As an analysis of the manganese dioxide showed the probable presence
of some manganese in the manganous condition, a sample was treated on
the water-bath for some days with dilute nitric acid while distilled
water was added from time to time to keep the dilution nearly constant.
This was done for the purpose of determining whether the manganous
manganese might not be extracted in the form of manganese nitrate. The
light brown oxide which was used in the previous experiments had been
prepared by adding a dilute solution of manganous sulphate to a hot
solution containing potassium permanganate in excess and dilute nitric
acid. No analysis of the oxide thus prepared was made at the time of
its preparation, but it has been shown by the work of others that the
oxide must have had at that time a composition as regards the relation
of manganese to oxygen, very nearly equivalent to that of MnO₂. During
the course of the experiments previously recorded, a determination of
the ratio of the manganese to the available oxygen in the compound was
made and found to be as
1.03 : 1.00
The substance gave 54.69 percent manganese and 15.44 percent available
oxygen.
A second analysis made some weeks later gave a ratio of manganese to
available oxygen of 1.06: 1.00.--
The substance gave 54.76 percent manganese
15.02 ” available oxygen.
The manganese was determined by the method of Gibbs[8] and the
available oxygen by oxalic acid and potassium permanganate.
[8] Silliman’s Am. J. Science (2) 44.216
It was this oxide which was treated with nitric acid in the manner
described. In the course of this treatment the light brown color
changed to black and the oxide became heavier. The dilute nitric acid
in which the oxide had been digested was found to contain manganous
manganese, but analysis of the black product showed that the oxide had
suffered a still further reduction. The ratio of manganese to available
oxygen was found to have risen from 1.06: 1.00 to 1.157: 1.000. The
analytical data are given below:--
The substance gave { 60.49 percent manganese }
{ 60.46 ” ” }
and
{ 15.23 percent oxygen }
{ 15.19 ” ” }
This ratio would correspond very nearly to a compound having the
composition MnO·6MnO₂ but it is by no means certain that the reducing
action of nitric acid was finished. The action of this oxide on
potassium permanganate was determined under the same conditions as in
the case of the brown oxide as described on page 14. The following
illustration of the proportions used is taken from the first experiment.