[ 569 ] 



LXVII. The Rate of Chemical Action in the Crystalline State. 

 By C. X. Einshelwood and E. J. Bowen, Ballid College, 

 Oxford*. 



WITH regard to the study of reactions in the solid state, 

 a number of interesting observations on chemical 

 changes produced by the action of light have been recorded, 

 ca.. Lobry de Bruyn, Rec. Trav. xxii. 298, and Padoa, Atti 

 R. Accad. Lined, 1919 (v.) ii. 372, but these do not lend 

 themselves to exact measurement, and, moreover, the intensity 

 of the active light falls off rapidly in the interior of the 

 crystal. Apart from these investigations little is known 

 as to the mechanism of chemical reactions in the solid 

 state. 



Some previous experiments (Trans. Chein. Soo. 1920, 

 cxvii. 156) on the rate of decomposition of malonic acid in 

 the solid and supercooled liquid state, showed that the 

 decomposition was much more rapid in the superco ded liquid 

 than in the solid at the same temperature, and that it was 

 found difficult to obtain a definite value for the rate of 

 reaction in the solid state, large divergences being found 

 among specimens of apparently equal purity. As these 

 discrepancies might have been connected with the presence 

 of small quantities of liquid, the subject has been investigated 

 further by studying the decomposition of various crystalline 

 substances which do not melt, or at temperatures far below 

 their melting points. Irreversible reactions were naturally 

 chosen. 



The method of measurement used consisted in the determi- 

 nation of either the volume or the pressure of the gaseous 

 products. The substances were enclosed in bulbs connected 

 with gas-measuring apparatus and heated at constant tem- 

 perature in vapour baths. 



1. Evolution of Oxygen from Potassium Permanganate. 



The curves given in figures 1 and 3 show that the initial 

 rate of reaction is determined by the state of subdivision of 

 the potassium permanganate, being greater the finer the state 

 of subdivision. In the case of the large crystals the curve 

 shows a marked acceleration owing to the disintegration of 



* Communicated by the Authors. 



Phil. Mag. S. G. Vol. 40. No. 239. JSov. 1920. 2 P 



