534 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 54 



Mean, 49.259, ± .0036 



Hence Dy = 162.550, ±.0190. 



ERBIUM, HOLMIUM, THULIUM. 



Since the earth which was formerly regarded as the oxide of erbium 

 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. Nevertheless the work done by several investigators may prop- 

 erly be cited, if only for the sake of completeness. 



First, Delafontaine's ' early investigations may be considered. A sul- 

 phate, regarded as erbium sulphate, gave the following data. An oxalate 

 was thrown down from it, which, upon ignition, gave oxide. The per- 

 centages 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 experiments: 



Mean. 54.308, ± .0915 



Hence Er= 118.75. 



Bahr and Bunsen " give a series of results, representing successive puri- 

 fications 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 per cent, oxide. 



Hence Er = 169.59. 



Hoeglund,^ follov/ing the method of Bahr and Bunsen, gives these 

 figures : 



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

 2 .\nn. Cheni. Pharm., 137, 21. 1866. 

 3K. Svensk. Vet. Akad. Handlingar, Bd. 1, No. 6. 



