BISMUTH. 231 



Marignac's second method of determination was by conversion of the 

 oxide into the sulphate. The oxide was dissolved in nitric acid, and 

 then sulphuric acid was added in slight excess from a graduated tube. 

 The mass was evaporated to dryness with great care, and finally heated 

 over a direct flame until fumes of S0 3 no longer appeared. The third 

 column gives the sulphate formed from 100 parts of oxide : 



2.6503 Bi 2 O 3 gave 4.0218 Bi 2 (SO 4 ) 3 . Ratio, 151.749 



2.8025 4.2535 " " 151.775 



2.710 4.112 " " I5L734 



2.813 " 4- 26 7 " " 151.688 



2.8750 4.3 62 5 " ". I5I-739 



2.7942 " 4-2383 " " 151.682 



Mean, 151.728, .0099 



Hence, with O = 16 and S = 32.06, Bi = 208.16. 



This result needs to be studied in the light of Bailey's observation,* 

 that bismuth sulphate has a very narrow range of stability. It loses the 

 last traces of free sulphuric acid at 405, and begins to decompose at 418, 

 so that the foregoing ratio is evidently uncertain. The concordance of 

 the data, however, is favorable to it. 



The next determination of this atomic weight was by L6we,f who 

 oxidized the metal with nitric acid, and reduced the nitrate to oxide by 

 ignition. Special care was taken to prepare bismuth free from arsenic, 

 and the oxide was fused before weighing. In the paper just quoted 

 Bailey calls attention to the volatility of bismuth oxide, which doubt- 

 less accounts for the low results found in this investigation. The data 

 are as follows : 



Bi Taken. Bi^O^ Found. Per cent. Bi. 



11.309 12.616 89.640 



12.2776 !3'694 89.656 



Mean, 89.648, .0040 



Hence, if = 16, Bi = 207.84. 



In Classen's J work upon the atomic weight of bismuth, the metal 

 itself was first carefully investigated. Commercial samples, even those 

 which purported to be pure, were found to be contaminated with lead 

 and other impurities, and these were not entirely removable by many 

 successive precipitations as subnitrate. Finally, pure bismuth was ob- 

 tained by an electrolytic process, and this was converted into oxide by 

 means of nitric acid and subsequent ignition to incipient fusion. Results 

 as follows, with the percentage of Bi in Bi 2 O 3 added : 



* Journ. Chem. Soc., 51, 676. 

 tZeit. Anal. Chem., 22, 498. 

 \ Ber. Deutsch. Chem. Gesell., 23, 938. 1890. 



