280 Mr. W. C. D. Whetham on the 



those properties with the phenomena o£ osmotic pressure and 

 chemical activity. Hence there followed a general though 

 not universal adoption of the theory, despite the opposition 

 of some chemists. Lately, however, evidence has been offered 

 to show that the general connexion between the properties 

 of electrolytes, which seems to exist in the case of solutions 

 in water, fails when other solvents are used, and that the exact 

 numerical relations between, for example, conductivity and 

 osmotic pressure, which were at one time thought to hold, 

 are inexact at moderate concentrations even for aqueous 

 solutions. It has hence been argued that the fundamental 

 conceptions of the dissociation theory are erroneous, and that 

 it should no longer be accepted as a valid explanation of the 

 electrolytic phenomena. In the present stage of the dis- 

 cussion, it may be of interest to examine the foundations on 

 which the theory rests, and to inquire how far they are 

 affected by such criticism as we have indicated. 



The conception of the complete independence from each 

 other of certain parts of the dissolved molecules of electro- 

 lytes is attained by two distinct lines of research : (1) the 

 examination of the electrolytic conductivity; and (2) the 

 consideration of the thermodynamic theory of osmotic pressure 

 and allied phenomena. 



The appearance of the products of electrolysis at the elec- 

 trodes, and at the electrodes only, indicates that the opposite 

 parts of the solute must travel in opposite directions through 

 the liquid under the influence of the electric forces, while 

 Faraday's experiments show that the separation of a definite 

 quantity of substance at the electrodes is always associated 

 with the passage through the solution of a definite quantity 

 of electricity, which is proportional to the valency of the ion. 

 We are thus led to conclude that the process of electrolytic 

 conduction is a kind of convection, in which the opposite 

 ions are moved electrically through the liquid, and carry 

 with them definite electric charges. This view of the pheno- 

 mena was further developed by Kohlrausch, who showed 

 that a calculation of the velocities with which the ions moved 

 under a given electric potential gradient could be made from 

 a knowledge of the conductivity of the solution and of the 

 transport ratio, which had been investigated by Hittorf. 

 The numerical values of the mobilities of different ions 

 obtained by Kohlrausch's theory were confirmed by Lodge, 

 Whetham, Orme Masson, and Steele, who have experi- 

 mentally determined the velocity of certain ions by tracing 

 their effect on an indicator, or by measuring the rate of 

 motion of the boundarv between two different solutions. 



