Copper

Copper, a most useful and extensively distributed metal, which with its alloys has been employed in the arts even from pre-historic times. Though early weapons of pure copper have been found, its softness was a bar to its utility until the discovery cf bronze, its alloy with tin, which gives its name to the Bronze age. The Greek chalkos, and the Latin aes, apply apparently both to the metal and the alloy; but, from being obtained from Cyprus, the former acquired the name cyprium, corrupted into cuprum, whence its symbol in Chemistry is Cu. It is a bright metal of a peculiar red colour, having an atomic weight of 63.3, a specific gravity of 8.93, and a hardness between 2.5 and 3; very malleable and ductile, in tenacity second only to iron, in electric conductivity second to silver, and fusible at a red heat. Copper expands on solidifying from fusion. Like most of its compounds, it is partially volatile, imparting a brilliant green coloration to the flame. It dissolves in hydrochloric, sulphuric, and nitric acids, liberating hydrogen, sulphur-dioxide and nitric oxide respectively, the solutions turning blue on the addition of ammonia. Traces of copper occur in all soils, in some plants, and in the blood of animals. It forms nearly 6 per cent. of turacin, the red colouring-matter of the feathers of the turaco, or West African plantain-eater; and as a mineral it occurs native and in a number of ores. Of these, the chief are the sulphides or pyrites, chalcopyrite, redruthite, erubescite, and tetrahedrite; the oxides, especially cuprite and the carbonates, malachite and azurite, which are separately described. Native copper crystallises in cubes and in octahedra, often twinned, or in extensive dendritic masses, or it is wiry or in other massive forms. In the extensive deposits south of Lake Superior, a mass of native copper 45 feet by 22 by 8, weighing over 400 tons, has been found, and large quantities also occur in Siberia and in South Australia, generally associated with copper-ores, from which it may have resulted by reduction. From its oxides or carbonates, copper is obtained by simply heating the ore with carbon and silica; but its separation from its commoner ores, the sulphides, is a more complex process of repeated roastings, ending with poling, or stirring with a piece of green wood to get rid of the last traces of oxide present. The alloys of copper are even more important than the pure metal. With zinc it forms brass, English brass containing about 70 per cent. of copper, and Muntz's metal, or yellow sheathing, from 50 to 60 per cent. With tin it forms bronzes, ordinary bell-metal containing 80 per cent. of copper, speculum-metal 65 per cent., and phosphor-bronze 85 to 95 of copper with about 2 per cent. of phosphorus, and the remainder tin. Aluminium-bronzes contain from 90 to 97-1/2 per cent. copper and from 10 to 2-1/2 per cent. aluminium. German, or nickel, silver contains about 63 per cent. of copper, with from 11 to 19 per cent. of nickel and the remainder zinc. These alloys are hard and brittle if cooled slowly; soft and malleable, if plunged when red-hot into cold water. The once important copper mines of Cornwall are now mostly exhausted, the production of copper from British mines having fallen from nearly 16,000 tons in 1860 to 3,600 in 1880, and to 900 in 1889. Swansea is the chief centre of an enormous copper-smelting industry, for which copper to a value of over 6-1/2 million sterling was imported in 1890; 1-1/2 million cwt., valued at 4-1/2 million sterling, being re-exported. Of this importation, half comes from Spain, a quarter from the United States, and a quarter from Chili.