710 



DR A. CRUM BROWN ON ISOMERIC COMPOUNDS. 



Of these the latter only is admissible, for the theory of atomicity taken strictly 

 does not admit of free affinities in a molecule. This formula then must be 

 common to the two acids. 



5. In the abstract of this paper, published in the Society's " Proceedings," the 

 dehydrogenates and the bibromo derivatives of pyrotartaric acid were inadver- 

 tently included in the list of bodies probably absolutely isomeric. From the 

 relation of pyrotartaric acid to prop3dene, and of the latter substance to Friedel's 

 alcohol, we may deduce the following formula for pyrotartaric acid : — 



© © (? ^.) 

 ©--(«> -(i)-^-©-^ 



I I ! I 



(b 







If this formula be correct, it is obvious that there ma?/ be three metameric 

 dehydrogenates and bibromo derivatives. 



6. As the two atoms of hydrogen in the radical of maleic acid are, on the 

 theory of atomicity, in precisely similar positions, it is obvious that there cannot 

 be two metameric bromo-maleic acids. x\nd as Kekule has shown that there 

 are two acids, bromo-maleic and isobromo -maleic, these must be absolutely 

 isomeric. 



7. Two perfectly admissible formulae can be constructed to represent bibromo- 

 succinic acid : — 



& 



-. ^ 



V-J 



r 



I 



-0-9- 



-iy 



1 





© © 



^ 



(^) 





^ 





© 



© 



and 







But that these formulae do not correspond to bibromo-succinic and isobibromo- 

 succinic acids is plain from the following considerations. These acids are formed 

 by the direct addition of bromine to maleic and fumaric acids. The bromine 

 must therefore be combined with the two carbon equivalents, which in maleic 

 and fumaric acids are combined together, so that the latter of the two formulae 

 given above must be that of both brorainated acids. 



8. As the constitutional formula for succinic acid shows no difference as to 

 " chemical position" among the four atoms of hydrogen in the radical, there can 

 be only one formula for the substance produced, by replacing one of these atoms 



