( 620 ) 



case where the catalyst combines with the phosphorus to PJ 4 > 

 this substance commences al 80° to dissociate measurably [so that 

 its vapour density can only be determined at a low temperature 

 (Troost CR 95 293)] with separation of red phosphorus. We may, 

 therefore give here a fairly positive answer to the question : How is 

 it that the second division process proceeds more rapidly than the 

 original? Because PJ 4 dissociates much more rapidly than P 4 . 



But this is after all but a lucky circumstance, the real cause must 

 be sought in the tact that in order to obtain P 2 I 4 the P 4 molecule 

 must be dissociated to begin with. With A1C1 3 I have not been able 

 to find an additive product, only some indications that, besides the 

 allotropic transformation, a trace of PCI, is formed (even with per- 

 fectly dry substances the manometer, after a few hours' heating to 

 100°, showed a slight increase of the vapour pressure). 



The fact that the red phosphorus formed has in a high degree 

 the property of coprecipitating the catalyst might perhaps indicate the 

 possibility of a compound being formed between yellow phosphorus 

 and A1C1 3 ; from the above it follows that there is a possibility of 

 a certain reciprocal intluence 1 ) but I attribute this coprecipitation to 

 the colloid properties of the red phosphorus, which, when obtained 

 from solvents and also under the intluence of rays of light, carries 

 with it a certain quantity. 



But even if an additive product is found, the existence of this substance 

 is no more the cause of the acceleration than it is in the case of PJ 4 . 



On the contrary, I consider the formation of a compound of the 

 catalyst to be a case of "poisoning", caused by one of the reacting 

 molecules, just as arsenic and prussic acid are poisons for platinum, 

 because in combining with it, they prevent the entrance of 2 and 

 H s (respectively SO,); just as ether is a poison for A1CI 3 , because it 

 unites with it to a firm compound, which does not decompose until 

 over 100 J , the temperature at which the catalyst again recovers itself. 



Now, I cannot deny that we have not advanced much further 

 with this dissociation theory (which is also not absolutely novel) for 

 the question is now: How is it that a catalyst accelerates the 

 dissociation? But my object was to point out that the formation 

 (and eventually the admitting of the formation) of intermediate pro- 

 ducts can certainly never lead to an explanation of the catalytic 

 phenomena. 



2 nd Chem. Lab. University, Groningen. 



l ) I have also found a similar reciprocal influence in the action of G 3 H 5 Br on 

 A1C1 3 in which G 2 H 5 G1 and AlBr 3 are formed ; it undoubtedly points to a disso- 

 ciation. 



