RICHARDS AND ARCHIBALD. — ATOMIC WEIGHT OF CAESIUM. 465 



thoroughly washed in the gaseous state as well as twice distilled in 

 aqueous solution, rejecting the first and last portions. Hence there is 

 no possibility that the product could have contaiued either chlorine or 

 iodine. The trace of mother liquor included in the crystals of tribromide 

 was eliminated by means of several successive recrystallizations and 

 washings with hydrobromic acid. After drying the crystals as thoroughly 

 as possible iu a centrifugal machine, they were placed in a porcelain dish 

 and kept at a temperature of 80° C. in an electric drying oven until all 

 obvious signs of the extra bromine had disappeared. The pure white 

 bromide was then heated for eight hours at 150°, and subsequently dis- 

 solved in a little water and precipitated by means of pure concentrated 

 hydrobromic acid. The crystals were provisionally dried over potash 

 and were then ready to fuse. Like the chloride, they were not deliques- 

 cent in the ordinary air of the laboratory. 



The apparatus for fusing, bottling, and weighing the bromide was 

 similar to that used in the case of the chloride, except that an addition 

 was provided for the sake of introducing a slight amount of perfectly dry 

 hvdroiren bromide into the nitrogen during the fusion. * This was done 

 because the loss of a trace of bromine was feared, although indeed none 

 was ever noticed. After partial cooling the acid was wholly replaced by 

 pure dry nitrogen and finally by air, which had passed through a freshly 

 filled train of purifiers and freshly sublimed phosphoric oxide. The 

 fused product, like the chloride, affected neither methyl orange nor 

 phenol phthalein in the preliminary tests made to prove the normality 

 of the salt. Caesic bromide fuses at a point somewhat above 600° C, 

 although below the softening poiut of hard glass, but the exact point was 

 not determined. 



The analysis of the salt was less troublesome than the analysis of the 

 chloride, because of the very meagre solubility of argentic bromide, which 

 served as the means of precipitating the bromine. The silver used was 

 from the same sample as that used in the case of the chloride, its weight 

 was determined as before, and the very faint trace of bromide in the last 

 pure wash-waters was estimated with the nephelometer as in the case of 

 analyses 11, 12, and 13. 



The specific gravity of caesic bromide was found by Setterberg f to be 

 4.37 ; in verification of this value the following determinations of this 

 constant were made. At different times 0.9964 and 0.8456 gram of 



* Richards and Baxter, Proc. Am. Acad., 33, 124 (1897). 



t Oefvers. Stockh. Acad. Forh., 39, No. 6, 23 (1882). We are indebted to Mr. 

 F. R. Fraprie for this reference, which has been generally overlooked. 

 vol. xxxviii. — 30 



