24 = 405.07 "
This gives 405 ozs. 1 dwt. 10 grains to the ton.
The calculation becomes more complicated when, as is frequently the
case, the ore contains metallic particles. These show themselves by
refusing to pass through the sieve when the ore is powdered. When they
are present, a large portion, or if feasible the whole, of the sample is
powdered and sifted. The weights of the sifted portion and of the
"metallics," or prills, are taken; the sum of these weights gives that
of the whole of the sample taken. It is very important that nothing be
lost during the operation of powdering.
Each portion has to be assayed separately. It is usual to assay a
portion of the sifted sample, say, 20 or 50 grams, and to add to the
produce of this its share of the "metallics." This way of calculating,
which is more convenient than correct, is illustrated by the following
example:--
Weight of whole sample 400 grams
Made up of sifted portions 399 "
" "Metallics" 1 "
---
400 "
Twenty grams of the sifted portion, when assayed, gave 0.1050 gram of
silver. The whole of the "metallics" scorified and cupelled gave 0.842
gram of silver. Since the 20 grams assayed was 1-20th of the whole,
1-20th part of the 0.
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