Copper (Lat. cuprum, from Cyprus the island, in which the ores of this metal were mined by the ancient Greeks), one of the first metals known to man. Tubal Cain, the seventh in descent from Adam, we are told, was "an instructor of every artificer in brass and in iron." In the book of Job we read that "copper is molten out of the stone." Cheops, an Egyptian king of the fourth dynasty, it is recorded, worked a copper mine in the peninsula of Sinai. The ancient Egyptians employed an alloy of it for working hard stones, and Wilkinson suggests that they may have had the art of hardening it. The Syrians and Phoenicians, as also the Greeks and Romans, consumed the metal largely in the manufacture of monuments and statues of bronze. The single colossus of Rhodes, after having lain in fragments for nine centuries, is said to have required 900 camels to convey its pieces away. The ores seem, therefore, not only to have been worked extensively by the ancients, but the skill and facilities for producing large castings appear to have been quite equal to those possessed by the moderns. Besides its use as an alloy in the manufacture of bronze, it was also employed in coin in the pure state.
The metal itself was probably first discovered, as it is now found, in a native state, and by the melting of this the nature of the rich ores associated with it came to be known. The obscure races that inhabited this continent prior to the Indians possessed an acquaintance with it, as appears from the various small utensils of copper found in the ancient mounds of the western country; and the extensive mining works, probably of the same people, at Lake Superior (see Copper Mines), testify to the knowledge of it possessed by some ancient race of greater skill than the Indians. The Aztecs of Mexico made use of chisels and axes of copper, some of which are found with the large half-finished blocks of granite in the quarries of Mitla; and these naturally suggest the possibility of these people having had the art of giving to the metal hardness adapted to its use for quarry tools. Prescott points out other resemblances in their works to those of the Egyptians. The Peruvians, too, used copper for the same purposes; and Humboldt gives the composition of a chisel 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 0.1 per cent. iron. The Scandinavian tumuli, in Denmark, have afforded similar collections of copper utensils of very remote antiquity, many of which are preserved in the museum of Copenhagen; among them are knives, daggers, chisels, hammers, wedges, axes, etc. 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 Phillips 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 1/2 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, generally about one part of the latter in ten, and sometimes lead forms a small part of the alloy. During the middle ages there is little recorded concerning the working of copper mines and the use of the metal.
Copper has been obtained 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 productive 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 previous to its discovery in Cornwall. The mines of Cornwall, worked for tin at very early periods, appear to have been little regarded for the copper ores they contained before the middle of the 18th century. - Copper is a metal remarkable for its fine red color bordering upon yellow, and for its peculiar and disagreeable 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 1/13 inch in diameter sustaining a weight of 300 lbs. Its power of conducting heat is 2 1/2 times that of iron. It expands, when heated from 32° to 212° F., 1/582 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 undergoes no change in dry air, but when exposed to moist air it becomes slowly covered with a greenish coating, which is a hydrous carbonated oxide of the metal.
When heated to redness 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. Hydrochloric 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 sulphate 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, Cu2O. 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 converted 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, Cu2Cl, which is insoluble in water, though soluble in strong solutions of common salt and other chlorides. The black oxide, on the contrary, 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 copper, or blue vitriol, is best prepared by dissolving the oxide in dilute sulphuric acid, or by oxidizing at a low red heat the native compounds of sulphur and copper, as is done in the roasting of copper ores, which after this process give to water a solution of sulphate. This salt crystallizes in large blue prismatic crystals, which have the composition CuO, SO3 + HO, and contain almost exactly one fourth their weight of metallic copper. Besides its use in medicine, noticed hereafter, considerable quantities of sulphate of copper are consumed as an application to seed wheat to destroy the germs of the fungus known as smut. For this purpose 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 oxychloride of copper; and verditer, a carbonate of copper. Verdigris is the name given to various acetates of copper. A pure crystallized acetate is prepared by dissolving oxide of copper 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 copper 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 copper, 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 concretionary 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 carbonates contain water and an excess of oxide, constituting what are called basic carbonates. Malachite, from the large quantities in which it is sometimes found, is a valuable ore of copper. Chrysocolla is the name given to a green hydrated silicate of copper which sometimes accompanies the other oxidized ores of this metal, while atacamite is a green oxy chloride of copper which occurs in considerable quantities 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. Sulphur combines with copper in two proportions, corresponding to the two oxides already noticed. 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, containing, besides copper, portions of arsenic or antimony, 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 contains in its purest form 34.6 per cent, of copper, 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 importance as ores of the metal. - The uses of copper in the arts are very various, from its toughness, 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 impede 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 advantageous or economical to alloy copper with other metals. Thus, with zinc it forms brass; with tin, bronze and bell metal; and with zinc and nickel, German silver. An alloy of copper with from 5 to 10 per cent. of aluminum is known by the name of aluminum bronze, and from its golden yellow color, its great hardness and elasticity, and its resistance to oxidation, is susceptible of very many applications both useful and ornamental in the arts. It has lately been found that the union with copper of small portions of phosphorus imparts to this metal great hardness and great strength, so that it has been proposed to use the new phosphorus bronze, as it is called, for the manufacture of large guns.
Small quantities of copper are alloyed with gold and with silver to harden these metals, both for the purposes of coinage and for various articles of manufacture. - A minute portion of copper has been found in the human body, and is considered a normal constituent. Sulphate of copper (but not copper itself) is used in medicine as an emetic in the dose of about two grains, acting rapidly and safely. In smaller doses it is an astringent. Externally it is applied to chronic granulating surfaces as an astringent and stimulant. In appropriate cases it is better than the nitrate of silver. "When poisoning has taken place from this or other soluble salts of copper, the symptoms are chiefly those of gastro-intestinal irritation. Under these circumstances, milk and eggs should be administered, by which less soluble combinations of the metal are formed with the caseine and albumen they contain. The best antidote is ferrocyanide of potassium, which forms with the poison an insoluble ferrocyanide of copper.
The existence of a form of chronic poisoning due to the gradual absorption of copper compounds, and analogous to lead poisoning, has not been satisfactorily established. - See Coppee Mines, and Copper Smelting.