572 MINERALOGY 



Associated with cerium chemically is a group of elements, dis- 

 tinguished and separated from each other with difficulty ; they are 

 known as the 



Rare Earths 



Their hydroxides are precipitated' by either ammonia or sodium 

 hydroxide, which separates them from the alkali earths. From the 

 method of separation, the solubility of their oxalates, they are 

 divided into two groups : 



Group I. Gadolinite earths or Group II. Cerite earths 



Yttrium earths 

 Yttrium, Y., Atomic Lanthanum, La., Atomic 



weight 89. weight 139. 



Scandium, Sc., Atomic Cerium, Ce., Atomic weight . 140.5 



weight 44.1 Praseodymium, Pr., Atomic 



Samarium, Sm., Atomic weight 140.6 



weight 150.4 Neodymium, Nd., Atomic 



Gadolinium, Gd., Atomic weight 144.3 



weight 157.3 Thorium, Th., Atomic weight . 232.4 



Terbium, Tr., Atomic Some doubtful elements may 



weight 159.2 be added to this group 



Erbium, Er., Atomic 



weight 167.7 



Thulium, Tm., Atomic 



weight 168.9 



Ytterbium, Yb., Atomic 



weight 172. 



Dysprosium, Dy., Atomic 



weight 162.5 



They may be extracted from a mineral as follows. If the mineral 

 is insoluble in acids, it is mixed to a stiff paste with strong sulphuric 

 acid, the paste is heated carefully until the SO 3 fumes are driven 

 off, and then baked hard and dry ; the dry mass is pulverized and 

 leached with boiling water until all soluble salts are extracted. 



The free acid is neutralized with ammonia. To the hot solution 

 a few cc. of ammonium acetate and a large excess of a boiling 

 saturated solution of ammonium oxalate are added ; let cool and 

 stand overnight. The crystalline precipitate is composed of the 

 oxalates of the rare earths with the exception of thorium, which 

 is still in solution ; these are filtered, dried, and ignited to the ox- 

 ides. From the filtrate thorium is precipitated as hydroxide with 

 sodium hydrate. The ignited oxides are dissolved in the least 

 possible quantity of HC1, then saturate this solution with potas- 

 sium sulphate, let stand, filter, and wash with a strong solution of 



