The burned tin-stone should then be washed again on the strake, for in this
way the material which has been run together is carried away by the water
into the cross-trough, where it is gathered up and worked over, and again
washed on the strake. By this method the metal is separated from that
which is devoid of metal.
Cakes from pyrites, or cadmia, or cupriferous stones, are roasted in quadrangular pits, of which the front and top are open, and these pits are generally
twelve feet long, eight feet wide, and three feet deep. The cakes of melted
pyrites are usually roasted twice over, and those of cadmia once. These latter
are first rolled in mud moistened with vinegar, to prevent the fire from consuming too much of the copper with the bitumen, or sulphur, or orpiment, or
realgar. The cakes of pyrites are first roasted in a slow fire and afterward in
a fierce one, and in both cases, during the whole following night, "water is let in,
