Action of Potassium Permanganateupon a Manganese Oxide Derivedfrom Manganese Dioxide bySpontaneous Decomposition.
The oxide used in these experiments was one which had been prepared in the manner heretofore described by adding manganese sulphate to an excess of potassium permanganate. Soon after its preparation the ratio of manganese to available oxygen in it was found to be
1.018 : 1.000
At the time when it was used in these experiments, the ratio of manganese to available oxygen was found to be
1.198 : 1.000
Corresponding very nearly to the ratio of manganese to available oxygen in MnO·5MnO₂.
Experiment I.
230 m.g. of the oxide was treated with the quantity of permanganate calculated to be necessary for its oxidation to manganese dioxide. The mixture was kept at a temperature of 22°C. until the color of the permanganate disappeared. This required about ten hours.
An analysis of the oxide then gave a ratio of manganese to available oxygen
1.027 : 1.000
Experiment II
A repetition of experiment I. An analysis of the oxide after decolorization of the permanganate gave a ratio of manganese to available oxygen of
1.022 : 1.000
Experiment III
The conditions are the same as in the preceding experiments except that twice the amount of permanganate calculated for the conversion of the oxide into manganese dioxide was added.
An analysis of the residue after decolorization gave a ratio of manganese to available oxygen of
0.994 : 1.000
Experiment IV
A repetition of experiment III. An analysis of the residue gave a ratioof manganese to available oxygen of
0.995 : 1.000
Experiment V
A repetition of experiments III and IV. The ratio of manganese to available oxygen in the residue was
0.995 : 1.000.
The foregoing results indicate (experiments III, IV, and V) that the oxygen lost spontaneously by manganese dioxide prepared in the wet way, is fully recovered when the reduced oxide is treated with excess of potassium permanganate.
The ratio of the manganese to the available oxygen was determined in the following manner. The contents of the flask were filtered through asbestos and the flask and the precipitate washed with cold water. Thecontents of the filter were then returned to the flask and treated with an excess of a standard solution of oxalic acid and dilute sulphuric acid. After reduction the excess of the oxalic acid was determined by a standard solution of potassium permanganate.
The solution was then filtered, well washed and the manganese in the filtrate precipitated by the method of Gibbs. From the total amount of manganese found, there was deducted the quantity which was introduced in determining the excess of oxalic acid by potassium permanganate.