the channel, mixed with charcoal, the scum, as one might say, of the lead ;
the lead makes this scum when it becomes hot, but that less of it may be
made it must be stirred frequently with the bar.
Within the space of a quarter of an hour the crucible absorbs the lead ;
at the time when it penetrates into the crucible it leaps and bubbles. Then
the master takes out a little lead with an iron ladle, which he assays, in order
to find what proportion of silver there is in the whole of the alloy ; the
ladle is five digits wide, the iron part of its handle is three feet long and the
wooden part the same. Afterward, when they are heated, he extracts with
a bar the litharge which comes from the lead and the copper, if there be any
of it in the alloy. Wherefore, it might more rightly be called spuma of lead
than of silver34. There is no injury to the silver, when the lead and copper
are separated from it. In truth the lead becomes much purer in the crucible
of the other furnace, in which silver is refined. In ancient times, as the
author Pliny35 relates, there was under the channel of the crucible another
crucible, and the litharge flowed down from the upper one into the lower
one, out of which it was lifted up and rolled round with a stick in order that
it might be of moderate weight. For which reason, they formerly made it
into small tubes or pipes, but now, since it is not rolled round a stick, they
make it into bars.
If there be any danger that the alloy might flow out with the litharge, the
foreman keeps on hand a piece of lute, shaped like a cylinder and pointed at
both ends ; fastening this to a hooked bar he opposes it to the alloy so that
it will not flow out.
Now when the colour begins to show in the silver, bright spots appear,
some of them being almost white, and a moment afterward it becomes
absolutely white. Then the assistant lets down the water-gates, so that, the
race being closed, the water-wheel ceases to turn and the bellows are still.
Then the master pours several buckets of water on to the silver to cool it ;
others pour beer over it to make it whiter, but this is of no importance since
the silver has yet to be refined. Afterward, the cake of silver is raised with
the pointed iron bar, which is three feet long and two digits wide, and has a
wooden handle four feet long fixed in its socket. When the cake of silver has
been taken from the crucible, it is laid upon a stone, and from part of it the
hearth-lead, and from the other part the Htharge, is chipped away with a
hammer ; then it is cleansed with a bundle of brass wire dipped in water.
When the lead is separated from the silver, more silver is frequently found
than when it was assayed ; for instance, if before there were three unciae and
as many drachmae in a centumpondium, they now sometimes find three unciae
and a half36. Often the hearth-lead remaining in the crucible is a palm
deep ; it is taken out with the rest of the ashes and is sifted, and that which
remains in the sieve, since it is hearth-lead, is added to the hearth-lead37.
84The Latin term for litharge is spuma argenti, spume of silver.
"Pliny, xxxin, 35. This quotation is given in full in the footnote p. 466. Agricola
illustrates these " tubes " of litharge on p. 481.
'•Assuming Roman weights, three unciae and three drachmae per centumpondium
would be about 82 ozs., and the second case would equal about 85 ozs. per short ton.
"Agricola uses throughout De Re Metallica the term molybdaena for this substance.
