574 Messrs. Hinshelwood and Bowen on the Rate of 



of the reaction. This illustrates the point mentioned above 

 that the final retardation is virtually the result of a dis- 

 continuity due to the exhaustion of" the material. 



The Form of the Curves. 

 The equation of the change may be expressed thus : 



a + /(a?) represents the magnitude of the zone in the 

 crystal where decomposition takes place. It will depend 

 presumably on such factors as the nature of the space lattice 

 and the closeness of packing, h is a factor representing the 

 probability of a molecule in that zone acquiring sufficient 

 energy to break up. The expression differs from the usual 

 type in containing no term (c — x) to represent the decrease 

 in active mass with time. 



The actual form of the function f {x) cannot be arrived at 

 theoretically. Nevertheless by putting f(x) = bx 11 , we may 

 determine how n varies with x and thus form an idea of the 

 law of acceleration. Empirically it is found that n is 

 frequently almost constant. 



If 



■A + B*»' 



dt 



then 



lo s{t-(J) } =nlo ^ +lo s B - 



Plotting the values of log x and log ) -= ( -=-\ i , 



from the derived curve for tetranitroaniline a straight line 

 was obtained, the slope of which gave w = 0*85, so that 



dt 



A few other cases were tested. The derived curve was 

 not actually drawn, but an empirical equation was fitted to 

 the accelerating parts of the t, x, curves, the tangents at 

 various points were calculated and then the same procedure 



