924 



COPPER 



cupola,^. 614, with ore-cinder, yields the Spurstein, or concentrated matt. From 

 30 to 40 cwts. of Spurrost are smelted in 24 hours ; and from 48 to 60 per cent, of 

 Spurstein are obtained, the slag from the slate-smelting being employed as a flux. 

 The Spurstein contains from 50 to 60 per cent, of copper, combined with the sulphides 

 of copper, of iron, and silver. 



The Spurstein is now mixed with Dunnstein (a sulphide of copper and iron produced 

 in the original smelting), roasted 6 successive times, in quantities of 60 cwts., witli 

 brushwood and charcoal ; a process which requires from 7 to 8 weeks. The product 

 of this six-fold calcination is the GaKrrost of the Germans ; it has a colour like red 

 copper ore, varying from blue grey to cochineal-rod, with a granular fracture ; and may 

 be immediately reduced into metallic copper, which process is called KupfermacJten. 

 But before smelting the mass, it is lixiviated with water, to extract from it the soluble 

 sulphate, which is concentrated in leaden pans and crystallised. 



The lixiviated Gahrrbst mixed with from Jth to jkh of the lixiviated Dunnsteinrbst and 

 th to ^jth of the copper-slate slag are smelted with charcoal or coke fuel in the course 

 of 24 hours, in a mass of 60 or 80 cwts. The product is black copper, to the amount of 

 about $lh the weight, and th of Dunnstein or thin matt. This black copper contains 

 in the cwt. from 12 to 20 Loths (6 to 10 oz.) of silver. The Dunnstein consists of from 

 60 to 70 per cent, of copper combined with sulphur, sulphide of iron, and arsenic ; and 

 when thrice roasted, yields a portion of metal. The black copper lies undermost in 



,, _, the crucible of the furnace; above 



515 514 ^^ 



it is the Dunnstein, covered with 

 the strong slag, or copper cinder, 

 resulting from the slate-smelting. 

 The slags being raked off, and 

 the crucible sufficiently full, the 

 eye or nozzle hole is shut, the 

 Dunnstein removed by coolingtho 

 surface and breaking the crust, 

 which is about a J to J inch thick. 

 The same method is adopted for 

 taking out the black copper in 

 successive layers. For the desil- 

 vering of this, and similar black 

 E coppers, see SILVER. 



Fig. 514 is a vertical section 

 through the tuyere in the dotted 

 line \Boffig. 516. Fig. 515 

 is a vertical section through 

 the dotted line c D of Jig. 517. 

 a is the shaft of the furnace; 

 b, the rest, c c, the tuyeres ; d, 

 .A the sole or hearth-stone, which 

 has a slope of 3 inches towards 

 the front wall ; e c, &c., casing 

 walls of fire-bricks; //, &c., 

 filling-up walls, built of rubbish 

 stones; gg, amass through whicli 

 the heat is slowly conducted ; h h, the two holes through one or other of whicli 

 alternately the product of the smelting process is run off into the fore-hearth. Beneath 

 the hearth sole there is a solid body of loam ; and the fore-hearth is formed with 

 a mixture of coal-dust and clay ; k is the discharge outlet for moisture. Fig. 516 is 

 a horizontal section of the furnace through the hole or eye, on the dotted line E F 

 of fig. 514 ; fig. 517, a horizontal section of the shaft of the furnace through the /cm 

 along the dotted line o H of figs. 514 and 515. The height of the shaft, from tho 

 lino E F to the top, is 14 feet ; v from E to o, 25 inches ; from c to the line below f>, 



2 feet; from that line to tho line opposite g g, 2 feet. The width at the line g g is 



3 feet 3 inches, and ate, 26 inches. The basins, t i,fig. 516, are each 3 feet in diameter 

 and 20 inches deep. 



During tho l;ist twenty years few processes have undergone more extensive modifica- 

 tions than that used for the extraction of copper and silver from the copper-schists of 

 Mansfeld ; and it is therefore necessary to present a short account of the series of 

 operations at present employed. 



The cupola furnace now used differs greatly, both in construction and dimensions, 

 from that formerly employed in the district ; being in almost all respects, excepting 

 size, similar to the closed blast-furnaces used in this country for the manufacture of 

 cast iron. This furnace is circular, and 30 feet in height by about 7 feet in diameter 



