32 Mr. W. Sutherland on Ionization in Solutions 



approximate formula (30), which can be used for finding the 

 dielectric capacity of atoms of known ionic conductivity and 

 volume. 



J. J. Thomson and Nernst have suggested that ionization 

 is caused by large dielectric capacity of the solvent. This 

 means, of course, large in relation to the mean dielectric 

 capacity of the solute. Many authors have sought to show 

 that the degree of ionization in different solvents is propor- 

 tional to their dielectric capacity. But as we have proved 

 ionization to be almost always complete, this attempt to give 

 greater definiteness to the suggestion of Thomson and Nernst 

 falls to the ground. Large dielectric capacity in the solvent 

 facilitates ionization by reducing the electric forces between 

 the ions, by reducing their mutual potential electric energy. 

 By the same action it causes the ions to space themselves 

 approximately uniformly, and with each ion as far from its 

 neighbouring oppositely charged ions as is consistent with 

 uniform distribution. In my previous paper I suggested 

 that large dielectric capacity and ionization are both con- 

 nected with the electric doublets of latent valency in certain 

 atoms. A general theory of dielectric capacity both normal 

 and exceptional is much needed in the present state of 

 molecular physics. 



9. The Use of Molecular Conductivities and Diffusivities 

 for Calculating Molecular and Atomic Sizes. 



In my previous paper it was shown that ionic sizes can be 

 calculated from ionic velocities, but, the theory of that paper 

 being incomplete, the ionic size calculated came out approxi- 

 mately correct only by a certain compensation of errors. 

 But with the more accurate evaluation of atomic sizes by the 

 kinetic theory of gases, carried out by Jeans (Phil. Mag. [6] 

 viii. p. 700), with the aid of the magnitude of the electron 

 charge obtained by J. J. Thomson and his pupils, it is 

 possible to apply a fairly stringent test to the theory of the 

 present paper by using it in the calculation of atomic sizes. 

 The evaluations of Jeans could be improved by taking 

 account of the effect of cohesioual forces on the viscosity of 

 gases. But for present purposes his results suffice. He finds 

 the radius of the hydrogen molecule to be 1 x 10~ 8 cm. We 

 shall now calculate the radius of the hydrogen molecule in 

 the two following ways : — First from ionic conductivities. 

 Here we shall find first the radius of the largest fatty acid 

 ion in the last table by comparing (31) and (34). This ion 

 is selecied because we have seen that it belongs to a group 

 where the induced viscosity seems not to interfere seriously 



