SOME RECENT DEVELOPMENTS OF THE 

 ELECTROLYTIC DISSOCIATION THEORY 



By GEORGE SENTER, Ph.D. 

 Lecturer on Chemistry, Si. Mary's Hospital Medical School 



PAGE 



Introduction 381 



Osmotic Pressure 384 



Combination between Solvent and Solute. The Hydrate 



Theory 386 



Solvents other than Water 392 



Complex Ions 394 



Some Criticisms of the Theory 396 



Introduction 



The electrolytic dissociation theory, according to which the 

 molecules of the dissolved substance in solutions which conduct 

 the electric current are split up to a greater or less extent 

 into ions — atoms or groups of atoms associated with electric 

 charges — was proposed by the Swedish physicist Arrhenius in 

 1887. Thirty* years before, Clausius had been led by purely 

 physical considerations to the view that, in some cases, free ions 

 are present in solutions of electrolytes ; but he considered that 

 the proportion was probably too small to allow of detection by 

 chemical means. On the other hand, Arrhenius assumed that 

 in solutions which have a high conductivity the greater propor- 

 tion of the molecules of the solute are split up into ions, which 

 alone are effective in conveying the current, that the degree 

 of ionisation increases with dilution, and that in very dilute 

 (tAtt normal) solutions of such substances as sodium chloride 

 and hydrochloric acid, ionisation is practical^ complete. 

 According to this theory, the specific conductivity of a solution 

 depends only on the number of ions present per unit volume 

 and on their speed; and as the latter in dilute solution will not 

 be greatly affected by further dilution, the friction being prac- 

 tically the same as in pure water, the coefficient of ionisation at 

 a particular dilution — in other words, the proportion of the 

 solute split up into ions— can be determined by comparison of 



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