ATOMIC WEIGHTS 535 



Er,0,. i;n(S0j3. Per cent. Er,0,. 



1.8760 3.0360 • 61.792 



1.7990 2.9100 61.821 



2.8410 4.5935 61.848 



1.2850 2.0775 61.8.53 



1.1300 1.827 61.850 



.8475 1.370 61.861 



Mean. 61.8375, ±: .0063 



Hence Er = 170.61. 



According to Thalen/ spectroscopic evidence shows that the "erbia " 

 studied by Hoeghmd was largely ytterbia. 

 Hnmpidge and Burney ° give data as follows : 



1.9596 grm. Er,( 804)3 gave 1.2147 grm. ErA- 61.987 per cent. 



1.9011 " 1.1781 " 61.965 



Mean, 61.976, ± .0074 



Hence Er = 171.75. 



The foregoing data were all published before the composite nature of 

 the supposed erbia was fully recognized. It will be seen, however, that 

 three sets of results were fairly compai'able, while Delafontaine evidently 

 studied an earth widely different from that investigated by the others. 

 Since the discovery of ytterbium, some light has been thrown on the 

 matter. The old erbia is a mixture of several earths, to one of which, a 

 rose-colored body, the name erbia is now restricted. For the atomic 

 weight of the supposedly true erbium Cleve ^" gives three determinations, 

 based on syntheses of the sulphate after the usual method. His weights 

 were as follows, with the percentage ratio added: 



Mean, 61.309, ± .0068 



Hence Er= 166.31. 



The discussion over the complexity of erbia, however, did not stop with 

 the work of Cleve. Kriiss,* assisted by K. Hofmann, made a long series 

 of fractionations of erbium material, and gave crude atomic weight de- 

 terminations of them, which varied widely. The figures need not be 



1 Wiedemann's BeiblUtter, 5, 122. 18S1. 

 ^journ. Cheni. Soc, .So, 116. 1S79. 

 3K Svensk. Vet. Akad. Handlinsrar, No. 7. 1880. 

 < Zeitsch. anorg:. Chem., 3, 353. 1893. 



