( 619 ) 



changes can commence only with absorption of free energy, the 

 process will not take place unless a catalyst is added; this, therefore, 

 opens another road . . . Now, in my opinion too much attention is 

 paid to the milestones on that road and too little to the opening itself. 



This is chiefly caused by the fact that we know so little of the 

 so-called „passive resistances", for instance we cannot give a satisfactory 

 explanation of the fact that iodine acts much more rapidly at low tempe- 

 ratures on metals than does oxygen, although the potential decline is much 

 smaller. Still, 1 think that we must look for this mainly in the 

 ready dissociation of the iodine molecuie, always supposing that 

 atoms react more rapidly than molecules, a supposition, moreover 

 nearly a century old. 



If this should be so, the action of a catalyst must be sought for 

 in the increase of this dissociation. 



Now, we know of a number of reactions where the catalyst forms 

 undoubtedly a compound with one of the reacting molecules, 

 which additive product then reacts with the second molecule to form 

 the final product, with liberation of the catalyst, but even in such 

 a case, which is called by many "pseudo-catalysis" (Wagner, Z. Phys. 

 Ch. 28 p. 48), I do not consider the formation of this compound as some- 

 thing essential without which the acceleration would not take place. 



I certainly do not consider the formation of such an additive 

 product as being without any significance, as it is an indication 

 that the catalyst can exercise a particular influence on one of the 

 molecules ; the real increase of velocity is, in my opinion, due more 

 to that influence than to the formation of the additive product, and 

 in view of what precedes this, that influence consists presumably 

 of an increase of the dissociation (and through this of the active mass). 



It is, of course, obvious that a catalyst will act all the more 

 energetically when the additive products are [more labile. I have 

 already mentioned platinum and now point also to the H-ions 

 with which, the formation of additive products, for instance when 

 accelerating saponification, is far from probable. As a very lucid 

 example, I mention the different catalytic influence which iodine 

 and AlClg exert on the transformation of yellow into red phosphorus. 



From the researches of Brodie (Ann. de Ch. Ph. 1853 p. 592) 

 which I have found fully confirmed, a small quantity of iodine 

 can convert a large quantity of yellow phosphorus very rapidly 

 into red phosphorus at 110°. (As in many other cases, there is a limit 

 because the catalyst is precipitated by the colloidal phosphorus formed. 



The velocity at the ordinary temperature is very small but becomes 

 plainly perceptible at 80°. We are undoubtedly dealing here with a 



