Part 1

Dissertation presented for the degree of Doctor of Philosophy to the Board of University Studies of the Johns Hopkins University

by Arthur John Hopkins. 1893.

Acknowledgment----

The work recorded in this paper is the result of a suggestion given by Professor H. N. Morse. It has received his careful attention throughout its course. For his instruction and exact criticism, I wish to offer my acknowledgment and thanks. I wish also to express to Professor Ira Remson my appreciation of his interest and instruction and to offer to Dr. J. S. Ames my thanks for his instruction in Physics----

Table of Contents.

Page.

I Introduction 1

II Description of Apparatus 3

III Action of Manganese Dioxide on Potassium Permanganate in acid solution 9

IV Action of a Black Oxide of Manganese on Potassium Permanganate 24

V The Amount of Nitric Acid Neutralized 31

VI The Stability of Manganese Dioxide 34

VII The Effect of Varying Quantities of Manganese Oxide and Potassium Permanganate 39

VIII The Reduction of Neutral Potassium Permanganate by Manganese Oxide at Ordinary Temperature 45

IX Action of Potassium Permanganate upon a Manganese Oxide Obtained from Manganese Dioxide by Spontaneous Decomposition 50

Conclusion

Introduction.

The usual laboratory solution of potassium permanganate must be frequently restandardized. A slight loss in strength may be detected after standing even a few days and this change becomes more rapid as the decomposition proceeds. When one looks for the cause of this increase in the rate of the decomposition of the permanganate, the attention is naturally directed to the brown manganese oxide which separates from the solution. A desire to ascertain whether the presence of this oxide influences the rate of the decomposition suggested the experiments here described.

The fact that potassium permanganate may react with certain so-called peroxides with evolution of oxygen, has long been known and it appeared possible that a similar reaction may take place between manganese dioxide and potassium permanganate.

Morse and Allen investigated the reaction between lead dioxide and potassium permanganate and there is embodied in Allen’s dissertation a statement of the earlier work in this line with references to the literature on the subject.

Johns Hopkins University 1892

They have shown that in the presence of a quantity of dilute nitric acid which is equivalent to the potassium in the potassium permanganate used, lead dioxide reduces the permanganate to manganese dioxide without itself suffering reduction, while in the presence of an excess of stronger nitric acid, e.g. normal to eight normal, the lead dioxide is also reduced.

The following equations represent the reactions referred to:

I, when the nitric acid is equivalent to the potassium in the potassium permanganate,

2 KMnO₄ + 3 PbO₂ = K₂O + 3 PbO₂ + 2 MnO₂ + 1½ O₂.

II, when the nitric acid is in excess,

2 KMnO₄ + 3 PbO₂ = K₂O + 3 PbO + 2 MnO₂ + 3 O₂.

The reducing action of manganese dioxide upon potassium permanganate was suspected from the observed increase in the rapidity of the decomposition of potassium permanganate solutions. But only a suggestion of such a reaction could be found in the literature. Thénard, in 1856 states that manganese dioxide may act upon potassium permanganate either as a reducing agent, in which act the manganese dioxide is changed to a manganate, or its influence may be catalytic, causing the evolution of oxygen. Again Mulder in 1858, ascribed the decomposition of potassium permanganate solutions to the presence of some potassium manganate.