The conclusions to be drawn from the foregoing results are (1) that dilute solutions of potassium permanganate are more stable both in diffused light and in darkness than the more concentrated ones, and (2) that the presence of manganese oxides hasten to an enormous degree the reduction of potassium permanganate even at summer temperatures. It will also be observed that this reducing action of the manganese oxide is greater in the stronger than in the more dilute solutions. It should be remarked that the summer of 1892 in which these experiments were made, was one of unusual heat. Action of Potassium Permanganate upon a Manganese Oxide Derived from Manganese Dioxide by Spontaneous Decomposition. The oxide used in these experiments was one which had been prepared in the manner heretofore described by adding manganese sulphate to an excess of potassium permanganate. Soon after its preparation the ratio of manganese to available oxygen in it was found to be 1.018 : 1.000 At the time when it was used in these experiments, the ratio of manganese to available oxygen was found to be 1.198 : 1.000 Corresponding very nearly to the ratio of manganese to available oxygen in MnO·5MnO₂. Experiment I. 230 m.g. of the oxide was treated with the quantity of permanganate calculated to be necessary for its oxidation to manganese dioxide. The mixture was kept at a temperature of 22°C. until the color of the permanganate disappeared. This required about ten hours. An analysis of the oxide then gave a ratio of manganese to available oxygen 1.027 : 1.000 Experiment II A repetition of experiment I. An analysis of the oxide after decolorization of the permanganate gave a ratio of manganese to available oxygen of 1.022 : 1.000 Experiment III The conditions are the same as in the preceding experiments except that twice the amount of permanganate calculated for the conversion of the oxide into manganese dioxide was added. An analysis of the residue after decolorization gave a ratio of manganese to available oxygen of 0.994 : 1.000 Experiment IV A repetition of experiment III. An analysis of the residue gave a ratio of manganese to available oxygen of 0.995 : 1.000 Experiment V 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.