336

COPPER.

have access to play upon the surface of the hearth, and to heat it to a proper pitch formaking the metal flow.

The weight of the charge should be proportional to the capacity of the furnace, andsuch that the level of the metallic bath may be about an inch above the nozzle of thebellows; for, were it higher, it would obstruct its operation, and were it too low, thestream of air would strike but imperfectly the surface of the metal-, and would fail toeffect, or would retard at least, the refining process, by leaving the oxydation and vola-tilization of the foreign metals incomplete.

As the scoriae form upon the surface, they are drawn off with an iron rabble fixed tothe end of a wooden rod.

Soon after the copper is melted, charcoal is to be kindled in three iron basins linedwith loam, placed alongside the furnace, to prepare them for receiving their charge ofcopper, which is to be converted in them, into rosettes.

The bellows are not long in action before the evaporation of the mineral substancesis so copious, as to give the bath a boiling appearance ; some drops rise up to the roofof the reverberatory, others escape by the door, and fall in a shower of minute sphericalglobules. This phenomenon proves that the process is going on well; and, when itceases, the operation is nearly completed. A small proof of copper, of the form of awatch-case, and therefore called monlre , is taken out from time to time, upon the roundend of a polished iron rod, p»eviously heated. This rod is dipped two or three inchesinto the bath, then withdrawn and immersed in cold water. The copper cap is detachedfrom the iron rod, by a few blows of a hammer; and a judgment is formed from its thick-ness, color, and polish, as to the degree of purity which the copper has acquired. Butthese watches need not be drawn till'the small rain, above spoken of, has ceased to fallAt'the end of about 11 hours of firing, thp numerous small holes observable in the firstwatch samples begin to disappear; the outer surface passes from a bright red to a darkerhue, the inner one becomes of a more uniform color, and always less and less markedwith yellowish spots. It will have acquired the greatest pitch of purity that the processcan bestow, when the watches become of a dark crimson color.

Care must be taken to stop this refining process at the proper time ; for, by prolong-ing it unduly, a small quantity of cupreous oxyde would be formed, which, finding nooxygen to reduce it, would render the whole body of copper hard, brittle, and incapableof lamination.

The basins must now be emptied of their burning charcoal, the opening of the tuylremust be closed, and the melted copper allowed to flow into them through the tap-hole,which is then closed with loam. Whenever the surface is covered with a solid crust, itis bedewed with water; and as soon as the crust is about inch thick it is raised uponhooks above the basin, to drain off any drops, and then carried away from the furnace.If these cajtes, or rosettes, be suddenly cooled by plunging them immediately in water,they will assume a fine red color, from the formation of a film of oxyde.

Each refining operation produces, in about 12 hours, 1 7 tons of copper, with the con-sumption of about i. of a ton of dry wood. 0

Care should be taken that the copper cake or rosette be all solidified before plungingit into water, otherwise a very dangerous explosion might ensue, in consequence of thesudden extrication of oxygen from the liquid metal, in the act of condensation. On theother hand, the cake should not be allowed to cool too long in the air, lest it get peroxv-dized upon the surface, and lose those fine red, purple, and yellow shades, due to a fib* 1of the protoxyde, which many dealers admire.

When a little oxyde of antimony and oxyde of copper are combined with copperthey occasion the appearance of micaceous scales in the fractured faces. Such metais hard, brittle, yellowish within, and can be neither laminated nor wire-drawn. Thesedefects are not owing to arsenic, as was formerly imagined; but, most probably? t0antimony -in the lead, which is sometimes used in refining copper. They are moteeasily prevented than remedied.

According to M. Frerejean, proprietor of the great copper works of Vienne,_ ir jDauphiny, too low a temperature, or too much charcoal, gives to the metal a cU ^ r if? 0structure, or that of divergent rays; in either of which states it wants tenacity* Thigh a temperature, or too rapid a supply of oxygen, gives it a brick red co * or K eradiated crystallization without lustre, or a very fine grain of indeterminate form;last structure being unsuitable for copper that is to be worked under the hammer orthe rolling-press.. The form which indicates most tenacity is radiated with roinfibres glistening in. mass. Melted copper will sometimes pass successively thro rthese three states in the space of ten minutes. lar

Fig. 316 represents a roasting mound of copper pyrites in the Lower Hartz, near Gosw l •where a portion of the sulphur is collected. It is a vertical section of & ^ rU ? C ^nidquadrangular pyramid. A layer of wooden billets is arranged at the base of the P3 rin the line a a.

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