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.