156 CHEMISTRY: W. D. HARKINS 
here has a much wider range of apphcation, since it may be used to indicate 
the internal structure of a Hquid, to predict the distribution (partition and 
adsorption) of components between different phases, interfaces, and surfaces 
(these will be designated by the term regions), and is of great importance in 
theories of ideal and non-ideal solutions: — in other words it is a theory of 
what is called by Washburn^ the 'thermodynamic environment.' This in the 
sense of our theory would be designated as the electromagnetic environment. 
Application to Interfaces and to Distribution between Regions. — While in 
applying the hypothesis, the intensity of the stray fields around the molecules 
is of primary importance, at least one additional principle must be used if the 
direction which any change will take by itself is to be predicted. As might 
be expected the second law of thermodynamics is of fundamental importance 
in this connection, and for this purpose it may be stated in the form: Any 
change which takes place by itseh in a system will proceed in the direction 
which will result in a decrease in the free energy of the system. Thus a sur- 
face will decrease in area by itself, but will not increase. Since a rapid varia- 
tion of the intensity of the stray field with the distance in any direction, is ac- 
companied by a high concentration of free energy, the second law indicates 
that in any change which takes place by itself, the variation in the stray field 
becomes less abrupt. If we imagine the surface of a liquid up to a bounding, 
surface plane, to have just the same structure as the interior of the liquid, 
then the actual surface always has a smaller free energy^ than would be 
given by calculation for this imaginary surface, and therefore the drop in in- 
tensity of the stray electromagnetic field at the actual surface is always less 
than it would be at a surface of the structure of the imaginary surface. Since 
a molecule is often made up of several species of atoms, the stray field around 
it is often unsymmetrical. Thus many organic molecules, such as the pri- 
mary normal alcohols, acids, amines, nitro compounds, nitriles, ethylene and 
acetylene derivatives, etc., consist of a paraffin chain around which the stray 
field has a relatively low intensity (a so-called non-polar group), while at the 
other end of the molecule there is a group containing oxygen or nitrogen, 
sometimes with metals in addition, around which the intensity of the stray 
field is relatively high (a polar group). Such molecules may be designated as 
folar-nonpolar , and designated by the symbol o , where o represents the 
polar, and the nonpolar end of the molecule. If molecules of this type, 
such as butyric acid (C3H7COOH), are put in a two phase system consisting 
of a polar liquid such as water, and a nonpolar liquid such as octane, then the 
free energy of the interface will be less when the transition from one liquid to 
the other is made by molecules of butyric acid, with their polar ends turned 
toward the water, and their nonpolar ends turned toward the octane, since 
in this way the abruptness of the transition is decreased. 
The problem here arises as to the distribution of molecules of the polar- 
nonpolar type between the two liquid phases, their surfaces, and the interface 
