ing again melted, but
the latter being subjected to a powerful and persistent roasting,
during which, after a part of the sulphur, antimony, and arsenic
had been exhaled, a kind of distillation of sulphate of copper and
sulphate of iron took place, which appeared as "stone," or in balls
on the surface of the quartz, and could be easily detached. [135]

[The Smelter.] The furnace or smelting apparatus consisted of a round
hollow in clayey gound, thirty centimeters in diameter and fifteen
deep; with which was connected a conical funnel of fire-proof stone,
inclined at an angle of 30 deg., carrying up two bamboo-canes, which were
fitted into the lower ends of two notched pine-stems; in these two
slips, covered all over with dry grass or feathers, moved alternately
up and down, and produced the current required for the smelting.

[Smelting.] When the Igorots obtained black copper or native copper by
blasting, they prevented loss (by oxidation) by setting up a crucible
of good fire-proof clay in the form of a still; by which means it was
easier for them to pour the metal into the forms which it would acquire
from the same clay. The furnace being arranged, they supplied it
with from eighteen to twenty kilograms of rich or roasted ore, which,
according to the repeated experiments of Hernandez, contained twenty
per cent of copper; and they proceeded quite scientifically, always
exposing the ore at the mouth of the funnel, and consequently to the
air-drafts, and placing the coals at the sides of the furnace, which
consisted of loose stones piled one over another to the height of fifty
centimeters. The fire having been kindled and the blowing apparatus,
already described, in operation, thick clouds of white, yellow, and
orange-yellow smoke were evolved from the partial volatilization of the
sulphur, arsenic, and antimony, for the space of an hour; but as soon
as only sulphurous acid was formed, and the heat by this procedure
had attained its highest degree, the blowing was discontinued and
the product taken out. This consisted of a dross, or, rather, of the
collected pieces of ore themselves, which, on account of the flinty
contents of the stones composing the funnel, were transformed by the
decomposition of the sulphurous metal into a porous mass, and which
could not be converted into dross nor form combinations with silicious
acid, being deficient in the base as well as in the requisite heat;
and also of a very impure "stone,"