OP ARTS AND SCIENCES. 125 



X. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



By Hexry B. Hill. 



Presented February 1, 1882. 

 I. Ox DiBROMACRTLIC ACID. 



In a communication upon furfurol and certain of its derivatives 

 which I laid before the Academy a year ago, I described a dibro- 

 macrylic acid * which O. R. Jackson and I had some time before ob- 

 tained from mucobromic acid by the action of alkalies. Although we 

 had not been able to prepare the acid in a state of perfect purity, still 

 our results seemed to us sufficient for its identification, and since it 

 then appeared that a more extended study of it would interfere with 

 other investigators in the same field, further work upon it had been 

 for the time given up. Not long afterward it became evident that 

 our hesitation upon this account had been quite unnecessary ; but it 

 was not until recently that I was able to take up again the study of 

 this acid. I have now obtained results which correct our previous 

 observations in several important particulars. 



For the preparation of the acid O. R. Jackson and I used 

 chiefly the barium salt, which crystallized well from water or dilute 

 alcohol, and which gave us constant analytical results. The air-dried 

 salt lost nothing in vacuo over sulphuric acid, or when heated to 80°, 

 and the percentage of barium which it contained agreed closely with 

 that required by the formula Ba(C3lIBr202)2- ^^ therefore with 

 little hesitation considered the salt anhydrous, and were inclined to 

 ascribe the slight loss of weight which we noticed at 100° to a slow 

 decomposition. The acid made from carefully-prepared barium salt 

 crystallized well, melted quite sharply at 83-84°, but on analysis 



* These Proceedings, Vol. XVI. (x. s. vni.) p. 192. 



