The sulphur from such a mixture can best be extracted if the upper pots are
placed in a vaulted furnace, like those which I described among other
metallurgical subjects in Book VIII., which has no floor, but a grate inside ;
under this the lower pots are placed in the same manner, but the plates
must have larger holes.
Others bury a pot in the ground, and place over it another pot with a
hole at the bottom, in which pyrites or cadmia, or other sulphurous stones
are so enclosed that the sulphur cannot exhale. A fierce fire heats the
sulphur, and it drips away and flows down into the lower pot, which contains
water. (Illustration p. 582).
Bitumen14 is made from bituminous waters, from liquid bitumen, and
from mixtures of bituminous substances. The water, bituminous as well as
14The substances referred to under the names bitumen, asphalt, maltha, naphtha,
petroleum, rock-oil, etc., have been known and used from most ancient times, and much of our
modern nomenclature is of actual Greek and Roman ancestry. These peoples distinguished
three related substances,—the Greek asphaltos and Roman bitumen for the hard material,—
Greek pissasphaltos and Roman maltha for the viscous, pitchy variety—and occasionally the
Greek naphtha and Roman naphtha for petroleum proper, although it is often enough referred
to as liquid bitumen or liquid asphaltos. The term petroleum apparently first appears in
Agricola's De Natura Fossilium (p. 222), where he says the " oil of bitumen . . . now
