Attention has for some years been directed to the commercial advantage of smelting copper-ore by electric agency. Several years ago, Messrs. Claubry and Dechaud submitted to the French Academy of Sciences a plan in which the ore was first to be converted into a sulphate of copper by ordinary chemical means, and then the copper precipitated from a solution of this salt by electricity. In 1843 and 1844 Mr. Wall took out patents ; and Mr. Ritchie, in 1844, took out another patent, having similar objects in view, namely, to se parate the pure copper from the impurities of the ore, while in either a melted or a liquid state, by electric agency. Electro-smelting however has not yet been practised to any considerable extent.
Various important applications are made of copper in the state of sheets or rolled copper. Copper, like most of the unmixed metals, is generally rolled hot, being malleable at all degrees of heat till it approaches its melting point. Most of its alloys with zinc, forming brass, are malleable only when cold, with the exception of one or two lately brought into use, which are extremely malleable at a cer tain high temperature. Copper for the pur pose of rolling leaves the smelting works in cakes about 12 X 181 inches, each weighing about 90 lbs. The cakes are put into muffles, where they are uniformly heated ; and the heated copper is drawn between cast-iron rollers. This double process of heating and rolling is repeated until the cake of copper is reduced to the form of a sheet. An oxide forms on the surface during these operations ; but this is easily removed by the applica tion of a saline liquid, aided by heat. The edges are then trimmed, and the sheet copper is fit for application to manufacturing purposes.
Copper forms valuable alloys with other metals. Those which result from its union with tin and with zinc are the most important, such as Bronze, Bell-Metal, and Brass. Tute nag is an alloy of copper, zinc, and a little iron. Tembac, Dutch Gold, Similor, Prince Rnpert's Metal, and Pinchbeck, are alloys con taining more copper than exists in common brass. Manheim Gold is a peculiar alloy of copper and zinc, which is said to consist of three parts of copper and one part of zinc. Pack fang, or the white copper of China, is an alloy of copper, nickel, and zinc, now exten sively employed in this country under the name of German Silver.
The compounds of copper with non-metallic substances are numerous and important. The oxides are often employed to give a blue colour to other substances. The sulphuret constitutes one of the most valuable ores of copper.
Acetate of Copper, more commonly known as verdigris, is much employed in painting, dye ing, and calico-printing. The Arsenite of Copper forms Scheele's Green, a well known valuable pigment. Green Verditer and Re finers' Trerditer are obtained from Carbonate of Copper, and Blue Verditer from the Nitrate. Sulphate of Copper, under the name of Blue Vitriol, is largely employed by colour makers, dyers, and others.
The principal peculiarity of manufactures in copper arises from the facility with which it may be fashioned by the hammer. The processes of casting and rolling, both of which are extensively practised in the manufacture of copper goods, so closely resemble the like operations upon other metals, that they do not require further notice ; but the operations of the coppersmith are very distinct from any other branch of metallic manufactures. For example, in the manufacture of the lower half or hemisphere of the large vessels called svgar-pans, used in sugar-refining, the copper is in the firstplace cast into a form resembling that of a double convex lens, or spectacle , glass, thickest in the middle, and diminishing gradually towards the edges. This lens is then subjected to the powerful blows of a tilt hammer, directed more continuously near the centre than near the edges. This hammering while it reduces the thickness of the copper, makes it curl up at the edges, and assume a dished or hollow form. Another process no less peculiar to the manufacture of copper is the hammering, technically called planishing, by which the metal is rendered dense and firm, and its toughness is increased. Any one who examines a large copper vessel will perceive, both in the hammer-marks and in the density and close grain of the surface, evidences of the planishing process.
It is by the combined operations of casting, rolling, hammering, and planishing, aided by the fastening processes of riveting and solder ing, that nearly all articles of copper are made. There are five different modes of forming copper piping out of sheet metal; in the first the edges of the sheet, which is curved round a mandril, are made to meet without over lapping, and united by a hard solder ; in the second they overlap, and are united by soft solder ; in the third they overlap, and aro secured by rivets: in. the fourth the edges are folded one over another, and made close and firm by hammering; while in the fifth both edges of the pipe are turned back, and covered with a strip of sheet metal, the two edges of which are turned in and hammered down.