570 Messrs. Hinshelwood and Bowen on the Rate of 



the crystal and consequent increase of surface as the reaction 

 proceeds. Clearly, then, the reaction is a heterogenous one 

 and takes place only in a zone near the surface. The final 

 retardation is of the nature of a discontinuity due to the 

 exhaustion of the reserve of material ; but is rounded off 

 owing to the earlier extinction of the smaller particles. 

 Experiments VIII. and IX. show that manganese dioxide 

 exerts no catalytic action to account for the acceleration, 

 which must be due entirely to the physical cause. 



Fior. 1. 



Q So 



Ah 



40 

















~ 





















1/ 

































ny 





























GO niNUTES. 



I. Finely ground KMn0 4 (agate mortar) at 240° C. 

 II. Finely ground KMn0 4 (porcelain mortar) at 240° C. 

 III. Large crystals KMn0 4 at 240° C. 



2. Evolution of Oxygen from Solid Solutions of Potassium 

 Permanganate in Potassium Per chlorate. 



When potassium permanganate is dissolved in solid 

 potassium perchlorate the rate of reaction is lowered. 

 Figure 2 shows the results obtained with mixed crystals 

 containing 82 per cent, and 26*8 per cent, of potassium 



