224 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the remaining samarium and yttrium earths, were separated from the 

 others, and the fractionation was continued as before. 



No further accumulation of samarium could be detected, after seven- 

 teen more series of crystallizations had been completed, in a spectro- 

 graphic examination of the more soluble fractions of the one hundred 

 and third series. Nevertheless the two most soluble fractions, 1615 and 

 1616, were rejected, and the next, 1614, was removed for subsequent 

 analysis. 



The sharpness with which the samarium is removed from the neodym- 

 ium by the crystallization of the double ammonium nitrates is striking 

 in comparison with the difficulty in eliminating the last traces of 

 praseodymium in the same way. After the removal of only eight frac- 

 tions, 1302 to 1309, the last of which was comparatively rich in sama- 

 rium, seventeen series of crystallizations failed to reveal any residual 

 samarium. On the other hand, when the fractions 1303 to 1309 were 

 subjected to further fractional crystallization by themselves, the least 

 soluble fraction of the fourteenth series was found to contain about 

 one half per cent of praseodymium, estimated spectrographically as de- 

 scribed later. By the same method fraction 1302, which contained 

 more praseodymium than any one of the seven crystallized, was found 

 to contain only 0.2 per cent of this impurity. Demar^ay ^ and Feit 

 and Przibylla ^ have emphasized the fact that neodymium and sama- 

 rium may be separated with equal facility by crystallization as double 

 magnesium nitrates. 



At this point it seemed reasonably certain that practically all the 

 more soluble rare earth impurities had been eliminated, while evidence 

 of praseodymium could still be seen in the absorption spectra of all the 

 fractions. For the removal of the praseodymium and at the same time 

 cerium and lanthanum, if present, crystallization of the nitrates from 

 concentrated nitric acid was next undertaken, since in this process 

 these elements accumulate in the mother liquors.*^ 



The ammonium nitrate was removed from the different fractions by 

 evaporation and ignition, concentrated nitric acid was added, and the 

 crystallization was carried through sixty-seven series. The same num- 

 bering was continued, except that the order of the one hundred and 

 third series was reversed to give the less soluble fractions the lower 

 numbers as before, 1613 becoming 1613a and 1596 becoming 1630. 

 During these sixty-seven series no fractions were rejected at the less 

 soluble end, although the extreme mother liquor was frequently re- 



1 Compt. Rpnd., 130, 1021 (1900). 



2 Loc. cit., 207. 



^ Demargay, loc. cit. 



