OF ARTS AND SCIENCES. 181 



tion we were obliged to use three parts of strong nitric acid (sp. gr. 

 1.42) diluted with twice its weight of water to one part of the acid. 

 After continued boiling the acid was dissolved, and from the clear 

 solution, by extraction with ether, we were able to isolate only dibrom- 

 maleic acid, which melted at 125°, and gave by sublimation an anhy- 

 dride which melted at 114-115°. The barium salt was prepared by 

 neutralizing the acid in aqueous solution with baric carbonate, and 

 precipitating the filtered solution with alcohol. This salt, when re- 

 crystallized from water and dried by exposure to the air, gave the 

 percentage of barium required by baric dibrommaleate. 



0.5259 grm. of the air-dried salt gave on ignition with HgSO^ 0.2765 

 grm. BaSO^. 



Calculated for BaCjBr.O^ . 2 HjO. Found. 



Ba 30.78 30.91 



By the oxidation of tribrompyromucic acid with nitric acid dibrom- 

 maleic acid is, therefore, formed according to the equation, 



CgHBrgOs + 2 + H,0 := CJI.Br.p, + CO2 + HBr. 



Theoretical Considerations. 



It is evident that definite conclusions as to the relative position of 

 the bromine atoms in the various substituted pyromucic acids which 

 we have described may be drawn from the products which result from 

 the oxidation, and at the same time it seems to us that certain of our 

 observations enable us to discriminate between the two structure for- 

 mula; for pyromucic acid which have hitherto seemed most probable. 

 The behavior of pyromucic acid with phosphorus pentachloride, as 

 shown by the experiments of Lies-Bodart,* or of its ethyl ether with 

 acetyl chloride, as shown by Schmelz and Beilstein,t rendered it cer- 

 tain that pyromucic acid could not contain its tiiird oxygen atom in 

 the form of hvdroxyl. Limpricht's t experiments with furfurau (tetra- 

 phenol), and the indifference shown by pyromucic acid toward nascent 

 hydrogen, excluded the possibility of the presence of an aldehyde or 

 ketone group. The absence of both of these forms of oxygen has 

 more recently been confirmed by the experiments of Odernheimer,§ 



* Ann. Cliem. u. Pharm., 0. 327. 



t Ibid., Suppl., iii. 270. } Ibid., clxv. 282. 



§ Ber. der deutscli. chem. Gesell, xvi. 2988. 



