1904.] Studies on Enzyme Action. 203 



Method of Measuring the Reaction Velocity. 



All the experiments mentioned in the present communication were 

 carried out in a thermostat at a temperature of 10 (constant to ^y ). 

 Ninety cubic centimetres of the very dilute enzyme solution was placed 

 in each bottle, 10 c.c. of a solution of the substance whose action was 

 to be investigated (respectively 10 c.c. of water in the control experi- 

 ments) added ; after the lapse of a certain time (period of incubation) 

 100 c.c. of approximately /i/50 hydrogen peroxide (also at 10) added, 

 and the mixture shaken. From time to time 25 c.c. of the mixture 

 were pipetted out, run into sulphuric acid, which stops the action, and 

 titrated with m/500 permanganate. 



It may be mentioned that the enzyme solution was so active, com- 

 pared with the amount of organic matter present, that no appreciable 

 error (less than T \j- c.c.) was caused through the reduction of KMn0 4 

 by organic matter. The hydrogen peroxide used was obtained from 

 Merck and was quite pure. 



The enzyme solution was prepared according to the method given 

 in my former paper,* and being kept in an ice-box retained its activity 

 without appreciable change for several days. 



Nearly all the substances used in the experiments were obtained 

 from Kahlbaum, the others were the purest obtainable in London. 



The water used for dilution was distilled water freed from carbon 

 dioxide by the passage of a current of pure air through it for some 

 time. 



Effect of Acids on the Reaction Velocity. 



In order to show clearly the nature of the results obtained, I give 

 here (p. 204) full details of measurements on the effect of HC1, H^SO^ 

 and HNOs on the reaction-velocity. In order to economise space, only 

 the " constants " of subsequent experiments will be given. 



The value of the constant in the control experiment was 0'0250. 

 The numbers under Cn 2 o 2 give the concentration of the H 2 2 at the 

 time indicated, expressed in cubic centimetres of 1/500 molar KMn0 4 . 

 The constants in the third column are calculated on the assumption 

 that the reaction-velocity is proportional to the H 2 2 concentration, 



that is, that - ^ = KiC H2 o 2 where C H . 2 o 2 is the concentration at 

 dt 



-I r\ 



the time t. Integrating, we obtain 0'4343Ki = - - log ~, where Ci 



t-2 ?i L/2 



and C-2 are two successive measurements, and t z ti the interval of 

 time between them. 



The effect of hydrochloric acid, sulphuric acid, nitric acid, benzoic 

 acid, succinic acid, and acetic acid, on the rate of reaction has been 



* Loc. cit. 



