246 
Lead . 
small portion which penetrates into the cupeli, the thick = 
ness of which is only about 2 3-4 inches, and which is sup- 
ported under the arch of the furnace by two bars of iron. 
A pair of leather bellows drive the litharge towards the 
anterior part of the furnace, from which it falls, without 
interruption, on the floor of the foundry, while, to fill up 
the vacuity left by the oxyd running off, an ingot of lead 
placed close to the base of the bellows is made to advance 
gradually into the interior part of the furnace. This lead, 
by fusing, keeps the cupeli full till towards the end of the 
operation. 
If I have here given a short view of the process of the 
English, it is only to shew that it is possible to perform 
operations of refining by employing only a small quantity 
of ashes for the construction of cupells. Those in ques- 
tion do not absorb 90 pounds of oxyd in the large quan- 
tity of lead which is refined. 
It is then proved that metallurgists have always endea- 
voured to obtain the greatest quantity possible of litharge, 
and little ashes impregnated with oxyd ; but as they 
thou gilt that they ought not to deviate from the docimas- 
tic process, they have always constructed their cupells of 
ashes. 
It has been seen that in cupellation on a small scale, 
lead, in proportion to its oxydation, penetrates the ashes. 
When no more is left, the small button of silver remains 
pure at the bottom of the bason under a spherical form. 
This operation takes place with the more celerity, as the 
surface of the mass is always convex fn these small ves- 
sels ; which allows the oxyd to flow as on an inclined 
plane, towards the edges of the cupeli, where it is imme- 
diately Imbibed. 
The case is not the same with cupells on a large scale, 
which are several yards in diameter : bellows must be ap- 
plied, the wind of which serves not only for accelerating 
