136 
MR. W. R. BOUSFIELD : IONIC SIZE IN RELATION TO 
be Cr l5 Cr 2 , Cr 3 , and the viscosity of the whole p = C£/3r = CR, if R, is the radion 
of the whole, since If = 2/3 r. 
We have determined the values of the radions for K, Na and Cl ions in Part III. (g) 
of this paper. In extending the conception of the radion to the molecules of the 
solvent or to other molecules, its magnitude in any particular case must be measured 
in the same ionic units, and by reference to the scale furnished by the ions whose 
radions we have determined. Thus we know, upon our theory, the radions of K and 
Cl ions, which are approximately equal, and we find that the introduction of such 
ions into water makes, speaking roughly, no change in the viscosity of the water. This 
tells us at once (if we neglect the small change in the water radion which is probably 
produced by the solute) that the radion of water is of about the same magnitude as 
the radions of the K and Cl ions. As a fact, the introduction of these ions slightly 
diminishes the viscosity of water and hence the radion of the uncombined water in 
the solution should be somewhat greater than the radions of K and Cl ions. 
There is good reason for believing that the introduction of a solute into water 
somewhat lowers the radion of water, since the process of abstraction of water 
molecules by the solute breaks up some of the molecular complexes of the un¬ 
combined water and therefore lowers the average molecular size of the un-combined 
water. The investigation of the amount of this lowering is a complex matter, and 
we shall neglect it, as it does not seriously affect the general character of our results, 
though it involves a slight loss of accuracy. 
The fundamental constant C of our viscosity equation is calculated from the 
experimental data in reference to water and K.C1 and NaCl solutions, but it is not 
necessary to give the details of the process. The justification of the value given and 
also of the theory involved is to be found in the correspondence between obser\ ed 
and calculated values given later. The value of C determined from the data at 
18° C. is C = 0-54. 
No closer adjustment of its value is at present attainable. This value gives the 
radion for pure water as 
R = 77 /C = g ;^ 0514 = 0-01947. 
(y’) Experimental Verification. —We now proceed to test the hypothesis by 
reference to the experimental data before given. Taking first the simple case of 
mixtures of KC1 and NaCl normal solutions, we have here solutions which do not 
materially change their state of aggregation upon mixing. We can therefore take 
the radions of the solutions before mixing as being identical with their radions when 
mixed. The radion of the normal KC1 solution is 
rj/C = g;gi° 37 -^ = 0-01929. 
The radion of the NaCl normal solution is 
n!C = 0 01 14 3 -g = 0-02117. 
a 0 ■ 5 4 
