Dr. F. H. Thomson's Historical Notes of Copper Smelting. 329 



allowed to flow into a pit of water. In this process the product 

 becomes much enriched ; in fact, about one-third copper, or four times 

 as rich as the average ores formerly used. Should the slags from this 

 process contain copper, which they generally do, the smelter returns 

 them, to go through the operation again. Often the ores are refractory 

 or tough when fused. The addition of a little fluor-spar corrects this. 



The calcination of the coarse metal, or the third process, is simply a 

 repetition of the first. The heat is kept up for twelve hours : this is 

 denominated calcining the coarse metal. 



The fourth is the melting of the calcined coarse metal, and is con- 

 ducted in a furnace similar to number two, some slags, containing 

 oxide of copper, being added, along with pieces of furnace bottoms 

 impregnated with metal. 



In this operation the oxide of copper in the slags becomes reduced by 

 a portion of the sulphur which combines with the oxygen, and passes off 

 as sulphurous acid gas, while the metal thus reduced enters into com- 

 bination with the sulphuret. Sometimes a little uncalcined ore is 

 added, to assist the operation, which it does by the sulphur which it 

 contains. 



The slag being skimmed off, the charge is either tapped into water 

 or run into sand beds. The metal now contains 60 per cent., and is 

 called fine metal. 



Fifth, is calcination again. 



Sixth, melting of the calcined fine metal. This again is a mere 

 repetition of the melting process. 



The resulting metal contains from 80 to 90 per cent., and is called 

 coarse copper. It is run into moulds or pigs. 



Seventh is chiefly an oxidizing process, and the furnaces are called 

 roasters, and of the same construction as the melting ones. The pigs 

 are exposed in these furnaces to the action of the air at a high tem- 

 perature, till fusion takes place. By this means all volatile matter is 

 expelled and the metal oxidized. This continues from twelve to 

 twenty-four hours, according to the state of the furnace, and then run 

 into sand beds. It is now called blistered copper, and has a spongy 

 appearance, from the escape of the gas disengaged in the process of 

 cooling. It is now fit for the refining, being almost, if not altogether, 

 free from foreign matter. 



The eighth and last process, called refining or toughening, is a very 

 delicate operation, and requires the skilled workman to conduct it. 

 The furnace is much the same as the common melting furnace, only 

 with an inclination to the front door. The heat is at first kept 

 moderate, so as to complete the oxidation, in case the copper should not 



