BRONZE.
The chemical symbol for cop per is Cu (cuprum), and the atomic weight of the metal is 63.1 if H ----- 1, and 63.6 if 0 = 16. Performs two distinct series of salts, known respectively as "cuprous° ind °cupric° com pounds, In the cupric series the metal is a dyad, while in the cuprous series it enters into the ordinary formulm as though it were a monad. (See CHEMISTRY). Structusal formulm have been given, however, which indicate that the metal is really a dyad in both cases. The cupric series of salts embraces those compounds that are most famil iar in the arts. Cupric oxide (lmown also as copper monoxide, or black oxide) is formed when metallic copper is heated in the presence of air. It may occur as a brownish-black amor phous powder, or in lustrous monoclinic crystals. Cupric oxide is used in the laboratory for effecting the combustion of organic substances, the oxide being intimately mixed with the body to be oxidized, and the whole raised to a red heat, at which temperature the cupric oxide readily gives up its oxygen to either hydrogen or carbon. Cupric oxide (the formula of which is CuO) is soluble in acids, and yields, with them, salts which crystallize well. If a solution of any of these salts be made alkaline by the addition of a caustic alkali, a light blue pre cipitate of cupric hydrate, Cu(OH)2, is thrown down. Upon heating to 212° F., this parts with a molecule of water and becomes reduced to the black oxide, CuO. If cupric hydrate be pre cipitated by adding the calculated quantity of sodium hydrate to a solution of c,opper sulphate, and the prccipitate is mashed and dissolved in ammonium hydrate, a blue solution is obtained, which is sometimes called "cupro-ammonium hydroxin,0 and which possesses the singular power of dissolving cellulose (q.v.) without chemical change. When pure cupric oxide is desired, it is most conveniently prepared by heating cupric nitrate to redness. Cupric nitrate is readily prepared by dissolving metallic copper in nitric acid_ It crystallizes in large blue prisms, having the composition Cu(NO2).-i 61-120. Ordinary copper sulphate (cupric sul phate, or °blue vitriol))) is manufactured in large quantities by dissolving scales of copper oxide (CuO) in sulphuric acid. It forms large blue triclinic crystals, which have the composition CuSO4-1- 5H20. The sulphate is used in calico printing, and in the manufacture of various copper pigments such as Brunswick green and Scheele s green. Cupric chloride, CuCti, is formed by dissolving cupric oxide in hydro chloric acid, or by acting upon metallic copper by chlorine gas. It is soluble in alcohol or
water, and forms acicular crystals having the formula Cuas 21-120. Cupric sulphide, CuS, is the familiar black precipitate that is obtained when sulphuretted hydrogen gas is passed through an acid solution of a copper salt. (See Escrcat. ANALYSIS ) . Copper carbonate, CuCO2, has not been prepared in the pure state, but a green precipitate having the formula CuCO22± Cu(OH)2 is thrown down when car bonate of potassium or of sodium is added to a solution of a copper salt ; this precipitate be ing identical in composition with the mineral malachite. Cuprous oxide, Cui0, or red oxide of copper, occurs native in red octahedral crystals, and it may also be prepared artificially by heating a mixture composed of equivalent parts of cupric oxrde and finely divided metallic copper, or (more conveniently) by heating a nuxture of equal parts of cupric oxide and ammonium carbonate, (N112)2CO2,. over a Bunsen burner, until all the ammonia is expelled. It is a crystalline powder of a carmine color, melting at a strong red heat, and is used in glass manufacture for the production of a ruby color. The precipitation of this oxide from cer tain test-solutions is used as a test for the presence of sugar in urine. (See URINARY ANALYSIS). Cuprous oxide dissolves in various acids with the production of colorless salts, which are unstable, since they readily absorb oxygcn and pass into the corresponding cupric salts. The most important cuprous salt is the chloride, which has the formula Cusa, and is formed by heating metallic copper to dull red ness in a current of hydrochloric acid gas, or by dissolving a mixture of cupric oxide and me tallic copper •in hot hydrochloric acid. It is a white crystalline powder, insoluble in water or alcohol, or in dilute nitric or sulphuric acids, but dissolving in ammonia, or in hot hydro chloric acid. Its solution in either of ,these menstrua possesses the remarkable property of absorbing carbon monoxide gas. Copper may be detected in solution (1) lly the formation of the black sulphide when a stream of sulphur etted hydrogen gas is passed through the acid ified solution; (2) by the precipitation of the blue hydroxide, which blackens upon heating; (3) by the deep blue color that its salts give upon the addition of ammonia; and (4) by the precipitation of a red film of metallic copper when a clean, bright fragment of iron is im mersed in the solution.