~Determination of the acidity of an ore.~--Most ores have the power of
destroying more or less of the alkalinity of a cyanide solution and in a
proportionate degree of damaging its efficiency. An assay is needed to
determine how much lime or soda must be added for each ton of ore in
order to counteract this. Whether this acidity should be reported in
terms of the lime or of the soda required to neutralise it will depend
on which of these reagents is to be used in the actual practice. Again,
if the ore is washed with water before treating with cyanide on the
large scale, then the assay should be made of the acidity of the ore
after a similar washing.
The _standard solutions of acid and alkali_ used for this determination
may be one-fifth normal. 200 c.c. of the normal solution should be
diluted to 1 litre in each case, 1 c.c. of the resulting solutions would
be equivalent to 8 milligrams of soda (NaHO) or 5.6 milligrams of lime,
CaO. It must be remembered this refers to the pure bases in each case.
Suppose it is desired to report as so many lbs. of lime to the short ton
(2000 lbs.) of ore. Since 1 c.c. of the standard solution is equivalent
to 5.6 milligrams of lime, if we take 2000 times this weight of ore
(_i.e._ 11,200 milligrams or 11.2 grams) for the assay, each c.c. of
standard solution will be equivalent to 1 lb.
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