OF VITAL PHENOMENA 83 



two stages, the sum of which takes less time than the uncatalyzed 

 reaction. In this way is explained the action of nitrous oxide 

 in the oxidation of sulphurous acid, and the action of sulphuric 

 acid in the conversion of alcohol into ether. 



The catalyzer may change the course of the reaction, as in 

 the observation of Slator (1903) on the chlorination of benzol, 

 in which the CI may be substituted or simply added. Different 

 catalyzers favor one or the other form of combination. This is 

 illustrated in enzymes by the difference in the form of proteolysis 

 produced by pepsin and by trypsin. 



In case of reactions in a heterogeneous system, of which a 

 diphasic system is the simplest case, not only the rate of the 

 chemical reaction but also the rate of diffusion may enter into 

 the rate of transformation of the substance. 



In the first case, the second phase may be a better medium 

 for the reaction than the first phase, and so act as a catalyzer. 

 Bredig (1901) showed that methyl acetate dissolved in benzol is 

 not saponified, even with the addition of triethylamine. If the 

 mixture is shaken with 2.5 per cent water to form an emulsion, 

 saponification takes place with great rapidity, because the water 

 dissociates the triethylamine, and the resulting OH ions catalyze 

 the saponification of the methyl acetate. The same principle seems 

 to be involved in the catalysis of the union of hydrogen and 

 oxygen by means of palladium or other noble metals. The 

 palladium dissolves these gases, forming a so-called solid solu- 

 tion. Hoitsema (1895) has shown that the amount of hydrogen 

 dissolved by the palladium is proportional to the square root 

 of the hydrogen pressure, and the hydrogen, therefore, does not 

 exist in the metal as H 2 but as H. If this atomic hydrogen is 

 more active than molecular hydrogen, the catalytic action of the 

 palladium is explained. 



The second phase of a diphasic system may increase the rate 

 of reaction by adsorption. Bayliss (1915 b) has shown that 

 enzymes may act in a medium in which they are insoluble. We 

 shall consider this aspect of the subject under the head of oxida- 

 tion (Chapter XV). 



In case the rapidity of the chemical reaction in or on the 

 second phase is very great, perhaps too great to measure, the 

 rate of transformation is determined by the rate of diffusion 



