126 PROCEEDINGS OP THE AMERICAN ACADEMY 



proved to contain too high a percentage of bromine. Since the acid 

 made from the lead salt had given us precisely the same unsatisfactory 

 results, we thought it probable that the impurities which were found 

 in the acid thus made were introduced by a decomposition of the acid 

 itself in its liberation from its salts. A more careful study of this 

 reaction subsequently convinced me, however, that such was not the 

 case. Certainly no carbonic dioxide, bromacetylen, or hydrobromic 

 acid could be detected as resulting from such decomposition when 

 dilute sulphuric acid was added in slight excess to a boiling aqueous 

 solution of the barium salt. I therefore turned my attention to a 

 further purification of the salts. 



Since repeated recrystallization of the barium salt failed to give me 

 any much better product, I thought it worth while to determine the 

 variation of composition introduced by one set of crystallizations from 

 water. I therefore dissolved 30 grammes of white well-crystallized 

 salt (A) in 380 cc. of hot water. On cooling 6.5 grms. of the salt 

 (I.) separated, and by successive filtration, evaporation, and cooling 

 I obtained the fractions (II.) 8.9 grms., (III.) 6.9 grms., and (IV.) 

 4.8 grms., the remaining 2.9 grms. being lost in the filter-papers 

 upon which the successive portions were dried. An analysis of these 

 air-dried salts gave the following results : — 



A. 0.5669 grm. substance gave 0.2239 grm. BaSO^. 



I. 0.5713 grm. substance gave 0.2276 grm. BaSO^. 



II. 0.5139 grm. substance gave 0.2036 grm. BaSO^ . 



III. 0.5665 grm. substance gave 0.2231 grm. BaSO^ . 



IV. 0.5003 grm, substance gave 0.1941 grm. BaSO^ . 



Calculated for Calculated for 



Ba(C3HBr202)2. Ba(C3HBr20o)2.H20. A. 

 Ba 23.03 22.35 23.21 



From these results it was evident that the barium salt contained a 

 persistent impurity which could not be removed by fractional crys- 

 tallization, and that the constancy of its composition was accidental. 

 I next tried the beautifully crystalline acid potash salt which I have 

 already described,* and found that it gave results which were all that 

 could be desired. This salt can easily be made by neutralizing a 

 weighed amount of the ordinary acid melting at 82-84° with potassic 



* Loc. cit. p. 194. 



