CERIUM. 335 



CERIUM. 



Although cerium was discovered almost at the beginning of the present 

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

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

 vestigation 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 chloride as follows. The third column shows the amount of CeO 2 

 proportional to 100 parts of AgCl : 



CeO 2 . AgCl. Ratio. 



5755 grm. 1.419 grm. 4O-557 



.6715 " 1.6595 " 40.464 



1.1300 " 2.786 " 40.560 



.5366 " i.33'6 " 40.297 



Mean, 40.469, .0415 



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

 a fourth column I show the amount of Ce0 2 proportional to 100 parts of 

 BaS0 4 : 



Sulphate. CeO^. BaSO Ratio. 



1.379 grm. .8495 grm. 1.711 grm. 49.649 



1.276 " .7875 " 1.580 " 49.836 



1.246 " .7690 " 1.543 " 49.838 



1.553 " .9595 " 1.921 " 49.948 



Mean, 49.819, .042 



Beringer also gives a single analysis of the formate and the results of 

 one conversion of the sulphide into oxide. -The figures are, however, 

 not valuable enough to cite. 



The foregoing data involve one variation from Beringer's paper. 

 Where I put Ce0 2 as found he puts Ce 2 O s . The latter is plainly inad- 

 missible, although the atomic weights calculated from it agree curiously 

 well with some other determinations. Obviously, the presence of didym- 

 ium in the salts analyzed tends to raise the apparent atomic weight of 

 cerium. 



Shortly after Beringer, Hermann f published the results of one experi- 

 ment. 23.532 grm. of anhydrous cerium sulphate gave 29.160 grm. of 

 BaS0 4 . Hence 100 parts of the sulphate correspond to 123.926 of BaS0 4 . 



*Ann. Chem. Pharm.,42, 134. 1842. 



t Journ. fur Prakt. Chem., 30, 185. 1843. 



