594 



of the theoretical investigation of C was increased by a remark 

 of Holst'), who concinded from the investigations on the compres- 

 sibility, that for snbstances as water and ammonia the molecules of 

 which possess an electric moment such as that of a donblet, C is 

 negative in (he considered temperature interval, while for normal 

 substances 6' is found positive. A calcidation of (' for molecules 

 whose attraction Ts ecpnvaleni to that of a douldet at their centre 

 and a comparison of this result e.g. with that for molecules like 

 those considered in this communication or with that for (|uadruplets 

 will have to prove whether really the deviating behaviour of (' for 

 the substances mentioned n)ust be ascribed to the molecule possessing 

 an electric moment such as thai of a doublet. The calculation of 6' 

 for doublets and (juadruplets must however be postponed till later. 



§ 2. Deduction of a y enen 1 1 e.i^pression for the third virin I coefficient 

 for material points inhich exert central forces on each other. This 

 deduction is analogous to that of the second virial coefficient for this 

 case given in Snppl. Leiden N'. 24ft § 5, which pai)er may be referred 

 to with respect to the method and the notations already used there. 



Definition of the macro-complexion. 



Generalizing (23) I.e., the 7i,, molecules in di\d>o^ will now be 

 distinguished in : 



?iiia single molecules (with no other molecule within their sphere 

 of action), 



Hii/,1 molecules belonging to pairs with a mutual distance between 

 r, and 7', -|- dr^, 



'/iiiij molecules belonging to pairs with a mutual distance between 

 r, and r, -|- (h\ 



etc. 



?iiie,,, molecules belonging to sets of three, the mutual distances 

 of which are resp. lying between /■, and r, -f- dr^, r, and r, -|- dr^, 

 /•, and /'g -|- dr^, 



etc. (2) 



We define the group macro-complexion") by giving the numbers 

 //,,o . • . without attending to any individuality of the molecules. 



The individual macro-complexion*) is defined as follows: 



nwa definitely indicated molecules are single. 



. ') G. Holst. Leiden Suppl. N". 41/". These Proceed. Jan. 1917, Holst points 

 there also to the importance of the knowledge of tlie behaviour of C for the deter- 

 mination of the molecular weight from the gas density, comp. also H. Kamerlingh 

 Onnes and W. H. Keesom. Die Zustandsgleichung. Leiden Suppl. W. 2.3 §§ 77—80. 

 -) Comp. Leiden Suppl. N^ 24a § 2 (These Proceed. .June 1912j. 



