Acid and alkaline hydrolysis of gelatin

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Abstract
A study has been made of the thermal decomposition of an alkaline ossein‐gelatin in dilute solutions of hydrochloric acid and sodium hydroxide within a pH range of 3·05 to 9·85. Reaction temperatures of 60°, 70° and 80° have been employed, the reaction being followed by the decrease in jelly strength, measured by the Bloom Gelometer, of gels, matured at 10°, after having undergone thermal treatment in the sol form.The reaction is found to be first‐order, and catalysed by both hydrogen ions and hydroxyl ions. Variation of the velocity coefficient with pH is represented by a catenary curve that exhibits a fairly well defined point of minimum velocity at pH 6°4.The catalytic coefficients of the hydrogen and hydroxyl ions have been determined for the reaction temperatures employed.The reaction velocity coefficient varies with temperature according to the equation of Arrhenius, and values of the heat of hydrolysis have been calculated from it. These were found to be considerably higher on the acid side of the isoelectric point than on the alkaline side, up to pH 9°35, beyond which they rise again. This variation with the pH of the sol has been explained by visualizing the mechanism of the reaction as being different for concentrations of catalyst greater than, and less than, about 0°03N.

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