Messrs Laby and Carse, On a relation, etc. 295 



The constancy of the product — ionic linear dimensions x ve- 

 locity — for a homologous series of the organic ions in the table is 

 in accordance with the hydrodynamical equation 



va = ~- (body of any shape) 



F 



= - — ■ (sphere, no slipping), 



where F is the same for all the ions in the table, and /x is the 

 viscosity of infinitely dilute aqueous solutions (i.e. of water) at 

 25° C $ is a constant for ions of the same shape *. Thus we find 

 under the physical conditions mentioned in the table 



va = -~ x constant, 



S would be approximately constant for the members of a homo- 

 logous series since their graphical formulae are similar; according 

 to this view the chemical property that determines the velocity of 

 ions of the same volume is the shape of the ion. 



Conclusions. 



1. The linear dimensions of thirty-one ions of the homolo- 

 gous series — formic-caproic acids, pyridines, amines, anilines — have 

 been calculated from molecular and atomic volumes. The veloci- 

 ties of these ions in cm. /sec, volt/cm. have been given. It is 

 found that the velocity of an ion of these series is closely inversely 

 proportional to its linear dimensions. 



2. It is shown that these results may be accounted for by 

 considering the motion of an ion through an electrolyte as similar 

 to that of a body through a viscous medium. 



We intend continuing work in this direction. We wish to 

 thank Mr Whetham, F.R.S., for some kindly criticism. 



* Lamb, 'Treatise on the Motion of Fluids. 



Cavendish Laboratory, 

 March, 1906. 



