484 Albert P. Mathews 



of the number of valences by the molecular weight, I do not 

 see. 



It appears, then, that refraction, dispersion and cohesion 

 all involve the valence electrons, but the connection between 

 cohesion and valence is far closer and simpler than the other 

 relationships appear to be. The relationship of valence to 

 light is necessarily a less direct one, refraction depending 

 on the rate of vibration of the electron. It is said 1 that if the 

 natural period of the molecule (electron) is slightly less than 

 the frequency of a light wave the light will be accelerated; 

 if greater, retarded. It is evident that in dispersion other 

 properties of the electrons than number come into play, and, 

 hence, the relationship between dispersion and number is 

 not so simple and direct. Double bonds, neighboring groups, 

 etc., influence the periods of the electrons and so influence the 

 dispersive power; whereas these factors appear to play no 

 important part in cohesion. 



The relation between the refraction of light of one wave 

 length and the valence number is still less direct than be- 

 tween dispersion and valence, but still a general relation 

 exists which for substances of the same type is rather uniform, 

 as shown by Traube 2 for many liquids and by Cuthbertson 3 

 for several gases. 



Another very interesting fact correlating the refractive and 

 cohesive properties of matter is the resemblance between the 

 constant "K" of the Ketteler dispersion formula and the 

 value M 2 K of cohesion. Thus with the Ketteler formula 

 n* = a 2 -- K P + D X\/(P X\) the constant "K," Drude 

 found, could be computed with a fair approximation, in some 

 cases at any rate, from the sum of the valences, the molecular 

 weight and the density, and this result was confirmed by 

 Erfle. 4 This constant "K," therefore, contains at least 



1 Cotter, J. R.: "Dispersion," Encyclo. Brit., nth edition, 8, 317. 



2 Traube: Ber. chem. Ges. Berlin, 40, 130 (1907). 



3 Cuthbertson: Proc. Roy. Soc., 8aA (1909-1910); Phil. Mag., [6] 21, 69 

 (1911); Phil. Trans., 204, 323 (1905); 207, 135 (1907). 



4 Erfle: "Optische Eigenschaften und Elektronen Theprie." Annalen der 

 Physik, [4] 24 (1907). 



