1 823.] Process of smelting Copper. 119 



phuret. That there may be a sufficient quantity of sulphur in 

 the furnace to promote these charges, it is sometimes necessary, 

 when the calcined metal is in a forward state, to carry a small 

 quantity of raw or uncalcined metal, so that a clean slag may be 

 obtained. 



The slags from this operation are skimmed off through the 

 front door, as in the ore furnaces. They have a high specific 

 gravity, and should be sharp, well melted, and free from metal 

 in the body of slag. Such particles of metal as are drawn off, 

 which, from the thinness of the slags, will commonly happen, 

 should sink to the bottom of the slag while it is in the liquid 

 state. These slags, as has been before observed, are melted 

 with the ore, not only for the purpose of extracting the copper 

 they may contain, but on account of their great fusibility, as, 

 being composed chiefly of the black oxide of iron, they fuse 

 readily, and act as solvents for other substances, earthy mat- 

 ters, &c. In some cases, the slags from the metal furnaces 

 are melted in a distinct furnace with some small coal or carbo- 

 naceous matter, and in this case, the slags resulting therefrom 

 are even sharper than those from the metal furnaces, they have a 

 crystalline splendent appearance, and crystals are frequently to 

 be observed in the interior. 



The metal in the metal furnace, after the slag is skimmed off, 

 is either tapped into water, as from the ore furnaces, or into 

 sand beds, according to the mode of treatment it is to be sub- 

 jected to in subsequent operations. In the granulated state, it 

 is called fine metal; in the solid form, blue metal, from the colour 

 of its surface. The former is practised when the metal is to be 

 brought forward by calcination. Its produce in fine copper is 

 about 60 percent. 



Process V. — Calcination of the Fine Metal. 



This is performed in the same manner as the calcination of the 

 coarse metal. 



Process VI. — Melting of the calcined Fine Metal. 



This is performed in the same manner as the melting of the 

 coarse metal ; the resulting product is a coarse copper from 80 

 to 90 per cent, of pure metal. 



Process VII. — Roasting. 



This is chiefly an oxidizing process. It is performed in fur- 

 naces of the same description as the melting furnaces, although 

 distinguished by the appellation of roasters. 



The pigs of coarse copper from the last process are filled into 

 the furnace, and exposed to the action of the air, which draws 

 through the furnace at a great heat ; the temperature is gradually 

 increased to the melting point, and the expulsion of the volatile 

 substances that remained is thus completed, and the iron or 



