This demands an
approximate knowledge of the quantity of copper contained in the ore and
a separation of the bulk of the impurities.
For the titration there is required a standard solution of potassium
cyanide made by dissolving 42 grams of the salt, known to dealers as
Potassium Cyanide (Gold), in water and diluting to one litre: 100 c.c.
of this will be about equivalent to one gram of copper. For poor ores
the solution may conveniently be made half this strength.
The solution of the ore and the separation of the copper as sulphide are
effected in the same ways as have been already described for
electrolysis. Similarly, too, the sulphide is attacked with 15 c.c. of
nitric acid and the assay boiled down to 10 c.c. Add 20 c.c. of water
and warm, filter into a pint flask, wash well with water, and dilute to
about 150 c.c.; add 30 c.c. of dilute ammonia, and cool.
Prepare a standard by dissolving a quantity of electrotype copper
(judged to be about the same as that contained in the assay) in 20 c.c.
of water and 10 c.c. of nitric acid, boil off the nitrous fumes, and
dilute to 150 c.c.: add 30 c.c. of dilute ammonia and cool.
Fill a burette with the standard cyanide solution. The burette with
syphon arrangement, figured on page 52, is used. A number of titrations
can be carried on at the same time provided the quantity of copper
present in each is about the same.
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