Copper

Copper, probably the first metal employed by man, was early obtained from Cyprus, whence the name. Some prehistoric weapons are of unalloyed copper; the early use of Bronze (q.v.) was very extensive. Like gold and silver, copper is found native, but rarely and in small quantities. It can be extracted from its ores at a comparatively low heat, and is not altered by exposure to dry air; although in moist air, in the presence of carbonic acid, it soon takes on a coating of the green carbonate of copper. It has a characteristic fine red colour and takes a brilliant polish. It is nearly nine times heavier than water, its specific gravity being from 8.8 to 8.95. Next to silver it is the best conductor of heat and electricity, hence its many useful applications. Its point of fusion lies between silver and gold, but unlike these metals, it absorbs oxygen when strongly heated in the air, and scales of black oxide form rapidly on its surface. Copper is moderately hard, and is highly malleable, ductile, and tenacious, although not so strong as iron. When held, in the form of sheet or wire, in a flame, it communicates to it a highly characteristic green colour. Whereas steel is hardened by being heated to redness and suddenly cooled in cold water, copper is softened by the same process. Copper forms two important compounds with oxygen—cuprous and cupric oxides.