162 CERITE. 



of the protochlorides (of didymium and lanthanum) is 

 again precipitated by potassa, and the precipitate 

 treated a second time with potassa and chlorine-gas. 



The oxide of cerium can be obtained nearly pure if 

 the mixed oxides are first treated with dilute and then 

 with concentrated nitric acid, which dissolves out the 

 lanthanum and didymium. The solution is evapo- 

 rated, the salt ignited, and the oxide again treated with 

 very dilute nitric acid. The oxide of cerium remains 

 undissolved. 



From the solution the didymium and lanthanum 

 are precipitated by ammonia and dissolved in sul- 

 phuric acid. If the dried mixture of salts is dissolved 

 in water until it is saturated at 5 or 6, and this solu- 

 tion heated to 30, the sulphate of the oxide of lantha- 

 num separates, while the didymium remains in solu- 

 tion. By repeating the operation both salts may be 

 obtained in a pure state. The salt of lanthanum is 

 colorless, and that of didymium dark rose-red. 



Another method of approximate separation is the 

 following. The cerite is decomposed by sulphuric 

 acid, the mass lixiviated, the solution purified with 

 sulphuretted hydrogen, an excess of hydrochloric acid 

 added, and the cerite oxides precipitated by oxalic 

 acid. The precipitate is washed by decantation, dried 

 and mixed with half its weight of magnesia alba and 

 so'me water, rubbed together, arid dried in a porcelain 

 dish, the bottom of which is heated to dull redness, 

 and the heat continued with constant stirring until it 

 lias become a cinnamon-brown powder, which contains 

 all the cerium as oxide. It is then dissolved in warm 

 concentrated nitric acid. The deep brownish-red solu- 

 tion contains a double salt of the nitrate of the oxides 

 of cerium and didymium with the nitrates of the oxide 

 of lanthanum and magnesia, which may be obtained 

 in deep reddish-yellow rhombohedral crystals. The 

 red solution is evaporated to a syrupy consistency, 



