Mercury, which if present would interfere, is
separated because of the insolubility of its sulphide in nitric acid.
Bismuth is precipitated only after the main portion of the copper is
thrown down. It renders the copper obviously unsuitable for weighing. It
darkens, or forms a greyish coating on, the copper; and this darkening
is a delicate test for bismuth. In assaying ores containing about three
and a half per cent. of copper, and known to contain bismuth in
quantities scarcely detectable in ordinary analysis, the metal deposited
was distinctly greyish in colour, and would not be mistaken for pure
copper. Ten grams of this impure copper were collected and analysed,
with the following results:--
Copper 99.46 per cent.
Bismuth 00.30 "
Iron 00.14 "
Arsenic 00.10 "
------
100.00
The quantity of copper got in each assay was 0.175 gram, and
consequently the bismuth averaged 0.00053 gram.
To separate the bismuth in such a case the deposit is dissolved off by
warming it in the original solution. The bismuth is precipitated by the
addition of ammonic carbonate, and the solution, after filtering and
acidifying with nitric acid, is re-electrolysed.
~Determination of Copper in Commercial Copper.~--Take from 1 to 1.5
gram, weigh carefully, and transfer to a beaker; add 20 c.
Pages:
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368