VELOCITY OF REACTION. HOMOGENEOUS SYSTEMS 65 



APt, i.e. of the product of the initial concentration of the 

 catalytic agent here ammonia of the substrate here 

 ethyl-acetate and of time. Evidently here the product 

 KP may be regarded as the constant of the reaction. 



From the analysis given above we find that the validity 

 of the rule of Schiitz indicates that the active part of the 

 catalysor, ammonia or pepsin, etc., is inversely propor- 

 tional to the products formed. This occurs in the case of 

 ammonia because the product, NH 4 -ions, gives a com- 

 pound with the active part, the hydroxyl-ions, which is dis- 

 sociated to a very low degree. Probably the case is similar 

 in all the processes in homogeneous media studied below 

 and belonging to this group (peptic or tryptic digestion). 

 In heterogeneous media other circumstances, such as 

 change of solubility, may play a role ; perhaps this occurs 

 in the saponification by means of lipases. 



One of the most interesting investigations in this line was 

 done as early as 1895 by Sjoqvist. 1 He dissolved 2.23 g. 

 of egg-albumen, which by dialysis had been nearly puri- 

 fied from salts, in 100 c.c. of four solutions, which further- 

 more contained 0.005 gramme-molecules (=0.1875 g.) 

 HC1 and 2.5, 5, 10, or 20 c.c. of pepsin. In this homo- 

 geneous system the albumen slowly digested at 37 C. At 

 the same time the conductivity gradually diminished, and 

 this diminution was regarded as a measure of the velocity 

 of digestion. At given intervals samples were taken from 

 the solution and rapidily cooled to 1 8 C., at which tem- 

 perature the velocity of digestion might be practically 

 neglected. The determination of the conductivity was 

 made at this temperature in the ordinary manner. 



1 Sjoqvist : Skandinav. Archivf. Physiologie, 5 (1895). 

 F 



