ATOMIC WEIGHTS 



505 



The value La = 138.8 is essentially tliat found by Jones, whose work is 

 entitled to high credit. Braimer, liowever. by two distinct methods, 

 found La = 139, with much to be said in favor of his determinations. 

 The question as to the trne atomic weight of lanthanum is therefore not 

 closed; and it should be taken up anew by means of other methods than 

 those heretofore employed. 



CERIUM. 



Although cerium was discovered almost at the beginning of the nine- 

 teenth century, its atomic weight was not properly determined until after 

 the discovery of lanthanum and didymium by Mosander. In 1842 the 

 investigation was undertaken by Beringer/ who employed several methods. 

 His cerium salts, however, were all rose-colored, and therefore were not 

 wholly free from didymium ; and his results are further affected by a 

 negligence on his part to fully describe his analytical processes. 



First, a neutral solution of cerium chloride was prepared by dissolving 

 the carbonate in hydrochloric acid. This gave weights of eerie oxide and 

 silver cliloride as follows. The third column shows the amount of CeOo 

 proportional to 100 parts of AgCl : 



Mean, 40.469, ± .0415 



Hence Ce= 143.02. 



The analysis of the dry cerium sulphate gave results as follows. In 

 a fonrtli column I show the amount of CeO.. proportional to 100 parts 

 of BaSO.: 



Mean, 49.819, ± .042 

 Hence Ce= 142.44. 

 Berinarer also sfives a single analvsis of the formate and tlie results of 



^Ann. Chem. Pharm., 42, 134. 1S42. 



