If 10 grams of silver
are cupelled with 10 grams of lead, there will be a loss of about 50
milligrams of silver, which is in round numbers 1-30th of the
corresponding copper loss; with 10 grams of gold and 10 grams of lead,
the loss will be 4 or 5 milligrams, which is about 1-12th of the
corresponding silver loss.
~Determination of Silver in Assay Lead.~--Scorify 50 grams of the lead
with 0.5 gram of powdered quartz or glass at not too high a temperature.
When the eye has "closed in," pour; reject the slag, and cupel the
button of lead. Remove the cupel from the muffle immediately the
operation is finished. Weigh, and make a prominent note of the result in
the assay book, as so many milligrams of silver contained in 100 grams
of lead.
~Determination of Silver in Red Lead or Litharge.~--Fuse 100 grams of
the oxide with from 10 to 20 grams of borax; and in the case of litharge
with 2 grams or with red lead 4 grams of flour. Cupel the lead, and
weigh the button of silver. Note the result as in the last case.
~Determination of Silver in Argentiferous Lead.~--Be careful in taking
the sample, since with rich silver lead alloys the error from bad
sampling may amount to several parts per cent. Cupel two lots of 20
grams each, and weigh the buttons of silver. Add to these the estimated
cupel loss, and calculate the result.
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