Dry methods of coppe•-smelting may be classi fied as follows: Blast-furnace smelting, also known as the German or the Swedish process; reverberatory smelting, also known as the Eng lish process: and the converter or Bessemer process, used only in reducing copper mattes. The blast-furnace or German process, consists in roasting the ores in special appliances, followed by smelting the roasted material with coke or charcoal in blast-furnaces. The series of chemical reactions which take place during these opera tions are rather too technical to be treated here; the result is copper matte, a mixture of copper sub-sulphide and a portion of the original impuri ties of the ore. This matte is then commonly en riched by partly calcining it and again smelting it in the blast-furnace; this second process is not always employed. The matte direct front the original smelting or front the second enriching process is roasted and then smelted with sili ceous fluxes in addition to the carbon which is used in the first smelting to produce coarse or black copper. In the reverberatory process the ore is first partly calcined. and is then smelted in a reverberatory furnace with a quartz lining, with the addition of siliceous materials or ores if necessary. The resulting matte is then concentrated by being partially roasted and then smelted in reverberatory furnaces. The matte resulting from the concentrating process is con verted into crude copper by partial roasting fol lowed by fusion in reverberatory furnaces. The converting process is not applied to ores, but is usually employed to reduce to coarse copper the matte produced by either the blast-furnace or the reverberatory process. It consists in blow ing a highly subdivided stream of air under pressure through molten matte which is eon. tabled in a pear-shaped or cylindrical converter lined with quartz ore material. The matte to be blown is first melted in cupolas and from them run into the converter. Neither the blast furnace nor the reverberatory process is cone trimly used iu the pure form, but tire two are combined in an attempt to unite the advantages of both.
Wet methods of reduction consist in getting into aqueous solution, by means of suitable sol vents, the copper, which must necessarily occur in some combination suitable for solution and of precipitating it from these solutions by means of suitable precipitants. The copper precipitate
thus obtained is refined in the dry way. The ores from which copper is extracted in the wet way contain it in the form of oxide, carbonate, sulphate, and sulphide. From all these ores. except the sulphide, the copper can he dissolved with sufficient rapidity by the aid of a cheap solvent, and as the more energetic solvents are too costly to be applied on a large scale, sulphide ores are transformed into some form suitable for solution by cheap solvents such as water, hydrochloric acid, sulphuric acid, or solutions of metallic chlorides. To explain the applica tion and action of the different solvents and pre cipitants with different classes of ores would re• quire entering into details of too technieal character. In all cases, however, the copper is brought into solution as a sulphate or a chlo ride, and precipitated from solution by means of iron as metallic copper, or. in exceptional cases, by other precipitants which produce compounds of copper.
The electroonetallurgical method of extraction is mostly used in separating copper from alloys of copper and the precious metals. The process is as follows: The ingot of alloy is attached to a conductor from one pole of a dynamo and a sheet of copper is connected to the other pole, and both are immersed in acid solution of sul phate of copper. A current is then passed through the solution between the two poles, the effect of which is to dissolve from the ingot the copper and deposit it on the copper plate, leaving the other metal, which falls as mud to the bot tom of the tank. Strictly speaking, this is a refining process as applied to alloys rather than an extracting process, but it. has been adapted to the extraction of copper from the ore and matte, although it has not been extensively employed for this purpose. This same process can be used for refining coarse copper. but it is too costly a process for simply purification and is seldom used unless the copper is alloyed with gold, silver, or nickel. The usual method of refining coarse copper is to fuse it in a reverberatory furnaee, subjecting it to the oxidizing influence of the air, and then to reduce the cuprous oxide formed by stirring the molten mass with a green wood pole. Consult Peters, Modern Copper ;gulch fag (New York, 1899).