Copper combined with sulphur is one of the most common ores of this metal. According to the experiments of Proust, the natural production, known by the name of copper pyrites, is a sulphuret of copper combined with an additional por tion of sulphur. It is distinguished by its brittleness, metallic lustre, and yellow colour.
The alloys of copper (that is, those in which this metal predominates) are more numerous and more important in the arts than those of any other metal. Many of them are perfectly well known, and have been in use from very ancient times ; of many, the exact composition, and particu larly the mode preparing, are kept as secret as possible ; for even when the precise composition of an alloy is found by chemical analysis, it may often be extremely difficult to produce a mixture by common methods, which shall have exactly the same shade of colour, the same malleability, texture, susceptibility of polish, or some other excellence, which, perhaps, a mere accident has dis covered to the possessor.
The principal objects of alloying cop per appears to be, to render it less lia ble to tarnish, and especially to be act ed on by common animal or vegetable substances, to make it more fusible, and harder, and able to take a higher polish, and to alter its colour either to a golden yellow or silvery white. All these ob jects are attainable by different alloys. Copper, alloyed with gold, silver, and platina, is seldom, if ever, used in the proportions in which it would be reck oned as alloy of copper, being much too costly for any purpose of manufac ture ; with this exception, however, that a very small portion of silver much im proves the composition of the alloy of copper and tin, when used as bell metal or speculam•metal. Copper is used largely as an alloy of gold and silver,'and it is often plated with one or the other.
Tutenag is a white alloy of copper, zinc, and iron, according to Keir, which is very hard, tough, and sufficiently duc tile to be into- various articles of furniture, sg*, ch as caeldlesticks, &c. which take a high polish, and when made of the better sort of tutenag are hardly distin guishable from silver. The inferior kinds are still white, but with a brassy yellow. The Chinese petong is anothef fine, white, malleable alloy of copper, the composition of which is not exactly known, but it contains% • small portion of silver. Copper unites with lead very
intimately by fusion, gut when a mass of this alloy is exposed to a heat less than that at which the whole melts, the lead alone sweats out, leaving almost all the copper in a porous or honey-combed state. When the-copper holds a small portion of silver, the lead carries the latter out with it, and this is the prin ciple of the old processs of eliquation, formerly much used in the extracting of silver from copper ores. Copper, with about a fourth of its weight pf lead, forms pot-metal, used by the ancients for their coins.
Copper, nearly saturated with zinc, forms brass, the most important of all the alloys of this metal See BRASS. With a much less proportion of zinc, the colour of the alloy approaches very near ly to that of gold, and the malleability increases. Mixtures chiefly of these two metals are used to form a variety of yellow or gold-coloured alloys, known by the names of tombac, Manheim, or Dutch gold, tinsel, similar, Prince Ru pert's metal, Pinchbeck, &c. ; but the precise composition varies according to the fancy or the experience of different manufacturers. The Dutch gold may be beaten out into extremely fine leaves, which, when fresh, have nearly the bril liance of gold-leaf, and are used as a cheap imitation of it ; but they tarnish very soon. The mixture may be made, either by directly melting copper and .zinc, or by mixing brass and copper. In either case the copper should be melted first, and the zinc added afterwards, the whole stirred together with wood, cover ing it with a little charcoal, and poured out immediately, to prevent the loss by the burning off the zinc. A kind of tombac is the material of which a large propor tion of the Roman coins was composed : Klaproth, on analyzing several struck dur ing the first century of the emperors, found them all to consist either of pure copper, or of copper and zinc, in which the lat ter metal- made generally from a fifth to a sixth of the mass. A little tin and lead were found in some ; but in such small proportion as to appear only an acci dental impurity.