c. of dilute hydrochloric acid, should not
decolorise any of the permanganate of potassium solution; this shows the
absence of ferrous salts. And 20 c.c. of the same solution, boiled with
20 c.c. of the ferrous sulphate solution, should not decrease the
quantity of "permanganate" required for the titration of the ferrous
sulphate added. In a series of experiments on the various methods of
reduction, the following results were got. The modes of working were
those already described.
(1) _With Stannous Chloride._--Twenty c.c. of the ferric chloride
solution required, after reduction with stannous chloride, 20 c.c. of
"permanganate." Fifty c.c. of a solution of ferrous chloride, which
required on titration 49.8 c.c. of "permanganate," required for
re-titration (after subsequent reduction with stannous chloride) 50 c.c.
of the permanganate solution.
(2) _With Sulphuretted Hydrogen._--Two experiments with this gas, using
in each 20 c.c. of the ferric chloride solution, and 10 c.c. of
hydrochloric acid, required (after reduction) 20.2 c.c. and 20.1 c.c. of
"permanganate." Repeating the experiments by passing the gas through a
nearly boiling solution, but in other respects working in the same way,
21.3 c.c. and 21.6 c.c. of the permanganate solution were required. The
sulphur was not filtered off in any of these.
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