ATOMIC WEIGHTS 



499 



Gibbs cites tliree determinations, by the same method, made by Shap- 

 leigh, who found La = 139.75, 139.73 and 139.67. The weighings, how- 

 ever, are not given, and the data are unavailable for present purposes. 



In 1901 Bodman ' published three determinations, based on syntheses 

 of lanthanum sulj^hate. The figures are : 



Mean, 57.508, ± .0070 



Hence La = 138.94. 



In 1902 Jones" published his elaborate series of determinations, based 

 upon scrupulously purified materials. He effected twelve syntheses of 

 lanthanum sulphate from the oxide, and examined his product carefully 

 for acid sulphate, whose presence would tend to lower the apparent atomic 

 weight of the metal. This source of error Jones regards as excluded from 

 his determinations. His results are as follows: 



Mean, 57.544, ± .0006 



Hence La= 138.78. 



The atomic weight determinations by Brauner and Pavlicek '' included 

 a study of both the sulphate and the oxalate methods. In lanthanum 

 sulphate the acid salt was always found to be present, and its amount was 

 determined by titration, with sodium hydroxide, using ethjd-orange as 

 an indicator. The excess of acid thus measured tends to lower the 

 apparent atomic weight of lanthanum, and Brauner argues very forcibly 

 that all previous determinations of atomic weights among the rare earths 



^ Bihang Svensk. Vet. Aknd. Handl., 26 (2), No. 3. 1901. 



^Amer. Chem. Journ., 28, 23. 1902. 



^Journ. Chem. Soc, 81, 1243. 1902. Preliminary notice in Proc. Chem. Soc, 17, 63. 1901. 



