The detection of small quantities of gold and silver is of
considerable importance, and advantage can be taken of the ease with
which they are separated from potassium cyanide solution by the
electric current for this purpose.
_Silver_.--Silver is obtained as chloride in the course of analysis.
To confirm for the metal electrolytically, this precipitate is
dissolved in potassium cyanide and the resulting solution electrolyzed
with a current of 1-1.5 c.c. A spiral of platinum wire is employed as
the anode, from which the silver may be dissolved by means of nitric
acid, and tested for by hydrochloric acid or by sulphureted hydrogen.
0.0001 grm. of silver in 150 c.c. of solution can be detected thus,
and one hour is sufficient for the deposition.
_Gold_.--Gold is deposited under similar conditions to silver from
cyanide solutions. The deposit, which is rather dark colored, can be
dissolved in aqua regia and confirmed for by the Cassius' purple test.
Here again 0.0001 grm. of metal in 150 c.c. of solution can be
detected without any difficulty.
As gold and silver are both extracted from quartziferous ores by
treatment with potassium cyanide solution according to the
MacArthur-Forrest process of gold extraction (this Journal, 1890,
267), this electrolytic method should prove very useful.
Pages:
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202