40 PHYSICAL PROPERTIES AND COMPOSITION 



historical development of the subject. It started from 

 the assumption made in the characteristic equation of 

 a space or sphere of action occupied by matter, but then 

 took the form of certain empirical rules as to the total 

 volume, and the survey thus obtained takes in the eolli- 

 gative relations in their complete extent from the greatest 

 dilution in ideal gases to the greatest density at the 

 absolute zero. 



Since, however, the additive method does not give clear 

 results when the total volume is alone taken into considera- 

 tion, it seems desirable, in accordance with the molecular 

 mechanical view, to try the hypothesis of space partly 

 filled with matter, and partly not, although direct experi- 

 mental confirmation is then no longer possible on account 

 of the assumption involved not being accessible to 

 experiment. 



It is Traube 1 in particular who has taken this view, 

 dividing the total volume into the interspace or co-volume 

 k and the true molecular volume, and regarding the latter 

 as of an additive or partly constitutive nature ; hence 



It is next assumed that k is constant (25-9 at 15), which 

 cannot be either proved or disproved, since the co- volume 

 is not directly measurable, but which may be brought into 

 accordance with the facts by the additive relations arising 

 if a sufficient number of constitutive influences are allowed 

 for. For the hydrocarbons 2 at 15 the result is 



M v = 25-9 + 2 ^-(8-1 +13-25 +i-7g + 3-4 r), 



where A v has the values 9-9 and 3-1 for the carbon and 

 hydrogen atoms respectively, and E, B, q, r, are the number 

 of hexamethylene and benzene rings, and double or triple 

 linkages. 



1 Ahrens, Sammlung von Vortriigen, 1899 ; Biltz, Praxis der Molekulargewichts- 

 lestimmung, 1898, p. 154 ; Nasini, Gazz. Chim. ital. 27 (ii), p. 533. 



2 Btrl. Ber. 28. 2926. 



