114 J- F - MCCLENDON. 



1 am indebted to several persons for suggestions, especially 

 to Dr. Ralph Lillie 1 and Professor B. M. Duggar. 



I. INTRODUCTION. 



The object of this paper is to bring the "vital" phenomena, 

 as far as possible, within the scope of physics and chemistry, and 

 not to elucidate physical and chemical processes. It should 

 therefore be borne in mind that the osmotic phenomena of 

 "dead" systems are not all satisfactorily explained. 



The Vant Hoff-Arrhenius theory of osmosis concerns itself 

 with the number of particles, molecules and ions, in solution, 

 and is applicable to dilute solutions, in which the total volume of 

 the dissolved particles is negligible. However, in more con- 

 centrated solutions, the volume of the dissolved particles is of 

 the same importance as the volume of the molecules in gases, as 

 expressed in Van der Waal's equation. Also the dissolved 

 particles bind molecules of the solvent and so reduce the volume 

 of the free solvent. 



That the molecules and ions of a dissolved substance bind 

 some molecules of the solvent, follows from the work of Jones 

 and his collaborators. 2 Compare also the work of Pickering. 3 

 Jones concludes that the larger the number of molecules of water 

 of crystallization, the greater the hydrating power of a substance 

 in aqueous solution. The number of molecules of water bound 

 by one molecule of the solute usually increases with dilution up 

 to a certain point (the boundary between concentrated and 

 dilute solutions, beyond which there is no heat of dilution). 

 The bond between ions and the solvent is also indicated by the 

 phenomenon known as "electrical transference." It an elec- 

 trolyte and a non-electrolyte be dissolved in water and an 

 electric current passed through the solution, water will be carried 

 along with the ions to the electrodes. 



With these corrections, the Vant Hoff-Arrhenius theory 

 accounts for osmotic pressure, but does not show why main 

 substances exert no osmotic pressure, in other words, why no 



J Cf. this journal, 1909. XVII., 188. 



2 "Hydrates in Aqueous Solution," Pub. No. 8, Carnegie Ins. Wash., 1907. 

 ' Whetam, "The Theory of Solution," 1902, Cambridge, p. 170. 



