18 PROCEEDINGS OF THE AMERICAN ACADEMY 



grammes (in vacuum) of silver were dissolved and precipitated by 

 a slight excess of the acid, yielding 2.79184 grammes (in vacuum) 

 of argentic bromide. Hence the percentage of silver in the precip- 

 itate was 57.444 (according to Stas, 57.445). The baric bromide 

 made from this acid was recrystallized, ignited at dull redness, 

 dissolved, allowed to stand exposed to the air, filtered, crystallized, 

 dehydrated, and fused at bright redness by means of an alcohol 

 lamp. Finally, after solution, filtration, slight acidification with 

 hydrobromic acid, and two successive crystallizations, the small 

 amount of substance which remained was used for Analyses 3 and 4 

 (Preparation No. l.b). The salt contained in the last mother 

 liquor was fused into an absolutely clear limpid liquid, dissolved, 

 faintly acidified, filtered, and recrystallized, the crj'stals being 

 washed with alcohol, and finally analyzed under the designation 

 No. l.c (Analysis 5). It is needless to say that in all the con- 

 cluding operations platinum vessels and the purest water alone 

 were used. 



The second general method used in the preparation of baric 

 bromide was based upon the decomposition of baric bromate. This 

 salt was obtained in a very pure state by repeated recrystallization 

 of the bromate remaining from the first preparation of hydrobromic 

 acid by the method described above. In the course of the recrys- 

 tallization it was noted that the glittering hard crystals emit bril- 

 liant flashes of bluish light upon being rubbed between the surfaces 

 of moistened glass apparatus. This phenomenon takes place when 

 there is no conceivable trace of organic matter present, and may be 

 noticed even in the daylight. The substance was graduall}^ raised 

 to a dull red heat by means of a Berzelius lamp, no emission of 

 light being noticed during its decomposition. The resultant baric 

 bromide was dissolved, filtered, crystallized twice, washed with al- 

 cohol, and dried. After fusion over the spirit lamp the substance 

 was redissolved, filtered, acidified with hydrobromic acid, and 

 finally crystallized twice from water. Each yield of crystals was 

 washed four times with the purest alcohol. In the first mother 

 liquor a notable trace of sodium was found by the usual spectro- 

 scopic treatment, but no trace of calcium or strontium. The 

 purest crystals were divided by yet another crystallization into 

 three fractions, which we may call II. a, II. b, and II. c. The last 

 was obtained by the evaporation of all the mother liquor decanted 

 from the first two. 



The third method used for the preparation of baric bromide 



