126 
MR. W. R. BOUSFIELD: IONIC SIZE IN RELATION TO 
out in the tables, together with the total volume of the pair of ions, which is indicated 
by the letter I w , and is the sum of the volumes of the two ions. 
The above are the figures which will most frequently be required. Where the 
values for other concentrations are wanted they can be calculated in the ma nn er 
above indicated. It will be noticed that the volume of the sodium ion greatlv exceeds 
that of either the K or Cl ion, indicating that the sodium ion is combined with about 
four times as much water as either of the other two ions. 
Part IV.— Ionic Size in Relation to Density. 
(a) Solution Volume a Linear Function of Ionic Volume .—As explained in the 
former paper, the solution volume derived from density observations is a measure of 
the amount of contraction which takes place on solution, and therefore a measure 
of the amount of water entering into combination with the solute. The ionic 
volumes at different dilutions should be nearly proportional to the amounts of 
water in combination with the ions, if the volume of water is large compared with 
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X 
X 
FCl 
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x=/owc Vcn 
?/ -Sol UT/Ot 
UME. 
v Volume 
oCN. 
4 5 6 7 
Diagram IV. 
the volume of the ionic nucleus. Hence, if our theory is correct, we ought to find 
the solution volume approximately a linear function of the ionic volume of the pairs of 
ions in dilute solutions. 
In the following tables are set out the solution volumes for KC1 and NaCl solutions 
from 0 to 6 per cent,, together with the ionic volumes taken from Tables XIII. 
and XIV. The solution volumes are calculated from the densities by means of the 
formula 
1 100/1 1 
