480 gram of
copper.
In this series the difference of half a c.c. means about 0.15 per cent.
on the ore; with a little practice it is easy to estimate whether the
whole or half of the last addition should be counted.
To get satisfactory results, the manner of finishing once adopted must
be adhered to.
The following experiments show the effect of variation in the conditions
of the assay:--Use _a solution of copper nitrate_, made by dissolving 10
grams of copper in 50 c.c. of water and 35 c.c. of nitric acid, and
diluting to a litre. 100 c.c. = 1 gram of copper.
~Effect of Varying Temperature.~--In these experiments 20 c.c. of copper
nitrate were used, with 10 c.c. of nitric acid, 30 c.c. of dilute
ammonia, and water to 200 c.c. The results were--
Temperature 15° 30° 70° 100°
Cyanide required 21.5 c.c. 20.8 c.c. 19.7 c.c. 18.8 c.c.
The temperature is that of the solution _before_ titrating. These show
the importance of always cooling before titrating, and of titrating the
assay and standard at the same temperature.
~Effect of Varying Bulk.~--The quantities of copper, acid, and ammonia
were the same as in the last-mentioned experiments. The results were:--
Bulk 100.0 c.c. 200.0 c.c. 300.0 c.c. 400.0 c.c.
Cyanide required 23.3 " 21.
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