Attention is drawn to the necessity of taking the values of the critical increments into account when the velocity constants for reactions of any pair of glucosides are compared. The ratio of the velocity coefficients for the hydrolysis of any two glucosides, determined at the same temperature, varies with temperature except in the special case when both hydrolyses have the same critical increment. Different values given by various investigators for the same ratio are shown to be due to the fact that comparative experiments have been carried out at different temperatures with two glucosides possessing different critical increments of hydrolysis. In the light of these considerations it becomes necessary to revise certain deductions which have been drawn from the comparison of rates of hydrolysis of glucosides by acids (at fairly high temperatures) with the rates of hydrolysis of glucosides by enzymes (at relatively low temperatures).

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