COPPER 



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metallic surfaces. After 4 or 5 hours, no more slag appeared, and then the fire was 

 increased. The melted mass now began to boil or work (travailler), and continued so 

 to do for about J of an hour, or an hour, after which the motion ceased, though the firo 

 was kept up. The Gahrproof was now taken ; but the metal was seldom fine in less than 



513 



| of an hour after the boil was over. Whenever the metal was run off by the tap-hole 

 into the two basins, h k, called split-hearths, a reddish vapour or mist arose from its 

 surface, composed of an infinite number of minute globules, which revolved with 

 astonishing velocity upon their axes, constituting what the Germans called Spratzen 

 (crackling) of the copper. They were composed of a nucleus of copper covered with a 

 film of oxide, and were used as sand for strewing upon manuscript. The copper was 

 separated by sprinkling water upon the surface of the melted metal, in the state 

 of rosettes, which were immediately immersed in a stream of water. This refin- 

 ing process lasted about 16 or 17 hoirrs ; the skimmings weighed about 50 cwts. ; the 

 refuse was from 15 to 17 per cent.; the loss from 2 to 3 per cent. The Gahrslag 

 amounted to 1 1 cwts. 



Smelting of the Mansfeld Copper- Schist, (Kupferschiefer). The cupreous ore is first 

 roasted in large heaps of 2,000 cwts., interstratified with brush-wood, and with some 

 schists rich in bituminous matter mixed with the others. These heaps are 3 ells high, 

 and go on burning 15 weeks in fair and 20 in rainy weather. The bituminous matter 

 is decomposed ; the sulphur is dissipated chiefly in the form of sulphurous acid ; the 

 metal gets partially oxidised, particularly the iron, which is a very desirable circumstance 

 for the production of a good smelting slag. The calcined ore is diminished ith in 

 bulk and |th in weight ; becoming of a friable texture and a dirty yellow colour. The 

 smelting furnaces are cupolas (Schachtbfen), 14 to 18 feet high; the fuel is partly 

 coal and partly coke from the Berlin gas-works and from Silesia. The blast is now 

 given by a cylinder, but formerly with the old barbarous Blasebdlgen, or wooden bel- 

 lows of the household form. The smelting was formerly conducted as follows : 



The copper-slate is sorted, according to its composition, into slate of lime, clay, 

 iron, &c. ; by a mixture of which the smelting is facilitated. For example, 1 post or 

 charge may consist of 20 cwts. of the ferruginous slate, 14 of the calcareous, 6 of the 

 argillaceous, with 3 of fluor-spar, 3 of rich copper slags, and other refuse matters. 

 The nozzle at the tuyere is lengthened 6 or 8 inches, to place the melting heat near 

 the centre of the furnace. In 15 hours 1 Fuder of 48 cwts. of the above mixture may 

 be smelted, whereby 4 to 5 cwts. of matt (Kupferstein) and a large body of slags are 

 obtained. The matt contains from 30 to 40 per cent, of copper, and from 2 to 4 Loths 

 (1 to 2 oz.) of silver. The slags contain at times ith their weight of copper. 



The matt is composed of the sulphides of copper, iron, silver, zinc, along with some 

 arsenical cobalt and nickel. The slaty slag is raked off" the surface of the melted matt 

 from time to time. The former is either, after being roasted six successive times, 

 smelted into black copper, or it is subjected to the following concentration process : 

 It is broken to pieces, roasted by brushwood and coals three several times in brick- 

 walled kilns, containing 60 cwts., and turned over after each calcination ; a process 

 of 4 weeks' duration. The thrice-roasted mass, called Spurrbst, being melted in the 



