( 617 ) 



Platinum, for instance, powerfully accelerates the decomposition of 

 hydrogen peroxide, ozone, nitric acid, hydrazine etc. 



Aluminium chloride causes a direct splitting of the homologues of 

 benzene, of the very stable polyhalogen derivatives, of aromatic 

 ethers, of sulphury.l chloride, etc. The number of these decomposi- 

 tions is so considerable that, in other cases where we cannot prove 

 a direct dissociation by the catalyst, we may still argue that it takes 

 place primarily, or rather that an already present but exceedingly 

 small dissociation is accelerated in such a manner that a system 

 attains the stable condition of equilibrium much sooner than without 

 the catalyst. 



The great evolution of heat in the process 



HCCI3 + 3 C 6 H 6 + (A1G1 S ) = (C 6 H 5 ) 3 CH + 3 HOI 4- (A1C1 3 ) 

 points to the fact that the system to the right is more stable than 

 that to the left. I attribute its slow progress when no A1C1 3 is used 

 to the small dissociation velocity of chloroform : the catalyst accelerates 

 this dissociation so that the stable condition of equilibrium is attained 

 in a short time. This reaction gets continuously more violent (the 

 temperature being kept constant). This phenomenon may be readily 

 explained if we bear in mind that the reaction proceeds in different 

 stages (C 6 H 5 CHC1 2 , CHC1 (C 6 H 5 ) 2 and CH(C 6 H 5 ) 8 are formed in suc- 

 cession) and that the chlorinated intermediate products are decomposed 

 much more readily than CHC1 3 . 



If sulphur is boiled with benzene and aluminium chloride we obtain 

 almost exclusively (C 6 H 5 ) 2 S, (C„H 4 ) S S 2 and H 2 S. Without the catalyst 

 hardly any action takes place because the dissociation of S 8 in benzene 

 solution at 80° is negligible : (if sulphur is boiled with toluene H 2 S and 

 condensation products are formed without A1C1 3 being present) the alumi- 

 nium chloride accelerates the reaction S 8 — »4S 2 , and consequently 

 the formation of the condensation products. This explanation is 

 therefore quite the same as that given for the reaction of P< with 

 benzene and aluminium chloride ; the sole difference is that in the 

 latter the second stage of the reaction consists exclusively in the 

 condensation of P 2 to red phosphorus, a condensation to which 

 sulphur does not seem to be liable to the same extent, so that the 

 dissociated sulphur forms with benzene the above products. 



I consider the formation of a compound of the catalyst with one 

 of the reacting substances of importance for the taking place of the 

 reaction in so far only that one phase can be formed ; otherwise it 

 rather obstructs the reaction, because the catalyst becomes to a 

 certain extent paralysed. One of the most powerful catalysts, platinum, 

 is actually characterised because it does not (or at least with great 



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