Influence of Atomic Weight. 



375 



are symmetrically arranged; whilst in those containing an 

 odd number the arrangement is generally asymmetrical. 





Benzene, 



Toluene, 

 C 6 H g CH 3 . 



Paraxylene. 



C 6 H,(CH 3 ) 2 . 



Pseudo- 



curaene. 



C 6 H 3 (CH 3 )3. 



Durene. 



6 H 2 (CH 3 ) 4 



Melting- 1 _ 

 point. J 



Boiling- 1 _ 

 point. J ~~ 



7° 

 81° 



Liquid. 

 111° 



15° 

 136° 



Liquid. 

 166° 



80° 

 191° 



Groebe (JBer. deut. diem. Ges. vii. p. 1629) has shown that, 

 as a general rule, diphenylene compounds boil 40° higher than 

 the corresponding compounds of diphenyl, phenanthrene alone 

 being an exception ; thus : — 





Benzo- 

 phenone, 



;co. 

 o g h/ 



Diphenylene 

 ketone, 



1 >o. 



6 H 4 



Diphenyl 

 methane, 



)0H 2 . 



Diphenylene 

 methane, 



1 )0H 2 . 



Boiling- 1 _ 

 point. J ~~ 



295° 



336° 



262° 



302° 



As regards the boiling-points of isomerides, Naumann 

 (Ber. deut. diem. Ges. vii. pp. 173, 206) has pointed out 

 that the simple chain formulae allow of greater condensation 

 of the molecule, and consequently give a higher boiling-point ; 

 whilst the more this form is disturbed by side chains, the 

 lower the boiling-points. Also, the boiling-points of meta- 

 merides of analogous constitution and containing 0, are the 

 lower the nearer the O is to the centre of the chain of atoms ; 

 thus : — 



Butyl alcohols 



fCH 3 .CH 2 CH 2 .CH 2 .OH 



Boiling-point. 



1161 

 \ CH 3 . CH 3 CHOH . CH 3 99 / 



Methylpropyl ether. . . CH 3 . CH 2 CH 2 . O . CH 3 511 



Diethyl ether CH 3 . CH 2 . O . CH 2 . CH 3 35 / 



The theory has been advanced by Burden (Phi]. Mag. [4] 

 xli. p. 528) that at the boiling-point (Bar. = 760) the velocity 

 of the molecules is a constant for all liquids, viz. =1140 feet 

 per second. This number is obtained by the use of the equation 



t, fat b.-p.)= 273 + b -P- X / ( vel <>c% of H gjjjjTgg 

 V, \V) 273 V vapour-density of the liquid ? 



the velocity of H at 0° C. being = 6050 feet per second. For 

 the raison d'etre of this equation, reference must be made to 

 the original paper. Burden gives a large number of Tables 



202 



