Or wrap each button of silver in
20 grams of assay lead, and re-cupel side by side with two fresh lots of
20 grams each of the alloy. Calculate the loss incurred, and add on to
the weight of the two fresh buttons got.
~Determination of Silver in Bullion.~--The remarks made under the last
heading as to the importance of correct sampling apply with equal force
here. Make a preliminary assay by cupelling 0.1 gram of the alloy with 1
gram of assay lead; calculate the percentage composition. Refer to the
table on page 105 to find what weight of lead is required for cupelling
1 gram of alloy.
Weigh out four lots of 1 gram each, and wrap them in the required
quantity of lead. Make two check pieces by weighing up two lots of fine
silver equal to that which you believe to be present in the assay
pieces; add copper to make up the weight to 1 gram, and wrap in the same
quantity of lead as was used for the assays.
[Illustration: FIG. 43.]
Prepare six cupels and charge them in the annexed order (fig. 43), and
cupel. Guard against spirting. Clean and weigh the buttons of silver.
Add the mean loss on the two check pieces to the mean weight of the four
assay pieces; this multiplied by 1000 will give the degree of fineness.
~Determination of Silver in Copper.~--The silver is best separated in
the wet way before cupelling, but if the proportion is not too small, it
can be found by cupellation.
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