This is regulated in weighing up the
ore. The flasks must of course be marked, and should be arranged in
series on a bench in front of a good light and at such a height that the
liquid can be looked through without stooping. Supposing about 50 c.c.
of cyanide will be required, 30 c.c. should be run into each, and each
addition be recorded as soon as made; then run 15 c.c. into each. The
solutions will now probably show marked differences of tint: add 1 c.c.
of cyanide to the lighter ones and more to the darker, so as to bring
the colours to about the same depth of tint. They should all be of
nearly equal tint just before finishing. At the end add half a c.c. at a
time until the colours are completely discharged. A piece of damp filter
paper held between the light and the flask assists in judging the
colour when nearly finished. Overdone assays show a straw yellow colour
which deepens on standing.
The following will illustrate the notes recorded of five such assays and
one standard:--
(1) 30 c.c. 15 c.c. 5 c.c. 2 c.c. 1 c.c. 1/2 c.c. -- c.c. = 53-1/2 c.c.
(2) 30 " 15 " 1 " 1 " 1 " 1/2 " -- " = 48-1/2 "
(3) 30 " 15 " 3 " 1 " 1 " 1/2 " -- " = 50-1/2 "
(4) 30 " 15 " 5 " 2 " 1 " 1/2 " 1/2 " = 54 "
(5) 30 " 15 " 2 " 1 " 1 " 1/2 " -- " = 49-1/2 "
(6) 30 " 15 " 2 " 1 " 1 " 1/2 " 1/2 " = 50 standard
Three grams of ore were taken, and the standard contained 0.
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