Mechanism of Molecular Action. 801 



From this it follows that f (0) and F(0) may be written in 

 the forms 



where <f>{6) is the same in each case, and A, A', k, k' are 

 constants such that 



A — A! =zb and ;/ ==a. 



Now b is a constant found (Planck) to have values differ- 

 ing greatly from zero. Hence A and A' are not equal, and 

 cannot both be zero at the same time. It follows, then, that 

 at least one and probably both of the above expressions 

 involve a true exponential. That is to say, if the velocity of 

 forward action can be expressed completely as 



then the velocity of back action can be expressed as 



where the parts of the expressions denoting the change with 

 temperature are both of the same form, and can only vary 

 in the values to be assigned to the constants A and A', k 

 and k' . 



Part II. 

 Actions other than Unimolecular Actions. 



When an action takes place between a number of sub- 

 stances its velocity is proportional to the product of the 

 concentrations of the reacting substances ; this shows that 

 action is dependent upon the collision of suitable molecules. 



It is not every collision of the required molecules that can 

 produce reaction ; for the total number of collisions varies 

 as the square root of the absolute temperature, whereas the 

 number of effective collisions (the velocity of the action) 

 has been shown above to vary as some function involving 



e U; *. 



* Empirical formula expressing the change of velocity with tempe- 

 rature, are, with one exception (Warder's), exponential in form. 



