Thus Mr. Lowe found
.073 per cent. of silver and .00033 per cent. of gold in such a
material. The lead volatilised from a gold bullion assay would need to
be ten times as rich as this to account for a loss of gold equal to the
hundredth part of a milligram. Dr. Rose, in the paper already quoted,
believes that on a .5 gram charge of standard bullion the loss from
volatilisation is not less than .025 nor more than .05 milligram of
gold.
By way of conclusion it may be said that the cupellation loss of gold is
about .07 per cent., and that it is largely met or even over corrected
by a compensating error due to silver retained in the gold after
parting.
~Inquartation.~--The method of separating the gold from the silver in
gold-silver alloys by boiling with nitric acid does not act equally well
in all cases. An alloy half silver half gold, rolled to thin sheet and
boiled for half an hour with nitric acid, may still retain more than
two-thirds of its silver. An alloy of 1 part gold and 1.7 parts of
silver gives up practically the whole of its silver under similar
treatment. The gold is left in a coherent, though easily broken, sheet
retaining the shape of the original alloy. The gold thus left is quite
spongy and porous, so that the acid can penetrate into its innermost
portions. But if the silver is in large excess in the alloy, the
removal of the silver is less complete, and the residual gold, instead
of holding together in a form easy to manipulate, falls to a powder
which requires care and time in its treatment.
Pages:
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280