Abstract
In investigating the effect of the light from the quartz mercury-vapour amp on the electrode potentials of solutions of various electrolytes, a very marked and rapid change was noticed in the case of potassium permanganate. The nature of the effect suggested that it is the result of a photo-decomposition of the potassium permanganate, and the following research was undertaken to confirm the hypothesis and discover the mechanism of the chemical change. A study of the literature revealed the fact that little work has been accomplished on the photo-chemistry of the permanganates. Pouguet has stated that, in the presence of a depolariser (oxalic acid), potassium permanganate is light-sensitive, reduction taking place to potassium manganate. Matthews and Dewey noticed a very slight decomposition, with the separation of a brown oxide, when a strong solution of permanganate is illuminated by a quartz mercury-vapour lamp. They were unable to obtain any quantitative data on the rate of decomposition, nor were any experiments made to elucidate the mechanism of the process.

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