=Chemical Properties.=—The atomic weight of copper is 63·57. The metal is unchanged in dry air at ordinary temperatures; in the presence of moisture and of carbon dioxide a green coating of basic carbonate is produced. When heated in air, a black scale, consisting of cuprous oxide, Cu_{2}O, is obtained, which is readily detached by quenching and hammering. Water at ordinary temperatures is without effect upon copper; concentrated sulphuric and nitric acids have little action upon it in the cold, but attack it on heating. The best solvent for the metal is dilute nitric acid, which dissolves it very readily. Copper is liable to corrosion when subjected, whilst hot, to the action of chlorine or hydrochloric acid gas; this action has provided an explanation of the corrosion of copper boiler tubes where the coal employed had been exposed to sea water. Copper is deposited from solution as a dull red, spongy mass, by iron, zinc, or aluminium, but it is more electro-positive than gold or silver, and readily precipitates these metals from solutions of their salts, these effects being extensively made use of in practice. The metal possesses a powerful affinity for sulphur, and this property has very important applications in the smelting processes. Copper readily alloys with gold, silver, tin, zinc, and nickel, but not with lead or iron. References. Composition and Properties of Metal for Railway and Locomotive Work (p. 20). _Proc. Inst. Mech. Eng._, 1893; Dean, p. 139; Blount, p. 164; Watson, p. 168; Gowland, p. 176; Aspinall, p. 193; Tomlinson, p. 182. Webb, F. W., “Locomotive Fire-box Stays.” _Proc. Inst. C.E._, 1902. Milton, J. T., “The Treatment of Copper for Steam Pipes.” _Inst. Marine Eng._, 1908–9. Hughes, G., “Non-ferrous Metals in Railway Work.” _J. Inst. Metals_, Sept. 1911. Law, E. F, “Alloys.” Influence of Impurities on the Electrical Conductivity of Copper (p. 24).