Lead . 
-251 
the gutter must be opened, and must be dug in propor- 
tion to the diminution of the mass, taking care that no 
lead escapes, and particularly towards the end of the ope- 
ration ; for it would carry with it a great deal of silver, 
which would be lost. You must proceed in this manner 
till the silver has acquired its vivid colour - r taking care to 
increase the fire in proportion to the diminution of the 
mass ; especially when the operation is nearly terminated, 
because the silver then is collected together : and, as it is 
much more difficult to be kept in fusion than the small 
quantity of lead which remains united with it, it could be 
refined only in an imperfect manner at an insufficient tern- 
perature ; and instead of about a twentieth of lead, which 
the silver generally contains in the German refining- hous- 
es, it would remain charged with a great deal more, which 
would render it more difficult to proceed to a second ope- 
ration, called the refining of silver , by which it is carried 
to the required degree of purity. The Germans call this 
second process fiber brennen , burning silver. 
Those accustomed to the refining of lead according ta 
the German method, will be able to perform that which 
I here propose ; for, though the cupell be of sand instead 
of ashes, the operation must be conducted in the same 
manner. 
It has been seen that the English refine a large quan- 
tity of lead in a small cupell : in the like manner, a great 
deal of metal may be made to pass by that which I pro- 
pose, if care be taken to add more metal as that which is 
.oxy dated escapes. If we suppose that the cupell is capa- 
ble of containing four or five tons of lead, above sixteen 
may be refined at one operation ; which will not be at- 
tended with the inconveniences of the English process, 
I have reason to think that a cupell of sand well con- 
structed may serve for several operations without the ne- 
cessity of re- constructing it each, time, as is the case with 
