antimony - Sciencemadness.org

188 THE METALLURGY OF ANTIMONY.
rather less than an equal bulk of water, and boiled until free from
chlorine. In practice, half an hour is a sufficient length of time ; the
most practical and most delicate test of the absence of free chlorine
in the cold solutions is the sense of smell. The assays should not
be boiled to a smaller bulk than 150 c.c, as the chloride of antimony
is volatile. Allow the assay to cool; when quite cold, fill the" flask
with CO2 from a Kipp apparatus charged with marble and HC1, add
20 c.c. of a fresh 20 per cent, solution of KI, and titrate as rapidly as
possible with stannous chloride. This is made by dissolving 10 grms.
of tin, or 20 grms. SnCl2 2 aq., in 300 c.c. HC1 and diluting to 1 litre.
It should be kept under CO2, and must be standardised, every time it
is used, against a standard solution of bichromate made by dissolving
exactly 16 grms. of fine K2Cr.2O7 in 1 litre of distilled water. 100 c.c.
bichromate « 2 grms. Sb, and 100 c.c. SnCl2 = about 1 grm. Sb. The
assays, if overdone, are brought back with the standard bichromate
(rapidly), but should only require a few drops at most, otherwise the
accuracy of the assay is impaired.
The assays •have a great tendency to absorb oxygen after titration ;
hence the necessity for a CO2 atmosphere and rapid titration, especially
in presence of As and Cu. Further, the reaction in the case of As is
not instantaneous, and only proceeds to completion at the same rate
as the iodine is liberated by SnCl2—being to some extent reversible.
Acid solutions of AsCl3, Cu2Cl2, FeCl2, and of KI readily absorb
oxygen from the air, while SbCl3 is scarcely affected. The bichromate
remains quite constant, and it may be standardised against pure iron
as a check on the weighing up. In standardising the stannous
chloride, pour a little KI solution and starch paste into an 8-oz.
flask, fill the flask with CO2, and run in rapidly 20 c.c. SnCl2 from
the burette. Then titrate rapidly with K2Cr207.
As=Sb = Cu2 = Fe2=O.
1 per cent. As = l 6 per cent. Sb. 1 per cent. Cu=0*945 per cent. Sb.
1 per cent Fe = l*03 per cent. Sb.
2. Analysis of Antimony Ore (the following is an abstract
from Thos. Brown, Jr.'s, article on the determination of antimony
in ores, in the Jowrn. of Am. Chem. Soc, Sept. 1899).—Impurities
such as silica, iron, and lime would not materially interfere with
the schemes of analysis used. Lead, mercury, copper, tin, and
arsenic, when found in quantities larger than traces, should be
separated from the antimony when its determination is by the
method of sulphides; also tin and arsenic when the oxide method is
used. A preliminary qualitative test should always be made for the