Law of Molecular Attraction. 493 



Kleeman's equation for this substance is unquestionably due 

 to the fact that his equation does not represent the facts. A 

 similar examination of the other substances tested will 

 compel the same conclusion. 



Regarding the tests made by Kleeman of his relation, 

 I would say that he used the unrevised data given in my 

 earlier papers. His tests are therefore not as correct as it is 

 possible to make them. His own tests do, however, when 

 the substances measured by Young are considered, completely 

 bear out the statement here made that his equation does not 

 represent the facts. In the light of the results he gives I do 

 not see how it was possible for him to claim that the equation 





e = constant 



is as accurate as 



d 2 ~T> 2 

 L-E g 



= constant. 



Also I would point out that I had previously investi gated * 

 the important equation of Dieterici for all of the substances 

 which Kleeman examines. And the relation between 

 Dieterici's equation and mine which Kleeman points out in 

 later papers, had already been discussed either by Steinhausf 

 or by myself {. 



Kleeman further states § that an infinite number of 

 equations must exist giving true relations between the heat 

 of vaporization and the density of a substance,, and therefore 

 that the law of molecular attraction cannot be deduced from 

 any such relation. Several different phases of this position 

 should be clearly understood. 



1. It is impossible to get more out of a mathematical 

 process than we put in. This is universally admitted, and 

 Kleeman'' s conclusions, if correct, must be as he states, a 

 consequence of the nature of the heat of evaporation. 



2. When one simply measures the heat of vaporization of 

 a given substance under a given set of conditions, there is no 

 a priori method of finding out what that heat went to do. 

 Were it not for other known facts one might suppose that 

 there was no attraction whatever between the molecules and 

 that all of the heat was expended in pushing back the 

 external pressure. This hypothesis is readily disproved, and 

 the amount of energy that was actually used in pushing 



* Journ. Am. Chem. Sci. xxxi. p. 1099 (1909). 



t Studien zum Problem der Zustandsgleichung , p. 38, etc. 



% Loc. cit. 



§ Phil. Mag. xx. p. 901 (1910) and later articles. 



