44 



On Kohlrausch's Theory of Ionic Velocity. 



Kohlrausch calculates the relative velocity of the two ions 

 U = u + v from the molecular conductivity k/m, where k = spe- 

 cific conductivity of the solution, and m its contents in gramme 

 equivalents of salt, TJ 1 ==u-+-v = k/m. If now we suppose that 

 at any instant only 1/nth of the number of molecules are active, 



we should apparently have to put U 2 = — in order that the 



same current may be carried, which would give U 2 = nUi. 



But this U 2 represents the actual velocity of the ions while 

 they are " free," and if we take a u dynamical " view of the 

 dissociation equilibrium, they are only free for 1/nth of their 

 time ; while combined they have no relative velocity, and so 



their average velocity for any long time is -112 = 11!, the same 

 as on Kohlrausch's hypothesis. 



The investigation alluded to above, at which I am now 

 working, seems to yield excellent 

 results for certain cases, though it is 

 of somewhat limited application. It 

 consists in observing the phenomena 

 at the junction of two salt-solutions, 

 one of which is differently coloured 

 to the other, when a current of elec- 

 tricity is passed across it. Salts are 

 chosen which have one ion in com- 

 mon and the other different. Let 

 us represent them by AB and CB, 

 and consider the junction pheno- 

 mena. The effect of the molecular 

 interchanges will be a motion of B 

 ions in one direction, and a motion 

 of C ions and of A ions in the other. 

 When a C ion crosses the boundary, 



it again forms CB, but the colour of CB is different to that 

 of AB, hence the boundary between the colours will move. 



The method will be discussed when more experimental 

 results are obtained ; it appears that by measuring the rate of 

 this motion the velocity of the ions can be arrived at. The 

 present is merely a preliminary communication in explanation 

 of the experiments shown to the Physical Society of .London 

 on the occasion of their recent visit to Cambridge. 



— CB 



