96 Dr. L. Silberstein on Molecular 



special importance. Whatever the nomenclature, the ap- 

 proximate constancy of these extra-terms in a multitude 

 of cases remains a very characteristic feature. 



Our above remarks apply equally to the following exam- 

 ples, for which it will be enough to quote the final results 

 only. These examples are taken from Auwers and Eisen- 

 lohr's paper, Berl. Chem. Berichte, xliii. 813. The molecular 

 refractivities i\ 7 , calculated and observed, are for the D-line,. 

 and the dispersions ^ are from H a to H y : — 



Trimethijlstyrol [C 6 H 5 . C(OH 3 ) : C(CH 3 ) 2 ] 



T 



cale. 

 obs. : 



A r cak , = 49-05 2 ealc . = 1-85 



AW = 49.55 Sobs. = 2-23 



"exaltation" +0-50 +0-38 = 2] percent. 



u-Meihylstyrol [C 6 H 5 . C(CH 3 ) : CH 2 ]. 



39-85 1-63 



40-49 2-11 



+ 0-G4 



+ 0-48 = 29 per cent. 



Styrol [C 6 H 5 .CH:CH 2 ]. 





35'24 



1-53 



36-34 



2-14 



+ 1-10 



+ 0-61 = 40 per cent. 



From these examples we see that, while the "exaltation 5 * 

 of molecular refractivity is comparatively small, the "exal- 

 tation " of dispersion is very large, amounting in the last 

 example to 40 per cent,, and Auwers and Eisenlohr (loc. cit.} 

 quote cases in which it becomes enormous, 107 per cent., 

 153 per cent., and even 277 per cent. Whole classes of cases 

 in which there is a considerable " depression '' will be found 

 in Briihl's papers, Berl. Chem. Ber. xl. (1907), pp. 878, 900, 

 1159 et seq. The ever growing hierarchy of rules indicating 

 how to treat the exceptions to the law of additivity, although 

 undoubtedly helpful to the chemist, is the clearest confession 

 of non-ad ditivity. 



Again, quite apart from the numerical magnitude of 

 disagreement, there are, so to say, qualitative objections 

 to the additive law, which seem very striking, and which, 

 as far as I know, have been entirely overlooked. Thus, 



