A N T I M O N Y : ITS HISTORY, CHEMISTRY, MINERALOGY ...

THE ANALYSIS OF ANTIMONY COMPOUNDS. 187
any electrolysis is still proceeding on the newly attacked part of the
electrode; but this is not satisfactory. Generally at the cathode
the antimony deposit is bright, metallic, and silver-gray in colour, and
the anode is covered with sulphur. The sulphide solution must not
contain any polysulphides. They are, however, produced in the
electrolyte during the course of the electrolysis; and, as soon as they
are discovered, hydrogen peroxide must be added, and also a fresh
amount of sodium monosulphide. If the current used is allowed to
continue for too long a time, the edges of the deposit may be dissolved;
and this redissolved antimony cannot be separated from the electrolyte.
Hence it is preferable to carry out the electrolysis with hot solutions
and strong currents in a short time. The deposit of antimony on
the platinum electrode can be removed by means of hot nitric acid,
or be converted into the white oxide of antimony, which is redissolved
by adding tartaric acid and rinsing out with hot water." *
C. Special Methods.
1. For Alloys of Tin, Lead, Antimony, and Cofper containing
little Arsenic, such as type-metal, solder, anti-friction metals, etc.f
SbCl5 in HC1 solution oxidises KI. The liberated iodine may be
titrated with stannous chloride—not with hypo.
In this method the presence of tin (as SnCl4) and lead has no effect
wkatever on the titration; indeed, the titration is done with SnCl2.
Coppej:, arsenic, and iron, when present in solution in their highest
state of oxidation, are reckoned as antimony, and should be estimated
and allowed for, this being preferable to separating the Sb from them.
Fe is rarely present, but in the case of alloys with more than 1 per
cent. As, it is advisable to dissolve in aqua regia and to separate the
Sb and As as sulphides, as it appears that in some cases, when an
alloy rich in arsenic and tin is boiled with HC1, there is a considerable
evolution of H3As. This matter is under investigation. Arsenic,
however, is rarely present in the above alloys in quantities greater
than 1 per cent. 1-3 grms. of fine filings are weighed into a 16-oz.
flask and boiled gently with 150 c.c. HC1 until action ceases and
most of the Pb and Sn is dissolved. To complete the solution, add
cautiously a cold saturated solution of KC1OS, which also peroxidises
the metals. After solution is complete, add a little KCIO3, and make
sure that excess of chlorine is present. The solution is diluted with
* Taken from Neumann's work.
f Taken from Tlie Assay of Tin and Antimonyt by L. Parry, Mining Journal
Office, London, 1900.