When he has compressed the bellows, he introduces this bar as quickly as
possible into the crucible through the pipe between the two nozzles, and
takes out samples two, three, or four times, until he finds that the copper is
perfectly refined. If the copper is good it adheres easily to the bar, and
two samples suffice ; if it is not good, then many are required. It is
necessary to smelt it in the crucible until the copper adhering to the bar is
seen to be of a brassy colour, and if the upper as well as the lower part of
the thin layer of copper may be easily broken, it signifies that the copper
is perfectly melted ; he places the point of the bar on a small iron anvil,
and chips off the thin layer of copper from it with a hammer.25
If the copper is not good, the master draws off the " slags " twice, or
three times if necessary—the first time when some of the cakes have been
melted, the second when all have melted, the third time when the copper has
been heated for some time. If the copper was of good quality, the " slags "
are not drawn off before the operation is finished, but at the time they are to be
drawn off, he depresses the bar over both bellows, and places over both a
stick, a cubit long and a palm wide, half cut away at the upper part, so that it
may pass under the iron pin fixed at the back in the perforated wood. This
he does likewise when the copper has been completely melted. Then the
assistant removes the iron plate with the tongs ; these tongs are four feet
three palms long, their jaws are about a foot in length, and their straight part
measures two palms and three digits, and the curved a palm and a digit.
The same assistant, with the iron shovel, throws and heaps up the larger
pieces of charcoal into that part of the hearth which is against the little wall
which protects the other wall from injury by fire, and partly extinguishes
them by pouring water over them. The master, with a hazel stick inserted
25This description of refining copper in an open hearth by oxidation with a blast and
" poling "—the gaarmachen of the Germans—is so accurate, and the process is so little changed
in some parts of Saxony, that it might have been written in the 20th century instead of
the 16th. The best account of the old practice in Saxony after Agricola is to be found in
Schlüter's Hütte Werken (Braunschweig, 1738, Chap, cxvin.). The process has largely been
displaced by electrolytic methods, but is still in use in most refineries as a step in electrolytic
work. It may be unnecessary to repeat that the process is one of subjecting the molten mass
of impure metal to a strong and continuous blast, and as a result, not only are the impurities
to a considerable extent directly oxidized and taken off as a slag, but also a considerable amount of copper is turned into cuprous oxide. This cuprous oxide mostly melts and
diffuses through the metallic copper, and readily parting with its oxygen to the impurities
further facilitates their complete oxidation. The blast is continued until the impurities are
practically eliminated, and at this stage the molten metal contains a great deal of dissolved
cuprous oxide, which must be reduced. This is done by introducing a billet of green wood
(" poling "), the dry distillation of which generates large quantities of gases, which reduce the
oxide. The state of the metal is even to-day in some localities tested by dipping into it the
point of an iron rod ; if it be at the proper state the adhering copper has a net-like appearance,
should be easily loosened from the rod by dipping in water, is of a reddish-copper colour
and should be quite pliable ; if the metal is not yet refined, the sample is thick, smooth, and
detachable with difficulty ; if over-refined, it is thick and brittle. By allowing water to run
on to the surface of the molten metal, thin cakes are successively formed and taken off. These
cakes were the article known to commerce over several centuries as " rosetta copper." The
first few cakes are discarded as containing impurities or slag, and if the metal be of good
quality the cakes are thin and of a red colour. Their colour and thinness, therefore, become a
criterion of purity. The cover of charcoal or charcoal dust maintained upon the surface of
the metal tended to retard oxidation, but prevented volatilization and helped to secure the
impurities as a slag instead. Karsten (Archiv., ist series, p. 46) gives several analyses of the
