OF ARTS AND SCIENCES. 151 



aud these must consequently be rejected. There remain therefore for 

 the acid in question but two possible formulae, — 



CBr^ CHBr 



II II 



CH and CBr 



I I 



COOH COOH 



The formation of two isomeric dichlordibrompropionic acids by the 

 addition of chlorine to the dibromacrylic acid and of bromine to the 

 analogous dichloracrylic acid, as Mabery and I have shown, would 

 seem again to be decisive in favor of the first of these formula}, since 

 its adoption would give, — 



CBr^Cl CCljBr 



I I 



CHCl and CHBr 



I I 

 COOH COOH 



as the structure of the two isomeric dichlordibrompropionic acids, 

 while the second formula would give in either case the same com- 

 pound, — 



CHBrCl 



I 

 CBrCl 



I 

 COOH 



Although it was by no means impossible that a molecular rearrange- 

 ment had taken place in one of these two reactions, still it seemed 

 improbable, since the reactions were apparently neat, and in the treat- 

 ment with chlorine, where such a change would be more naturally 

 expected, no bromine could be detected in the escaping chlorine. 

 On the other hand the adoption of the formula, — 



CBrg CCI2 



II II 

 CH and CH 



I I 



COOH COOH 



for the derivatives of mucobromic and mucochloric acids presented 

 difficulties quite as serious. In the first place the dicliloracrylic acid 



