982 COPPER 



loam, placed alongside the furnace, to prepare them for receiving their charge of 

 copper, which is to bo converted in them, into rosettes. 



The bellows are not long in action before the bath assumes a boiling appearance ; 

 gome drops rise \ip to the roof, others escape by the door, and fall in a shower of 

 minute spherical globules. This phenomenon proves that the process is going on 

 well ; and, when it ceases, the operation is nearly completed. A small proof of 

 copper, of the form of a watch-case and therefore called montre, is taken out from 

 time to time upon the round end of a polished iron rod, previously heated. This rod 

 is dipped 2 or 3 inches into the bath, then withdrawn and immersed in cold water. 

 The copper cap is detached from the iron rod by a few blows of a hammer, and 

 judgment is formed, from its thickness, colour, and polish, as to the degree of purity 

 which the copper has acquired. These watches need not be drawn till the small rain, 

 above spoken of, has ceased to fall. At the end of about 11 hours of firing, the 

 numerous small holes observable in the first watch samples begin to disappear ; the 

 outer surface passes from a bright red to a darker hue, the inner one becomes of a 

 more uniform colour, and always less and less marked with yellowish spots. It has 

 acquired the greatest pitch of purity that the process can bestow when the watches 

 become of a dark crimson colour. 



Care must be taken to stop this refining process at the proper time ; for, by unduly 

 prolonging it, a small quantity of cuprous oxide would be formed, which, finding 

 nothing to reduce it, would render the whole body of the copper hard, brittle, and 

 incapable of lamination. 



The tuyere being closed, the basins must be emptied of their burning charcoal, and 

 the melted copper allowed to flow into them through the tap-hole, which is then 

 stopped with loam. Whenever the surface is covered with a solid crust, it is sprinkled 

 with water; and as soon as the crust is about 1-J inch thick it is raised upon hooks 

 above the basin, to drain off any drops, and then carried from the furnace. If these 

 cakes, or rosettes, be suddenly cooled by plunging them immediately into water, they 

 assume a fine red colour, from the formation of a film of oxide. 



Each refining operation produces, in about 12 hours, l^tlis ton of copper, with the 

 consumption of about Jths of a ton of dry wood. 



Care should be taken that the copper cake, or rosette, be perfectly solidified before 

 plunging it into water, otherwise a very dangerous explosion might ensue. On the 

 other hand, the cake should not be allowed to cool too long, lest it get oxidised upon 

 the surface, and lose those fine red, purple, and yellow shades, duo to a film of the 

 suboxide, which many dealers admire. 



When antimony or oxide of copper are combined with copper, they occasion the 

 appearance of micaceous scales in the fractured faces. Such metal is hard, brittle, 

 yellowish within, and can be neither laminated nor wire-drawn. These defects are 

 not owing to arsenic, as was formerly imagined ; but, most probably, to antimony in 

 the lead, which is sometimes used in refining copper. They are more easily prevented 

 than remedied. 



According to Mr. Frerejean, proprietor of the great copper works of Vienne, in 

 Dauphiny, too low a temperature, or too much charcoal, gives to the metal a cubical 

 structure, or that of divergent rays ; in either of which states it wants tenacity. Too 

 high a temperature, or too rapid a supply of oxygen, gives it a brick-red colour, a 

 radiated crystallisation without lustre, or a very fine grain of indeterminate form ; the 

 last structure being unsuitable for copper that is to be worked under the hammer or 

 in the rolling-mill. The form which indicates most tenacity is radiated with minute 

 fibres glistening in mass. Melted copper will sometimes pass successively through 

 these three states in the space of ten minutes. 



Fig. 532 represents a roasting mound of copper pyrites in the Lower Harz, near 



532 



Goslar, where a portion of the sulphur is collected. It is a vertical section of a trun- 

 cated quadrangular pyramid. A layer of wooden billets is arranged at the base of the 

 pyramid in the line a a. 



