372 Prof. H. E. Armstrong on Loiu-Temperature Research 



bj bromine and converted into derivatives of the corresponding 

 paraffin ethane, in which the carbon atoms are united by single 

 affinities : 



H.CO 



C H, + Bp. = BpC Ho . C HoBp 



The hydrocarbon discovered by Faraday in 1825, now known as 

 lenzene on account of its relationship to benzoic acid, has peculiar 

 properties w^hich distinguish it from the paraffins and the ethenes, its 

 behaviour being apparently that of a saturated and not that of an 

 unsaturated hydrocarbon : to judge from its composition, CgHe, 

 assuming that the six carbon atoms are united together in a ring by 

 single affinities and that six of the affinities are satisfied by hydrogen, 

 six affinities still remain to be accounted for : as the compound 

 appears to be saturated, these must be disposed of in some other way. 

 There has been much dispute on this matter : Sir James Dewar, as 

 far back as 1867*, himself suggested a way out of the difficulty but 

 the arguments are now against the ingenious solution of the problem 

 which he put forward. Kekule, in 1865, enunciated his celebrated 

 hypothesis that the carbon atoms in benzene are united in a ring 

 alternately by single affinities as in the paraffins and by double 

 affinities as in the ethenes ; he represented it, therefore, by the 

 formula : — 



H 



/\ 



H C C H 



II I 



H C C H 



\ / 

 C 

 H 



On this assumption, the behaviour of benzene should be that of 

 ethylene exaggerated, which is in no way the case ; gradually, this 

 objection has been recognised and Kekule's formula no longer holds 

 the field. At present, the tendency is to accept the centric formula 

 as a more suitable symbol. In this the six affinities not engaged 

 in the ring and not saturated by hydrogen are represented as acting 

 towards a common centre and as neutralising one another by their 



* On the Oxidation of Phenyl Alcohol, and a ]\Iechanical Arrangement 

 adapted to illustrate structure in the Non-saturated Hydrocarbons. Proc. 

 Boy. Soc. Edin. 1866-7. 



