Mr. J. Napier on Copper Smelting. 487 



throws up jets of metal, forming a miniature volcano. These 

 phsenomena are caused no doubt by the presence of gases in the 

 copper. Several metals when in fusion absorb oxygen ; but the 

 fact that copper, when it sets in this way, does not refine well 

 by the operation of poling, which would soon take away oxygen, 

 is presumptive that the gas which escapes is not oxygen, and 

 renders probable the prevailing idea that it is caused by the 

 presence of sulphur or sulphurous acid. 



When the setting of the metal in the ladle is favourable, the 

 charge is ready for the operation of poling. A quantity of 

 charcoal or anthf^cite coal is first thrown upon the metal to 

 prevent oxidation by the air, and then the end of a large pole of 

 green wood, generally of birch or oak, is inserted into the melted 

 copper, and kept pressed down to the bottom of the metal, which 

 occasions violent ebullition, the metal spurting and boiling with 

 loud noise. The action which takes place during this operation 

 will be apparent to every one slightly versed in chemistry — the 

 reduction of any oxide or suboxide. But the reason why such 

 an operation as poling is required, is owing to the peculiar 

 nature of copper in relation to its oxides. If, for example, a 

 quantity of melted lead be exposed to the air, it oxidates, but the 

 oxide formed floats upon the surface of the metal, and may be 

 reduced by putting wood or other carbonaceous matters on the 

 surface; but when copper is so oxidated, the oxide formed is 

 dissolved in the metal as completely as a salt is dissolved in 

 water, which renders the copper brittle. To put pieces of wood 

 or charcoal upon the surface would not remove the oxygen; 

 hence the necessity of poling in order to bring the carbonaceous 

 matters into contact with the dissolved oxide. 



The copper before poling has a granular fracture and a red- 

 brown colour ; as the poling proceeds, these appearances change. 

 The refiner takes from time to time small samples, called assays, 

 which he hammers and breaks for examination. When it reaches 

 the proper pitch, the assay bends without breaking ; a small cut, 

 however, is made with a chisel on the centre of the assay, so 

 that in bending it opens up and shows the fracture, which when 

 tough, or in pitch, should have a fibrous silky lustre and light 

 colour. When this pitch is attained, the pole is withdrawn and 

 a larger sample taken out, termed a trial, and cast in a small 

 mould. It is then beat by sledge hammers into a plate ; if the 

 copper be good, this plate should not crack on the edge, and the 

 surface will be smooth and not scaly ; if it crack, the copper is 

 not in a good condition, and it would not be safe to take out if 

 it is intended to be used for hammered work. But frequently 

 copper that will not hammer will stand rolling into sheets with- 

 out much loss. Previous to taking out the trials a quantity of 



