IN AQUEOUS SOLUTION, AND THE EXISTENCE OF- COMPLEX IONS. 
109 
not destroyed or moved liy the current if p' is constant^" On the other liajid, p' 
varies, it will move in the positive or negative direction according as the change in 
p' is in the one or the other direction; it is further shown that such a sharp 
houndary may be formed during electrolysis, provided that p/ changes in such a way 
that the following; ion moves slower than that in the solution it follows. 
The case of the houndary between two electrolytes having a common ion is 
discussed by Kohlrausch in this paper and also by Weber (‘ Sitzungsber. k. Akad. 
Wiss.,’ Berlin, 1897, 936), and Massox (‘Phil. Trans.,’ A, 1899, vol. 192, p. 331). 
Kohlrausch and Massox arrive independently at the conclusion that tire con¬ 
centration of the two solutions becomes mechanically adjusted during electrolysis, 
so that 
c p 
c! p' ’ 
where c and d represent the concentration of the two solutions, and p and p' the 
transport number of the non-common ions. 
Massox gives experimental proof of this for the case of a soluti(rn of cojrper chloi ide 
- following potassium chloride. 
The stalrility of such a margin is dependent on the relation between the velocity ot 
the following and the preceding ions. The fact that the boundary between certain 
pairs of solutions was stable when the current moved in one direction, but shorved 
signs of mixing when sent in the opposite direction, was first explained l)y 
Whetham (‘Phil. Trans.,’ A, 1893, p. 337). 
Some of tlie phenomena at the junction of two solutions had been previously 
observed by Gore (‘Boy. Soc. Proc.,’ 1880-1881), hut were not looked at from the 
present standpoint. 
Weber shows mathematically that the boundary is stable when the slower ion 
follows the faster one, and experimental proof of this is given independently ])y 
Massox, who found the relative velocities of the potassium and cldorine ions in 
potassium chloride to he the same whether the anion was followed by the chromate 
or the tartaric ion. 
For the velocity of the boundary when this condition is fulfilled, Weber gives the 
equation 
ilx, ill 
(It {U -t- r)r ’ 
where the symbols have the same slgnificati<m as before. The velocity is lienee 
determined by u and c, the velocity and ionic concentration of the jirecedlng ion. For 
• ( l.dO 7 V 
the anion boundary — = - - ; hence if c = cs the relative velocities of the two 
(It (u -h r)q ^ 
margins gives at once u/v. 
* Such a margin is obviously lost by diffusion unless some special condition for its maintenance is 
fulfilled. 
