CHEMISTRY: W. D. HARKINS 
543 
in the value of the constant is obtained if the molecular orientation in 
the surface is taken into consideration, which was not done by Ramsay 
and Shields. While the values which are thus obtained are still some- 
what larger than the normal, it must be remembered that such complex 
molecules may vibrate in parts, which might very well give larger 
amounts of kinetic energy available for transformation into potential 
energy. 
While Ramsay and Shields evidently did not see at all the important 
theoretical basis for their method it is nevertheless true that their 
equation involved the entropy of formation of the surface, and therefore 
kept closer to this basis than the very great number of supposedly 
improved equations which have been developed from it. 
In so far as the experimental results for the temperature coefficients 
of free surface energy as determined by Ramsay and Shields can be 
trusted, our calculations show that the normal value of the surface 
entropy per degree per molecule is very close to the normal value 
(2.96 X 10-^^ ergs) for the following substances over a wide temperature 
range: benzene, carbon tetrachloride, ethyl acetate, ethyl ether, methyl 
formate, and chlorobenzene. The results of Baly and Donnan give 
2.8 X 10-^^ for liquid nitrogen, and 2.75 X 10-^^ for liquid oxygen. 
On the other hand the values for argon (1.6 X 10-^^) and for mercury 
(1.5 X 10-^^), though not so well established experimentally, are not 
very much above 50% of the normal values, and the work of Jaeger 
indicates that molten salts also give low values. Unfortunately the 
data for argon were obtained over such a small temperature range that 
the entropy obtained may be very much in error. In the case of mer- 
cury and the molten salts, those who belong to the extreme association 
school would assume that the entire deviation is due to molecular asso- 
ciation, but I am not at all convinced that the association is at all 
definite, especially since our present knowledge of the structure of 
metals and salts indicates that there may not be such a thing as a 
definite molecular weight in any case. This subject will be treated 
more comprehensively in a later paper. 
A general form of the entropy principle. — In the preceding paragraph 
I have presented the entropy principle in its relation to the formation 
of surfaces, in which case it seems to hold remarkably well. Possibly 
it is only in the formation of surfaces that such a relation will be found 
to hold with exactness, as the following reasoning will indicate. In 
the formation of a surface the total energy converted into molecular 
potential energy must be of such a magnitude as to overcome the 
