~Determination of Copper in a Manganese Ore.~--Treat 3 grams of the ore
with 20 c.c. of hydrochloric acid, and evaporate to dryness. Take up
with 10 c.c. of hydrochloric acid; dilute to about 200 c.c., and pass
sulphuretted hydrogen until the solution smells of the gas; filter,
burn, take up with 5 c.c. of dilute nitric acid, add 10 c.c. of dilute
ammonia, and filter into the Nessler tube, and make up with the washings
to 50 c.c. Into the "standard" tube put 5 c.c. of dilute nitric acid and
10 c.c. of dilute ammonia. Make up to nearly 50 c.c. with water, and run
in the standard copper until the colours are equal. In a determination 4
c.c. (= 2.0 milligrams of copper) were required; this in 3 grams of ore
= 0.07 per cent.
~Determination of Copper in "Black Tin."~--Weigh up 3 grams of the dried
ore, boil with 10 c.c. of hydrochloric acid, and afterwards add 1 c.c.
of nitric; boil off nitrous fumes, evaporate to about 5 c.c., dilute to
50 c.c., add 20 c.c. of dilute ammonia; stir, and filter. If much iron
is present, dissolve the precipitate of ferric hydrate in acid, and
reprecipitate with ammonia. Mix the two filtrates, and dilute to 100
c.c. Take 50 c.c. for the test. A sample of 3 grams of an ore treated in
this way required 5.2 c.c. of standard copper to produce equality of
tint. This gives 0.
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