ELECTRICAL AND OTHER FACTORS 241 



unstable and breaks down in the manner already 

 indicated. 



Catalytic effects due to simple increase in concentra- 

 tion are accordingly to be distinguished from those which 

 depend on the appearance of special relations of some 

 kind between the molecules of the substrate and of the 

 catalyzer. In the latter case the formation of combina- 

 tions differing from the substrate in reactivity, e.g., 

 velocity of hydrolysis or oxidation, becomes possible; 

 and when these temporary combinations break down, 

 setting free the catalyzer and enabling the latter to 

 repeat the combination, the total effect is the same as if 

 chemical change in the substrate alone were accelerated. 

 The general theory of intermediate compound formation 

 would thus apply to any specific adsorption-catalysis. 

 The adsorbent would correspond to the enzyme, and the 

 theory of such catalysis need not differ in principle 

 from that of catalysis in homogeneous solutions; e.g., 

 H-ion catalysis. At present, however, there appears to 

 be no completely satisfactory theory of this type of 

 catalysis. 



With regard to other conditions which may enter in 

 cases of heterogeneous catalysis, it has been suggested 

 that the increased reaction-velocities shown by many 

 substances (sugars, etc.) in protoplasm are phenomena 

 of the same kind as the differences of velocity shown by a 

 given reaction in different solvents, as observed by 

 Menschutkin and others.' Bredig compares a particle 

 of a solid catalytic agent with a drop of liquid, and regards 

 the formation of an adsorption-film as equivalent to 



'Menschutkin, Z. physik. Chem., XI (1887), 611; von Halban, 

 ibid.y LXXXII (1913), 325. Cf. Hober, op. cit., p. 704. 



