CERIUM. 339 



The cerio oxide in this case was perfectly white. The cerium oxalate 

 which yielded it was precipitated boiling by a boiling concentrated solu- 

 tion of oxalic acid. The precipitate stood twenty-four hours before 

 filtering. 



In 1875 Buehrig's * paper upon the atomic weight of cerium was issued. 

 He first studied the sulphate, which, after eight crystallizations, still 

 retained traces of free sulphuric acid. He found, furthermore, that the 

 salt obstinately retained traces of water, which could not be wholly ex- 

 pelled by heat without partial decomposition of the material. These 

 sources of error probably affect all the previously cited series of experi- 

 ments, although, in the case of Wolf's work, it is doubtful whether they 

 could have influenced the atomic weight of cerium by more than one or 

 two tenths of a unit. Buehrig also found, as Marignac had earlier shown, 

 that upon precipitation of cerium sulphate with barium chloride the 

 barium sulphate invariably carried down traces of cerium. Furthermore, 

 the eerie oxide from the filtrate always contained barium. For these 

 reasons the sulphate was abandoned, and the atomic weight determina- 

 tions of Buehrig were made with air-dried oxalate. This salt was placed 

 in a series of platinum boats in a combustion tube behind copper oxide. 

 It was then burned in a stream of pure, dry oxygen, and the carbonic 

 acid and water were collected after'the usual method. Ten experiments 

 were made; in all of them the above-named products were estimated, 

 and in five analyses the resulting eerie oxide was also weighed. By de- 

 ducting the water found from the weight of the air-dried oxalate, the 

 weight of the anhydrous oxalate is obtained, and the percentages of its 

 constituents are easily determined. In weighing, the articles weighed 

 were always counterpoised with similar materials. The following weights 

 were found : 



Oxalate. Water. CO 2 . CeO. z . 



9.8541 grm. 2.i987grm. 3.6942 grm 



9.5368 " 2.1269 " 3-5752 " 



9.2956 " 2.0735 " 3.4845 " 



10.0495 " 2.2364 " 3-774 " 



10.8249 " 2.4145 " 4.0586 " 



9.3679 " 2.0907 " 3-5 118 " 4-6150 grm. 



9.7646 " 2.1769 " 3.6616 " 4.8133 " 



9.9026 " 2.2073 " 3.7139 s " 4-8824 " 



9.9376 " 2.2170 " 3.7251 " 4-8971 " 



9.5324 " 2.1267 " 3-5735 " 4-6974 " 



These figures give us the following percentages for C0 2 and Ce0 2 in the 

 anhydrous oxalate : 



* Journ. fi'ir Prakt. Chem., 120, 222. 1875. 



