214 



which do not depend on the nature of the reacting substances. 



As a ditFerence of entropy is a measure for a greater or less 

 probability, and as this probability must refer to the reaction setting 

 in more or less easily, both this difference of energy and this pro- 

 bability can be calculated by the. aid of this formula from two 

 observations at different temperatures, and by carrying out this cal- 

 culation with and witiiout a catalyst it can be ascertained in what 

 way these two relations are modified by the catalyst. 



As appears from the following communication, this calculation 

 has been applied by E. van Thiel to the acetylalion of diphenyl- 

 amin with acetic acid anhydride both in presence of /;-bi-omo (niethyl)- 

 |)henylsulplionic acid as catalyst and without it, and tlie remarkable 

 result has been obtained ihat in the presence of a catalyst the 

 factor {Et — ■ E) is about doubled, B becoming also considerably 

 larger. The conclusion may be drawn from this that in this case 

 by the addition of a catalyst more than double the energy is, indeed, 

 required to cause the molecules to react than without it, but that 

 this unfavourable factor is far more than compensated by the so 

 much greater probability for the setting in of the reaction in the 

 presence of the catalyst. 



In his address at the spring meeting of the Ned. Chem. Ver. 

 (Dutch Chemical Association) of April 20 1922 Scheffek expressed 

 this as follows: the hill of energy that is to be surmounted becomes, 

 indeed, higher, but the road across it, becomes very much broader. 



Though it may be more or less a coincidence that in the case 

 examined by van Thiel the hill of energy is so much higher in 

 the presence of a catalyst than without it, it is yet the confirmation 

 of ray view that the formation of a compound between the catalyst 

 and the substances to be activated sooner hampers than pi'omotes 

 the reaction, and that the catalyst performs its accelerating action 

 not by combining with these molecules, but in spite of this combination. 



The acceleration of the reaction takes place because simultaneously 

 with the formation of this compound a change of condition sets in, 

 the dislocation, in which the conditions for the occurrence of the 

 reaction become so much more favourable. The conception of dislo- 

 cation has found a confirmation through Schkffer's theoretical investi- 

 gation, and a measure in the variation of the quantity B of his 

 formula. 



In conclusion it may still be pointed out that the thermo-dynamic- 

 kinetic considerations have not brought the question tohy a catalyst 

 creates favourable conditions, nearer to its solution. The possibility 

 may be considered of the molecules assuming a certain position, 



