CHEMISTRY: W. D. HARKINS 
159 
the ordinates give the surface tension; the abscissae, the logarithm of the 
concentration, and the adsorption is obtained from the slope of the respective 
curve by means of the Gibbs equation, /j, = where is the adsorption, 
7 is the surface tension, and c is the concentration of the solute. The curve 
for the water- vapor interface hes to the left of that for the water phase of 
the two phase system, which indicates that the restraining force of the former 
interface is the higher. The curve marked I. B. P. represents that which 
would be obtained for the benzene of the two phase system if the butyric 
acid in this phase were not associated. The horizontal distance between 
this curve and that for the actual benzene phase is a measure of the degree of 
association. 
When applied to the structure of a liquid our hypothesis indicates that 
when the molecules are not wholly symmetrical, there will be more or less 
grouping of the parts of the molecules around which the stray field is the 
most intense, the extent of the grouping being a function of the temperature 
also. It is probable that liquids of this class have more, but a less definite, 
structure than is commonly supposed. If molecules of the polar-nonpolar 
type are dissolved in a nonpolar liquid this grouping is commonly spoken 
of as association of the solute; in a polar solvent it is considered as the solva- 
tion or hydration of the solute, in pure hquids it is designated as the associa- 
tion of the liquid. These groupings are constantly being modified by the 
kinetic agitation, the other factors being the intensity of the stray field, and 
the space available for the grouping. 
A discussion of electrical theories of surface phenomena will be found in 
papers by Hardy ;^ Langmuir;^ Harkins, Brown, and Davies;^" Harkins, 
Davies and Clark,^^ and by Frenkel.^^ The present paper will be published 
in a much more complete form in the Journal of the American Chemical 
Society, in which there will be taken up the question of what is known as 
specific adsorption. 
1 Gibbs, Trans. Conn. Acad., New Haven, Oct. 1875-May 1876, (108-248), and May 1877- 
July 1878, (343-524). 
2 Lewis, Wm. Mc, Phil. Mag., London, 28, 1914, (104-16). 
3 Rothmund, Loslichkeit und Loslichkeitsheeinfliissigimg, Leipzig, 1907, p. 118. 
"Hildebrand, /. Amer. Chem. Soc, Easton, Pa., 38, 1916, (1452-73). 
5 Washburn, Physical Chemistry, Chapter XIII, pp. 134-42, also pp. 143, 224, 273. 
6 Harkins, Davies, and Clark, /. Am. Chem. Soc, 39, 1917, (553-70, 594-5). 
7 Harkins and Humphrey, Ihid., 38, 1916, (228-46); Harkins and Brown, Ibid., 38, 1916, 
(246-52), and April 1919. 
8 Hardy, London, Proc. Roy. Soc, B, 86, 1911-12, (634). 
^Langmuir, /. Amer. Chem. Soc, 39, 1917, (1848-1906); these Proceedings, 3, 1917, 
(251-7). Abstract in Met Chem. Eng. 15, 1916, (468). 
10 Harkins, B own, and Davies, Ihid., 39, 1917, (354-64). 
"Harkins, Davies, and Clark, loc. cit., 1917, (541-96). 
12 Frenkel, Phil. Mag., London, 33, 1917, (297-322). 
