90 



Mr. E. Matthey. 



[Feb. 10, 



means, is at once rendered available, but with the drawback that not 

 only is there a very considerable loss of bismuth by volatilisation 

 during the cupellation, but the subsequent recovery of the metal, 

 which in the state of oxide has been absorbed by the cupel, is 

 rendered necessary, involving a tedious and troublesome smelting* 

 operation, the employment of expensive fluxes, and a further con- 

 siderable loss of metal. 



Bearing in mind the close resemblance of bismuth to lead in its 

 behaviour in the cupellation process, I directed my attention to its 

 separation from gold by means of the addition of a small proportion 

 of zinc — a method known as the Parkes process, as employed for the 

 separation of silver from lead. And this I found successful, the 

 natural separation of these two metals during the process of cooling 

 proving to be similar in both cases. 



The operation as carried out by me is as follows : — 



The Bismuth holding the gold is melted at the ordinary tempera- 

 ture, about two per cent, of melted zinc is then added, and the 

 whole brought to a dull red heat. The alloy is then well stirred, 

 and the temperature gradually lowered. When at a black heat the 

 slight crust formed on the surface is skimmed off and the metal 

 again treated with a further quantity of zinc at the higher tempera- 

 ture. The whole of the gold will be found in these skimmings, and 

 the bismuth will be thus freed from it. 



The skimmings, consisting of bismuth, gold and zinc, and zinc 

 oxide, I now treat by a process which quickly renders the gold avail- 

 able, and at the same time has the effect of refining the gold from all 

 impurities excepting silver during the actual process of extraction. 



This small proportion of bismuth litharge and its charge of gold 

 is fused in a clay crucible with a little borax, and allowed to cool 

 down in the crucible, or it is poured into a mould with the bismuth 

 litharge, which being perfectly liquid, allows the metallic gold to 

 separate by its own gravity, and during its fusion absorbs any base 

 metals associated with it as oxides. The bismuth litharge, in fact, 

 acts as a refining agent to the gold, which, when cold, is^ detached from 

 it. This bismuth slag is broken up, re-fused with a little metallic 

 bismuth, and is so freed from the last trace of gold which is collected 

 by the bismuth, and subsequently extracted. The bismuth litharge 

 so freed from gold is then reduced by fusion with carbon to its 

 metallic state. 



The quantity of bismuth litharge holding the gold is exceedingly 

 small in proportion to the bulk of metal originally treated, as the 

 figures hereinafter given will show ; but, by this process the bismuth 

 is at once freed from its gold contents with little time, labour, or 

 expense. 



I have continuously carried out this method of treatment with the 



