OF ARTS AND SCIENCES. 181 



addition of plumbic acetate to an aqueous solution of the acid, and 

 when air-dried it was found to contain a molecule of water. 



Since its discovery by Kekule, the acid prepared in this way has 

 been mentioned but twice, as far as I know ; and these notices con- 

 tain no additional facts which could serve to assist in its identification. 

 Bourgoin * gives its melting point as 110°, and asserts that it distils 

 imaltered. Fittig and Petri,t in their attempts to prepare the tri- 

 bromsuccinic acid, which had been described by Bourgoin, obtained 

 dibromsuccinic acid and a substance crystallizing in hemispherical 

 aggregations, which, from their melting point (112°) and volatility 

 with steam, they recognized as dibrommaleic acid. 



In 1873 Limpricht and Delbriick J described an acid of the same 

 composition, which they made by the action of bromine and water 

 upon mucobromic acid. They found it difficult of purification ; and, 

 in their study of it, they were to all appearance hampered by lack of 

 material. The acid melted at 108-120°, and by sublimation it was 

 converted into its anhydride, C^BrgOg, which melted at 95-120°. The 

 barium salt they obtained in colorless, tabular crystals, to which they 

 assigned the formula, BaC4Br20^.2H20. The silver salt they found 

 to be insoluble ; but it did not explode either by heat or percussion. 

 They assumed, apparently without hesitation, that this acid was 

 isomeric with that of Kekule, and therefore named it dibromfumaric 

 acid. 



The acid made by the action of bromine upon mucobromic acid, 

 which I have just described, agreed in most respects closely with the 

 acid described by Kekule ; and yet the higher melting point and the 

 ready formation of the anhydride rendered a further comparison neces- 

 sary in order to settle the question of identity. 



In the preparation of dibrommaleic acid, I followed in general the 

 method of Kekule ; but, since this was to be the main product of the 

 reaction, I was obliged to use a greater proportion of bromine and 

 water, in order to get any considerable yield. 



I obtained good results by using to one part of succinic acid two of 

 water and four of bromine, and heating twenty hours at 140°. The 

 mother liquors from which the greater part of the dibromsuccinic acid 

 had been separated were distilled, the distillate neutralized with baric 

 carbonate, and the baric dibrommaleate precipitated from the filtered 



* Bull. Soc. Chim. [2], xxi. 404; xxii. 443. 

 t Ann. Chem. u. Pliarra., oxcv. 76. 

 } Ann. Chem. u. Pbarm., clxv. 294. 



