118 Prof. H. E. Armstrong and Mr. E. Horton. [Jan. 26, 



increasing the concentration of the urea, the amount of action taking place 

 was diminished rather than increased, little advantage being obtained by 

 using solutions stronger than M/5. This remarkable result is brought out 

 very clearly in Table III and in the graph on p. 117. 



It will be noted that up to the time of complete hydrolysis of the urea 

 present in the M/5 solution practically the same amounts of change took 

 place in this solution and in that which was five times as strong ; moreover, 

 that in the still stronger 5M solution less than half as much urea underwent 

 conversion as was hydrolysed in that of one-fifth the concentration. 



Influence of the Products of Change. — As it appeared probable from these 

 observations that the products of change were exercising a marked influence, 

 experiments were made to test the influence of ammonia. The effect 

 produced by this substance was found to be very considerable : not only was 

 the rate of hydrolysis limited but the graphs representing the course of the 

 change appeared flattened out from the outset, not curved as they are when 

 no ammonia is added. 



In an experiment in which 10 per cent, of the ammonia producible by the 

 hydrolysis of the urea used was added at the outset, a small proportion of 

 enzyme being used, the change followed an almost linear course during the 

 first two hours, until over 50 per cent, was hydrolysed (Table IV, and the 

 lowest pair of curves in the lower graph on p. 119). 



Table IV. — Hydrolysis of Urea in the presence of Ammonia and 

 Ammonium Carbonate. 



Percentage of urea hydrolysed in solution containing 



13-9 

 21 -8 

 27-4 



When ammonic carbonate (equivalent to one-tenth of the urea used) was 

 siibstituted for ammonia, though at first a decided retardation was obvious 

 this was not so decided as in the case of ammonia and gradually (as 



