220 PROCEEDINGS OF THE AMERICAN ACADEMY. 



concentrate in the mother liquors in another, continuing the crystalliza- 

 tion in any one form until impurities which accumulate in the mother 

 liquors have been eliminated as completely as possible. 



In the present instance the material was crystallized first as double 

 ammonium nitrate from dilute nitric acid, then as nitrate from concen- 

 trated nitric acid. According to Auer von Welsbach,^ in crystalliza- 

 tion as double ammonium nitrates the bases separate in the order, 

 lanthanum, cerium, praseodymium, neodymium, samarium, terbium- 

 and yttrium-earths, while according to Demarc^ay,^ in the crystalliza- 

 tion of the nitrates from nitric acid the solubility first decreases with 

 increasing atomic weight through gadolinium, 157.2, and then in- 

 creases. In the crystallization as double ammonium nitrates samarium 

 and the more soluble earths were eliminated, while in the crystallization 

 of the nitrates from nitric acid the solubility of the first four of the 

 above nitrates is reversed and the lanthanum, cerium and praseodym- 

 ium were removed in the mother liquors. 



Three and one half kilograms of neodymium ammonium nitrate, very 

 kindly furnished by Dr. H. S. Miner of the Welsbach Light Company, 

 served as a starting point in the preparation of pure material. The 

 history of this material is somewhat uncertain, but, as nearly as can be 

 determined, is as follows : Swedish cerite [was decomposed with acid 

 and the rare earths were precipitated as oxalates, from which the oxides 

 were obtained by ignition. These oxides were then treated with nitric 

 acid and the insoluble basic eerie salt was produced by heating. The 

 lanthanum, praseodymium, neodymium, samarium, yttrium, etc., were 

 obtained in solution. After the addition of ammonium nitrate the 

 material had received, probably, about 150 to 250 crystallizations. Our 

 treatment showed it to contain considerable lanthanum, cerium, and 

 praseodymium, and a small amount of samarium. Probably traces of 

 other rare earths were present, but no evidence of their existence was 

 found even in the extreme fractions of the purified material. 



In the further purification to which we subjected the double neodym- 

 ium ammonium nitrate the usual method of fractional crystallization 

 was followed : The whole material (1) was crystallized and the crys- 

 tals (2) were separated from the mother liquor (3). The crystals were 

 dissolved and again crystallized, the crystals becoming (4) and the 

 mother liquor (5). The mother liquor (3) was evaporated to crystalli- 

 zation, and the crystals were combined with (5), while the mother 

 liquor formed (6), and so on indefinitely. After the first few series of 



1 Sitzungsber. Akad. Wiss. Wien., 112, 1043 (1903). 



2 Compt. Rend., 122, 728 (1896); 130, 1021 (1900). 



