Finally, the gold is taken out of this and quenched, and if there is a
blackish colour settled in it, it is melted with a little of the chrysocolla
which the Moors call borax ; if too pale, it is melted with stibium, and
acquires its own golden-yellow colour. There are some who take out the
molten copper with an iron ladle and pour it into another crucible, whose
aperture is sealed up with lute, and they place it over glowing charcoal,
and when they have thrown in the powders of which I have spoken, they
stir the whole mass rapidly with an iron rod, and thus separate the gold
from the copper ; the former settles at the bottom of the crucible, the latter
floats on the top. Then the aperture of the crucible is opened with the
red-hot tongs, and the copper runs out. The gold which remains is re-heated
with stibium, and when this is exhaled the gold is heated for the third time
in a cupel with a fourth part of lead, and then quenched.
The fourth method is to melt one and a third librae of the copper
with a sixth of a libra of lead, and to pour it into another crucible smeared on
the inside with tallow or gypsum ; and to this is added a powder consisting of
half an uncia each of prepared sulphur, verdigris, and saltpetre, and an uncia
and a half of sal coctus. The fifth method consists of placing in a crucible
one libra of the copper and two librae of granulated lead, with one and a half
unciae of sal-artificiosus ; they are at first heated over a gentle fire and then
over a fiercer one. The sixth method consists in heating together a bes of
the copper and one-sixth of a libra each of sulphur, salt, and stibium. The
seventh method consists of heating together a bes of the copper and one-sixth
each of iron scales and filings, salt, stibium, and glass-galls. The eighth
method consists of heating together one libra of the copper, one and a half
librae of sulphur, half a libra of verdigris, and a libra of refined salt. The
ninth method consists of placing in one libra of the molten copper as
much pounded sulphur, not exposed to the fire, and of stirring it rapidly
with an iron rod ; the lump is ground to powder, into which quicksilver
is poured, and this attracts to itself the gold.
Gilded copper articles are moistened with water and placed on the fire,
and when they are glowing they are quenched with cold water, and the gold
is scraped off with a brass rod. By these practical methods gold is separated
from copper.
Either copper or lead is separated from silver by the methods which I
will now explain.26 This is carried on in a building near by the works, or
in the works in which the gold or silver ores or alloys are smelted. The
middle wall of such a building is twenty-one feet long and fifteen feet high, and
from this a front wall is distant fifteen feet toward the river ; the rear wall
"Throughout the book the cupellation furnace is styled the secunda fornax (Glossary,
Treibeherd). Except in one or two cases, where there is some doubt as to whether the author
may not refer to the second variety of blast furnace, we have used " cupellation furnace."
Agricola's description of the actual operation of the old German cupellation is less detailed
than that of such authors as Schlüter (Hütte-Werken, Braunschweig, 1738) or Winkler (Beschreibung der Freyberger Schmelz Hüttenprozesse, Freyberg, 1837). The operation falls into four
periods. In the first period, or a short time after melting, the first scum—the abzug—arises.
This material contains most of the copper, iron, zinc, or sulphur impurities in the lead.
In the second period, at a higher temperature, and with the blast turned on, a second scum
