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Abstract
Precipitation behaviour with ethanol of normal and deionized gelatins from each of the four types has been examined. The apparent difference in precipitability between normal and deionized gelatins has been found to result from a marked difference in pH dependence. This is cancelled by adding small amount of salts to the deionized gelatin and is ascribed to a salt effect. The amount of salts is at most one third of the total equivalent ofcarboxy groups in the sample. However, in the regions where the gelatin molecule is a simple electrolyte (pH 4, pH > 9), the sensitivity to salt is much less.
By a suitable selection of pH and other conditions a fraction free of either oil or rx2 component can be obtained. The precipitation method seems more favourable than ethanol coacervation for this purpose.
Notes
A part of this paper was presented at the 1992 Annual Conference of The Society of Photographic Science and Technology of Japan and the 1994 Autumn Conference of the same Society.