Transfer to a large Cornish crucible and fuse under a loose cover at a
high temperature for from 15 to 20 minutes. When fluid and tranquil pour
into a mould. When the slag has solidified, but whilst still hot, quench
by dipping two or three times in cold water. Avoid leaving it in the
water so long that it does not dry after removal. When cold separate the
button, or perhaps buttons, of regulus by crumbling the slag between the
fingers. See that the slag is free from regulus. It should be light
coloured when cold and very fluid when hot. Reject the slag.
Powder the regulus in a mortar and transfer to a small crucible.
Calcine, with occasional stirring, until no odour of sulphurous oxide
can be detected. Shake back into the mortar, rub up with about 1 gram of
powdered anthracite, and re-calcine for 10 minutes longer.
Mix the calcined regulus with 10 grams of tartar, 20 grams of soda, and
3 grams of borax; and replace in the crucible used for calcining. Fuse
at a bright red heat for 10 or 15 minutes. Pour, when tranquil.
As soon as solid, quench in water, separate the button of copper, and
save the slag.
To refine the copper a very hot fire is wanted, and the fuel should not
be too low down in the furnace. Place the crucible well down in the fire
and in the middle of the furnace. The same crucible is used, or, if a
new one is taken, it must be glazed with a little borax.
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