DR A. CRUM BROWN ON ISOMERIC COMPOUNDS. 717 



primary affinities correspond to the intra-radical or extra-radical affinities* of 



fH (0, 



KoLBE ; for instance, in formic acid, — C { O" or C, ^' H , the H and the OH (or 0- HO) 



(OH ' (oho 



are united to the extra-radical affinities, but by carrying out Butlerow's reason- 

 ing, we are led to the conclusion, that the H is united to a primary, and the OH 

 to a secondary affinity, unless we suppose that the free affinity of methyl is 

 different from that of formyl. 



It is not impossible that such a difference may exist, but till this point is 

 settled, and till we know whether the two free affinities of (CO)" are similar or 

 not, it is impossible satisfactorily to compare the two theories. 



The other attempt mentioned above to explain cases of absolute isomerism, in 

 harmony with the theory of atomicity, is that of Professor KEKUL:6.f After 

 shortly recounting the principal facts, more minutely described in his admirable 

 researches on organic acids, he says, — " All these facts find, in my opinion, to a 

 certain extent, their explanation in the following considerations : — According to 

 the views on the atomicity of the elements which I communicated some time 

 since, succinic acid and its homologiie pyrotartaric acid may be regarded as 

 closed molecules, that is, all the affinities of the atoms composing the molecule 

 are saturated by other atoms. Both acids contain two atoms of hydrogen re- 

 placeable by radicals, because two atoms of hydrogen are united to the carbon 

 group by means of oxygen. These two replaceable (typical) atoms of hydrogen 

 may be easily exchanged for metals, because, besides the two atoms of typical 

 oxygen {i.e., oxygen united by only one affinity to carbon), there are other two 

 atoms of oxygen united to carbon by both affinities, which, therefore, in the 

 language of the typical theory, belong to the radical. If these two atoms of 

 hydrogen are represented apart from the rest, as is done by means of the typical 

 formulae, — 



C.H.O. C,H,0, 



}° 



H„ ' f ^2 h' j ^2 



or still more clearly by the graphic representations which I have made use of 

 more than once in another place, j it will be readily seen, that in succinic acid 



* I use the terms intra- and extra- radical affinities as abbreviations for the carbon affinities 

 with which the intra- and extra- radical oxygen atoms are combined. 



j" Ijoc. cit. 



I In order to elucidate this passage as much as possible, I append the graphic representa- 

 tions referred to : — 



Succinic Acid. Pyrotartaric Acid. 



c H'^H c 



iNi iNi #^^ O O ##^## ilNi i 



H C ^'H C H«H C 



