_Introduction._
The usual laboratory solution of potassium permanganate must be
frequently restandardized. A slight loss in strength may be detected
after standing even a few days and this change becomes more rapid
as the decomposition proceeds. When one looks for the cause of this
increase in the rate of the decomposition of the permanganate, the
attention is naturally directed to the brown manganese oxide which
separates from the solution. A desire to ascertain whether the presence
of this oxide influences the rate of the decomposition suggested the
experiments here described.
The fact that potassium permanganate may react with certain so-called
peroxides with evolution of oxygen, has long been known and it appeared
possible that a similar reaction may take place between manganese
dioxide and potassium permanganate.
Morse and Allen investigated the reaction between lead dioxide and
potassium permanganate and there is embodied in Allen’s dissertation[1]
a statement of the earlier work in this line with references to the
literature on the subject.
[1] Johns Hopkins University 1892
They have shown that in the presence of a quantity of dilute nitric
acid which is equivalent to the potassium in the potassium permanganate
used, lead dioxide reduces the permanganate to manganese dioxide
without itself suffering reduction, while in the presence of an excess
of stronger nitric acid, e.g. normal to eight normal, the lead dioxide
is also reduced.
The following equations represent the reactions referred to:
I, when the nitric acid is equivalent to the potassium in the potassium
permanganate,