136 PROCEEDINGS OP THE AMERICAN ACADEMY 



Calculated for Ca(C3lIBr20i,).2. Found. 



Ca 8.03 8.0G 



Potassic Dlbromacrylate, KC3HBr20.^. The potjissium salt was 

 made from the acid by neutralization with potassic carbonate. It 

 crystallized in leafy plates which were anhydrous. 



0.6842 grm. of the air-dried salt gave on evaporation with HgSO^ 

 and ignition 0.2229 grm. K^SO^ . 



Calculated for KCaHBr.p^ 

 K 14.58 



Found. 

 14.62. 



A comparison of these results with those which one of us has pre- 

 sented in the preceding paper will be facilitated by the following 

 table, which gives the mean of each series of results : — 



Since the identity of the dibromacrylic acid formed by the sub- 

 traction of hydrobromic acid from the tribrompropionic acid melting 

 at 92° with that derived fron^ mucobromic acid was thus established 

 with precision, it seemed to us of interest to study a little more closely 

 the tribrompropionic acid which this same dibromacrylic acid forms 

 by the addition of hydrobromic acid. Mr. C F. Mabery * had with 

 one of us already proved that such an addition product could be formed, 

 but it had been prepared solely from the impure acid melting at 83- 

 84" and very little studied. "We therefore at first undertook its prep- 

 aration in larger quantity from pure acid melting at 85-86°. 



Tribrompropionic Acid, CgllgBr^O^, . When dibromacrylic acid 

 made by the action of baric hydrate upon mucobromic acid is heated 

 with three or four times its weight of hydrobromic acid saturated at 

 0° for eight or ten hours, at 100° the needle-like prisms disappear and 

 are replaced by rectangular plates of the new tribrompropionic acid. 

 With the pure acid no carbonization such as had been noticed in work- 

 ing with the impure acid was observed even at 120°, and we therefore 



* These Proceedings, Vol. XVI. (n. s. viii.) p. 197. 



