It is clear that the rate of the reduction of the permanganate is greatly increased by increasing the quantity of the manganese oxide.
After reduction of the permanganate, the contents of the flasks were in every case filtered and the filtrate tested by Crum’s reaction for the presence of manganese. No manganese was found. The absence of manganese in the filtrate shows that the reduction of the permanganate was not due to the formation of manganese nitrate, though it will be clear from the results of subsequent experiments that the presence of nitric acid exerts an influence on the rate of the reduction.
B. In neutral solution.
The condition were the same as under A, except that the nitric acid was omitted. Those flasks containing potassium permanganate and one, two and seven molecular equivalents respectively of the manganese oxide were immersed in the water-bath as before.
| No. I | containing one molecule of oxide and | 57 hours |
| one molecule KMnO₄ was reduced in | ||
| No. II | containing two molecules of oxide and | 35 hours |
| one molecule KMnO₄ was reduced in | ||
| No. III | containing seven molecules of oxide | 2¾ hours |
| and one molecule KMnO₄ was reduced in | ||
C. In alkaline solution.
The conditions were the same as under B, except that five molecules of potassium hydroxide were added for each molecule of the permanganate.
| No. I | containing one molecules of oxide for | 91¾ hours. |
| each molecule KMnO₄ was reduced in | ||
| No. II | containing two molecules of oxide | 55(?) hours. |
| for each molecule KMnO₄ was reduced in | ||
| No. III | containing seven molecules of oxide for | 10 hours. |
| each molecule KMnO₄ was reduced in | ||
It appears that potassium permanganate is less easily reduced by manganese oxide in neutral than in acid solutions and in alkaline that in neutral solutions.