550 



It is supposed that the atoms consist of' (or at least are populated 

 bv) electrons and that thej hold together by means of force regions 

 between these corpuscles; the catalytic action may then be described 

 as a change of these force regions on the approach of the catalyst. 

 If this is so, we have in the jmre photocatalysis the simplest 

 catalytic actions and the study of these phenomena will no doubt 

 much deepen our insights. ^) 



On penetrating further into the phenomena in general we are 

 obliged to resolve the substance into steadily decreasing units and 

 the same has happened with the special phenomena called catalytic; 

 here it will just be shown that what takes place in the atoms will 

 be of preponderating importance. But just as we have not been able 

 to find the ideal catalyst among the atoms, we cannot expect to 

 meet it among the electro-magnetic equilibria-perturbations, only 

 the limit of our insight in the catalytic phenomena has advanced 

 a step. 



II. 



1. During this niainly inductive development of my ideas my 

 pupil H. J. PiuNs had found a synthesis of chloropropane derivatives 

 and I advised him to couple this experimental subject with a survey 

 of the different cases in the reaction of Fkiedel and Crafts. ^) 



With this, however, he did not content himself, but starting from 

 the "Principle of Reciprocity" he has endeavoured to furnish an 

 explanation of the catalytic phenomena in general, with the reaction 

 of FiuEDEi. and Crafts as a special case. 



The result of this is given in his dissertation ("Bijdrage tot de 

 kennis der katalyse", Delft 1912) and supplemented with a few 

 subsequent articles (Journ. f. pr. Chem. N. F. 89, 425 (1914) ; 

 Chem. Weekbl. 11, 474 (1914). 



In order to reproduce Prins's intention in the simplest possible 

 manner, I will quote a few parts of his deduction, taking the liberty 

 to omit the, in my opinion, non-essential matter. 



^) The simplest case is the pholocatalytic change of a nionalomic element. 



2) The reaction of Fr. and Gr. offers us already a great diversity of catalytic 

 reactions, because AIGI3 can form all khids of compounds. Only in such cases 

 where it unites neither with the initial products nor with tlie end product, or attacks 

 this secondarily do we approach a case of pure catalysis. 



The number of these cases is very small, the chlorination of benzene is a very 

 appropriate example thereof; here the quantity of the catalyst is minimal indeed 

 (see hu'lher). 



