteemed as ready for refining, and, in this state, consists of copper 98.1, iron .7, manganese, cobalt, and nickel .3, arsenic and tin .4, sulphur .2. The Siemens Regenerative Furnace is esteemed as the best for refining. Its form is reverberatory, almost like the roasting-furnace, except that the bed inclines towards the reservoir at the end, where, by means of a door, the refined metal may be skimmed off and dipped out. When the metal has collected, it is subjected to polling by thrusting a piece of green oak to the bottom and holding it there. Dipping tests by the refiner indicate when the metal has attained the proper degree of fibre. When the polling ceases the surface is at once covered with charcoal, and a little lead added if the copper is required for rolling or forging; but no lead is employed when the best quality of commercial copper is made. See REFINING.
The wet process of grinding and roasting, by which means sulphuric acid is formed, and attacks the oxide of copper. The sulphate resulting from this treatment is dissolved, and the copper precipitated by peroxide of iron. Dilute sulphuric acid and muriatic acids scarcely act upon copper; boiling oil of vitriol attacks it, with evolution of sulphurous anhydride. Nitric acid, even dilute, dissolves it readily, with evolution of nitric acid. Copper unites readily with almost all other metals in certain proportions, and not a few of its compounds are of the highest importance in the arts; it may be said that copper is even more important and valuable as a constituent element in a large number of alloys than it could possibly be as a pure metal. It is somewhat difficult to make castings free from blow-holes with pure copper. An excellent remedy for this is to flux with about one ounce of zinc to each four pounds of copper.
Copper combines easily with gold in all proportions, with the result of increased fusibility and hardness; but the ductility is impaired as the hardness increases, its greatest degree of hardness occurring when the proportion of copper is 1/18. The increased fusibility of the alloy admits of its being used as a solder for gold.
Bronze, brass, and German-silver are the principal alloys in which copper enters as a chief ingredient. With zinc, it forms brass; with lead, pot, metal; with zinc and nickel, German-silver; with zinc, tin, and arsenic, tombac; with tin, bronze.
The aluminum bronzes consist of pure copper alloyed with from 1 3/4 to 10 per cent aluminum. Phosphor bronze has from 2 1/2 to 15 per cent tin and from 1/4 to 2 1/2 per cent phosphorus, according to what it may be required for. Besides these there are the very numerous and excellent copper alloys for manufacturing purposes, in which the three metals, tin, zinc, and lead, are mixed with it in varying quantities; and others again in which sulphur, bismuth, antimony, cobalt, nickel, silver, iron, etc., are employed in small proportions. See BRASS; BRONZE; GERMAN-SILVER; ZINC; LEAD; POT-METAL; TOMBAC; ALUMINUM-BRONZE; PHOSPHOR-BRONZE; SILVER; ALLOYS; SOLDERS; FONTAINMOREAU'S BRONZES; MUSIC-METAL.
Copperas (Green copperas).--The commercial name for sulphate of iron, a compound of the protoxide of iron with sulphuric acid. It is largely manufactured from iron pyrites, which furnishes by oxidation both the acid and the base. It is often a beautiful mineral, the crystals being a very perfect shape. See SULPHUR.