If the residual gold is broken up,
move the crucible so as to bring the particles together, so that they
may cohere. Wash three or four times with distilled water, about half
filling the crucible each time and decanting off against the finger. Dry
the crucible in a warm place; and when dry, but whilst still black, take
the gold up on a small piece of pure lead. Half a grain of lead is
sufficient, and it is best to hold it on the point of a blunt penknife,
and press it on the gold in the crucible. The latter generally adheres.
Transfer to a small smooth cupel and place in the muffle. When the
cupellation has finished, the button of gold is measured as already
described.
PRACTICAL NOTES ON THE IODIDE PROCESS OF COPPER ASSAYING.
For the following remarks and experiments we are indebted to Mr. J.W.
Westmoreland, who has had considerable experience with the process.
Having dissolved the ore he converts the metals into sulphates by
evaporating with sulphuric acid. The copper is then separated as
subsulphide by means of hyposulphite of soda, and the precipitate is
washed, dried, and calcined. The resulting oxide of copper is then
dissolved in nitric acid; and to the concentrated solution, a saturated
solution of carbonate of soda is added in sufficient quantity to throw
down a considerable proportion of the copper.
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