When it
has attained the temperature of the furnace the coarse copper is dropped
into it and the furnace closed. The copper will melt almost at once with
a dull surface, which after a time clears, showing an "eye." Some
refining flux is then shot in from the scoop (fig. 48), and, when the
assay is again fluid, it is poured. When cold the button of metal is
separated.
[Illustration: FIG. 48.]
The button of "fine" copper is flat or pitted on its upper surface, and
is coated with a thin orange film; it must have the appearance of good
copper. If it is covered with a red or purple film, it is overdone or
"burnt." If, on the other hand, it has a rough, dull appearance, it is
not sufficiently refined. Assays that have been "burnt" are rejected.
Those not sufficiently fine are treated as "coarse copper," and again
put through the refining operation.
~Cleaning the Slags.~--These are roughly powdered and re-fused with
tartar, etc., as in the fusion for coarse copper. The button of metal
got is separated (if big enough refined) and weighed.
The details of the process are slightly varied by different assayers:
the following will be good practice for the student.
~Determination of Copper in Copper Pyrites.~--Powder, dry, and weigh up
20 grams of the ore. Mix with 20 grams each of powdered lime and fluor,
15 grams each of powdered glass and borax, and 5 or 10 grams of nitre.
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