Phenolic Solutions by Seeds of Hordeum vulgare. 135 



account for the relative differences in the absorption constants. At any 

 given temperature the magnitudes of the other physical properties of the 

 aqueous phenolic solutions are practically the same. This does not mean 

 that these factors have no influence at all on the rate of absorption. 

 Indeed, they must exert a more or less pronounced influence on the rate of 

 diffusion of a solution across a semipermeable membrane. Bartrell, for 

 instance, has shown* that solutions diffusing through copper ferrocyanide 

 and other membranes obey Poiseuille's law, according to which the rate of 

 diffusion of a solution across a membrane would be inversely proportional to 

 its viscosity. It has also been shown in the case of barley that if a series of 

 temperatures are chosen, the rate of diffusion of moisture into the seeds is 

 proportional to the corresponding vapour pressures. 



The only legitimate conclusion to draw from the preceding work is that 

 when the osmotic pressures, vapour pressures, and viscosities of a series of 

 solutions of 'permeable solutes are equal, their rates of diffusion across the 

 barley membrane are inversely proportional to their surface tensions. 



A close relationship between the rate of diffusion of solutions of permeable 

 solutes and their surface tensions might be anticipated. When a solution 

 has a lower surface tension than the pure solvent, it has also a lower intrinsic 

 pressure. In terms of the Laplace theory of capillarity this implies that, by 

 some means or another, the solute molecules have diminished the attractive 

 power of the solvent molecules for one another. The solvent molecules will 

 therefore tend to diffuse over the surface of the barley membrane all the more 

 readily, and from thence on to the surfaces of the solid particles of absorbent 

 material within the seeds.f 



These considerations must be confined, however, to solutions of solutes 

 which are permeable to the membrane, and not extended to osmotic phenomena 

 as a whole, as I. Traube has attempted to do.* Driving forces due to 

 differences in osmotic pressure on the two opposite sides of the membrane 

 must be eliminated. This is not the case when the membrane is impermeable 

 to the solute and pure water alone enters the seed. 



* Bartell, 'J. Phys. Chem.,' vol. 15, p. 659 (1911). 



t The relationship between the intrinsic pressure, or "attraction pressure," and other 

 physical properties such as surface tension, lowering of vapour pressure, compressibility 

 of solution, etc., has been worked out in detail by I. Traube (' J. Phys. Chem.,' vol. 14 

 p. 452 (1910), and many other papers). In particular low surface tension, and therefore 

 low intrinsic pressure, is accompanied by abnormally high vapour pressure. For instance, 

 it has been shown in Table XI on p. 134 of the present paper that the partial vapour 

 pressure of water in phenol solutions is equal to that of pure water. The fact that it is 

 not greater, however, shows incidentally that the moisture does not pass across the 

 membrane as vapour. 



\ I. Traube, loc. cit. 



VOL. LXXXIX. — B. 



