86 Mr. J. Napier on Copper Smelting. 



In some of the smelting-works certain modifications of the 

 process described for the coarse metal are adopted. Instead of 

 tapping the mat into a pit of water, it is let out into sand-beds, 

 and when cool broken up and removed to another furnace, and 

 fused along with the scorise or slag from the roasting furnace, 

 containing about from 8 to 10 per cent, of copper. This en- 

 riches the coarse metal, and produces a mat termed occasionally 

 white metal, of an average composition of — 



Copper 40 



Iron 30 



Sulphur 28 



Silica 2 



100 



This metal is tapped into a pit of water in the same way as 

 the coarse metal, and laid aside for calcination. This operation 

 of fusing, added to an additional two or three hours of extra 

 calcination of the granulated metal, saves an operation in a more 

 advanced stage of the process. The ceconomy of this modifica- 

 tion is not so apparent as to cause its general adoption, although 

 it would require no alteration of furnace. The advantages it is 

 said to possess are greatly neutralized by disadvantages attending 

 some of the after operations, which will be better judged of when 

 these are described. 



Another modification which we have had considerable expe- 

 rience in carrying out is the following. The coarse metal is 

 tapped into sand-beds, broken up, and removed to another fur- 

 nace of an extra large size, as it requires but a low heat to fuse. 

 About 4 tons of the coarse metal are fused in this furnace, with 

 4 cwt. of salt cake (sulphate of soda), and 2 cwt. of coal. When 

 in perfect fusion the whole is well stirred with an iron rabble, 

 and the furnace immediately afterwards tapped into sand-moulds ; 

 as soon as the metal sets (becomes solid), and while red-hot, the 

 pigs or ingots are thrown into a tank of water, which is caused 

 to boil by the heat of the metal ; at the same time the metal 

 falls into an impalpable powder, similar to slaking lime. The 

 soda salt, which is reduced or decomposed in the fusion, dissolves 

 in the water, forming a strong alkaline ley, and the powder is 

 thus boiled in a caustic alkali, by which means all impurities 

 capable of being dissolved in hot alkaline leys are separated from 

 the metal, such as oxides and sulphurets of tin, antimony, and 

 arsenic. After the boiling has ceased for some time, the alkaline 

 solution is let off and i-un into the horizontal culverts leading 

 from the calcining and fusing-furnaces, where the water is eva- 

 porated, and a part of the soda recovered with any copper that 

 may have been carried over, the water also assisting the conden- 



