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. The contents 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.
Summary of Conclusions—
I
Potassium permanganate in weakly acid, in neutral, and in alkaline solutions, is reduced by manganese dioxide which has been prepared in the wet way, with evolution of one and one half atoms of oxygen for each molecule of the permanganate. In other words, the permanganate is reduced to manganese dioxide.
II