The effect of
fusing a regulus with a basic slag is well seen when _sulphide of lead_
is fused with _carbonate of soda_; the result is a button of metal (more
or less pure), and a slag containing sulphides of lead and sodium; and
again, if sulphide of lead be fused with an excess of oxide of lead, a
button of lead will be got, and a slag which is simply oxide of lead
(with whatever it may have taken up from the crucible), or if a
sufficient excess has not been used, oxide of lead mixed with some
sulphide. When (as is most frequently the case) the desire is to prevent
the formation of regulus, these reactions may be taken advantage of, but
otherwise the use of a flux having any such tendency must be avoided. A
good slag (from which a regulus may be easily separated) may be obtained
by fusing, say, 20 grams of ore with borax 15 grams, powdered glass 15
grams, fluor spar, 20 grams, and lime 20 grams; by quenching the slag in
water as soon as it has solidified, it is rendered very brittle.
Sulphide of iron formed during an assay will remain diffused through
the slag, instead of fusing into a button of regulus, if the slag
contain sulphide of sodium. The same is true of other sulphides if not
present in too great a quantity, and if the temperature is not too high.
_Speises_ are compounds of a metal or metals with arsenic.
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