PROTEOLYTIC ENZYMES AS CATALYSORS 395 



of such a character as to strongly suggest that they play an im- 

 portant part in determining the course of the reaction. Thus 

 in the presence of aluminium chloride, sulphuryl chloride and 

 sulphur chloride react thus : 



S0 2 C1 2 + S 2 C1 2 = S0 2 + 2 SC1 2 



and it appears that the aluminium chloride aids the reaction 

 through the formation of double compounds with the various 

 molecular species which participate in the reaction, for many 

 such compounds are known, for example A1 2 C1 2 2 S0 2 , AlClsSCU, 

 and so forth (20). 



A very decisive series of instances of catalysis through the 

 formation of] intermediate compounds has been established by 

 the painstaking and extensive researches of Stieglitz (1) (127) 

 (128). In the presence of acids the iminoesters (in aqueous 

 solution) are decomposed into ammonia and the corresponding, 

 sparingly ionized organic acid. It has been shown by Stieglitz, 

 with the utmost quantitative precision, that the catalytic action 

 of the mineral acid, in this reaction, is accomplished through 

 the formation of salts of the catalysing acid with the ester, since 

 the molecular species which actually undergoes hydrolysis in 

 this system is the ester-ion and the salts of the ester are much more 

 completely electrolytically dissociated than the ester itself, so that 

 the active mass of the substrate is increased by the presence of the 

 catalysor. Similarly, in the catalytic decomposition of methyl 

 acetate by acids an oxonium salt of the ester with the acid is 

 formed and it is the positive ion of this salt which undergoes 

 hydrolysis. Now this latter is a "typical" instance of catalysis. 

 The catalytic agent is not used up during the reaction, it can be 

 recovered from the system unaltered when the reaction is com- 

 plete, and the equilibrium of the reaction is not measurably 

 disturbed by the presence of the catalysor. Nevertheless, in a 

 comprehensive mathematical analysis of the conditions which 

 must actually obtain in such a system, Stieglitz has shown that 

 the point of equilibrium must be shifted by the catalysor, albeit 

 to an immeasurably slight degree, and that in the specific instance 

 under consideration the equilibrium is only inappreciably shifted 

 simply because the quantity of the compound which is formed 

 at any moment, between the catalysor and the substrate, is 

 evanescently small, since these salts are subject to very extensive 



