﻿34 On the Ideal Re fr activities of Gases. 



A question of great chemical interest is that of the in- 

 fluence of the constitution of the molecule on the refractivity. 

 This has already been studied by Briihl *, who from a con- 

 sideration of the uncorrected values arrived at the conclusion 

 that : "... die Molekularref raktion der Gase ist keine rein 

 additive, sondern eine unter gewissen Umstanden deutlich 

 konstitutive Eigenschaft derselben." A similar view was 

 later expressed by C. and M. Outhbertson f . Such a con- 

 clusion could not, however, be final until account had been 

 taken of the reduction to the ideal state. In Table IV. are 

 given the values of the refractivities of a few gases calculated 

 from those of their simpler constituents, and the observed 

 refractivities of the same gases, all reduced to the ideal 

 state. 



Table IV. 



Some additive relation underlying the whole series is 

 immediately apparent. In the cases where the elements of 

 the constituent compound gases (<?. g. CO) are united by 

 different linkages from those in the more complex gases 

 (e. g. C0 2 ), the divergence from the additive relation, how- 

 ever, becomes considerable. Thus, if the refractivity of 

 methane be calculated from that of the saturated hydro- 

 carbon ethane, it is in much better agreement with the 

 observed value than when it is calculated from that of the 

 unsaturated hydrocarbon acetylene. 



The results collected in Table IV. show that, even with 

 the ideal refractivities, the conclusion of Briihl still holds 

 good. 



* J. VV. Briihl, Zeitschr. physik. Chem. vii. p. 1 (1891). 



t C. and M.Cuthbertson, Proc. Roy. Soc. A. Ixxxiii.p. 171 (1909). These 

 authors applied a correction in the cases of sulphur dioxide and hydrogen 

 sulphide by multiplying the refractivity by the ratios of the theoretical 

 to the observed densities. 



