192 Albert P. Mathews 



ical coefficient, the value of C is, for fairly complex substances, 

 about 2.80 X io" 37 ; but in the simple gases, such as N 2 O, 

 H 2 , O 2 , N 2 , etc., it is uniformly lower and about 2.25. The 

 question is, therefore, whether this formula does not give an 

 exact value for M 2 K, or whether the relation of M 2 K to the 

 weight and valence is only approximate and does not remain 

 the same for the simple substances. It is possible that the 

 ratio 27/64 in the "a" formula is not the same for all sub- 

 stances, but may vary a little with the complexity, or com- 

 pressibility, of the molecule. To solve this uncertainty, T 

 have computed M 2 K directly from the surface tension of the 

 liquid gases by the half empirical formula which holds pretty 

 well for more complex substances: M 2 K(i/7; 1 i/^) = 

 3SV*[(T C 6)/(T c -- T 6)] 2/ I have used the data of 

 Baly and Donnan in this calculation. I also calculated M 2 K 

 from the latent heat of vaporization from figures given by 

 Dewar in his article on Liquid Gases in the Encyclopedia 

 Britannica, by the formula: L E = a(i/V 1 i/VJ. a = 

 N 2 M 2 K. This formula neglects the heat used in the expan- 

 sion of the molecules in passing from the liquid to the vapor. 

 It generally gives, therefore, a value of M 2 K somewhat too 

 high. I have also computed M 2 K by the usual formulas in- 

 volving V c and T c instead of P c such as the surface tension 

 formula. In Table VII I have included the values thus cal- 

 culated for hydrogen, using successively the critical data of 

 Olszewski and Dewar. 



It is evident that a considerable uncertainty in the case 

 of hydrogen arises from the uncertainty of the critical data. 

 I think the P C V 2 C formula gives too high results. If we take 

 the mean of all it would be 37 .88161. With the valence 2 

 and the weight 2 this would give for "c" a value of 3.02 X 

 io~ 37 , which is close to the value obtained before. 



I have made similar calculations in the case of oxygen, 

 nitrogen, carbon dioxide and nitrous oxide. For the sake of 

 brevity I omit these and give in Table VIII only the mean 

 value for M 2 K for each gas. 



It is clear from Table VIII that with the exception of car- 



