018 COPPER 



the scoriae are mixed with pulverised coal, or other carbonaceous matters. The copper 

 and several other metals are deoxidised, and furnish a white and brittle alloy. Tho 

 scoriae resulting from this melting are in part employed in the first melting, and in 

 part thrown away. They are crystalline, and often present crystals in the cavities, 

 which appear to be those of bisilicate of iron. They have a metallic lustre, and break 

 into very sharp-edged fragments. Tho white metal is melted again, and then added 

 to the product of the second fusion. 



Fifth Operation: Calcination of the second Matt, or fine-metal. This is executed in 

 precisely the same way as that of the first matt. It lasts 24 hours; and the charge is 

 usually 3 tons. 



Sixth Operation : Melting of the calcined fine-metal. This fusion is conducted like 

 that of the first matt. The black, or coarse copper, which it produces, contains from 

 70 to 80 per cent, of pure metal ; it is run into ingots, in order to undergo the opera- 

 tion of roasting. 



The scoriae are rich in copper ; they are added to the fusion of the calcined coarse- 

 metal of the fourth operation. 



In many smelting-houses, the fifth and sixth operations have of late years been 

 omitted. The second matt is run into pigs, under the name of blue-metal,to be imme- 

 diately exposed to roasting. 



The disposition of the canal c c,fig. 501, which introduces a continuous current of 

 air to the hearth of the furnace, accelerates and facilitates the calcination of the matt; 

 an advantage which has simplified the treatment, by diminishing the number of cal- 

 cinations. 



Seventh Operation : Boasting the coarse-copper, the product of the sixth Operation. 

 The chief object of this operation is oxidation ; it is performed either in an ordinary 

 roasting furnace, or in one similar to Jiff. 507, which admits a constant current of 

 air. The pigs of metal derived from the preceding melting are exposed, on the hearth 

 of the furnace, to the action of the air ,which oxidises the iron and other foreign metals 

 with which the copper is still contaminated. The duration of the roasting varies from 

 12 to 24 hours, according to the degree of purity of the crude copper. The temperature 

 should be graduated in order that the oxidation may be complete, and that the volatile 

 substances which the copper still retains may escape in the gaseous form. The fusion 

 must take place only towards the end of the operation. 



The charge varies from a ton and a quarter to a ton and a half. The metal 

 obtained is run out into moulds of sand. It is covered with black blisters, like ce- 

 mentation steel ; whence it has got the name of blistered copper. In the interior of 

 these pigs the copper presents a porous texture, occasioned by the ebullition produced 

 by the escape of gases during the moulding. The copper being now almost entirely 

 freed from sulphur, iron, and the other substances with which it was combined, is 

 in a fit state to be refined. This operation affords scoriae, which are very heavy, and 

 contain a great deal of oxide of copper, and sometimes even metallic copper. They 

 are known as roaster-slag. 



These scoriae, as well as those of the third melting and the refining, are added to 

 the second fusion, as we have already stated, in describing the fourth operation. 



In some works, the roasting is several times repeated upon the blue-metal, in order 

 to bring it to a state fit for refining. 



Eighth Operation : Refining or Toughening. The pigs of copper intended for 

 refining are placed on the sole of the refining furnace through the door in the side. 

 A slight heat is first given, to finish the roasting or oxidation, in case this operation 

 has not already been pushed sufficiently far. The fire is to be increased by slow 

 degrees, so that, by the end of six hours, the copper may begin to flow. When all 

 the metal is melted, and the heat is very considerable, the workman lifts the door 

 in the front, and withdraws with a rake the few scoriae which may cover the copper- 

 bath. These are red, lamellated, very heavy, and closely resemble protoxide of copper. 



The refiner then takes an assay with a small ladle, and when it cools, breaks it in 

 a vice, to ascertain the state of the copper. From the appearance of the assay, the 

 aspect of the bath, the state of the fire, &c., he judges if he may proceed to the 

 toughening, and what quantity of wooden spars and wood-charcoal he must add to 

 render the metal malleable, or, in the language of the smelters, bring it to the 

 proper pitch. When the operation of refining begins, the copper is dry or brittle, 

 and of a deep red colour approaching to purple. Its grain is coarse, open, and some- 

 what crystalline. 



To execute the refining, the surface of the metal is covered with wood-charcoal, and 

 stirred with a spar or rod of birch or other wood. The gases which escape from the 

 wood occasion a brisk effervescence. More wood-charcoal is from time to time 

 added, so that the surface of the metal may be always covered with it, and the stir- 

 ring is continued until the operation of refining is finished ; a circumstance indicated 



