374 PROCEEDINGS OF THE AMERICAN ACADEMY. 



utmost significauce. The cold fused transparent or trauslucent mass 

 is much less hygroscopic than the powder from which it was made. 



The importance of driving out every trace of water from the salt 

 before weighing cannot be overestimated. Systematic experiments* 

 with baric bromide and chloride led to the conclusion that probably 

 neither of these salts retains water at a red heat, and it was to be ex- 

 pected that the same fact might be true of the substance in hand. In 

 order to test the jioint, four grams of very pure strontic bromide dried 

 at about 400° were fused in a stream of hydrogen bromide. The mass 

 gained nearly six milligrams in weight, showing that the loss of bro- 

 mine in the air at 400° much more than counterbalanced a possible 

 trace of water. Again, 11.2G10 grams of the same specimen, dried 

 at 305° until constant in weight, were found to weioh 11.2630 grams 

 after fusion as before. Since these gains corresponded closely with 

 losses of bromine found alkalimetrically in similarly heated but unfused 

 samples, it is evident that very little if any water can be held by the 

 dried salt. It has already been pointed out that no absolute proof of 

 such a fact is possible ;t and these experiments, together with the 

 analogy furnished by the more manageable barium salts, seem to be 

 the last resort. The apparatus used for these experiments v/ill be 

 described under the heading " Method of Analysis." 



The specific gravity of anhydrous strontic bromide has been found 

 by Bodeker to be 3.96. Since no more recent data regarding this 

 constant could be found, another determination, described below, 

 seemed to be needed. 3.2560 grams of a pure specimen which had 

 been fused in the air and dried at 200° in the pycnometer were found 

 to displace 0.6678 gram of toluol at 24°. Since the specific gravity 

 of the toluol under these conditions, referred to water at 4°, was found 

 to be 0.8618, that of the strontic bromide referred to the same stan- 

 dard must be 4.203. Again, 2.3065 grams of strontic bromide which 

 had been fused in a stream of hydrobromic acid displaced 0.4699 gram 

 of toluol, thus having a specific gravity of 4.229. The mean of these 

 determinations, 4.216, was adopted as the basis of the reduction of the 

 weighings to the vacuum standard. 



Strontic bromide, like baric bromide and chloride, may be evapo- 

 rated to apparent dryness over a free flame in a platinum dish without 

 losing a trace of halogen. Experiment showed that, upon mixing pure 

 bromide of strontium with small quantities of bromide of calcium and 



* These Proceedings, XXVIII. 12; XXIX. 58. 

 t These Proceedings, XXVIII. 14. 



