BOOK VII.
INCE the Sixth Book has described the iron tools,
the vessels and the machines used in mines, this
Book will describe the methods of assaying1 ores;
because it is desirable to first test them in order
that the material mined may be advantageously
smelted, or that the dross may be purged away and
the metal made pure. Although writers have mentioned such tests, yet none of them have set down the
directions for performing them, wherefore it is no
wonder that those who come later have written nothing on the subject.
By tests of this kind miners can determine with certainty whether
ores contain any metal in them or not ; or if it has already been
indicated that the ore contains one or more metals, the tests show whether
it is much or little ; the miners also ascertain by such tests the method by
which the metal can be separated from that part of the ore devoid of it ;
and further, by these tests, they determine that part in which there is much
metal from that part in which there is little. Unless these tests have been
carefully applied before the metals are melted out, the ore cannot be smelted
without great loss to the owners, for the parts which do not easily melt in the
fire carry the metals off with them or consume them. In the last case, they pass
off with the fumes ; in the other case they are mixed with the slag and furnace
accretions, and in such event the owners lose the labour which they have spent
in preparing the furnaces and the crucibles, and further, it is necessary for them
to incur fresh expenditure for fluxes and other things. Metals, when they have
been melted out, are usually assayed in order that we may ascertain what proportion of silver is in a centumpondium of copper or lead, or what quantity of
gold is in one libra of silver ; and, on the other hand, what proportion of copper
or lead is contained in a centumpondium of silver, or what quantity of silver is
contained in one libra of gold. And from this we can calculate whether it
will be worth while to separate the precious metals from the base metals, or
not. Further, a test of this kind shows whether coins are good or are
debased ; and readily detects silver, if the coiners have mixed more than is
lawful with the gold ; or copper, if the coiners have alloyed with the gold or
silver more of it than is allowable. I will explain all these methods with the
utmost care that I can.
1We have but little record of anything which could be called " assaying " among the
Greeks and Romans. The fact, however, that they made constant use of the touchstone
(see note 37, p. 252) is sufficient proof that they were able to test the purity of gold and silver.
The description of the touchstone by Theophrastus contains several references to " trial "
by fire (see note 37, p. 252). They were adepts at metal working, and were therefore familiar
with melting metals on a small scale, with the smelting of süver, lead, copper, and tin
ores (see note I, p. 353) and with the parting of silver and lead by cupellation. Consequently,
it would not require much of an imaginative flight to conclude that there existed some system
of tests of ore and metal values by fire. Apart from the statement of Theophrastus referred
to, the first references made to anything which might fill the rôle of assaying are from the
Alchemists, particularly Geber (prior to 1300), for they describe methods of solution,
precipitation, distillation, fusing in crucibles, cupellation, and of the parting of gold and silver
by acid and by sulphur, antimony, or cementation. However, they were not bent on
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