antimony - Sciencemadness.org

186 THE METALLURGY OF ANTIMONY.
The other volumetric methods that may be mentioned are :—
(1) Solution of precipitated Sb in H2S04and titration with KMnO4.
(2) Titration of precipitated Sb with FeCl8 in a boiling HC1
solution.
(3) Titration of precipitated Sb with bichromate after solution in
FeCl3.
(c) Electrolytic,—(a) According to Smith, antimony, when precipitated
from a solution of its chloride, or from that of antimony
potassium oxalate, does not adhere well to the cathode. From a
solution of potassium antimonyl tartrate it is deposited very slowly. A
cold ammonium sulphide solution is good, but its use is not pleasant.
Hence potassium or sodium sulphide is resorted to, but must not
contain iron or alumina. The antimony solution, mixed with 80 c.c.
of sodium sulphide (sp. gr. 1*13-1*15), is diluted with water to
125 c.c, and acted upon at 60°-65° by a current of N.D.100 =
1 ampere and 1-1-1*7 volts. Two hours are required to fully precipitate
the metal. Then treat the metal with water and pure
alcohol. Dry it at 90°. The solution must be absolutely free from
polysulphides. But as the antimony sulphide obtained in the ordinary
course of analysis always contains sulphur, this must be eliminated.
Add 50-70 c.c. of a 25 per cent, solution of sodium sulphite to the
solution after the addition of sodium sulphide in excess; then heat
the liquid until it is completely decolorised, and allow it to cool. It
is best to pass a current of 0*25 ampere. Wash deposit with water,
alcohol, and ether.
(/3) The sulpho-salts of antimony, as proposed by Parrodf and
Mascazzini, Luckow, Classen and Y. Reiss, and Classen and Ludwig,
are the best for obtaining an antimony deposit by electrolysis.
" The determination of antimony by the electrolysis of its sulphosalts
is one of the most convenient and useful of all electrolytic
methods, and is one that is frequency used in actual practice. It
is especially convenient, because the form of solution in which the
antimony is obtained in the usual course of separation from the other
metals can be directly electrolysed.
"A solution of 1 grin, tartar emetic in water is treated with a
solution of sodium sulphide until the precipitate which first forms is
redissolved. The mixture, after dilution to 150 c.c, is electrolysed
at normal temperature with a current of 05 to 1*0 ampere and 1*3
to 1*8 volts. To see whether.all the antimony has been deposited,
a small test portion of the electrolyte is taken and is heated with a
few drops of dilute sulphuric acid, and if antimony is present there
will appear a reddish colour. One may raise the basin to see whether