3G0 THE ATOMIC WEIGHTS. 



GADOLIxNIUM. 



This element, discovered by Marignac, must not be confounded with 

 the mixture of metals from the gadolinite earths to which Nordenskiold 

 gave the same name. Several determinations of its atomic weight have 

 been made, but Bettendorff's only were published with proper details.* 

 He effected the synthesis of the sulphate from the oxide, and his weights 

 were as follows. The percentage of Gd^.O.,, in 0^1,(80^., is given in the 

 third column : 



Mean, 60.0S0, ± .0013 



Hence, with SO3 ^= 79.465, Gd = 155.575. 



If =- 16, Gd = 156.761. 



Boisbaudran f found Gd = 155.33, 156.06, 155.76, and 156.12. The last 

 he considers the best, but gives no details as to antecedent values. He 

 also quotes Marignac, who found Gd ■■= 156.75, and Cleve, who found 

 154.15, 155.28, 155.1, and 154.77. Probably these all depend upon 

 SO3 = 80. 



ERBIUM. 



Since the earth which was formerly 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. Nevertheless the work done by several investigators may prop- 

 erly be cited, since it sheds some light upon certain important problems. 



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: 



*Ann. Chem. Pharm., 270, 376. 1S92. 



tCompt. Rend., iii, 409. 1890. 



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



