The following experiments were made for the purpose of determining the effect of varying quantities of manganese oxide on the time required for the reduction of potassium permanganate.
A. In the presence of nitric acid.
The ratio of manganese to available oxygen in the material used for these experiments was determined and found to be
1.018 : 1.000
The experiments were conducted after the same manner as those previously described.
Different portions of the manganese oxide were weighed out and treated in the flasks used in the previous experiments with the quantities of permanganate which were found by calculation to have the desired molecular ratios to the oxide.
A quantity of N/10 nitric acid equivalent to the potassium of the potassium permanganate was added. The flasks were then immersed in the bath of boiling water and the time required for the disappearance of the permanganate color noted.
The ratios of the oxide to the permanganate and the times required for the reduction of the latter are embodied in the following table.
| Molecular Ratio Oxide to KMnO₄ | 1:1 | 2:1 | 3:1 | 4:1 | 5:1 | 6:1 | 7:1 |
|---|---|---|---|---|---|---|---|
| Time of decolorization in minutes | |||||||
| 1” | 120 | 68 | |||||
| 2” | 110 | 65 | |||||
| 3” | 150 | 65 | |||||
| 4” | 150 | 80 | |||||
| 5” | 120 | 75 | |||||
| 6” | 120 | 75 | |||||
| 7” | 175(?) | 78 | 53 | ||||
| 8” | 160 | 79 | 54 | ||||
| 9” | 145 | 41 | 30 | ||||
| 10” | 120 | 50 | 36 | ||||
| 11” | ? | 47 | 32 | ||||
| 12” | 110 | 37 | 30 | ||||
| 13” | 64 | [10] | 20(?) 20(?) | ||||
| 14” | 72 | 5(?) | 5(?) | ||||
| 15” | 85 | 5(?) | 5(?) |
The results appearing in the table on the same horizontal lines are those of experiments made simultaneously, that is, the flasks in these experiments were immersed at the same time and in the same water-bath. These, that is the results appearing on the same horizontal line, and these only are comparable, since it was found that very slight differences in the temperature of the bath were of great influence on the length of time required for the reduction of the permanganate.