CAPILLARY CONSTANTS 



443 



dissolved gas, by the nature of the gas in contact with the liquid 

 surface, by pressure, by the state of molecular aggregation of 

 the liquid, and above all by temperature. In the earlier 

 researches on the subject, comparisons were made at the same 

 temperature, but it was recognised by Schiff that surface- 

 tensions should be compared at corresponding temperatures — 

 that is, at temperatures which are equal fractions of the critical 

 temperatures of the liquids under comparison. Unfortunately 

 the critical temperatures of comparatively few organic com- 

 pounds have been directly determined, and it was supposed 

 that these conditions were fulfilled at the boiling-points (under 

 atmospheric pressure) of the liquids examined. If this be the 

 case, the ratio of the boiling-point to the critical temperature 

 of all liquids should be the same when temperatures are 

 measured on the absolute scale. The degree of exactness with 

 which this condition is fulfilled is exhibited in the table given 

 below, which shows the value of this ratio calculated for a 

 number of substances of very diverse boiling-points. 



Table II. 1 



It seems, therefore, that the condition is approximately fulfilled, 

 and, calculating from the carbon compounds only, the relation 



1 The data for the calculations in this table have been taken from Kaye and 

 Laby's Tables of Physical and Chemical Constants, 191 1. 



