When the eye has
disappeared--that is, when the layer of slag has quite closed in--a
pinch of powdered culm wrapped in tissue paper is added. As soon as the
slag has again become tranquil, the scorifier is taken out, and its
contents are poured into a mould (fig. 40), the slag is detached, and
saved. If the button of metal weighs more than 30 grams, its size is
reduced by another scorification in the same scorifier, which should
have been replaced in the muffle immediately after the contents had been
poured out. If the ore is not a very rich one, the button of lead will
carry practically all the silver; but with rich ores it is more
satisfactory to save the slag, and subsequently to melt it down with the
cupel on which the lead has been treated, so as to recover the silver
lost in the slag, together with that absorbed in the cupel, at one
operation. Or, if the cupellation loss is neglected or calculated in
some other manner, the slag or slags from the scorifier may be powdered
and mixed with 20 grams of oxide of lead, 5 grams of borax, and 1 gram
of charcoal. This should be melted down in a small crucible, and the
resulting button of lead cupelled.
[Illustration: FIG. 40.]
If the scorification has been unsatisfactory, the quantity of silver
obtained from the slag will be by no means inconsiderable.
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