long; its sharp edge is a palm wide ; the round end is three digits thick ; the
wooden handle is four feet long.
The master throws pulverised earth into a small vessel, sprinkles water
over it, and mixes it; this he pours over the whole hearth, and sprinkles
charcoal dust over it to the thickness of a digit. If he should neglect this,
the copper, settling in the passages, would adhere to the copper bed-plates,
from which it can be chipped off only with difficulty; or else it would adhere
to the bricks, if the hearth was covered with them, and when the copper is
chipped off these they are easily broken. On the second day, at the same
time, the master arranges bricks in ten rows; in this manner twelve
passages are made. The first two rows of bricks are between the first and
the second openings on the right of the furnace; the next three rows are
between the second and third openings, the following three rows are
between the third and the fourth openings, and the last two rows between
the fourth and fifth openings. These bricks are a foot and a palm long, two
palms and a digit wide, and a palm and two digits thick; there are seven of
these thick bricks in a row, so there are seventy all together. Then on the
first three rows of bricks they lay exhausted liquation cakes and a layer five
digits thick-of large charcoal; then in a similar way more exhausted
liquation cakes are laid upon the other bricks, and charcoal is thrown upon
them ; in this manner seventy centumpondia of cakes are put on the
hearth of the furnace. But if half of this weight, or a little more, is to be
" dried," then four rows of bricks will suffice. Those who dry exhausted
liquation cakes20 made from copper " bottoms " place ninety or a hundred
centumpondia?1 into the furnace at the same time. A place is left in the front
part of the furnace for the topmost cakes removed from the forehearth in
which copper is made, these being more suitable for supporting the exhausted
liquation cakes than are iron plates; indeed, if the former cakes drip copper
from the heat, this can be taken back with the liquation thorns to the first
furnace, but melted iron is of no use to us in these matters. When the cakes
of this kind have been placed in front of the exhausted liquation cakes, the
workman inserts the iron bar into the holes on the inside of the wall, which
are at a height of three palms and two digits above the hearth; the hole to
the left penetrates through into the wall, so that the bar may be pushed back
*°A further amount of lead could be obtained in the first liquation, but a higher temperature is necessary, which was more economical to secure in the " drying " furnace.
Therefore, the " drying " was really an extension of liquation ; but as air was admitted the
lead and copper melted out were oxidized. The products were the final residual copper,
called by Agricola the " dried " copper, together with lead and copper oxides, called by him
the " slags, " and the scale of copper and lead oxides termed by him the " ash-coloured
copper." The German metallurgists distinguished two kinds of slag : the first and principal
one, the darrost, and the second the darrsöhle, this latter differing only in that it contained
more impurities from the floor of the furnace, and remained behind until the furnace cooled.
Agricola possibly refers to these as " more liquation thorns," because in describing the
treatment of the bye-products he refers to thorns from the process, whereas in the description
of " drying " he usually, refers to " slags." A number of analyses of these products, given
by Karsten, show the " dried " copper to contain from 82.7 to 90.6% copper, and from 9.4
to 17.3% lead; the " slag " to contain 76.5 to 85.1% lead oxide, and from 4.1 to 7.8%
cuprous oxide, with 9 to 13% silica from the furnace bottoms, together with some other
uIf Roman weights, this would equal from 6,360 lbs. to 7,066 lbs.
