The copper ores of Anglesca are wrought nearly in the same way. The ore there, after being reduced to fragments, is put into a kiln, the flues of which termi nate in a close chamber. Heat is then applied to the ore, and the sulphur, which sublimes, is carried through the flue, and condenses in the chamber. Fresh quan tities of the ore are from time to time introduced, and the roasting is in this way kept up for several months.
The poorer part of the ore only is smelted in Angle sea, the richer portion being exported.
The smelting of the ore is carried on in a series of reverberatory furnaces, having tall flues to increase the draught. In these the ore mixed with a little coal dust is fused, and purified by repeated fusions. By this means, twelve hundred weight of the roasted ore about one-fourth of a hundred weight of malleable metal and each charge of the furnace, which is about twelve hundred weight, is finished in five hours.
In Hungary, the copper ore is treated in the same way, but the purification of the metal is accomplished by means of lead. For this purpose the metal is fused in a furnace, and about one twelfth or one-fifteenth of lead is added, which forms a scoria along with the im purities of the copper. This is removed as it is formed, and the copper is left in its pure state, after which it is kept fused for some time. To ascertain when tile whole of the impurities of the copper have been removed, the workman takes out a little of the melted metal on the end of a smooth iron rod. If the metal be pure, this falls off when it is dipt into cold water.
The purity of the metal is also known by the redness of the scoria, that of the impure copper being always dark coloured.
The thin sheets of copper used in the arts, are pre pared when the metal is in a state of fusion in the fur nace. For this purpose, when the whole of the impu rities have been removed, the metal is allowed to cool to near its point of congelation. A wet broom is then drawn along its surface, by which means a thin layer of it is made to pass into the solid state. This is removed, and immediately plunged into water, by which it ac quires a fine red colour ; and the process is repeated till the whole is formed into thin sheets.
Copper, in a state of considerable purity, is some times procured from the springs which contain the sul phate of this metal. With this view, pieces of iron are
put into the water, by which the copper is precipitated, owing to the superior affinity of the iron for the acid, aided, perhaps, by a galvanic action. When the whole of the iron is dissolved, the matter deposited is raked out, and is fused in a furnace, either alone or mixed with sonic of the poorer copper ore.
The deposit obtained in this way, when fused alone, commonly yields about 50 per cent, of copper.
Assay of Cofilzer Ores.—The assay of copper ores may be made either in the dry or in the humid way; the former, however, when the sulphurets are employed, is imper fect ; but when any of the oxides or carbonates are to be assayed, this method answers very well. The ore, after being reduced to powder, is mixed with charcoal, and exposed to a strong heat in a crucible, removing the scoria as it is formed. As the ore contains other metals besides copper, this process must be repeated several times before we obtain it pure. These ores are, how ever, seldom employed in metallurgy ; it is necessary, therefore, to have recourse to other means, to ascertain the value of those which are used to yield copper. For this, the ore must be digested in muriatic acid, to which a little nitric acid is added, by which we obtain the dif ferent metals in solution. From this the copper may be procured, either oxidated or in the metallic form, the other metals in the solution being previously separated. Lead, if present, may be thrown down by sulphate of soda and iron, by the addition of ammonia in excess.
The quantity of copper may then be ascertained, either by precipitating it by sub-carbonate of soda, or, which is better, by the immersion of a plate of iron. For this purpose the solution is diluted with water, and a piece of polished iron is put into it, which soon becomes co vered with a coating of copper, and as the decomposi tion proceeds, the metal is deposited in thin plates. When the whole of it is separated, it is collected, wash ed, and weighed. Towards the end of the process, the fluid should be heated, which favours the separation of the copper.