COPPER, a metallic element occurring abundantly in nature, and widely used in the arts, both in the pure state, and as an essential constituent of many alloys. It has been known from the earliest times, and is frequently men tioned by the ancient writers. Prehistoric weapons, tools and ornaments of copper, as well as domestic implements, remain in pro fusion to this day; and it has been commonly asserted that copper was known and used be fore iron, though some authorities consider the evidence of this to be inconclusive. The Romans obtained their best copper from Cyprus, an island in the Mediterranean Sea, and for this reason the metal was lcnown as Cypriot's as, or gCyprian brass? a name that was later con tracted to cuprum and cuper.
Physkal Copper is red in color, and crystallizes in cubes, octahedra and other forms of the isometric system, twinned crystals being quite common. When in a finely divided condition it has a specific gravity of about 8.36; but the specific gravity of native copper is 8.84, and that of hanunered or elec trically deposited copper is about 8.95. It melts at about MOO° F., and has a specific heat of about 0.093, and a coefficient of linear expan sion of about 0.0000092, per Fahrenheit degree. Its tensile strength varies greatly, according to the physical condition of the metal. The fol lowing data are commonly used in engineering practice, as corresponding to the tensile strength in pounds, per square inch of sectional area: Cast copper, 19,000; sheet copper, 30,000; cop per bolts, 36,000; copper wire, 60,000. The ther mal conductivity of copper, at ordinary tem peratures, is about 0.74 times that of silver. The specific electrical resistance of hard-drawn copper is 1,620 ohms, and that of annealed cop per is 1,584 ohms. A wire of the metal that is one metre long and one millimeter in diameter has a resistance of 0.0206 ohms if hard drawn, and 0.202 if annealed. These data are for the pure metal, at the temperature of freezing water. The electrical resistance of copper in creases by about 0.388 of 1 per cent for each Centigrade degree of riie of temperature. The electncal resistance is also greatly increased by the presence of small percentages of iron, zinc, tin, phosphorus or arsenic, and hence great at tention is paid to the purity of the copper that is intended for use in electrical conductors.
Copper is very malleable and ductile, and may be drawn into small wire and hammered into exceedingly thin sheets. An alloy consisting of 11 parts of copper and 2 of zinc is even more malleable than copper itself, and may be ham mered into foil comparable in appearance with gold-leaf, for which it is used as a substitute in certain kinds of work, under the name of ((Dutch metal? Copper becomes very soft and malleable when it is strongly heated and im mediately immersed in cold water, its behavior under these circumstances being diametrially opposed to that of steel. It may be forged into any shape, but it will not bear more than a red heat, since it becomes brittle at higher tempera tures. It does not oxidize readily under or dinary conditions, but becomes superficially tar nished with a coating of carbonate that resists the subsequent action of the oxygen of the air. Copper often gives poor castings, apparently be cause the molten metal absorbs gases, and these, when given off again at the moment of solidifi cation, make the casting porous. The castings are said to be much more sound when a small quantity of phosphorus is added to the molten metal —usually in the form of phosphor-copper. The large copper cylinders that are used in calico-printing are cast in molds, and are sub sequently hammered under a steam-hammer until the metal is sound, and then turned down in a lathe until the surface is true and free from defects.
Alloya.—Many alloys of copper are used in the arts, chiefly under the name of (brasses" or *bronzes? Originally a brass was defined as an alloy of copper and zinc, while a bronze was defined as an alloy of copper and tin. This con vention is still retained in a general way, but the same names are applied also, and very com monly, to numerous ternary alloys, containing copper, zinc and tin, which pass by insensible gradations from a true brass to a true bronze; so that %rase) and Thronze) can no longer be regarded a,s very definite terms. Alloys of per with aluminum arc called “bronzes,)) even when no tin is present. See ALLOYS ; BRASS ;