244 THE ATOMIC WEIGHTS. 



Hence Yb == 172.761, dr .038. If = 16, then Yb = 

 173.158. If SO 3 = 80, Yb = 173.016. The true number 

 cannot be far from 173. 



ERBIUM. 



Since the earth which was formerl.y regarded as the oxide 

 of this metal is now known to be a mixture of two or three 

 different oxides, the older determinations of its molecular 

 weight have little more than historical interest. Nevertl e- 

 less the work done by several investigators may properly be 

 cited, since it sheds some light upon certain important prob- 

 lems. 



First, Delafontaine's "^^ early investigations may be consid- 

 ered. A sulphate, regarded as erbium sulphate, gave the 

 following data. An oxalate was thrown down from it, 

 which, upon ignition, gave oxide. The percentages in the 

 fourth column refer to the anhydrous sulphate. In the last 

 experiment water was not estimated, and I assume for its 

 water the mean percentage of the four preceding experi- 

 ments : 



Mean, 54.308, dr .0915 



Bahr and Bunsen f give a series of results, representing 

 successive purifications of the earth which was studied. 

 The final result, obtained by the conversion of oxide into 

 sulphate, was as follows : 



.7870 grm. oxide gave 1.2765 grm. sulphate. 61.653 P^^ cent, oxide. 



Hoeglund,! following the method of Bahr and Bunsen, 

 secured these results : 



* Ann. Chem. Pharm., 134, 108. 1865. 



f Ann. Chem. Pharm., 137, 21. 1866. 



% K. .Svenska Vet. Akad. Handlingar, Bd. i, No. 6. 



