PROCEEDINGS 
OF THE 
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A relation between the velocity cmd volume of organic ions in 
aqueous solutions. By G. A. Carse, Emmanuel College, and 
T. H. Laby, Emmanuel College, 1851 Exhibition Scholars. 
(Communicated by Professor Thomson, F.R.S.) 
[Read 12 Nov. 1906.] 
In a previous number of the Proceedings*, we have shown that 
theoretical and experimental considerations suggest that the 
motion of an ion in electrolytic conduction is analogous to the 
motion of a small body through a viscous medium. To test this 
view of the mechanism of electrolytic conduction, the linear 
dimensions of a number of the ions of homologous organic acids 
and bases were calculated from molecular volumes and the atomic 
volume of hydrogen. It was found that the products, ionic volume 
x linear dimension of the ion, were sensibly constant for the 
members of such homologous series. 
This was shown to be in accordance with the hydrodynamical 
equation 
F 
where F is the driving force acting on the ion, v its velocity, a its 
linear dimension, S a constant depending on its shape, and g the 
viscosity of the electrolyte. In the case of a sphere moving 
through a fluid with no slipping this equation is 
F 
va - „ . 
0 7 T/jL 
When very dilute aqueous solutions at a given temperature, 
and ionic velocities under a held of one volt per cm. are con- 
sidered, g and F are constant, and the value of va for a given ion 
equals the product of a constant into an expression depending on 
the shape of that ion. It would thus appear that the similarity 
of shape of the ions of a homologous series would lead to the 
constancy of va for such a series. In the paper referred to va has 
been calculated for 7 fatty acids, 5 homologues of pyridine, 8 of 
aniline, and 11 amines, the values given below being obtained: — 
* Camb. Phil. Soc. Vol. xm, pt v, p. 287 (1906). 
1 
m i oi 
VOL. XIV. PT. I. 
