The method of dissolving varies with the nature of the ore. With 5 grams
of pyrites, a single evaporation with 20 c.c. of nitric acid will give a
residue completely soluble in 30 c.c. of hydrochloric acid. If the ore
carries oxide of iron or similar bodies, these are first dissolved up by
boiling with 20 c.c. of hydrochloric acid, and the residue attacked by
an addition of 5 c.c. of nitric. When silicates decomposable by acid are
present, the solution is evaporated to dryness to render the silica
insoluble; the residue extracted with 30 c.c. of hydrochloric acid, and
diluted with water to 150 c.c. It is advisable to have the copper in
solution as chloride. To separate the copper, heat the solution nearly
to boiling (best in a pint flask), and pass a rapid current of
sulphuretted hydrogen for four or five minutes until the precipitate
settles readily and the liquid smells of the gas. When iron is present
it will be reduced to the ferrous state before the copper sulphide
begins to separate. The copper appears as a brown coloration or black
precipitate according to the quantity present. Filter through a coarse
filter, wash with hot water containing sulphuretted hydrogen, if
necessary. Wash the precipitate back into the flask, boil with 10 c.c.
of nitric acid, add soda till alkaline, and pass sulphuretted hydrogen
again.
Pages:
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351