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Thuringian pyrites, in which there is gold, sulphur, and vitriol, after the last
particle of vitriol has been obtained by heating it in water, is thrown into a
furnace, in which logs are placed. This furnace is very similar to an oven
in shape, in order that when the ore is roasted the valuable contents may not
fly away with the smoke, but may adhere to the roof of the furnace. In this
way sulphur very often hangs like icicles from the two openings of the roof
through which the smoke escapes.
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If pyrites or cadmia, or any other ore containing metal, possesses a good
deal of sulphur or bitumen, it should be so roasted that neither is lost. For
this purpose it is thrown on an iron plate full of holes, and roasted with charcoal placed on top ; three walls support this plate, two on the sides and the
third at the back. Beneath the plate are placed pots containing water, into
which the sulphurous or bituminous vapour descends, and in the water the
fat accumulates and floats on the top. If it is sulphur, it is generally of a
yellow colour ; if bitumen, it is black like pitch. If these were not drawn
out they would do much harm to the metal, when the ore is being smelted.
When they have thus been separated they prove of some service to man,
especially the sulphurous kind. From the vapour which is carried down, not
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