ATOMIC AVEIGHTS 533 



TERBIUM. 



The older determinations of atomic weight, made upon terbium prepa- 

 rations of doubtful character, may well be ignored. Boisbaudran ' has 

 published two estimates of this constant. First, for two preparations, 

 one with a lighter and one with a darker earth, he gives Tb=: 161.4 and 

 163.1. In his second paper he makes Tb = 159.01 to 159.95; probably 

 with SO3 = 80. According to Feit' Tb = 158.6. Emma Potratz,' by 

 various methods, found Tb = 154, approximately. For all of these de- 

 terminations the essential details are lacking. 



The series of determinations by Urbain * is more satisfactory. The 

 octohydrated sulphate was converted into the anhydrous salt by careful 

 heating, with the following results : 



.0008 

 Hence Tb = 159.201, ±.0130. 



DYSPROSIUM. 



The atomic weight of dysprosium has been well determined by Urbain 

 and Demenitroux." They reduced the octohydrated sulphate to oxide, 

 by calcination, with the following results, taking all their data as one 

 series : 



iCompt. Rend., 102, 396, and 111, 474. 1886-1890. 

 = Zeitsch. anorg. Cheni., 43, 280. 1905.' 

 3 Chem. News, 92, 3. 1905. 



<Compt. Rend., 142, 957. Preliminary papers by Urbain are in C. R. 141, 521; ihid.. 142. ,27; 

 Bull. Soc. Chim. (3), 33, 403. See alai -Jonrn. Chim. Pliys., 4, 321. 

 = Compt. Rend., 143, 598. 1906. 



