VELOCITY OF REACTIONS 33 



The third example is borrowed from Sorensen, 

 and concerns the well-known influence of acids on 

 the peptic digestion at 5 2° C. The maximum occurs 

 at a concentration of the hydrogen-ions equal to about 

 001 normal, when the time of digestion is short 

 (1 hour). If this time increases, the maximum moves 

 to higher concentrations and lies at about 006 normal 

 for 49 hours. 



In order to show that similar effects are known 

 from general chemistry, I have added an example 

 dealing with the decomposition of hydrogen peroxide 

 by means of colloidal platinum at 25 C, according 

 to measurements by Bredig and v. Berneck. Here 

 we find a maximum of the velocity of reaction or a 

 minimum of the time necessary to decompose 50 per 

 cent (the quantity tabulated) when sodium hydrate 

 is present to the concentration of about 0-02 normal. 



If we investigate the influence of the concentra- 

 tion on the velocity of reaction we discover a new 

 discrepancy between these reactions and ordinary 

 monomolecular reactions. If we use sugar solutions 

 of moderate concentration (about 10 per cent) and 

 vary the concentration of the invertase, we find that 

 the reaction constant remains unchanged, i.e. the 

 quantity of sugar decomposed in unit of time is 

 proportional to the concentration of the enzyme. 

 But if we change the concentration of sugar, keeping 

 that of invertase constant, we arrive at quite different 

 results, as is seen from the following figures of 

 Henri, which indicate the number (n) of milli- 

 grammes of sugar inverted during the first minute, 



D 





