﻿902 Dr. So C. Bradford on the 



the aggregate. These effects are the more likely with solutes 

 having large molecular fields. Or again, as pointed out 

 above, there may be a closer approximation of solute and 

 solvent particles, on account of a suitable relation between 

 the positions of the electric charges, with a corresponding 

 alteration in the external field around the particles. Thus it 

 is possible that a solute may reduce the surface tension of a 

 solvent although the molecular field of the solute may be the 

 greater. This effect is the more likely with solutes having 

 hydroxyl or acidic hydrogen groups. 



Such considerations do not increase the prospect of 

 finding an exact ratio between the increments of surface 

 tension and freezing-point depression. On this account the 

 constancy in this ratio shown by the few substances for 

 which there are data available is the more striking. In the 

 table below, the observed depressions of the freezing-point are 

 taken from Landolt and Bornstein's Tabellen, 1912. But as 

 the determinations of surface tension were not made for the 

 same concentrations as the freezing-point observations, the 

 values given in the table were read from smooth curves 

 drawn through points corresponding to the published figures, 

 taking the surface tension of water as the zero point on each 

 curve. On account of the sparseness of the observations 

 there is a slight uncertainty in the values at the lower 

 concentrations. More extensive determinations are desirable 

 and are being undertaken. 



The last column but one in the table shows the ratio 

 between the increments in surface tension and depression of 

 freezing-point, the normal depression being taken as 1°"86 

 per gram-mole per litre. The chlorides of barium, calcium, 

 magnesium, and strontium behave like those of sodium or 

 potassium. Copper and magnesium sulphates are the only 

 other substances for which both cryoscopic data, and surface- 

 tension determinations by the method of capillary rise, are 

 available. Surface tensions observed by other methods do 

 not correspond with the values obtained from the capillary 

 rise, nor are they proportional to the increments in the 

 depression of the freezing-point. The above-mentioned 

 sulphates give depressions of freezing-point at moderate 

 concentrations which are even less than the normal, so that 

 it is clear that some disturbing factor, such as aggregation, 

 comes into play. 



With these two exceptions the constancy in the ratio is 

 remarkable, being in many cases about 0'64. It is interesting 

 to inquire the meaning of this figure. It has been assumed 

 that the surface tension of a liquid is proportional to its 



