0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c.
"Hypo" required 1.0 " 10.0 " 20.0 " 50.0 " 100.0 "
showing the results to be exactly proportional.[58]
~Determination of Copper in Copper Pyrites.~--Take 2 grams of the dried
and powdered ore and treat in a porcelain dish with 20 c.c. of nitric
acid, and evaporate to dryness. Take up with 30 c.c. of hydrochloric
acid, dilute, and transfer to a pint flask; make up with water to 200
c.c., warm, and pass sulphuretted hydrogen to excess. Filter, and wash
the precipitate with water acidified with sulphuric acid. Wash the
precipitate back into the flask, and dissolve with 15 c.c. of nitric
acid. Evaporate almost to dryness; add 20 c.c. of water, and boil till
free from nitrous fumes; filter off the sulphur and gangue; neutralise
with soda, avoiding excess; add 1 or 2 c.c. of acetic acid, and shake
till clear. Add 5 grams of potassium iodide, dilute to 100 c.c., and
titrate. The following is an example:--
0.5 gram of copper required 50.5 c.c. "hypo."
The assay required 55.6 " "
which is equal to 27.5 per cent. of copper.
COLORIMETRIC PROCESS.
This is based on the blue coloration of ammoniacal copper solutions. The
quantity of copper in 100 c.c. of the assay solution should not be more
than 15 milligrams, or less than half a milligram.
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