OF ARTS AND SCIENCES. 285 



small volume on the water bath, and finally to dryness over sulphuric 

 acid. It formed a deliquescent amorphous crust, in which the potas- 

 sium was determined after drying at 80°. 



1.0508 grm. of the salt dried at 80° gave 0.3124 grm. K^SO^. 



Calculated for KCiClBr^O,. Found. 



K 12.92 " ' 13.36 



Argentic a-Chlordihromacrylate, AgCaClBr.^O^. — The silver salt 

 was prepared by the addition of argentic nitrate to an aqueous solution 

 of the barium salt. It separated as a curdy precipitate, which could be 

 recrystallized from hot water without perceptible decomposition. It 

 crystallizes in rhombic plates, and is not affected by ordinary daylight. 



0.4715 irrm. of the salt save 0.1799 grm. AgCl. 



Calculated for AgCsClBivO,- Found. 



Ag 29.07 " ' 28.72 



/J-Chlordibromacrylic Acid. 



The readiness with which chlortribrompropionic acid is decomposed 

 by alkaline hydrates has ali'eady been described,* and chlordibrom- 

 ethylen was identified as one of the products when the decomposition 

 was effected with the aid of heat in a strongly alkaline solution. 



A more careful study of the conditions has shown that a halogen 

 atom may be eliminated without sevei'ing the connection of the carbon 

 atoms. If the solution is kept cold, and a calculated amount of the 

 alkaline hydrate — by preference baric hydrate — is added slowly, it 

 will retain its acid reaction until the change represented by the fol- 

 lowing equation is iiearly complete : 



2C3ClBr30,Il2 + 2BaO,_,H2 = Ba(aClBr,0,)2 + BaBr^ + 4H2O. 



The solution must then be made slightly alkaline, and kept so for 

 twenty-four hours. On acidifying with hydrochloric acid, the resulting 

 chlordibromacrylic acid is partially precipitated as an oil, and the 

 remainder may be extracted from the solution with ether. 



The acid is purified by crystallization from hot water, in which it is 

 far more soluble than in cold. It is very soluble in ether and alcohol, 

 less soluble in carbonic disulphide and chloroform. By slow evapora- 

 tion from a solution in carbonic disulphide it crystallizes in oblique 

 prisms, which melt at 99°. 



* These Proceedings, Vol. XVIII. p. 45. 



