Chemistry. — ““ Urease and the radiation-theory of enzyme action’, III. 
By Dr. H. P. BARENDRECHT. (Communicated by Prof. J. BöESEKEN). 
(Communicated in the meeting of May 3, 1919). 
8. The influence of other substances on the urease activity. 
The question was raised, whether in these concentrated solutions 
of urea the H-ion concentration was perhaps lowered also through 
the slightly alkaline substance urea itself. 
The electrometrie measurement of the py in the 8°/, phosphate 
solution showed indeed a distinct increase after addition of 8°/, urea. 
It was, however, soon established, that this increase was not due 
to a shifting of the true reaction to the alkaline side, but to a 
diminution of both H-ions and QOH-ions, or, in other words, to a 
decreased dissociation of H,O in these concentrated solutions of urea. 
This conclusion was readily arrived at by the following experiments. 
The py was determined again in 8°/, phosphate solutions. Then 
a second time after addition of a small amount of ammonia (1 c.c. 
of 7 N). For each of these estimations 10 c.c. of 9.6°/, phos- 
phate was brought with water or diluted ammonia to 12 c.c. 
The results obtained are summarised as follows: 
PH in: 
| Diffe- | Phosphate | Diffe- | Phosphate + 1 c.c. 
Phosphate + 8 %/, urea | rence | alone rence | NH; 51, N 
6.79 0.11 6.68 | 0.03 6.71 
6.97 0.08 6.89 0.03 6.92 
7.59 0.10 7.49 0.07 | 7.56 
1.93 0.10 1.83 0.18 | 8.01 
8.20 0.10 8.10 0.34 8.44 
As will be seen from SÖRENSEN's determinations of pg in standard 
phosphate mixtures, the buffer-value of these solutions becomes 
considerably diminished, when py approaches 8. Therefore the same 
