DIELECTRIC CONSTANT 85 



a result that is approximately confirmed by the values for 

 benzene, since 



7) 19 . 6 0-88 7) at 100 and 760 mm. 0-0026, 



whence 



K-i 1-318 



= 



7^(7^ + 2) ~ 0-88 x 3-218 

 and 



K 9 l 0-0027 



* . _ _ L 



_ ____ _ _ _ 



7> 2 (K + 2) 0-0026 x 3-0027 



There is therefore no exact agreement, but a somewhat 

 extensive approximation 1 , and we shall consequently mention 

 a further relation, pointed out by Guye. 



Since 



it follows that 



N--I 



and the volume M v actually occupied by the molecular 

 weight M 



M N 2 i 



the molecular refraction for infinite wave-length. This 

 serves to explain the additive properties of the molecular 

 refraction, the quantity in question being a measure of the 

 space occupied by matter, and since the critical coefficient 



T 



- according to p. 48 is so too, we have 



- A 



P k MR 



^ = constant, 



^k 

 this is roughly the case 2 : 



1 Lebedew, Wied. Ann. 44. 304 ; Ratz, Zeitschr.f. Phys. Chern. 19. 94. 



2 Altschul, Zeitschr.f. Phys. Oiem. n. 595 ; Nasini, 1. c., 16. 249. 



