Weigh up 3 grams of the metal, wrap in 30
grams of sheet lead, and cupel; when the cupellation has proceeded for
fifteen minutes, add 20 grams more lead, and continue till finished.
Weigh the button of silver.
The cupellation loss will be five or six per cent. of the silver
present. Determine it by powdering the saturated portion of the cupel
and fusing in a large Cornish crucible with 30 grams each of soda and
borax, 10 grams of fluor spar, and 1-1/2 gram of charcoal. Cupel the
resulting button of lead, and add 10 grams more of lead towards the
close of the operation. Deduct the weight of silver contained in the
lead used from the weight of the two buttons, and calculate to ounces to
the ton.
In an experiment in which 0.1975 gram of silver was present, the weight
of the button from the first cupellation was 0.1867, and that of the
button from the second, after correcting for the lead added, was 0.0110
gram.
~Determination of Silver in Galena.~ _By Pot Assay._--Mix 20 grams of
the powdered ore with 30 grams of red lead, 20 grams of soda, and 5
grams of borax, as also with from 7 to 10 grams of nitre. Fuse and pour.
Clean the slag if the ore is rich. Cupel the buttons of lead. Make the
usual corrections and calculate in ounces to the ton.
_By Scorification._--Take 10 grams of the ore, 30 grams of lead, and
0.
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