Chapter 25

Many attempts have been made to use crude sulphide of copper or matte as an anode, and recover the copper at the cathode, the sulphur and other insoluble constituents being left at the anode. The best known of these is the Marchese process, which was tested on a working scale at Genoa and Stolberg in Rhenish Prussia. As the operation proceeded, it was found that the voltage had to be raised until it became prohibitive, while the anodes rapidly became honeycombed through and, crumbling away, filled up the space at the bottom of the vat. The process was abandoned, but in a modified form appears to be now in use in Nijni-Novgorod in Russia. Siemens and Halske introduced a combined process in which the ore, after being part-roasted, is leached by solutions from a previous electrolytic operation, and the resulting copper solution electrolysed. In this process the anode solution had to be kept separate from the cathode solution, and the membrane which had in consequence to be used, was liable to become torn, and so to cause trouble by permitting the two solutions to mix. Modifications of the process have therefore been tried.

Modern methods in copper smelting and refining have effected enormous economy in time, space, and labour, and have consequently increased the world's output. With pyritic smelting a sulphuretted copper ore, fed into a cupola in the morning, can be passed directly to the converter, blown up to metal, and shipped as 99% bars by evening--an operation which formerly, with heap roasting of the ore and repeated roasting of the mattes in stalls, would have occupied not less than four months. A large furnace and a Bessemer converter, the pair capable of making a million pounds of copper a month from a low-grade sulphuretted ore, will not occupy a space of more than 25ft. by 100ft.; and whereas, in making metallic copper out of a low-grade sulphuretted ore, one day's labour used to be expended on every ton of ore treated, to-day one day's labour will carry at least four tons of ore through the different mechanical and metallurgical processes necessary to reduce them to metal. About 70% of the world's annual copper output is refined electrolytically, and from the 461,583 tons refined in the United States in 1907, there were recovered 13,995,436 oz. of silver and 272,150 oz. of gold. The recovery of these valuable metals has contributed in no small degree to the expansion of electrolytic refining.

_Production._--The sources of copper, its applications and its metallurgy, have undergone great changes. Chile was the largest producer in 1869 with 54,867 tons; but in 1899 her production had fallen off to 25,000 tons. Great Britain, though she had made half the world's copper in 1830, held second place in 1860, making from native ores 15,968 tons; in 1900 her production was 777 tons, and in 1907, 711 tons. The United States made only 572 tons in 1850, and 12,600 tons in 1870; but she to-day makes more than 60% of the world's total. In 1879, Spain was the largest producer, but now ranks third.

The estimated total production for each decade of the 19th century in metric tons is here shown:--

1801-1810 91,000 1811-1820 96,000 1821-1830 135,000 1831-1840 218,400 1841-1850 291,000 1851-1860 506,999 1861-1870 900,000 1871-1880 1,189,000 1881-1890 2,373,398 1891-1900 3,708,901

The following table gives the output of various countries and the world's production for the years 1895, 1900, 1905, 1907:--

+---------------------+----------+----------+----------+---------+ | Country. | 1895. | 1900. | 1905. | 1907. | +---------------------+----------+----------+----------+---------+ | United States | 175,294 | 274,933 | 397,003 | 398,736 | | Spain and Portugal | 55,755 | 53,718 | 45,527 | 50,470 | | Japan | 18,725 | 28,285 | 36,485 | 49,718 | | Chile | 22,428 | 26,016 | 29,632 | 27,112 | | Germany | 16,799 | 20,635 | 22,492 | 20,818 | | Australasia | 10,160 | 23,368 | 34,483 | 41,910 | | Mexico | 12,806 | 22,473 | 70,010 | 61,127 | | Russia | 5,364 | 8,128 | 8,839 | 15,240 | | +----------+----------+----------+---------+ | World's production | 339,994 | 496,819 | 699,514 | 723,807 | +---------------------+----------+----------+----------+---------+

As the stock on hand rarely exceeds three months' demand, and is often little more than a month's supply, it is evident that consumption has kept close pace with production.

The large demand for copper to be used in sheathing ships ceased on the introduction of iron in shipbuilding because of the difficulty of coating iron with an impervious layer of copper; but the consumption in the manufacture of electric apparatus and for electric conductors has far more than compensated.

_Alloys of Copper._--Copper unites with almost all other metals, and a large number of its alloys are of importance in the arts. The principal alloys in which it forms a leading ingredient are brass, bronze, and German or nickel silver; under these several heads their respective applications and qualities will be found.

Oxides and hydroxides.

_Compounds of Copper._--Copper probably forms six oxides, viz. Cu4O, Cu3O, Cu2O, CuO, Cu2O3 and CuO2. The most important are cuprous oxide, Cu2O, and cupric oxide, CuO, both of which give rise to well-defined series of salts. The other oxides do not possess this property, as is also the case of the hydrated oxides Cu3O22H2O and Cu4O35H2O, described by M. Siewert.

Cuprous oxide, Cu2O, occurs in nature as the mineral cuprite (q.v.). It may be prepared artificially by heating copper wire to a white heat, and afterwards at a red heat, by the atmospheric oxidation of copper reduced in hydrogen, or by the slow oxidation of the metal under water. It is obtained as a fine red crystalline precipitate by reducing an alkaline copper solution with sugar. When finely divided it is of a fine red colour. It fuses at red heat, and colours glass a ruby-red. The property was known to the ancients and during the middle ages; it was then lost for several centuries, to be rediscovered in about 1827. Cuprous oxide is reduced by hydrogen, carbon monoxide, charcoal, or iron, to the metal; it dissolves in hydrochloric acid forming cuprous chloride, and in other mineral acids to form cupric salts, with the separation of copper. It dissolves in ammonia, forming a colourless solution which rapidly oxidizes and turns blue. A hydrated cuprous oxide, (4Cu2O, H2O), is obtained as a bright yellow powder, when cuprous chloride is treated with potash or soda. It rapidly absorbs oxygen, assuming a blue colour. Cuprous oxide corresponds to the series of cuprous salts, which are mostly white in colour, insoluble in water, and readily oxidized to cupric salts.

Cupric oxide, CuO, occurs in nature as the mineral melaconite (q.v.), and can be obtained as a hygroscopic black powder by the gentle ignition of copper nitrate, carbonate or hydroxide; also by heating the hydroxide. It oxidizes carbon compounds to carbon dioxide and water, and therefore finds extensive application in analytical organic chemistry. It is also employed to colour glass, to which it imparts a light green colour. Cupric hydroxide, Cu(OH)2, is obtained as a greenish-blue flocculent precipitate by mixing cold solutions of potash and a cupric salt. This precipitate always contains more or less potash, which cannot be entirely removed by washing. A purer product is obtained by adding ammonium chloride, filtering, and washing with hot water. Several hydrated oxides, e.g. Cu(OH)2·3CuO, Cu(OH)2·6H2O, 6CuO·H2O, have been described. Both the oxide and hydroxide dissolve in ammonia to form a beautiful azure-blue solution (Schweizer's reagent), which dissolves cellulose, or perhaps, holds it in suspension as water does starch; accordingly, the solution rapidly perforates paper or calico. The salts derived from cupric oxide are generally white when anhydrous, but blue or green when hydrated.

Copper quadrantoxide, Cu4O, is an olive-green powder formed by mixing well-cooled solutions of copper sulphate and alkaline stannous chloride. The trientoxide, Cu3O, is obtained when cupric oxide is heated to 1500°-2000° C. It forms yellowish-red crystals, which scratch glass, and are unaffected by all acids except hydrofluoric; it also dissolves in molten potash. Copper dioxide, CuO2H2O, is obtained as a yellowish-brown powder, by treating cupric hydrate with hydrogen peroxide. When moist, it decomposes at about 6° C., but the dry substance must be heated to about 180°, before decomposition sets in (see L. Moser, _Abst. J.C.S._, 1907, ii. p. 549).

Cuprous hydride, (CuH)n, was first obtained by Wurtz in 1844, who treated a solution of copper sulphate with hypophosphorous acid, at a temperature not exceeding 70° C. According to E. J. Bartlett and W. H. Merrill, it decomposes when heated, and gives cupric hydride, CuH2, as a reddish-brown spongy mass, which turns to a chocolate colour on exposure. It is a strong reducing agent.

Cuprous fluoride, CuF, is a ruby-red crystalline mass, formed by heating cuprous chloride in an atmosphere of hydrofluoric acid at 1100°-1200° C. It is soluble in boiling hydrochloric acid, but it is not reprecipitated by water, as is the case with cuprous chloride. Cupric fluoride, CuF2, is obtained by dissolving cupric oxide in hydrofluoric acid. The hydrated form, (CuF2, 2H2O, 5HF), is obtained as blue crystals, sparingly soluble in cold water; when heated to 100° C. it gives the compound CuF(OH), which, when heated with ammonium fluoride in a current of carbon dioxide, gives anhydrous copper fluoride as a white powder.

Cuprous chloride, CuCl or Cu2Cl2, was obtained by Robert Boyle by heating copper with mercuric chloride. It is also obtained by burning the metal in chlorine, by heating copper and cupric oxide with hydrochloric acid, or copper and cupric chloride with hydrochloric acid. It dissolves in the excess of acid, and is precipitated as a white crystalline powder on the addition of water. It melts at below red heat to a brown mass, and its vapour density at both red and white heat corresponds to the formula Cu2Cl2. It turns dirty violet on exposure to air and light; in moist air it absorbs oxygen and forms an oxychloride. Its solution in hydrochloric acid readily absorbs carbon monoxide and acetylene; hence it finds application in gas analysis. Its solution in ammonia is at first colourless, but rapidly turns blue, owing to oxidation. This solution absorbs acetylene with the precipitation of red cuprous acetylide, Cu2C2, a very explosive compound. Cupric chloride, CuCl2, is obtained by burning copper in an excess of chlorine, or by heating the hydrated chloride, obtained by dissolving the metal or cupric oxide in an excess of hydrochloric acid. It is a brown deliquescent powder, which rapidly forms the green hydrated salt CuCl2, 2H2O on exposure. The oxychloride Cu3O2Cl2·4H2O is obtained as a pale blue precipitate when potash is added to an excess of cupric chloride. The oxychloride Cu4O3Cl2, 4H2O occurs in nature as the mineral atacamite. It may be artificially prepared by heating salt with ammonium copper sulphate to 100°. Other naturally occurring oxychlorides are botallackite and tallingite. "Brunswick green," a light green pigment, is obtained from copper sulphate and bleaching powder.

The bromides closely resemble the chlorides and fluorides.

Cuprous iodide, Cu2I2, is obtained as a white powder, which suffers little alteration on exposure, by the direct union of its components or by mixing solutions of cuprous chloride in hydrochloric acid and potassium iodide; or, with liberation of iodine, by adding potassium iodide to a cupric salt. It absorbs ammonia, forming the compound Cu2I2, 4NH3. Cupric iodide is only known in combination, as in CuI2, 4NH3, H2O, which is obtained by exposing Cu2I2, 4NH3 to moist air.

Cuprous sulphide, Cu2S, occurs in nature as the mineral chalcocite or copper-glance (q.v.), and may be obtained as a black brittle mass by the direct combination of its constituents. (See above, METALLURGY.) Cupric sulphide, CuS, occurs in nature as the mineral covellite. It may be prepared by heating cuprous sulphide with sulphur, or triturating cuprous sulphide with cold strong nitric acid, or as a dark brown precipitate by treating a copper solution with sulphuretted hydrogen. Several polysulphides, e.g. Cu2S5, Cu2S6, Cu4S6, Cu2S3, have been described; they are all unstable, decomposing into cupric sulphide and sulphur. Cuprous sulphite, CuSO3·H2O, is obtained as a brownish-red crystalline powder by treating cuprous hydrate with sulphurous acid. A cuproso-cupric sulphite, Cu2SO3, CuSO3,2H2O, is obtained by mixing solutions of cupric sulphate and acid sodium sulphite.

Cupric sulphate or "Blue Vitriol," CuSO4, is one of the most important salts of copper. It occurs in cupriferous mine waters and as the minerals chalcanthite or cyanosite, CuSO4·5H2O, and boothite, CuSO4·7H2O. Cupric sulphate is obtained commercially by the 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 25O°-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 brochantite (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. Dioptase (q.v.) and chrysocolla (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 CHEMISTRY: ANALYTICAL. For the quantitative estimation, see ASSAYING: 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.

REFERENCES.--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 METALLURGY and ELECTRO-METALLURGY. For the chemistry of copper and its compounds see the references in the article CHEMISTRY: Inorganic. 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 IRON).

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. (L. J. S.)