ATOMIC WEIGHTS 331 



In Classen's ' 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. Eesults 

 as follows, with the percentage of Bi in BijOg added : 



Mean, 89.696, ± .0009 



Hence Bi = 208.92, or, reduced to a vacuum standard, 208.90. 

 Classen's paper was followed by a long controversy between Schneider 

 and Classen,^ in which the former upheld the essential accuracy of the 

 work done by Marignac and himself. Schneider had started out with 

 commercial bismuth, and Classen found that the commercial bismuth 

 which he met with was impure. Schneider, by various analyses, showed 

 that other samples of bismuth were so nearly pure that the common 

 modes of purification were adequate; but Classen replied that the original 

 sample used by Schneider in his atomic weight investigation had not 

 been reexamined. Accordingly, Schneider published a new series of de- 

 terminations ' made by the old method, but with metal which had been 

 scrupulously purified. Results as follows : 



Bi. BLO3. Per cent. Bi. 



5.0092 5.5868 89.661 



3.6770 4.1016 89.648 



7.2493 8.0854 89.659 



9.2479 10.3142 89.662 



6.0945 6.7979 89.653 



12.1.588 13.5610 89.660 



Mean, 89.657, ± .0015 



Hence with = 16, Bi = 208.05, a confirmation of the earlier deter- 

 minations. 



1 Ber. Deutsch. chem. Ges., 2.3. 038. 1S90. 



2Journ. prakt. Chem., 42, 568; 4a, 138; 44, 23 and 411. 



s Journ. prakt. Chem., 50, 461. 1894. 



