BOOK XI. 



543 



A — Furnace. B — Forehearth. C — Oblong moulds. 



placed apart by themselves, of which one basketful is mixed with the precious 

 thorns to be re-melted. The exhausted liquation cakes are " dried " at the 

 same time as other good exhausted liquation cakes. 



The thorns which are drawn off from the lead, when it is separated from 

 silver in the cupellation furnace^*, and the hearth-lead which remains in the 

 crucible in the middle part of the furnaces, together with the hearth material 

 which has become defective and has absorbed silver-lead, are all melted 

 together with a little slag in the blast furnaces. The lead, or rather the 

 silver-lead, which flows from the furnace into the fore-hearth, is poured out 

 into copper moulds such as are used by the refiners ; a centumpondium of 

 such lead contains four unciae of silver, or, if the hearth was defective, it 

 contains more. A small portion of this material is added to the copper and 

 lead when liquation cakes are made from them, if more were to be added 

 the alloy would be much richer than it should be, for which reason the wise 



**The skimmings from the molten lead in the early stages of cupellation have been 

 discussed in Note 28, p. 539. They are probably called thorns here because of the large amount 

 of copper in them. The lead from liquation would contain 2% to 3% of copper, and this 

 would be largely recovered in these skimmings, although there would be some copper in the 

 furnace bottoms — hearth-lead — and the litharge. These " thorns " are apparently fairly 

 rich, four unciae to the centumpondium being equivalent to about 97 ozs. per ton, and they 

 are only added to low-grade Uquation material. 



