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J. I. CRABTREE AND H. D. RUSSEU, [J. S. M. p. E.
similar case in which the acid content is distinctly above the normal limits permissible for satisfactory hardening of neutral gelatin. If a developed film containing appreciable quantities of developer is plunged immediately into the stop bath, the above conditions are reproduced in situ within the film and the solution immediately adjacent to it, that is, the developer locally neutralizes the excess acidity of the stop bath so that the chrome alum is then rendered capable of hardening the gelatin. In other words, the alkali held in the gelatin and on the surface of the film creates a local condition
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FIG. 2. Effect of the addition of sodium sulfite on the hardening properties of a 2 per cent chrome alum stop bath containing 1 cc. of sulfuric acid per liter.
in the stop bath as represented by the addition of a sufficient quantity of developer to the stop bath to produce maximum hardening as in the case of adding developer to a hardening fixing bath. Once the film is hardened and the alkali is neutralized by the acid, the excess free acid in the stop bath does not destroy the hardening already produced, because the acid content is relatively low and the chrome alum hardening is not readily affected by weakly acid solutions.
Eject of the Addition of Sodium Sulfite on the Hardening Properties of a Chrome Alum Stop Bath. — The effect of varying the concentration of sodium sulfite on the hardening properties of a stop bath con