EEVISIONS OF THE THEOEY OF ELECTEOLYSIS. 157 



Let me now recount several steps in the revision of electrolytic 

 theor}'. 



Grottlius supposed '' that at the moment of the segregated appear- 

 ance of the hydrogen and oxygen there takes place a division of their 

 natural electricity, either by their contact or by mutual friction, so 

 that the former assumes the positive, the latter the negative condi- 

 tion," and that the links of his chain exchanged j^artners in such a 

 way as to leave only the end links free. 



Clausius assumed " that the ions are not permanently united with 

 each other; that part of them exist in the liquid in an uncombined 

 state, wandering about seeking partners." The electric force imposes 

 on all free ions a uniform drift. To Clausius, therefore, should be 

 assigned the introduction of the theory of dissociation to explain 

 elect rolj^sis. But the dissociation of Clausius 'was only slight and 

 was conceived to be the accompaniment of a shifting and unstable 

 equilibrium. 



Scientific judgment respecting the assumption of Clausius re- 

 mained in abeyance for thirty years, when Arrhenius published his 

 celebrated memoir on The Dissociation of Substances Dissolved in 

 Water. An intermediate step, not originally devoted to the theory 

 of dissociation, was Van't Hoff's paper on The Role of Osmotic 

 Pressure in the Analogy between Solutions and Gases. The signifi- 

 cant feature of this paper is the generalization of Avogadro's law to 

 the effect that — 



The pressure which a gas exerts at a given temperature if a definite number 

 of molecules is contained in a definite volume is equal to the osmotic pressure 

 which is produced by most substances under the same conditions if they are 

 dissolved in any given liquid. 



The major part of Van't Hoff's paper deals with nonelectrolytes 

 or organic compounds, such as a solution of sugar, which show little 

 or no deviation from Avogadro's law as applied to osmotic pressure. 

 When he alludes to those substances which exhibit abnormally large 

 osmotic pressure, he acknowledges his indebtedness to the personal 

 suggestion of Arrhenius to the effect that the solutions obeying the 

 law of Avogadro are nonconductors of electricity, a fact indicating 

 that they are not broken down into ions, while solutions which give 

 higher values of the osmotic pressure than accord with the laws of 

 gases are all electrolytes. But if these suffer partial dissociation in 

 solution, then the number of particles is increased, each ion contrib- 

 uting to the pressure as much as a complete molecule. The excessive 

 osmotic pressure is thus accounted for. 



Arrhenius divided the molecules in a conducting solution into 

 active and inactive portions. The former are those whose ions are 

 independent of one another in their movements; the latter are the 



