CERIUM. 337 



One experiment was also made upon the oxalate : 



353 S rm - oxalate gave .1913 CeO 2 and .0506 H 2 O. 



Hence, in the dry salt, we have 63.261 per cent, of CeO 2 . 



In each sample of Ce0 2 the excess of oxygen over Ce 2 3 was estimated 

 by an iodometric titration ; but the data thus obtained need not be fur- 

 ther considered. 



In two papers by Rammelsberg* data are given for the atomic weight 

 of cerium, as follows. In the earlier paper cerium sulphate was analyzed, 

 the cerium being thrown down by caustic potash, and the acid precipi- 

 tated from the nitrate as barium sulphate : 



.413 grm. Ce 2 (SO 4 ) 3 gave .244 grm. Ce0 2 and .513 grm. BaSO 4 . 



Hence 100 BaSO 4 = 47.563 Ce0 2 , a value which may be combined with 

 others, thus ; this figure being assigned a weight equal to one experi- 

 ment in Bunsen's series : 



Beringer ............................... 49.819, .042 



Kunsen and Jegel ......................... 48.689, .077 



Rammelsberg ..... ....................... 47-5^3> -t- . 108 



General mean 49.360, =b .035 



It should be noted here that this mean is somewhat arbitrary, since 

 Bunsen and Rammelsberg's cerium salts were undoubtedly freer from 

 didymium than the material studied by Beringer, 



In his later paper Rammelsberg gives these figures concerning cerium 

 oxalate. One hundred parts gave 10.43 of carbon and 21.73 of water. 

 Hence the dry salt should yield 48.862 per cent, of CO 2 , whence Ce = 

 137.14. 



In all of the foregoing experiments the eerie oxide was somewhat col- 

 ored, the tint ranging from one shade to another of light brown according 

 to the amount of didymium present. Still, at the best, a color remained, 

 which was supposed to be characteristic of the oxide itself. In 1868, 

 however, some experiments of Dr. C. Wolff were posthumously made 

 public, which went to show that pure ceroso-ceric oxide is white, and 

 that all samples previously studied were contaminated with some other 

 earth, not necessarily didymium but possibly a new substance, the re- 

 moval of which tended to lower the apparent atomic weight of cerium 

 very perceptibly. 



Cerium sulphate was recrystallized at least ten times. Even after 

 twenty recrystallizations it still showed spectroscopic traces of didymium. 

 The water contained in each sample of the salt was cautiously estimated, 

 and the cerium was thrown down by boiling concentrated solutions of 



* Poggend. Annalen, 55, 65 ; 108, 44. 



t Amer. Journ. Science and Arts (2), 46, 53. 



