OP ARTS AND SCIENCES. 185 



this volatile product has been distilled off, but a trace of organic acid 

 can be extracted from the retort residue by ether. This acid is 

 chiefly mucobromic; but with it I have found dibrommaleic acid in 

 quantity barely sufficient for the recognition of its barium salt under 

 the microscope when precipitated from aqueous solution by alcohol. 

 The oxidation with nitric acid gives somewhat better results. When 

 mucobromic acid is boiled with ten times its weight of nitric acid of 

 sp. gr. 1.20, ca'rbonic dioxide is slowly given off, the escaping gas ren- 

 ders a solution of argentic nitrate turbid, and yet, if the heat is con- 

 tinued for several hours, a considerable portion of the mucobromic 

 acid is found to be converted into dibrommaleic acid. In one experi- 

 ment I obtained, after several hours' boiling, from 5 grm. of muco- 

 bromic acid 2.3 grm. of baric dibrommaleate and 1.5 grm. of unal- 

 tered mucobromic acid. This corresponds to nearly forty per cent of 

 the theoretical yield of dibrommaleic acid from the mucobromic acid 

 which entered into the reaction. Stronger nitric acid oxidizes more 

 rapidly, but the yield of dibrommaleic acid is smaller ; if much more 

 dilute acid is used, the mucobromic acid is hardly altered. 



Precisely the same effect is produced by long boiling with bromine 

 water, carbonic dioxide being evolved as before, and the yield of 

 dibrommaleic acid remaining essentially the same. The identity of the 

 acid made by bromine water was established by the analysis of the 

 barium salt. This salt was precipitated several times from aqueous 

 solution by alcohol, recrystallized from water, and contained then the 

 required percentage of barium. 



0.5493 grm. of the air-dried salt gave 0.2887 grm. BaSO^. 



Calculated for BaC4Br204.2H20. , Found. 



Ba 30.78 30.90 



Limpricht found that mucobromic acid was the only product when 

 pyromucic acid suspended in water was treated with an excess of 

 bromine at ordinary pressures. Since mucobromic acid is itself con- 

 verted into dibrommaleic acid by boiling it with bromine water, it fol- 

 lows that the latter acid must of necessity be formed in the preparation 

 of mucobromic acid. For its detection, the mother liquors, from 

 which the mucobromic acid had been separated as completely as pos- 

 sible, were distilled. The distillate, consisting chiefly of concentrated 

 hydrobromic acid (b. pt. 126°) was partially neutralized with potassic 

 carbonate, and thoroughly shaken out with ether. The residue left 

 on evaporation of the ether was taken up with water, and the acid 

 solution saturated with baric carbonate. Alcohol precipitated from 



