288 T. Brailsford Robertson: 



howewer, the velocity constant is, as usual in catalytic reac- 

 tions, multiplied by the active mass of the catalyst, that is, 

 in this instance, by the active mass of that product of the 

 reaction which acts as the catalysor. 



Provided the reaction is monomolecular in both directions, 

 that is, is of the type Ä^ ;^ A^, or if all the products of the 

 reaction, save the one which acts as the catalyst, are removed 

 as rapidly as they are formed so that their active mass may 

 be regarded as constant, then the same equation will continue 

 to represent the relation between the velocity of the reaction 

 and the mass of the product even when the velocity of the 

 reverse reaction, due to the accumulated mass of the product, 

 is of dimensions comparable with that of the forward reaction, 

 only in this case the constants have a somewhat different 

 meaning.^) 



The integral form of the above differential equation is: 



where A and K are constants and ^^ is the time at which x, the 

 mass of the product, is equal to ^/^A.^) 



A well-known instance of autocatalysis of this type is the 

 in Version of an aqueous Solution of sugar at 100°. The invert- 

 sugar which is produced during the reaction decomposes, giving 

 rise to an acid of unknown composition which accelerates the 

 in Version; the rate of formation of this acid being proportional 

 to the amount of invert-sugar present. Kullgren has shown 

 that the above equation accurately represents the progress of 

 the reaction.^) 



A similar instance is afforded by the hydrolysis of Methyl 

 Acetate. As is well-known the velocity of hydrolysis is greatly 

 accelerated by acids, nor is the acetic acid which is produced 

 by the reaction inactive in this respect. Under ordinary labo- 

 ratory conditions, when strong acids are used to accelerate the 

 hydrolysis, the influenae of the much weaker acetic acid is ne- 



*) T. Brailsford Robertson, Arch. f. Entwicklungsmechanik. 



2) Kullgren, Zeitschr. f. physikal. Chem. 41, 407, 1902. ■ 

 T. Brailsford Robertson, 1. c. 



3) Kullgren, 1. c. 



