FACTORS INFLUENCING IMBIBITION 



113 



the swelling of kelp stipe, but are known to influence many other processes, 

 the magnitude of their effects being in the order given. 



These so-called lyotropic effects are apparently due largely to differences 

 in the degree of hydration of various kinds of ions although other factors are 

 probably also involved. Their lyotropic effect on the swelling of kelp stipe, 

 agar, and other similar materials which bear a negative charge with respect 



0.I25M0.25M0.5M IM 



VOLUME MOLAR CONCENTRATION 



Fig. 23. Influence of cations on imbibition of water by kelp stipe. 

 Data of Wagner (1936). 



to water probably may be explained as follows: The negative charge on the 

 kelp stipe is apparently due to adsorption of hydroxyl ions, leaving hydrogen 

 ions in the outer zone of the electrical double layer. When immersed in a 

 solution of an electrolyte not only is water imbibed, but an exchange of 

 cations occurs, some of the cations in the electrolyte replacing hydrogen ions 

 in the kelp stipe. The displaced hydrogen ions of the double layer pair off 

 with the residual anions of the electrolyte. The water molecules associated 

 with the cations which enter the double layer will contribute to the total 

 hydration of the kelp. The different degrees of swelling caused by the differ- 

 ent cations is probably due partly to the different numbers of water molecules 



