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Rh oxidation of sulphuretted copper ores (see above, Metallurgy; wet methods), or by dissolving cupric oxide in sulphuric acid. It was obtained in 1644 by Van Helmont, who heated copper with sulphur and moistened the residue, and in 1648 by Glauber, who dissolved copper in strong sulphuric acid. (For the mechanism of this reaction see C. H. Sluiter, Chem. Weekblad, 1906, 3, p. 63, and C. M. van Deventer, ibid., 1906, 3, p. 515.) It crystallizes with five molecules of water as large blue triclinic prisms. When heated to 100°, it loses four molecules of water and forms the bluish-white monohydrate, which, on further heating to 250°–260°, is converted into the white CuSO4. The anhydrous salt is very hygroscopic, and hence finds application as a desiccating agent. It also absorbs gaseous hydrochloric acid. Copper sulphate is readily soluble in water, but insoluble in alcohol; it dissolves in hydrochloric acid with a considerable fall in temperature, cupric chloride being formed. The copper is readily replaced by iron, a knife-blade placed in an aqueous solution being covered immediately with a bright red deposit of copper. At one time this was regarded as a transmutation of iron into copper. Several basic salts are known, some of which occur as minerals; of these, we may mention (q.v.), CuSO4, 3Cu(OH2), langite, CuSO4, 3Cu(OH)2, H2O, lyellite (or devilline), warringtonite; woodwardite and enysite are hydrated copper-aluminium sulphates, connellite is a basic copper chlorosulphate, and spangolite is a basic copper aluminium chlorosulphate. Copper sulphate finds application in calico printing and in the preparation of the pigment Scheele’s green.

A copper nitride, Cu3N, is obtained by heating precipitated cuprous oxide in ammonia gas (A. Guntz and H. Bassett, Bull. Soc. Chim., 1906, 35, p. 201). A maroon-coloured powder, of composition CuNO2, is formed when pure dry nitrogen dioxide is passed over finely-divided copper at 25°–30°. It decomposes when heated to 90°; with water it gives nitric oxide and cupric nitrate and nitrite. Cupric nitrate, Cu(NO3)2, is obtained by dissolving the metal or oxide in nitric acid. It forms dark blue prismatic crystals containing 3, 4, or 6 molecules of water according to the temperature of crystallization. The trihydrate melts at 114.5°, and boils at 170°, giving off nitric acid, and leaving the basic salt Cu(NO3)2·3Cu(OH)2. The mineral gerhardtite is the basic nitrate Cu2(OH)3NO3.

Copper combines directly with phosphorus to form several compounds. The phosphide obtained by heating cupric phosphate, Cu2H2P2O8, in hydrogen, when mixed with potassium and cuprous sulphides or levigated coke, constitutes “Abel’s fuse,” which is used as a primer. A phosphide, Cu3P2, is formed by passing phosphoretted hydrogen over heated cuprous chloride. (For other phosphides see E. Heyn and O. Bauer, Rep. Chem. Soc., 1906, 3, p. 39.) Cupric phosphate, Cu3(PO4)2, may be obtained by precipitating a copper solution with sodium phosphate. Basic copper phosphates are of frequent occurrence in the mineral kingdom. Of these we may notice libethenite, Cu2(OH)PO4; chalcosiderite, a basic copper iron phosphate; torbernite, a copper uranyl phosphate; andrewsite, a hydrated copper iron phosphate; and henwoodite, a hydrated copper aluminium phosphate.

Copper combines directly with arsenic to form several arsenides, some of which occur in the mineral kingdom. Of these we may mention whitneyite, Cu9As, algodonite, Cu6As, and domeykite, Cu3As. Copper arsenate is similar to cupric phosphate, and the resemblance is to be observed in the naturally occurring copper arsenates, which are generally isomorphous with the corresponding phosphates. Olivenite corresponds to libethenite; clinoclase, euchroite, cornwallite and tyrolite are basic arsenates; zeunerite corresponds to torbernite; chalcophyllite (tamarite or “copper-mica”) is a basic copper aluminium sulphato-arsenate, and bayldonite is a similar compound containing lead instead of aluminium. Copper arsenite forms the basis of a number of once valuable, but very poisonous, pigments. Scheele’s green is a basic copper arsenite; Schweinfurt green, an aceto-arsenite; and Casselmann’s green a compound of cupric sulphate with potassium or sodium acetate.

Normal cupric carbonate, CuCO3, has not been definitely obtained, basic hydrated forms being formed when an alkaline carbonate is added to a cupric salt. Copper carbonates are of wide occurrence in the mineral kingdom, and constitute the valuable ores malachite and azurite. Copper rust has the same composition as malachite; it results from the action of carbon dioxide and water on the metal. Copper carbonate is also the basis of the valuable blue to green pigments verditer, Bremen blue and Bremen green. Mountain or mineral green is a naturally occurring carbonate.

By the direct union of copper and silicon, cuprosilicon, consisting mainly of Cu4Si, is obtained (Lebeau, C.R., 1906; Vigouroux, ibid.).

Copper silicates occur in the mineral kingdom, many minerals owing their colour to the presence of a cupriferous element. (q.v.) and (q.v.) are the most important forms.

Detection.—Compounds of copper impart a bright green coloration to the flame of a Bunsen burner. Ammonia gives a characteristic blue coloration when added to a solution of a copper salt; potassium ferrocyanide gives a brown precipitate, and, if the solution be very dilute, a brown colour is produced. This latter reaction will detect one part of copper in 500,000 of water. For the borax beads and the qualitative separation of copper from other metals, see : Analytical. For the quantitative estimation, see : Copper.

Medicine.—In medicine copper sulphate was employed as an emetic, but its employment for this purpose is now very rare, as it is exceedingly depressant, and if it fails to act, may seriously damage the gastric mucous membrane. It is, however, a useful superficial caustic and antiseptic. All copper compounds are poisonous, but not so harmful as the copper arsenical pigments.

—See generally H. J. Steven’s Copper Handbook (annual), W. H. Weld, The Copper Mines of the World (1907), The Mineral Industry (annual), and Mineral Resources of the United States (annual). For the dry metallurgy, see E. D. Peters, Principles of Copper Smelting (New York, 1907); for pyritic smelting, see T. A. Rickard, Pyrite Smelting (1905); for wet methods, see Eissler, Hydrometallurgy of Copper (London, 1902); and for electrolytic methods, see T. Ulke, Die electrolytische Raffination des Kupfers (Halle, 1904). Reference should also be made to the articles and. For the chemistry of copper and its compounds see the references in the article. Toxicologic and hygienic aspects are treated in Tschirsch’s Das Kupfer vom Standpunkt der gerichtlichen Chemie, Toxikologie und Hygiene (Stuttgart, 1893).

COPPERAS (Fr. couperose; Lat. cupri rosa. the flower of copper), green vitriol, or ferrous sulphate, FeSO4·7H2O, having a bluish-green colour and an astringent, inky and somewhat sweetish taste. It is used in dyeing and tanning, and in the manufacture of ink and of Nordhausen sulphuric acid or fuming oil of vitriol (see ).

  COPPER-GLANCE, a mineral consisting of cuprous sulphide, Cu2S, and crystallizing in the orthorhombic system. It is known also as chalcocite, redruthite and vitreous copper (German, Kupferglaserz of G. Agricola, 1546). The crystals have the form of six-sided tables or prisms; the angle between the prism faces (lettered o in the figure) being 60° 25′. When twinned on the prism planes o, as is frequently the case, the crystals simulate hexagonal symmetry still more closely, as in the minerals aragonite and chrysoberyl. Twinning also takes place according to two other laws, giving rise to interpenetrating crystals with the basal planes (s) of the two individuals inclined at angles of 69° or 87° 56′ respectively. The mineral also occurs as compact masses of considerable extent. The colour is dark lead-grey with a metallic lustre, but this is never very bright, since the material is readily altered, becoming black and dull on exposure to light. The mineral is soft (H.=2½) and sectile, and can be readily cut with a knife, like argentite; sp. gr. 5.7. Analyses agree closely with the formula Cu2S, which corresponds to 79.8% of copper; small quantities of iron and silver are sometimes present.

Next to chalcopyrite, copper-glance is the most important ore of copper. It usually occurs in the upper part of the copper-bearing lodes, and is a secondary sulphide derived from the chalcopyrite met with at greater depths; sometimes, however, the two minerals are found together in the same part of the lodes. The best crystals are from St Just, St Ives, and Redruth in Cornwall, and from Bristol in Connecticut. Small crystals of recent formation are found on Roman bronze coins in the thermal springs at Bourbonne-les-Bains.

Copper-glance readily alters to other minerals, such as malachite, covellite, melaconite and chalcopyrite. On the other hand, it is found as pseudomorphs after chalcopyrite, galena, and organic structures such as wood; copper-glance pseudomorphous after galena preserves the cleavage of the original mineral and is known as harrisite.

Isomorphous with copper-glance is the orthorhombic mineral stromeyerite, a double copper and silver sulphide, CuAgS, which occurs in abundance in the Altai Mountains.

 COPPERHEADS, an American political epithet, applied by Union men during the Civil War to those men in the North who, deeming it impossible to conquer the Confederacy, were earnestly in favour of peace and therefore opposed to the war policy of the president and of Congress. Such men were not necessarily friends of the Confederate cause. The term originated in the autumn of 1862, and its use quickly spread throughout the North. In the Western states early in 1863 the terms “Copperhead”