THE YTTRIUM GROUP. 245 



Er^O.^. Er^{SO^^. Per cent. Er^O^ 



1.8760 grm. 3-0360 grm. 61.792 



1.7990 " 2.9100 " 61.821 



2.8410 " 4-5935 " 61.848 



1.2850 " 2.0775 " 61.853 



I. 1300 " 1.827 " 61.850 



.8475 " '-37° " 61.S61 



Mean, 61.8375, zh .0063 



Humpidge and Burney * give data as follows : 



1.9596 grm. Er2(SOj3 gave 1.2147 grm. Er.Pg. 61.987 per cent. 

 1.9011 " 1.1781 " 61.965 " 



Mean, 61.976, ± .0074 



Combining all four series we get the subjoined general 

 mean for the percentage of oxide in sulphate. Bahr and 

 Bunsen's single experiment is given the probable error of 

 one experiment in Hoeglund's series : 



Delafontaine 54- 308, d= -0915 



Bahr and Bunsen 61.653, ±.0178 



Hoeglund 61.8375,^.0063 



Humpidge and Burney 61.976, ±.0074 



General mean 61.860, ±.0046 



Rejecting the first 61.880, ±.0046 



From the mean of all, Er = 170.379, ± .082; or, if = 

 16, Er == 170.770. From Bahr and Bunsen's determination, 

 Er = 168.683 ; and from Humpidge and Burney's highest, 

 Er = 171.428. 



The foregoing data were all published before the com- 

 posite nature of the supposed erbia was fully recognized. 

 It will be seen, however, that three sets of results were fairly 

 comparable, 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 at least three 

 earths, to one of which, a rose-colored body, the name erbia 

 is now restricted. For the atomic weight of the true erbium 



* Journ. Chem. .Society, Feb., 1879, p. 116. 



