166 GADOLIN1TE. 



the usual precaution (i, 831), to separate the cerium 

 metals; the erbium and yttrium, which still remain in 

 solution, are again precipitated by oxalic acid ; the 

 oxalates are ignited ; and the residual oxides, after being 

 carefully freed from admixed carbonate of potassa by 

 boiling with water, are dissolved in nitric acid, and 

 again precipitated from the acid solution by oxalic 

 acid, this series of operations being repeated till the 

 solution of the mixed earths in nitric acid, when ex- 

 amined in the spectral apparatus, no longer exhibits 

 the absorption-bands characteristic of didymium. The 

 last portion of calcium and magnesium are separated 

 by precipitating the acid solution of the mixed earths 

 with ammonia, the calcium and magnesium then re- 

 maining in solution ; the precipitate is dissolved in 

 nitric acid ; and the solution, now containing nothing 

 but erbia and yttria, is precipitated by oxalic acid. 



To separate erbia and yttria, the oxalates are con- 

 verted into nitrates; the solution is evaporated in a 

 platinum dish, till the first bubbles of nitrous acid 

 make their appearance ; and the dish is quickly cooled 

 by placing it in cold water, whereupon the viscid mass 

 solidifies to an extremely brittle glass. On dissolving 

 the mass in a quantity of warm water just sufficient 

 to prevent the solution from becoming turbid on 

 boiling, nitrate of erbium, still containing yttrium, 

 separates on slow cooling in needles, which must be 

 separated from the mother liquor by decantation and 

 quickly rinsed with water containing about three per 

 cent, of nitric acid. This mother liquor, treated in a 

 similar manner, yields a second crop of crystals of 

 nitrate of erbium containing yttrium ; the mother 

 liquor of this yields a third crop, and so on, the pro- 

 portion of nitrate of yttria in the successive crops of 

 crystals continually increasing. By mixing a certain 

 number of the earlier and comparatively pure crops of 

 crystals, and treating them in a similar manner, pro- 



