CERITE. 



161 



dry ness, and ignited, a dark brown oxide is obtained, 

 from which a part, at least, of the oxide of lanthanum 

 may be obtained in a pure state. For this purpose, 

 the finely-powdered oxide is mixed with water, to 

 which nitric acid, free from nitrous acid, is added in 

 single drops with continual agitation, in proportion as 

 it is saturated. From the filtered solution, at a boiling 

 heat, carbonate of ammonia precipitates carbonate of 

 oxide of lanthanum in shining, crystalline scales. 



When the oxides precipitated by potassa are mixed 

 with a concentrated solution of potassa, and the latter 

 saturated with chlorine gas, and frequently agitated, 

 the cerium is converted into an insoluble yellow com- 

 pound of the sesquioxide, while didymium and lantha- 

 num, together with some cerium, are dissolved as 

 protochlorides. The yellow sesquioxide of cerium is 

 digested still longer with chlorine-water, filtered oft', 

 washed, and digested with dilute potassa to remove 



Fig. 17. 



hypochlorous acid ; any potassa which it has taken up 

 is then extracted by dilute nitric acid. The solution 



14* 



