134 Prof. A. J. Brown and Mr. F. Tinker. Absorption of 



(c) Vapour Pressure — In view of the predominance which has been given 

 to vapour pressure in various theories of the mechanism of osmosis, it 

 seemed of interest to obtain data with respect to the vapour pressures of 

 aqueous phenolic solutions. Owing to the experimental difficulties, and the 

 somewhat complicated apparatus required, it was not possible to measure 

 these in the present research. The nearest results available are those given 

 by Schreinemakers* which refer to aqueous' solutions of phenol at 56 - 3° C. 

 This temperature is considerably higher than those worked with in the case 

 of barley, and on this account the results are not absolutely comparable. 

 The surface tensions of the solutions are given side by side, for purposes of 

 comparison.t 



Table XI. — Vapour Pressures and Surface Tensions of Solutions of Phenol 



at 56-3° C. 



Percentage of 



Total vapour 



Partial vapour 



Surface 



phenol. 



pressure. 



pressure of water. 



tension. 





mm. 



mm. 





o-o 



125 



125 



66-7 



2 -0 



125 



125 



52 -5 



5-58 



127 



125 o 



42 -0 



7-42 



126 -5 



125 



39 -4 



Since the law that the absorption constant is inversely proportional to the 

 surface tension seems to hold for all temperatures,* it would follow that, 

 even at 56 - 3° O, the absorption constant for phenol would be large relative 

 to water, since the surface tensions are still widely different at that tem- 

 perature (see above Table). On the other hand, both the total and partial 

 vapour pressures of the phenol solutions of all concentrations differ very 

 slightly from the vapour pressure of pure water, and it will be seen that, 

 although the total vapour pressures of the phenol solutions are very slightly 

 greater than the vapour pressure of pure water, they are by no means great 

 enough to account for the large differences in the rates of absorption. 



Conclusions. 



It is apparent from what has preceded that the variations in the rate at 

 which phenolic solutions diffuse across the differentially permeable membrane 

 of barley are primarily associated with differences in the surface tensions of 

 the solutions. In the case of the phenolic solutions studied, the surface 

 tension is the only physical property whose variation is great enough to 



* Schreinemakers, 'Roy. Acad. Amsterdam Proc.,' vol. 3, pp. 1 and 701. 

 t The surface tensions are taken from R. P. Worley's paper (Ice. cit.). 

 X See p. 132. 



