The native arseniates of copper are analyzed by drying them first at a moderate heat; after which they are to be dissolved in nitric acid. To this solution, one of nitrate of lead is to be added, as long as it occasions a precipitate; the deposit is to be drained upon a filter, and the clear liquid which passes through, being evaporated nearly to dryness, is to be digested in hot alcohol, which will dissolve every thing except a little arseniate of lead. This being added to the arseniate first obtained, from the weight of the whole, the arsenic acid, constituting 35 per cent., is directly inferred. The alcoholic solution being now evaporated to dryness, the residue is to be digested in water of ammonia, when the cupric oxide will be dissolved, and the oxide of iron will remain. The copper is procured, in the state of black oxide, by boiling the filtered ammoniacal solution with the proper quantity of potash.
The analysis of muriate of copper—atacamite—is an easy process. The ore being dissolved in nitric acid, a solution of nitrate silver is added, and from the weight of the chloride precipitated, the equivalent amount of muriate or chloride of copper is given; for 100 of chloride of silver represent 93 of chloride of copper, and 43·8 of its metallic basis. This calculation may be verified by precipitating the copper of the muriate from its solution in dilute sulphuric acid, by plates of zinc.
The phosphate of copper may be analyzed either by solution in nitric acid, and precipitation by potash; or by precipitating the phosphoric acid present, by means of acetate of lead. The phosphate of lead thus obtained, after being washed, is to be decomposed by dilute sulphuric acid. The insoluble sulphate of lead being washed, dried, and weighed, indicates by its equivalent the proportion of phosphate of lead, as also of phosphate of copper; for 100 of sulphate of lead correspond to 92·25 phosphate of lead, and 89·5 phosphate of copper; and this again to 52·7 of the black oxide.
Copper forms the basis of a greater number of important ALLOYS than any other metal. With zinc it forms [Brass] in all its varieties; which see.
[Bronze] and [Bell Metal] are alloys of copper and tin. This compound is prepared in crucibles when only small quantities are required; but in reverberatory hearths, when statues, bells, or cannons are to be cast. The metals must be protected as much as possible during their combination from contact of air by a layer of pounded charcoal, otherwise two evils would result, waste of the copper by combustion, and a rapid oxidizement of the tin, so as to change the proportions and alter the properties of the alloy. The fused materials ought to be well mixed by stirring, to give uniformity to the compound. See [Bronze].
An alloy of 100 of copper and 4·17 of tin has been proposed by M. Chaudet for the ready manufacture of [medals]. After melting this alloy he casts it in moulds made of such bone-ash as is used for cupels. The medals are afterwards subjected to the action of the coining press, not for striking them, for the mould furnishes perfect impressions, but for finishing and polishing them.
By a recent analysis of M. Berthier, the bells of the pendules, or ornamental clocks, made in Paris, are found to be composed, of copper 72·00, tin 26·56, iron 1·44, in 100 parts.
An alloy of 100 of copper and 14 of tin is said by M. Dussaussy to furnish tools, which hardened and sharpened in the manner of the ancients, afford an edge nearly equal to that of steel.
Cymbals, gongs, and the tamtam of the Chinese are made of an alloy of 100 of copper with about 25 of tin. To give this compound the sonorous property in the highest degree it must be subjected to sudden refrigeration. M. D’Arcet, to whom this discovery is due, recommends to ignite the piece after it is cast, and to plunge it immediately into cold water. The sudden cooling gives the particles of the alloy such a disposition that, with a regulated pressure by skilful hammering, they may be made to slide over each other, and remain permanently in their new position. When by this means the instrument has received its intended form, it is to be heated and allowed to cool slowly in the air. The particles now take a different arrangement from what they would have done by sudden refrigeration; for instead of being ductile they possess such an elasticity, that on being displaced by a slight compression, they return to their primary position after a series of extremely rapid vibrations; whence a very powerful sound is emitted. Bronze, bell-metal, and probably all the other alloys of tin with copper present the same peculiarities.