190 
Lead 1 
this quantity they call a charge ; if the ore is very poor 
in lead, they put in somewhat more, and they work off 
three charges of ore in every twenty-four hours. In about 
six hours from the time of charging, the ore becomes as 
fluid as milk. Before the ore becomes fluid, and even 
whilst it continues in a state of fusion, a considerable 
portion of its weight is carried off through the chimney ; 
what remains in the furnace consists of two different sub- 
stances,— of the lead, for the obtaining of which the pro- 
cess was commenced,— and of the slag or scoria. The 
proportion between these parts is not always the same, 
even in the same kind of ore ; it depending much upon 
the management of the fire. The lead, being heavier 
than the slag, sinks through it as it is formed, and settles 
into the concavity of the bottom of the furnace. The 
pure slag, according to the idea here given, is that part of 
the ore of lead which is neither driven off by the heat of 
the furnace, nor changed into lead. In order to obtain 
the lead free from the slag which swims over it, the smelt- 
ers usually throw in about a bushel of lime ; not, as is 
usually supposed, in order to contribute towards the more 
perfect fusion of the ore, but to dry up the slag which 
floats upon the surface of the lead, and which, being as 
liquid as lead, might otherwise flow out along with it 
The slag being thus thickened by an admixture of lime, 
is raked up towards the sides of the furnace, and the lead 
is left at the bottom. There is a hole in one of the sides 
of the furnace, which is properly stopped during the 
smelting of the ore ; when the slag is raked off, this hole 
is opened, and being situated lower than the lead in the 
furnace, the lead gushes through it into an iron pot placed 
contiguous to the side of the furnace ; from this pot it is 
laded into iron moulds, each containing what they call a 
pig of lead ; the pigs, when cold, being ordinarily stamp 
td with the maker’s name, are sold under the name of 
