OP ARTS AND SCIENCES. 199 



may readily be made by acidifying the baric hydrate sohition of muco- 

 bromic acid, without removing the separated baric dibromacrylate, 

 and extracting the solution with ether. Tlie same compound, although 

 in smaller quantity, may also be obtained, after that portion of the 

 barium salt which separates spontaneously is removed. From dibrom- 

 acrylic acid it may be made by the action of baric hydrate in the cold. 

 For its preparation we usually have employed a solution of potassic, 

 instead of baric, hydrate. The proportions which we have found most 

 advantageous are 70 grm. of potassic hydrate and 400 c.c. of water to 

 100 grm. of mucobromic acid. Care must be taken in adding the muco- 

 bromic acid, and also in the subsequent acidification with hydrochloric 

 acid, that no sensible elevation of temperature takes place. When the 

 solution is partially acidified, the acid potassium salt of dibroraacrylic 

 acid usually separates in abundance, but dissolves ujDon further addi- 

 tion of acid. The solution is then thoroughly extracted with ether; 

 and this leaves on distillation a liquid residue, which, on cooling, 

 gradually solidifies in large, well-formed, monocliiiic (?) prisms. These 

 are readily soluble in water, alcohol, ether, or chloroform, and may be 

 purified by crystallization from hot benzol, or more conveniently by 

 melting with a little water. Thus purified, the substance melts at 

 104—105° ; and this melting point is not altered by repeated recrystal- 

 lizations from various solvents. 



I. 0.9023 grm. substance gave 0.6440 grm. CO^ and 0.0850 grm. 



H,0. 

 II. 0.4403 grm. substance gave 0.3157 grm. COj and 0.0433 grm. 



III. 0.2263 grm. substance gave 0.3386 grm. AgBr. 



IV. 0.2241 grm. substance gave 0.3321 grm. AgBr. 

 V. 0.2092 grm. substance gave 0.3139 grm. AgBr. 



IV V. 



63.66 63.03 63.84 



Although the percentages we have found show a considerable varia- 

 tion from those calculated for equal molecules of dibroraacrylic and 

 brompropiolic acids, they agree better with this than with any other 

 formula equally simple ; and, moreover, the qualitative behavior of 

 the substance is such as to render this formula tolerably certain. Its 



