174 PROCEEDINGS OF THE AMERICAN ACADEMY. 



position. While ignition in hydrogen causes reduction to the trioxide, 

 yet it is not easy to make certain that no higher oxide is retained in the 

 lower one. On the other hand the analysis of the anhydrous chloride 

 served so satisfactorily with neodymium that it seemed worth while to 

 apply the same method to praseodymium. The results amply justi- 

 fied our expectations. 



The Purification of the Praseodymium Material. 



Through the great kindness of Dr. H. S. Miner of the Welsbach 

 Light Co., Gloucester City, N. J., we were fortunate enough to secure 

 as a starting point about 10 kilograms of praseodymium ammonium 

 nitrate containing about 50 per cent, of the corresponding lanthanum 

 and cerium salts as well as a small proportion of neodymium. Since 

 one of the most rapid and effective methods of freeing praseodymium 

 from the closely related elements, lanthanum, cerium, neodymium, 

 and samarium, is the fractional crystallization of the above salt, 

 this method of purification was chosen. According to Auer von 

 Welsbach, 10 the bases separate in the order, lanthanum, cerium, 

 praseodymium, neodymium, samarium, terbium and yttrium earths. 

 The salt was crystallized in the usual way, that is, a concentrated, 

 hot solution containing a small amount of nitric acid was allowed to 

 cool and deposit the excess of salt, a period of 24 hours being allowed to 

 secure equilibrium between the crystals and liquid. The separation of 

 crystals and liquid was not completed by centrifugal drainage, be- 

 cause the labor and time involved in this operation are not repaid by 

 any considerable increased speed of purification. The details of the 

 crystallization are shown in the diagrams on pages 175 and 176. 

 In any given series of crystallizations a lower number always indicates 

 a less soluble fraction. A line not connecting an end fraction with 

 any fraction in a subsequent series indicates rejection. This crystal- 

 lization was begun by Mr. W. H. Whitcomb, continued by Mr. B. W. 

 Grimes and Mr. C. C. Wallace and completed by Mr. Stewart. 



In the early part of the crystallization it became obvious that the 

 original material consisted largely of the lanthanum salt, the least 

 soluble fraction quickly becoming essentially colorless. At the same 

 time the neodymium absorption bands, which were readily visible in 

 the original material, rapidly strengthened in the extreme mother 

 liquor. When this mother liquor was reduced to a volume of about 

 20 cc, fraction 63, its absorption spectrum was examined visually in 



10 Sitzungsb. Akad. Wiss. Wien, 112, 1043 (1903). 



