244 
Lead \ 
sels which are formed of them. No matter, indeed, is 
more proper than the latter for constructing small refining 
eu pells. 
The difficulty, and often even the impossibility, of ob- 
taining about 160 English gallons of ashes for each ope- 
ration of refining on a large scale in the German furnaces, 
made the proprietors have recourse to wood-ashes ; but, 
besides that these ashes are expensive, it often happens 
that they cannot be procured in sufficient qiiantit}^ They 
are even attended with one inconvenience^ which is, that 
they come off, and float on the fused lead ; the refining 
then fails : and this takes place every time that the ashes 
are badly prepared, that the cupell is insufficiently or not 
uniformly beat, or when the canals destined for the evapo- 
ration of the moisture are neither in sufficient number, 
nor properly arranged, nor covered with a stratum of 
scoriae, on which is established the bottom, that receives 
the ashes, and which ought to be constructed of the most 
porous bricks, in order that the water, with which it is 
necessary to moisten the ashes, may penetrate them in 
evaporating, may proceed to the bed of scoriae, and escape 
by the spiracles which are at the base of the furnace. 
To ascertain the proportion of lead in silver, it is suf- 
ficient to put some pennyweights into a small cupell of 
bone-ashes placed under the muffle of an assaying fur- 
nace. In proportion as the lead becomes oxvdated, it in- 
sinuates itself into the cupell, and the silver at last as- 
sumes that vivid appearance which announces that the 
whole lead is dissipated, that the silver it contained is re- 
fined, and has attained to its inaximum of purity. 
In refining on a large scale, the object also is to sepa- 
rate the silver from the lead, but not to make the whole 
of the latter penetrate into the cupell, which is even im- 
possible ; for in that case it would be necessary to have 
■t mucli larger quantity of ashes for the total absorption of 
