Action of a Black Oxide of Manganese
on Potassium Permanganate.——

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 gave54.76percentmanganese
15.02”available oxygen.

The manganese was determined by the method of Gibbs[8] and the available oxygen by oxalic acid and potassium permanganate.

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 ” ”