The Internal Pressures of Liquids 



605 



constant, "a," indeed, as van der Waal's has repeatedly 

 shown, should be considered constant unless association, or 

 quasi-association, occurs, "a" contains the factor N 2 , N 

 being the number of molecules in the volume, V, hence any 

 association will lower "a" by this factor. 



The wide divergence of these various values proposed for 

 the internal pressure is shown in Table i expressing the internal 

 pressure in atmospheres at zero degrees, except in the case of 

 Walden where the values are for the boiling points and Davies 

 fori 5 C. 



i 



In this paper are given the values of "a" obtained in several 

 quite different ways, all of which yield closely agreeing results. 



1. The first method is a computation from the surface 

 tension. The assumption involved in this method is the depth 

 of the surface film expressed in the number of molecular 

 layers. That the assumption is correct is proved by the out- 

 come. 



2. The second method is a modification of Thomas Young's 

 method combined with the law of Eotvos as developed in my 

 former paper, but with certain corrections. 



3. In the third method "a" is computed from van der 

 Waals' equation at the critical temperature, the assumption 

 being made that in all normal substances b c - = 2V == 2V C /S, 

 S being the critical coefficient and equal to RT C /V C P C . 



4. In the fourth method "a" is computed from the internal 



