made richer, to eighteen librae of it are added forty-eight librae of crude
ore, three librae of the stone from which iron is made, and three-quarters
of a libra of the cakes made from pyrites, and mixed with lead, all are
heated together in the crucible until they melt. When the slag and the
cakes melted from pyrites have been skimmed off, the alloy is carried to
other furnaces.
There now follows silver, of which the native silver or the lumps of rudis
silver34 obtained from the mines are not smelted in the blast furnaces, but in
small iron pans, of which I will speak at the proper place ; these lumps
are heated and thrown into molten silver-lead alloy in the cupellation furnace
when the silver is being separated from the lead, and refined. The tiny flakes
or tiny lumps of silver adhering to stones or marble or rocks, or again the
same little lumps mixed with earth, or silver not pure enough, should be
smelted in the furnace of which the tap-hole is only closed for a short time,
together with cakes melted from pyrites, with silver slags, and with stones
which easily fuse in fire of the second order.
In order that particles of silver should not fly away35 from the lumps
of ore consisting of minute threads of pure silver and twigs of native silver,
they are enclosed in a pot, and are placed in the same furnace where the rest of
the silver ores are being smelted. Some people smelt lumps of native silver
not sufficiently pure, in pots or triangular crucibles, whose lids are sealed with
lute. They do not place these pots in the blast furnace, but arrange them in
the assay furnace into which the draught of the air blows through small holes.
To one part of the native silver they add three parts of powdered litharge, as
many parts of hearth-lead, half a part of galena36, and a small quantity of
salt and iron-scales. The alloy which settles at the bottom of the other
substances in the pot is carried to the cupellation furnace, and the slags are
re-melted with the other silver slags. They crush under the stamps and
wash the pots or crucibles to which silver-lead alloy or slags adhere, and
having collected the concentrates they smelt them together with the slags.
This method of smelting rudis silver, if there is a small quantity of it, is the
best, because the smallest portion of silver does not fly out of the pot or the
crucible, and get lost.
If bismuth ore or antimony ore or lead ore37 contains silver, it is
smelted with the other ores of silver ; likewise galena or pyrites, if there is
a small amount of it. If there be much galena, whether it contain a large
or a small amount of silver, it is smelted separately from the others ;
which process I will explain a little further on.
s*Rudis silver comprised all fairly pure silver ores, such as silver sulphides, chlorides,
arsenides, etc. This is more fully discussed in note 6, p. 108.
ihEvolent,—volatilize ?
"Lapidis plumbarii facile liquescentis. The German Translation gives glaniz, i.e., Galena,
and the Interpretatio also gives glantz for lapis plumbarius. We are, however, uncertain
whether this ·" easily melting " material is galena or some other lead ore.
31Molybdaena is usually hearth-lead in De Re Metallica, but the German translation
in this instance uses pleyertz, lead ore. From the context it would not appear to mean hearthlead—saturated bottoms of cupellation furnaces—for such material would not contain
appreciable silver. Agricola does confuse what are obviously lead carbonates with his other
molybdaena (see note 37, p. 476).
