When the
crucible is at a good red heat, above the fusing point of copper, drop
the button of copper into it, and close the furnace. Watch through the
crevice, and, as soon as the button has melted and appears clear showing
an eye, shoot in 10 grams of refining flux, close the furnace, and, in a
few minutes, pour; then separate the button of copper. Add the slag to
that from the coarse copper fusion, and powder. Mix with 5 grams of
tartar, 0.5 gram of powdered charcoal, and 2 grams of soda. Fuse in the
same crucible, and, when tranquil, pour; quench, and pick out the prills
of metal.
If the copper thus got from the slags is coarse looking and large in
amount, it must be refined; but, if small in quantity, it may be taken
as four-fifths copper. The combined results multiplied by five give the
percentage of copper.
The refining flux is made by mixing 3 parts (by measure) of powdered
nitre, 2-1\2 of tartar, and 1 of salt. Put in a large crucible, and stir
with a red-hot iron until action has ceased. This operation should be
carried out in a well-ventilated spot.
For pure ores in which the copper is present, either as metal or oxide,
and free from sulphur, arsenic, &c., the concentration of the copper in
a regulus may be omitted, and the metal obtained in a pure state by a
single fusion.[50] It is necessary to get a fluid neutral slag with the
addition of as small an amount of flux as possible.
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