An illustration of the proportions in which the different substances were brought together in each of the three flasks is to be found in the following statement of the quantities used in the first experiment.
The variations from these proportions occurring in subsequent experiments are noted in the table giving the summary of the results. Usually about 150 m.g. of manganese dioxide were used and the solutions in the three flasks were brought to the same volume by addition of distilled water.
Experiment No. I
| Flask No. I | Manganese dioxide 150 m.g. |
| N/10 nitric acid 14.28 c.c. | |
| [= Mn. in KMnO₄ in No. II or No. III] | |
| Water, 27.12 c.c. | |
| [Total solution = 41.40 c.c.] | |
| Flask No. II | Potassium permanganate, 20 c.c. = 112.48 m.g. KMnO₄. |
| N/10 nitric acid 7.14 c.c. [= K in KMnO₄] | |
| Water, 14.26 c.c. | |
| [Total solution = 41.40 c.c.] | |
| Flask No. III | Potassium permanganate, 20 c.c. = 112.48 m.g. KMnO₄. |
| N/10 nitric acid 21.40 c.c. [= K + Mn in KMnO₄] | |
| Manganese dioxide 150 m.g. | |
The nitric acid in No. I is calculated to be the same as that remaining free after the potassium of the permanganate in No. III has been neutralized. It will be clear that the quantities of free nitric acid are the same in flask No. I and in flask No. III provided the potassium of the permanganate is appropriated by the nitric acid. Moreover each flask contains the same quantity of manganese dioxide and the volume of the liquid is the same in both.
On the other hand flask No. III contains permanganic acid. This arrangement was selected in order to determine how far the evolution of oxygen was influenced by the action of nitric acid on the manganese dioxide or by the spontaneous decomposition of permanganic acid. It was thought that if more oxygen should be obtained from flask No. III containing a mixture of permanganate, manganese dioxide and nitric acid, than from mixtures No. I and No. II, the larger volume must be due to the reduction of the permanganate by the manganese oxide.
The three flasks after having been filled as described were attached to the apparatus and then all submerged to the same depth in the boiling water of a single glass water-bath. The stop-cocks of the azotometers were then opened and the mercury allowed to fall to within about fifty millimetres of its level in the reservoirs. This difference in level was maintained as nearly as practicable by lowering the reservoirs commenserably with the increase in gas volume. No action could be observed in flasks No. I and No. II during the whole course of the experiment. The contents of flask No. III however gave off bubbles of oxygen immediately, the mercury fell in the azotometer and the dark purple of the permanganate solution in flask No. III became rapidly lighter. Within about five minutes it was reduced to a delicate pink but this tint persisted for about ten minutes when it also disappeared. Immediately after the disappearance of the permanganate color the solution was filled with a brown oxide which remained for about thirty five minutes when it subsided leaving the supernatant liquid clear. Notwithstanding the fact that the color of the permanganate had entirely disappeared and the suspended oxide had subsided within an hour after beginning the experiment, the flasks in the earlier experiments were allowed to remain for two hours longer. By admitting distilled water through the tube D [[see figure]] the gas was then forced over into the azotometer. Finally, the oxygen was determined in the manner previously described.
The following illustration from the first experiment may serve to show the method of calculating the results.
| I | II | III | ||||
|---|---|---|---|---|---|---|
| Total air and oxygen | = | 42.60 c.c. | 52.40 c.c. | 60.60 c.c. | ||
| Nitrogen after absorption of oxygen | = | 34.00 c.c. | 40.90 c.c. | 37.80 c.c. | ||
| Oxygen | = | 8.60 c.c. | 11.50 c.c. | 22.80 c.c. | ||
| Air = | 79.8% nitrogen | |||||
| 20.2% oxygen | ||||||
| Oxygen of air | × | 20.2 | = | 8.60 c.c. | 10.353 c.c. | 9.57 c.c. |
| Nitrogen found | 79.8 | |||||
| Oxygen obtained | = | 0.0 | 1.147 c.c. | 13.23 c.c. | ||
| Temperature | = | 21°C. | ||||
| Barometer | = | 737 mm. | ||||
| Oxygen obtained at Normal | = | 0 | 1.033 c.c. | 11.913 c.c. | ||
| The 20 c.c. KMnO₄ | = | 112.48 m.g. | ||||
| 1 atom of oxygen | = | 7.967 c.c. | ||||
| Atoms oxygen found | I | II | III | |||
| from the molecule KMnO₄ | = | 0 | 0.129 | 1.496 | ||
As at the end of the preceding calculation the results are expressed in the table following in terms of oxygen atoms obtained from each molecule of potassium permanganate [KMnO₄] reduced. Thus an equivalent of one atom of oxygen from one molecule of potassium permanganate would equal 15.96/157.67 of the weight of potassium permanganate used in the experiment. This weight divided by the weight of one cubic centimetre of oxygen gives the number of cubic centimetres of oxygen at normal, equivalent to one atom of oxygen from one molecule of potassium permanganate. The results obtained are tabulated as follows: