CATALYSTS AND ENZYMES 237 



of intermediate reaction fails entirely to account for the action 

 of negative catalysts, for Here the indirect action must go more 

 slowly than the direct one. Accordingly the direct reaction would 

 run at its own undiminished rate by itself, for the quantity of 

 catalyst is too small to take all the substratum at the beginning 

 and compel its conversion by the slower rate. 



The conclusion may accordingly be drawn that although inter- 

 mediate reaction may and probaby does occur, and increase reaction 

 velocity in a considerable number of catalytic reactions, it is evident 

 that this does not furnish a universal explanation of catalysis 

 applicable to all cases. 



III. Theory of Altered Solubility and Different Reaction Velocity 

 of the Substratum in the Catalyst. The outline of this theory was first 

 given by Faraday, who showed that all porous and finely divided 

 bodies, such as porcelain clay, wood charcoal, animal charcoal, 

 and some metals, notably platinum, possessed the property of 

 taking up different gases and condensing them, and ascribed to 

 this property the power such bodies were known to possess of 

 inducing or favouring chemical reaction as, for example, in causing 

 the union of a mixture of hydrogen and oxygen at ordinary tempe- 

 ratures in the case of spongy platinum. Such an effect can obviously 

 only obtain in a heterogeneous system that is, a system in which 

 there is discontinuity of structure and chemical composition for 

 in a homogeneous system there is no opportunity for variation 

 in concentration of the components of the system. For example, 

 in the above case of spongy platinum, there are portions of the 

 system where on account of the presence of the platinum within 

 molecular distance of action, the hydrogen and oxygen can become 

 condensed in the metal or on its surface, and the action can there- 

 fore proceed more rapidly than in those parts of the system outside 

 the range of action of the platinum where the reaction, if it proceeds 

 at all, can only proceed at the rate at which it takes place in the 

 absence of platinum. 



Similarly, in the case of a colloidal catalyst, such as most 

 enzymes are supposed to be, it may be supposed that the catalyst is 

 present in the form of ultra- microscopic particles suspended in the 

 solution, and that the substratum possesses a higher solubility in 

 the particles of the ultra-microscopic emulsion, or by surface tension 

 is attracted in increased concentration to the surface of the particles. 

 In either case a portion of the system is obtained in a state of 



