488 Mr. J. Napier on Copper Smelting. 



lead is generally added, from 10 lbs. to 30 lbs., to the charge ; 

 this softens the copper and renders it more tough. Sometimes, 

 when the trial cracks upon the edge, a little additional lead will 

 cure it. 



The addition of lead is supposed to effect the complete deoxi- 

 dizement of any remaining oxide of copper, and it is imagined 

 that all the lead comes off as scoria, or is volatilized. In our 

 analyses of copper, and they have been very numerous, the pre- 

 sence of lead was always detected wherever it had been added 

 in the refining operation, and often in quantity equivalent to 

 what had been added. Smelters finding in their practice that 

 copper made from the ordinary quality of ores will not roll 

 without lead being added, are of opinion that its presence is 

 essential for toughening the copper ; but it is only so when im- 

 purities are present. We have often seen copper refined without 

 lead ; and when the metal was pure and free from antimony, 

 was superior to those containing lead. Copper made from a 

 mixture of Cornish ores purified from antimony, tin, &c. in 

 the early stages of smelting, and refined without lead, has given 

 the following results : — A cake of 14 inches by 10 inches has 

 been rolled at one heat to 17 feet in length, with a wire edge; 

 and a cake from the same copper was hammered into a bowl 2 

 feet deep and 19 inches diameter without cracking. The neces- 

 sity of adding lead we consider to be owing to the presence of 

 antimony in the copper, the smallest trace of which without lead 

 makes it brittle ; while we have seen copper with half a per 

 cent, made to roll by the addition of lead. 



When the copper is brought to the proper pitch by the refi- 

 ning operation, it is ladled out into moulds. A ladle holds about 

 30 lbs. of fluid metal, three of which form a cake, the ordinaiy 

 size of which is 14 X 10 inches. Twenty moulds are set round 

 the floor in front of the furnace, three ladlefuls are poured 

 together into each mould, going over the whole, by which time 

 the cake first poured is set, and the mould is ready to receive 

 another charge. Each mould holds five such charges or cakes. 

 During the lading out the refiner takes an assay at short inter- 

 vals, as the metal is liable to get out of pitch, or become dry, as 

 underpoled copper is termed, in which case poling has to be 

 resumed. So much depends upon refining, that the best copper 

 by a defect in this operation will be rendered unmarketable. , 



It occasionally happens that poling is carried on too long; 

 in which case the metal assumes a light colour and a crystalline 

 structure, loses its toughness and becomes hard; when this 

 occurs, the charcoal is removed from the surface of the metal to 

 expose it to the air for some time and allow it to imbibe oxygen, 

 after which it is again poled as described. Both overpoled and 



