340 



Prof. H. E. Armstrong and others. [Jan. 1, 



interval of about 18 minutes, whilst in tbe absence of the cyanide this 

 amount is changed only after 55 minutes. In this case it was noted that 

 the solution became brown. 



It is noteworthy that hydrogen cyanide has relatively less influence than 

 carbonic acid in the later stages of the change. 



Influence of Methylurea. — In Part XV it is shown that methylurea has a 

 definite retarding effect. We have therefore carried out a further series 

 of experiments in which, in one case, only the amount of methylurea 

 present was varied, whilst in the other the action took place in presence 

 of carbonic acid. The results obtained with this substance when used in 

 presence of carbonic acid are of special interest in view of the close 

 relationship of urea and methylurea ; they are given in Table F and 

 in Diagram 17. It will be noticed that the addition to the M/5 solution 

 of urea of an equivalent amount of methylurea has a marked depressant 

 effect and that when the urea and the methylurea are present in the 

 ratio 1 : 4 the effect of the neutral substance is considerable. As practi- 

 cally the same alteration in osmotic conditions would be produced by 

 equivalent proportions of urea and methylurea, it is to be supposed that 

 the influence exercised by methylurea is due in part to the fact that it 

 shares the acid enzyme with the urea but it also interferes mechanically. 

 The results obtained in presence of carbonic acid are similar to those 

 obtained in its absence but action proceeds at accelerated rates. 



Table F. — Hydrolysis of Urea in M/5 Solutions in presence of Methylurea. 





Percentage of urea hydrolysed. 



Time 

 (minutes). 



Alone. 



In presence 

 of 



methylurea 

 M/5. 



In presence 

 of 



methylurea 

 4M/5. 



In presence 

 of 

 carbon 

 dioxide. 



In presence of 

 methylurea 

 (M/5) and 

 carbon dioxide. 



In presence of 

 methylurea 

 (4M/5) and 



carbon dioxide. 



5 

 10 

 15 

 20 

 30 

 40 

 45 

 60 

 75 

 90 

 120 



10 -o 

 16-7 

 22 -9 



36 -0 



47-9 

 57-0 

 66 -8 

 74 -0 

 88 -4 



9-7 

 15 -9 

 21-4 



34 -3 



44-1 

 53 -4 

 62-1 

 70 

 83 -9 



8-3 

 13-4 

 18 -0 



28 -4 



37-3 

 45 -2 

 53 -0 

 59-6 

 70 -6 



15 -9 

 27 -8 

 36 -9 

 49-0 

 66 -6 

 83 -9 



97 -9 



99 -6 



15 3 

 25 -0 

 35 -4 

 46 -0 

 62 -8 

 80 -6 



98 -6 



99 -8 



11-7 



22 -0 

 30 '9 

 39 -6 

 55 -1 

 70 -8 



94-1 



99 -6 



