542 
CHEMISTRY: W. D. HARKINS 
It is obvious that this depends either upon the approximation to a cubic 
lattice arrangement, or to a similarity in the surface arrangement in 
every case. It is therefore to be expected that the relation would not 
hold in any case where the molecular orientation in the surface is such 
as to cause a deviation from such similarity. 
While the normal value for the fraction of the molecular kinetic 
energy which is converted into the potential form is 144% of the mean 
molecular kinetic energy, which corresponds to a surface entropy of 
2.96 X 10-^^ ergs per molecule, and while what have been usually termed 
normal or unassociated liquids give these values very closely, certain 
liquids have been found for which the entropy value is lower. Thus 
the alcohols, organic acids, and water, give at ordinary temperatures 
not far from one-half the normal values (one- third in the case of water), 
but as the temperature increases, even for such liquids the entropy 
increases and approaches the normal value. Such results as these are 
easily explained on the basis of the assumption made by Ramsay and 
Shields and their followers in the association school, who consider that 
at low temperatures the molecules in such liquids are associated into 
larger groups than correspond to the formula weight, but that the 
association decreases as the temperature increases. 
Criticisms of the Ramsay-Shields method of determining molecular asso- 
ciation. — Certain sweeping criticisms of the Ramsay-Shields method of 
calculating the degree of molecular association which have been made, 
I consider to have no vaHdity. On the other hand objections might be 
raised which seem not to have occurred to the workers in this field. 
The most sweeping criticism of the method, which has been expressed 
many times, is that since it is a "surface tension method it gives no 
true indication of the molecular state of the liquid as a whole." From 
this view-point it is considered that it is not the association in the 
liquid, but the association in the surface, which is calculated by this 
method. With this criticism I disagree most strongly, for if Ramsay 
and Shields have calculated any association at all it is not that in the 
surface, but that which exists in the body of the liquid, as seems to me 
apparent from the entropy principle, for the kinetic energy which is 
converted into the potential energy of the surface is the molecular 
kinetic energy of the molecules just before they move into the surface. 
A second criticism which has been made is that very complex mole- 
cules, particularly those which contain several, paraffin chains such as 
tripahnatin and tristearin, give much too large values of the Ramsay- 
Shields constant. I have found, however, that a very great reduction 
