CERIUM. 337 



One experiment was also made upon the oxalate : 



.3530 grm. oxalate gave .1913 CeO.^ and .0506 H^O. 



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



In each sample of CeO^ the excess of oxygen over Ce^Oa was estimated 

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

 ther considered. 



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

 of cerium, as follows. In the earlier paper cerium suli)liate was analyzed, 

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

 tated from the filtrate as barium sulphate : 



.413 gim. Ce2''SO^)3 gave .244 grm. CeO^ and .513 grm. BaSO^. 



Hence 100 BaSO^ = 47.563 CeO.^, 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, zb .042 



Hunsen and Jegel 48.689, ± .077 



Rammelsberg ... 47-563, ± .108 



•_ 



General mean 49.360, it .035 



It should be noted here tliat this mean is somewhat arbitrar}^ 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 COj, 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 ].)osthumously made 

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

 that all sam[)les 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 ai)[)arent atomic weight of cerium 

 very perceptibly. 



Cerium sulphate was recr\'stallized 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. 

 22 



