ATOMIC VOLUME 37 



The calculated atomic volume of chlorine and bromine 



A v = 22-8 and 27-8, 

 for ^=35-45 79'9 6 



leads to the densities 



= 2- 



22-8 27- 



whilst 1-56 and 2-96 



at the boiling point have been observed 1 . 



On the other hand discrepancies occur which were partly 

 noticed by Kopp himself and depend primarily on the 

 constitution. 



A so-called double bond of oxygen requires a larger 

 volume than a single bond : thus in methyl alcohol 

 H 3 C O H if we subtract from M v = 42-6, the values for 

 carbon and hydrogen, 11+4 x 5-5 = 33, there remains 9-6, 



whilst in aldehyde H 3 CC<^ > M v = 56-9, and deducting 



22 + 4 x 5-5 = 44, there remains 12-9. 



There is a second limitation ; even without a change in 

 the linkage small differences in constitution lead to some- 

 what different volumes (Stadel), as may be seen from the 

 following data on molecular volumes : 



CH 3 CC1 3 (74-O 108 CHClBrCH 3 (82. 7 ) 96-5 



CH 2 ClCHCl 2 (ii3-7 ) 102.8 CH 2 BrCH 2 Cl(io7) 88 



These differences cannot be accounted for by the fact 

 that the boiling point is chosen instead of the critical point, 

 for even at the latter isomers are not strictly of the same 

 density ; e. g. the difference CH 2 does not always correspond 

 to the same differences in molecular volumes 



HCOOCH 3 171) H 3 COH 118) 



HCOOC 2 H 5 228 j 57 H 5 C 2 OH 167 J 4 - 



the final result is therefore that the molecular volume is 

 certainly not a simple additive quantity, as according to l< 

 p. 34, was to be expected. 



1 Berl. Ber. 31. 2762. 



