, antimony, mercury, lead, and copper.
_Antimony_.--The method employed in the case of antimony is that
adopted in its quantitative estimation by means of electrolysis, a
method which insures a complete separation from those metals with
which it is precipitated in the ordinary course of analysis--arsenic
and tin. This fact is of considerable importance in reference to the
special objects for which these methods have been worked out.
The precipitated sulphide is dissolved in potassium sulphide, and the
resultant solution, after warming with a little hydrogen peroxide to
discolorize any poly-sulphides that may be present, electrolyzed with
a current of 1.5-2 c.c. of electrolytic gas per minute (10.436 c.c. at
0 deg. and 760 mm. = 1 ampere), when the antimony is deposited as metal
upon the negative electrode. One part of antimony (as metal) in
1,500,000 parts of solution may be thus detected, a reaction thirty
times more delicate than the deposition by means of zinc and
potassium. The stain on the cathode, which latter is best used in the
form of a piece of platinum foil about 1 sq. cm. in diameter, is
distinct even with a solution containing 1/28 mgrm. of antimony; and
by carefully evaporating a little ammonium sulphide on the foil, or
by dissolving the stain in hot hydrochloric acid and then passing a
few bubbles of sulphureted hydrogen gas into the solution, the orange
colored sulphide is obtained as a satisfactory confirmatory test.
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