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MR. W. R. BOUSFIELD : IONIC SIZE IN RELATION TO 
Page 
(d) Extended conception of the radion.135 
(e) The general viscosity formula.135 
(/) Experimental verification of a 'priori formula ... . .136 
(g) Comparison Avith Gruneisen’s results. . ....141 
Part VI.—Ionic Size in Relation to Freezing-point Depression. 
(a) General considerations.142 
( b ) Effective molecular freezing-point depression a linear function of ionic volume.143 
(c) Effective molecular freezing-point depression a linear function of solution volume .... 146 
( d ) Correction of freezing-point depression by reference to ionic volumes.148 . 
Part VII.—Ionic Size in Relation to Refractive Power. 
Part VIII.—Concluding Observations. 
Appendix. 
Note on the Van’t Hoff laiv 
155 
Part I.— Introduction. 
The electrical conductivity of a solution depends upon the rates of transference of the 
ionised portions of the solute in opposite directions under the influence of the apjilied 
electro-motive force. These rates of transference under a given potential gradient are 
conditioned by the viscosity of the medium and the sizes and possibly the shapes of 
the ions. Increase of viscosity of the solution and increase in the sizes of the 
migrating ions both tend to diminish the rates of transference of the ions, and thus to 
lower the conductivity. If the ion enters into combination with one or more 
molecules of water, its size is necessarily increased, and the motion of the water¬ 
logged ion becomes more sluggish as the amount of water in combination increases. 
To separate the elements which determine the conductivity of an electrolytic solution, 
and to analyse the joint effect of variations in ionisation, viscosity and water com¬ 
bination is a matter of great difficulty, ’ but of much importance to the theory of 
solution. 
In a former paper (Bousfield on “ Ionic Sizes in Relation to the Conductivity of 
Electrolytes ” *) was proposed a method for effecting such an analysis based upon the 
expression evaluated by Stokes for the terminal velocity of a small sphere moving in 
a viscous medium. A consideration of the influence of the Avater in combination with 
the ion upon its mobility was used to obtain a correction of the coefficient of 
* Communicated to the Royal Society, February 10, 1905. Revised and published in the ‘ Zeit. fur 
Phys. Chem.,’ 53, 257, 1905. (See infra, Part VIII., p. 153.) 
