A large excess of bicarbonate ought to be avoided, because in a solution
of pure protochloride of manganese it renders the liquid milky and
turbid; the addition of more water, however, makes it clear. The
solution of bicarbonate must be free from organic substances which may
tend to remove the color of the chameleon solution. To ascertain this,
the latter is added to the former drop by drop so long as the color is
removed.
If it be desired to estimate the silica in the same test, the iron, as
when it is analyzed for silica, may be also dissolved in sulphuric acid,
and afterward oxidized with nitric acid, after which the solution is
boiled to near dryness, so that the organic substances are completely
destroyed. In order afterward, to drive off the nitric acid and get the
manganese with certainty reduced to protoxide, the solution is boiled
with a little hydrochloric acid. In this way the solution goes on
rapidly and conveniently, but the titration takes longer time than when
the iron is dissolved in hydrochloric acid, because the iron precipitate
is more voluminous, and, in consequence, longer in being deposited. To
diminish this inconvenience the solution ought to be made larger.
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