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Abstract
The addition of Phenidone to a hydroquinone developer does not increase the rate of autoxidation of the hydroquinone when the solution is exposed to air or to oxygen. The rate of autoxidation does not appear to be limited by the rate of solution of the gas because it can be varied over a wide range by changing the pH. The Phenidone has no effect at any pH, but when present in high concentration its rate of loss can become appreciable through dismutation of its semiquinone and it can compete with the hydroquinone. When the hydroquinone is present in concentrations above 2 g per litre its rate of autoxidation is insensitive to change in its concentration and is proportional to the area of the gas-solution interface. The evidence suggests that the critical stage of the autoxidation takes place at the gas-solution interface.
Notes
Paper presented at a symposium on “Photographic Processing” organized by the Science Committee of the Royal Photographic Society, 21-24 September 1971 at Brighton.