215 



which causes the collisions to take place on the reactive parts of 

 the molecules (van Thiel, see following communication), or it may 

 be supposed that the reactive surface is enlarged, etc. etc. It is 

 certain that these changes of position or of form must take place 

 very rapidly, and the catalyst must be under very favourable con- 

 ditions with regard to the molecules tl)at are to be activated, which 

 can hardly be imagined in another way than ensuing from a che- 

 mical affinity, which leads to dissociation equilibria that are esta- 

 blished very rapidly. 



Delft, May 1922. 



14 

 Proceedings Royal Acad. Amsterdam. Vol. XXV. 



