Chemistry. — "Catalysis. (Part VI). Temperature coefficients of 

 heterogeneous reactions:' By Nil Ratan Dhak. (Communicated 

 by Prof. Ernst Cohen). 



(Communicated in tlie meeting of February 22, 1919). 



Ill foregoing- papers'), the temperature coefficients of catalysed 

 and nncatalysed reactions in a liomogeneons medium have been 

 studied. It has been shown that a positive catalyst produces a lower- 

 ing in the value of the temperature coefHicient of the reaction, the 

 reverse is the case with a negative catalyst. It was also proved that 

 the higher the order of a reaction, the smaller is the temperature 

 coefficient. 



The object of this paper is to discuss the experimental researciies 

 and find, if 'possible, siinilar relations in the domain of heterogen- 

 eous reactions. 



In order to make clear the question of the temperatuie coefHicients 

 of heterogeneous reactions, it is necessary to indicate briefly their 

 characteristics. 



In a leaction between a liquid and a solid, according to the 

 diffusion theory of reaction velocity a thin layer of liquid adhering 

 to the solid remains unaffected by stirring and the reaction is main- 

 tained by the transport of dissolved substances across this layer of 

 diffusion. Moreover, it- is assumed that at the boundary surface 

 between two phases, the velocity of the chemical reaction is extreme- 

 ly high. When the diffusion is sufficiently slow compared with the 

 other stages of the reaction the velocity of the whole reaction will 

 be determined by the rate of diffusion alone. 



This theory was tirst proposed by Noyes and Whitney') for some 

 special cases, but its general applicability to various types of hetero- 

 geneous reactions was indicated by Neknst and Bkunner '), and has 

 since been accepted by several investigators as giving the best ex- 

 planation of facts in heterogeneous systems. 



On the other hand, the general applicability of the diffusion theory 



1) Jour. chem. soc 1917, 111, 707; Annales de chimie, 1919. 

 3) Zeit. Phys. Chem. 1897, 23, 689. 

 3) ibid. 1904, 47, 52, 56. 



