OP ARTS AND SCIENCES. 21 



with much water until no chlorine was to be found in the filtrate, 

 and was almost wholly decomposed by strong nitric acid. The 

 solution \vas diluted and shaken with the excess of baric chromate 

 for a long time. Upon the neutralization of the nitric acid in the 

 clear yellow filtrate with pure sodic carbonate, the baric chromate 

 was largely recovered, and after a thorough washing it was again 

 dissolved in nitric acid, and the baric nitrate was repeatedly crystal- 

 lized until it w^as wholly colorless and neutral. By means of 

 gradually increasing heat baric oxide was formed from this nitrate, 

 the ignition taking place in a platinum crucible, and continuing 

 until long after the frothing had ceased. The crucible itself lost 

 several milligrammes during the process. The brownish residue 

 was dissolved in water, and the clear colorless liquid was filtered 

 from the brown precipitate. The baric hydroxide was neutralized 

 with pure hydrobromic acid,* and the baric bromide was passed 

 many times through the often repeated round of fusion, solution, 

 filtration, and crystallization, until the fused cake was perfectly 

 clear and colorless. After being faintly acidified with hydro- 

 bromic acid, the pure salt was crystallized, washed, and dried as 

 usual. This specimen, which had been growing smaller and 

 smaller in amount during the manifold processes to w^hich it had 

 been subjected, was enough only for one analysis (Xo. 16) and 

 was designated V. 



Out of the baric bromate which remained from the fourth prep- 

 aration two other specimens of baric bromide were prepared. The 

 only point in which this preparation differed from the second method 

 was the fact of the strong acidification of the bromide with hydro- 

 bromic acid just before the final series of crystallizations. The 

 crystallization was then continued until the mother liquors proved 

 to be absolutely neutral. The purest crystals w^ere designated VI. a; 

 the mother liquor from them yielded VI. b (Analyses 17,18, 19). 



It seemed probable that, if all these preparations gave about the 

 same value for the molecular weight of baric bromide, they would 

 fix this constant with comparative certainty. It is doubtful if the 

 substance can be prepared in a state of absolute purity. Stas found 

 it impossible to prepare any of his haloid salts in such a state, f a 

 small amount of silica always remaining. The attempt was made 



* This acid was from the same sample as that employed in making specimens 

 I.b and I.e. 



t See Stas's " Untersuclmngen," Aronstein, pp. 269, 279, 346. 



