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.

That an approximately quantitative result can be obtained under the above conditions was shown in several cases in which deposition of 0.001 grm. of metal was confirmed with considerable accuracy, the spiral or foil being weighed before and after the experiment.

A comparison of the delicacy of these tests with the ordinary qualitative tests for antimony, mercury, lead, and copper by means of sulphureted hydrogen, showed that the two were equally delicate in the case of antimony and of copper, but that in that of mercury and of lead the electrolytic test was at least eight times the more delicate.  These comparisons were made in aqueous solutions.  In testing urine the value of the electrolytic method is still more evident, for here the color of the liquid interferes materially with the reliability of the ordinary qualitative tests when only very small quantities of the metals referred to are present.

Beyond the detection of mineral poisons, qualitative electrolysis can only offer attraction to analysts in special cases, and the data on the subject are to be found in the many electrolytic methods already published.  Beyond testing for gold and silver in this manner, I have not therefore examined the applicability of these methods further.

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.