574 The Hole of Diffusion in Catalysis of Hydrogen Peroxide. 



constant is great in comparison with the chemical velocity-constant. 

 This error is probably to be found in the assumption that the whole 

 surface of the platinum is, under ordinary conditions, active towards 

 hydrogen peroxide. 



We are not entitled to assume, from the above considerations, that 

 Nernst's hypothesis is true for the platinum catalysis, but only that the 

 diffusion-velocity is not great in comparison with the chemical velocity 

 (Cases 1 and 2, p. 569). Other considerations, however, such as 

 the small value of the temperature coefficient, make it probable that 

 the above hypothesis does apply to this particular action. Further 

 support for this view may, perhaps, be found in the fact that the 

 deviations from the simple logarithmic law in catalysis by platinum 

 have their exact analogy in the haemase catalysis. On the " chemical " 

 velocity hypothesis it would seem rather remarkable that two catalysors 

 of so different origin should show exactly similar behaviour, but this 

 becomes at once intelligible on Nernst's hypothesis, according to 

 which the chemical action plays quite a secondary part in the re- 

 action-velocities in question. 



In conclusion, I wish to acknowledge my obligations to Professor A. 

 W. Porter and Dr. Sand, with whom I have had the advantage of 

 discussing the subject-matter of the present paper. 



