568 
CHEMISTRY: W. D. HARKINS 
face. Thus, contrary to the rule found in the past, the surface or 
interface between octyl alcohol and water gives of energy when it is 
extended, but, nevertheless, the surface cannot he formed without the 
expenditure of work. The apparent contradiction is due to the fact that 
while the molecular motion aids in the, formation of an ordinary surface, 
in the case of the interface under discussion the molecular motion hinders 
the extension of the surface. This is in accord with the theory pre- 
sented in our earlier papers, and by Langmuir, that at such an interface 
there is an orientation of the molecules, since the molecular motion 
reduces the extent of the orientation. 
When the interface between octyl alcohol and water is pulled out 
adiabatically there is thus a heating of the surface, while an ordinary 
surface is cooled, so that the potential energy of the molecules is de- 
creased by passing into the alcohol-water interface. The negative sur- 
face energy, is, it is true, very small, with a numerical value of two 
ergs, per sq. cm., while the free surface energy is 8.33, and the latent 
heat is —10.3 ergs. In contrast with this, it is found that the total 
surface energy of the hexane-water interface is not only positive but 
large, with a value of 66.5 ergs. These relations are of considerable 
interest, and their bearing on interfacial structure, which is of great 
importance in physiology, will be discussed in a later paper in the 
Journal of the American Chemical Society. 
1 Dupre, Theorie Mecanique de la Chaleur, Paris, 1869, p. 69; Lord Rayleigh, London, 
Phil. Mag., (5) 30, 1890, (461). 
2 Hardy, London, Proc. Roy. Soc, 86B, 1911, (634). 
2 (a). Harkins, Brown, and Davies, /. simer. Chem. Soc, 39, 1917, (354-64). 
(b) . Harkins, Davies, and Clark, ibid., 541-96. 
(c) . Harkins and King, ibid., 41, 970-92, (1919), these Proceedings, 5, 1919, (152-9). 
4 Langmuir, /. Amer. Chem. Soc, 39, 1917, (1848-1906), these Proceedings, 3, 1917, 
(251-7) ; abstract in Met. Chem. Eng., 15, 1916, (468). Fraenkel, Phil. Mag., 33, 1917, (297- 
322). 
5 Einstein, Leipsig, Ann. Physik., 4, 1901, (513;. 
6 Kleemann, Phil. Mag., 18, 1909, (39, 491, 901). 
^ Harkins and Clark, unpublished calculations. 
8 van Laar, Zs. anorg. Chemie, 104, 1916, (57-156). 
9 Mathews, /. Physic Chem., 17, (603-28). 
10 Hildebrand, /. Araer. Chem. Soc, 41, 1919, (1067-80). 
11 Leipsig, Ann. Physik, 29, 1886, (655). 
