248 



Dr. W. M. Bayliss. 



[June 30, 



to be expected that, by passing an electric current through the membrane by- 

 putting a platinum anode inside the osmometer and a similar cathode in the 

 outer solution, the cations would be enabled to escape. This does in fact 

 happen. The osmotic pressure falls, the solution inside becomes turbid owing 

 to excess of free acid, while the outer fluid becomes alkaline. If the current 

 be stopped and the outer alkaline solution be replaced by water, the osmotic 

 pressure does not rise again until free alkali is added to replace that which 

 has been allowed to diffuse out by the agency of the electric current. If the 

 cation were a complex one containing colour acid it might be supposed that 

 the outer fluid would be coloured in the above experiment. This, in point of 

 fact, was the case to a slight degree. But parchment-paper is not absolutely 

 impermeable to Congo red and the permeability is somewhat increased by the 

 presence of alkali. The depth of colour did not seem to be greater than 

 would have been attained in the absence of the electric current, and in the 

 experiment described in the previous section, made for another purpose, no 

 colour passed through the membrane during the time of the experiment, 

 although considerable amounts of sodium hydroxide were formed. 



The degree to which parchment-paper of the thick kind used in my 

 experiments is permeable to the dye is actually very small. In an experi- 

 ment in which the outer water in the osmometer was not changed for ten 

 weeks the dye contained therein only amounted to O0078 per cent. 



There is a slight possibility that, in a metallic osmometer, closure of a 

 circuit between the two sides of the membrane may, to a very small extent, 

 enable Na" ions to escape. It seems most probable that polarisation would 

 rapidly annul such a current. As already stated, moreover, no diffusion of 

 alkali can be detected in the absence of an extraneous E.M.F. 



The problem dealt with in this section is closely connected with a funda- 

 mental difficulty in the Arrhenius theory of electrolytic dissociation. 

 According to the kinetic theory, the dissociated ions with which we are 

 concerned are free from mutual influence upon one another, so that there 

 should be no electrostatic attraction to prevent the diffusible ions from 

 passing freely through the membrane. The origin of the energy required to 

 separate the ions is a matter of some uncertainty. It has been suggested by 

 Larmor* that "internal potential energy is released owing to the ions 

 entering into relations of closer affinity with the solvent," and by Bousfield 

 and Lowryt that the affinity of the " ionic nucleus " for water is the main 

 source of the energy required. 



* " Wilde Lectures," ' Mem. Manchester Lit. and Phil. Soc.,' 1908, vol. 52, Mem. 10, 

 p. 37. 



t 'Trans. Faraday Soc.,' 1907, vol. 3, p. 125. 



