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74 THE ADVANCE OF PHOTOGRAPHY
the effect also vanishes if perfectly dry air is used. Hence Saeland comes to the conclusion that it only takes place when under conditions favourable for the production of hydrogen peroxide. He finds that a solution of that substance has an action upon the plate similar to that obtained with the metals. His assumption is supported by the further fact that all action is stopped when a transverse stream of air is allowed to pass at the rate of 5 metres per second.
Action of Hydrogen Peroxide on Plate. — The action of hydrogen peroxide upon the photographic plate has been investigated by Dr Otsuki in the laboratory of the Technical High School of Hanover (1905). He came to the conclusion that the effect produced on a photographic plate by hydrogen peroxide is due to the change in the bromide of silver contained in the sensitive layer of the plate. Silver bromide under the action of the peroxide changes most probably to a lower bromide of silver, which is easily reduced by the developer. The latent image produced by hydrogen peroxide consists of this' lower bromide of silver, and can be destroyed through the action of bromine vapour or bromine water. Thus in one of his experiments gelatino-bromide plates were exposed for two minutes to 30 per cent, aqueous solution of hydrogen peroxide, and then laid on a vessel containing concentrated bromine water for two hours, keeping the distance of 1 cm. between the plate and the surface of the bromine water. After thoroughly washing them under running water, they were developed for two minutes by means of 5 per cent, commercial rodinal. There was no darkening of the plate to be seen. If placed in a 5 per cent, bromine water for two minutes after exposure to the action of the peroxide, the same result was obtained. If developed for one minute by the rodinal immediately after exposure the plate became dark.
The question of these so-called Moser rays is, however,