570 Dr. George Senter. The Eole of Diffusion in the [Mar. 7, 



tion can only be accounted for by supposing that the process taking 

 place on the surface of a particle influences that of its neighbours by 

 some non-chemical means," and it is difficult to imagine any other 

 way in which this can be effected than by the production of convec- 

 tion currents. Sand suggests that these currents are set up in the 

 liquid by the bubbles of oxygen evolved, but this cannot be regarded 

 as a complete explanation of the observed facts. On this view we 

 would expect K to increase with increasing peroxide concentration 

 (owing to the more rapid evolution of oxygen), but this is not the 

 case. It has been found that K decreases,* though only to a small 

 extent, with increased peroxide concentration. Further consideration 

 shows, however, that this apparent contradiction can be satisfactorily 

 accounted for on the convection hypothesis. 



We must, as a matter of fact, consider three possible ways in which 

 K may be affected by the processes in question : 



(1) The particles themselves are in Brownian motion ;f they are 

 continually moving into fresh portions of the solution, and thus tend 

 to keep a constant concentration outside the adherent layer through 

 which diffusion is taking place. Further, owing to their motion, they stir 

 the liquid as a whole, and thus, with increasing concentration, the 

 average thickness of the layers on all the particles would be lessened, so 

 that K would increase more rapidly than the catalysor concentration. 



(2) Owing to evolution of bubbles of oxygen in the stronger 

 solutions, and consequent stirring of the liquid, the diffusion path 

 would be shortened, and K, as we have already seen, would increase 

 more rapidly than the platinum concentration. 



(3) The formation of bubbles on the surfaces of the particles would 

 interrupt the diffusion-layer and tend to retard the action. This 

 process on one particle would not, however, affect that on another, 

 so that, as far as this effect alone is concerned, the reaction-velocity 

 would be proportional to the platinum concentration. In solutions 

 containing the same amount of catalysor and different peroxide con- 

 centrations, we would expect this disturbing cause to increase with 

 the peroxide concentration, so that the greater velocity to be expected 

 from increased stirring might be more than neutralised by the cause 

 just mentioned. We have thus a simple explanation of the observed 

 fact that K decreases slightly with increase of H 2 2 . The fact that 

 K increases considerably during the action, which has up to the 

 present not been satisfactorily accounted for,J is probably due to a 

 combination of the two convection effects just discussed. 



* Bredig and Ikeda, loc. cit., p. 4. 



t Senter, loc. cit., p. 213. Compare Spring, ' Bull. Soc. China. Belg.,* vol. 19, 

 p. 219, 1900. 



J Compare Bredig and Ikeda, loc. cit., p. 5 ; Engler and Wohler, ' Zeit. Anorg. 

 Chemie,' vol. 29, p. 13, 1901. 



