Here it is treated with
chlorine by passing a current of that gas through it as long as
it causes a precipitate and for some time afterward. It is then
discontinued, the mixture allowed to deposit for a few moments, and
about two-thirds of the supernatant solution decanted; it is mixed with
some more water, and these decantations repeated until they pass away
without reaction, or by filtering it and washing on the filter; it is
then dissolved in hot hydrochloric acid, this nearly neutralized, a
solution of sesquichloride of iron is added, and again treated with an
excess of chlorine. After washing it is transferred to the flasks of
the apparatus mentioned in the first part of this paper, and estimated.
Myself and several others have found this always to be a true MnO_{2},
and not a varying mixture of protosesquioxide and binoxide, and will
thus yield accurate results. This reprecipitation may sometimes be
dispensed with by adding the iron salt before the first precipitation,
but it of course depends upon the other elements present.
From Compounds containing Cobalt, Cobalt and Nickel, Iron and group
III., together or with other elements.
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