167 
Process for Refining Lead „ 
test contain from about fifty to seventy pounds of alloy. 
This quantity is run into an iron pot, and set by until a 
sufficient number of pieces have been collected to make 
it worth while to take off a plate of pure silver from 
them. 
The quantity of alloy left in the working off each test 
must depend in a great measure upon the quantity of sil- 
ver it by estimation is supposed to contain. A sufficient 
quantity of lead should always be left in the alloy to make 
it fuse easily in the iron pot. 
When the test is removed from the furnace and broken 
up, the litharge will be found to have penetrated to 
an inconsiderable but equal depth in the ashes; that 
part not impregnated with litharge may be pulve- 
rised, mixed with fresh ashes, and again used for ano- 
ther test. 
The operation of taking off the silver pure differs in 
no respect from the foregoing, only more care is observ- 
ed in the working, not to suffer the escape of any me- 
tallic particles with the litharge, as that would occasion 
considerable waste of silver. As the process advances, 
and the proportion of silver to lead increases, the li- 
tharge assumes a darker colour, a greater heat becomes 
necessary, and at last the brightening takes place ; the 
interior of the furnace, which during the whole of the 
process had been very obscure and misty, clears up. 
When the operator observes the surface of the silver 
to be free from litharge, he removes the blast of the 
bellows, and suffers the furnace to cool gradually; 
as the silver cools many protuberances arise on the 
surface, and fluid silver is ejected from them with consi- 
derable force, which falling again on the plate spots it 
very fantastically with small globules. 
The latter portions of litharge bring o ver a considers- 
