Action of a Black Oxide of Manganese on Potassium Permanganate.---- As an analysis of the manganese dioxide showed the probable presence of some manganese in the manganous condition, a sample was treated on the water-bath for some days with dilute nitric acid while distilled water was added from time to time to keep the dilution nearly constant. This was done for the purpose of determining whether the manganous manganese might not be extracted in the form of manganese nitrate. The light brown oxide which was used in the previous experiments had been prepared by adding a dilute solution of manganous sulphate to a hot solution containing potassium permanganate in excess and dilute nitric acid. No analysis of the oxide thus prepared was made at the time of its preparation, but it has been shown by the work of others that the oxide must have had at that time a composition as regards the relation of manganese to oxygen, very nearly equivalent to that of MnO₂. During the course of the experiments previously recorded, a determination of the ratio of the manganese to the available oxygen in the compound was made and found to be as 1.03 : 1.00 The substance gave 54.69 percent manganese and 15.44 percent available oxygen. A second analysis made some weeks later gave a ratio of manganese to available oxygen of 1.06: 1.00.-- The substance gave 54.76 percent manganese 15.02 ” available oxygen. The manganese was determined by the method of Gibbs[8] and the available oxygen by oxalic acid and potassium permanganate. [8] Silliman’s Am. J. Science (2) 44.216 It was this oxide which was treated with nitric acid in the manner described. In the course of this treatment the light brown color changed to black and the oxide became heavier. The dilute nitric acid in which the oxide had been digested was found to contain manganous manganese, but analysis of the black product showed that the oxide had suffered a still further reduction. The ratio of manganese to available oxygen was found to have risen from 1.06: 1.00 to 1.157: 1.000. The analytical data are given below:-- The substance gave { 60.49 percent manganese } { 60.46 ” ” } and { 15.23 percent oxygen } { 15.19 ” ” } This ratio would correspond very nearly to a compound having the composition MnO·6MnO₂ but it is by no means certain that the reducing action of nitric acid was finished. The action of this oxide on potassium permanganate was determined under the same conditions as in the case of the brown oxide as described on page 14. The following illustration of the proportions used is taken from the first experiment. Experiment No. I