Phenolic Solutions by Seeds of Hordeum vulgare. 131 



constants of any solution at those temperatures are approximately propor- 

 tional to the corresponding vapour pressures. This result would seem to 

 suggest that there is intimate relationship between the absorption constant 

 and the vapour pressure of a solution. It will be shown later that there is 

 also a close connection between the absorption constant and the surface 

 tension. Apparently the absorption constant is one of the most important 

 constants for a solution in contact with a selectively permeable membrane. 



Relation between the Bate of Diffusion of the various Phenolic Solutions across 

 the Barley Membrane and the Physical Properties of the Solutions. 



It appeared to be of interest to correlate the rate of absorption with the 

 common physical properties which might exert an influence on the rate of 

 diffusion of a solution across the barley membrane. Such properties were 

 evidently osmotic pressure, vapour pressure, viscosity and surface tension. 

 Accordingly these properties were measured for the solutions in question, 

 with the exception of osmotic pressure. The latter was taken as being 

 practically identical for the seminormal phenolic solutions.* Any slight 

 differences there might be in them were obviously unable to account for the 

 great variations noticed in the magnitude of the absorption constants. 

 Further, if the osmotic pressure of the solution were the predominating 

 factor in determining the rate of diffusion across the membrane, the osmotic 

 pressures of the phenolic solutions ought to be negative, since they diffuse 

 across the membrane at a greater rate than pure water. The existence of a 

 solution with a negative osmotic pressure is most unlikely .f 



(a) Surface Tensions of the Solutions. — The surface tensions of the solutions 

 were measured by the capillary tube method, using a similar apparatus to 

 that employed by E. P. Worley in the determination of the surface tensions 

 of aqueous solutions of aniline and phenol.J The correct temperature was 

 attained by immersing the solutions in a thermostat with glass sides for a 

 few hours. The capillary rise was measured by means of a vertical catheto- 

 meter reading to 1/10 mm., whilst the capillary diameter was measured on 

 the microscope stage by means of a graduated eyepiece. Instead of deter- 

 mining the average diameter of the capillary it was thought advisable to 

 determine this at the point where the meniscus had been, a procedure which 



* See also footnote on p. 121. 



t The equality of the partial vapour pressure of water in solutions of ordinary phenol 

 to the vapour pressure of pure water (Table XI) would indicate that the osmotic 

 pressures of phenol solutions are zero. 



\ K. P. Worley, ' Chem. Soc. Journ.,' vol. 105, p. 260 (1914). 



