As the solutions thus
obtained will be still contaminated by some organic matter, it is
necessary to pass the current for a longer time than indicated above.
On the other hand, _urine_ can be tested directly for these poisons.
The presence of mercury or of copper may be detected by acidifying the
urine with 2-3 c.c. of nitric acid (conc.), and electrolyzing as
described. 0.0001 grm. of metal in 30 c.c. of urine can be detected
thus, or 1 part in 300,000 of urine.
Lead does not separate well as peroxide from urine, but if ammonium
oxalate be added, and the lead deposited as metal, the reaction is
quite as delicate as in aqueous solution, and 0.0001 grm. of lead can
be thus detected.
With antimony it is advisable to precipitate it first as sulphide, but
it can be detected directly, though not so satisfactorily, by
acidifying the urine with 2-3 c.c. of sulphuric acid (dil.), and
electrolyzing with a current of 1-5 to 2 c.c. In this case also it is
precipitated as metal upon the cathode (cp. Chittenden, Proceedings
Connecticut Acad. Science, Vol. 8).
In the presence of urine it is advisable to continue the passage of
the current for about twice the time required in the case of aqueous
solutions.
Pages:
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200