In both cases a current of 2-3 c.c. suffices to
effect the deposition in one hour.
Here, again, 0.0001 grm. of metal in 150 c.c. of solution can be
easily detected. With both solutions this amount gives a distinct
discoloration to the platinum spiral, on which the deposition is best
effected. As a confirmatory test the deposited metal is dissolved in
nitric acid and tested with sulphureted hydrogen, or the spiral may be
placed in a test tube and warmed with a crystal of iodine, when the
yellow iodide is formed. This latter reaction is very distinct,
especially in the case of the peroxide.
Of the above two methods, that in which an ammonium oxalate solution
is used is the more delicate, although it cannot be employed
quantitatively, owing to the oxidation of the metal that takes place.
An addition of 1 grm. of ammonium oxalate to the suspected solution is
sufficient.
_Copper_.--0.00005 grm. of copper can be very readily detected by
electrolyzing an acid solution in the usual way. A spiral of platinum
wire is employed as the cathode, and the presence of the metal
confirmed for by dissolving it in a little nitric acid, diluting with
water and adding potassium ferrocyanide.
To detect these metals in cases of poisoning, the organic matter with
which they are associated must first be destroyed in the usual way by
means of hydrochloric acid and potassium chlorate, and the
precipitates obtained in the ordinary course of analysis, then
subjected, at suitable stages, to electrolysis.
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