96 THE ROYAL SOCIETY OF CANADA 
tions that may be regarded as experimentally established and in ac- 
cordance with the principles of thermodynamics and the accepted laws 
of energy, cannot fail to afford interesting results. The present paper 
is an attempt to establish such a thermodynamic criterion. The degree 
of success of the attempt must be determined solely by its consistency 
with and ability to explain, experimental facts and obvious deductions 
from those facts. Whether tenable or untenable as a theory, the facts 
and deductions upon which the theory is based seem to justify at least 
a careful consideration before a final judgment is passed. 
The Theoretical Exposition 
In a recent paper on the “Range of Molecular Action and the 
Thickness of Liquid Films,” ! it was shown that for a number of sub- 
stances representing different classes of chemical compounds and for a 
considerable range of temperatures the surface tension of the liquid 
phase per unit area of cross-section is practically equal numerically to 
the pressure the substance would exert if it were a perfect gas. In the 
same connection it was shown that both the thickness of the liquid film 
and the molecular attraction in the film vary with the temperature. 
Hence the surface-tension is a function, not of the temperature alone, 
but of the thickness of the film as well, or, mathematically expressed, 
RP LE DR Lec ne (A) 
- 
m m 
where ¥ is the experimentally observed surface-tension, 7 the computed 
thickness of the liquid film, p the density of the liquid, m the molecular 
weight of the substance as a vapour, R the gas constant and T the 
absolute temperature. If this equation be analyzed and studied in 
connection with the established numerical relations of the experimental 
facts it shows that the value of the ratio p/m is independent of poly- 
merization. For it holds true for widely different sorts of substances 
and, so far as tested, for considerable differences in temperatures. 
Since m is the molecular weight of the substance in the form of vapour 
and (p/m) R.T gives the surface-tension per unit area of cross-section 
ate es : 
we have the striking fact that p = T, the pressure per unit area 
m 
the substance would exert as a perfect gas, is numerically equal to 
the tension per unit area exerted by the liquid film. If the number 


1 Jour. of Phys. Chem. 16 234 (1912). 
