however, for the tap-hole of the first of this kind is deeper in the furnace and
narrower than that of the third, and besides it is invisible and concealed.
It easily discharges into the forehearth, which is one and a half feet higher
than the floor of the building, in order that below it to the left a dipping-pot
can be made. When the forehearth is nearly full of the slags, which well up
from the invisible tap-hole of the furnace, they are skimmed off from the top
with a hooked bar ; then the alloy of gold or silver with lead and the melted
pyrites, being uncovered, flow into the dipping-pot, and the latter are made into
cakes ; these cakes are broken and thrown back into the furnace so that all
their metal may be smelted out. The alloy is poured into little iron moulds.
The smelter, besides lead and cognate things, uses fluxes which combine
with the ore, of which I gave a sufficient account in Book VII. The metals
which are melted from ores that fuse readily in the fire, are profitable because
they are smelted in a short time, while those which are difficult to fuse are
not as profitable, because they take a long time. When fluxes remain in the
furnace and do not melt, they are not suitable ; for this reason, accretions and
slags are the most convenient for smelting, because they melt quickly. It is
necessary to have an industrious and experienced smelter, who in the first
place takes care not to put into the furnace more ores mixed with fluxes than
it can accommodate.
The powder out of which this furnace hearth and the adjoining forehearth and the dipping-pot are usually made, consists mostly of equal proportions of charcoal dust and of earth, or of equal parts of the same and of
ashes. When the hearth of the furnace is prepared, a rod that will reach to the
forehearth is put into it, higher up if the ore to be smelted readily fuses, and
lower down if it fuses with difficulty. When the dipping-pot and forehearth
are finished, the rod is drawn out of the furnace so that the tap-hole is open,
and through it the molten material flows continuously into the forehearth,
which should be very near the furnace in order that it may keep very hot and
the alloy thus be made purer. If the ore to be smelted does not melt easily, the
hearth of the furnace must not be made too sloping, lest the molten fluxes
should run down into the forehearth before the ore is smelted, and the metal
thus remain in the accretions on the sides of the furnace. The smelter must
not ram the hearth so much that it becomes too hard, nor make the mistake
of ramming the lower part of the mouth to make it hard, for it could not
breathe17, nor could the molten matter flow freely out of the furnace.
The ore which does not readily melt is thrown as much as possible to the
back of the furnace, and toward that part where the fire burns very
fiercely, so that it may be smelted longer. In this way the smelter may direct
it whither he wills. Only when it glows at the part near the bellows' nozzle
does it signify that all the ore is smelted which has been thrown to the side of
the furnace in which the nozzles are placed. If the ore is easily melted, one
or two wicker baskets full are thrown into the front part of the furnace so that
the fire, being driven back by it, may also smelt the ore and the sows that
