A—Pot. Β—Circular fire. C—Crucibles. D—Their lids. E—Lid of the pot.
F—Furnace. G—Iron rod.
the black-coloured granules are taken out, and afterward thirty-three librae
of these granules are placed in an earthen crucible, if it has such capacity.
For every libra of silver granules, weighed before they were sprinkled with
From the necessity for some free métairies besides the gold in the first treatment, it will
be seen that a repetition of the sulphur addition and re-melting is essential gradually to enrich
the " lump". Why more copper is added is not clear. In the second melting, the ratio is
48 parts of the " gold lump", 12 parts of sulphur and 12 parts copper. In this case the added
copper would require about 3 parts sulphur, and if we consider the deficiency of sulphur
in the first operations pertained entirely to the copper, then about 2.5 parts would be required
to make good the shortage, or in other words the second addition of sulphur is sufficient.
In the final parting of the " lump " it will be noticed that the author states that the silver ratio
must be arranged as three of silver to one of gold. As to the recovery of the silver from the
regulus, he states that 66 librae of silver give 132 librae of regulus. To this, 500 librae of
lead are added, and it is melted in the " second " furnace, and the litharge and hearthlead made are re-melted in the " first " furnace, the cakes made being again treated in the
" third " furnace to separate the copper and lead. The " first " is usually the blast furnace,
the " second " furnace is the cupellation furnace, and the " third " the liquation furnace.
It is difficult to understand this procedure. The charge sent to the cupellation furnace
would contain between 3% and 5% copper, and between 3% and 5% sulphur. However,
possibly the sulphur and copper could be largely abstracted in the skimmings from the
cupellation furnace, these being subsequently liquated in the " third " furnace. It may be
noted that two whole lines from this paragraph are omitted in the editions of De Re Metallica
after 1600. For historical note on sulphur separation see page 461,
