assay ores, we can without great expense add to them a small portion of any
sort of flux, but when we smelt them we cannot add a large portion without
great expense. We must, therefore, consider how great the cost is, to avoid
incurring a greater expense on smelting an ore than the profit we make out of
the metals which it yields.
The colour of the fumes which the ore emits after being placed on a hot
shovel or an iron plate, indicates what flux is needed in addition to the lead,
for the purpose of either assaying or smelting. If the fumes have a purple
tint, it is best of all, and the ore does not generally require any flux whatever.
If the fumes are blue, there should be added cakes melted out of pyrites or
other cupriferous rock ; if yellow, litharge and sulphur should be added ; if
red, glass-galls17 and salt ; if green, then cakes melted from cupriferous stones,
litharge, and glass-galls ; if the fumes are black, melted salt or iron slag,
litharge and white Urne rock. If they are white, sulphur and iron which is
eaten with rust ; if they are white with green patches, iron slag and
sand obtained from stones which easily melt ; if the middle part of the
fumes are yellow and thick, but the outer parts green, the same sand and
iron slag. The colour of the fumes not only gives us information as to the
proper remedies which should be applied to each ore, but also more or less
indication as to the solidified juices which are mixed with it, and which give
forth such fumes. Generally, blue fumes signify that the ore contains azure ;
yellow, orpiment ; red, realgar ; green, chrysocolla ; black, black bitumen ;
white, tin18 ; white with green patches, the same mixed with chrysocolla ;
the middle part yellow and other parts green show that it contains sulphur.
Earth, however, and other things dug up which contain metals, sometimes emit similarly coloured fumes.
If the ore contains any stibium, then iron slag is added to it ; if pyrites,
then are added cakes melted from a cupriferous stone and sand made from
stones which easily melt. If the ore contains iron, then pyrites and sulphur
are added ; for just as iron slag is the flux for an ore mixed with sulphur, so
on the contrary, to a gold or silver ore containing iron, from which they are
are two precipitates possible, both referred to as feces,—the first, a precipitate of silver chloride
from clarifying the aqua valens, and the second, the residues left in making the acid by
distillation. It is difficult to believe that silver chloride was the feces referred to in the text,
because such a precipitate would be obviously misleading when used as a flux through the
addition of silver to the assays, too expensive, and of no merit for this purpose. Therefore
one is driven to the conclusion that the feces must have been the residues left in the retorts
when nitric acid was prepared. It would have been more in keeping with his usual mode
of expression, however, to have referred to this material as a residuus. The materials used
for making acid varied greatly, so there is no telling what such a feces contained. A list
of possibilities is given in note 8, p. 443. In the main, the residue would be undigested
vitriol, alum, saltpetre, salt, etc., together with potassium, iron, and alum sulphates. The
Probierbiichlin (p. 27) also gives this re-agent under the term Toden kopff das ist schiatti
oder feces auss dem scheydwasser.
17 Recrementum vitri. (Interpretatio Glassgallen). Formerly, when more impure
materials were employed than nowadays, the surface of the mass in the first melting
of glass materials was covered with salts, mostly potassium and sodium sulphates and
chlorides which escaped perfect vitrification. This " slag " or " glassgallen " of Agricola
was also termed sandiver.
18The whole of this expression is " candidus, candido." It is by no means certain
that this is tin, for usually tin is given as -plumbum candidum.
