CHAPTER VII. 



SALTS OF NEODYMIUM, PRASEODYMIUM, 



AND ERBIUM. 



Some of the more important investigations on the salts of the above- 

 named elements are the following: 



Bahr and Bunsen l in their early work on absorption spectra included 

 didymium and erbium. 



Becquerel, 2 in his study of spectra in the infra-red region, worked with 

 didymium. In his subsequent work 3 on the variation of absorption spectra 

 in crystals, the sulphate and nitrate of didymium were included. 



Becquerel 4 compared the absorption spectra of crystals of didymium 

 salts with the spectra of the aqueous solution of the same salts. He showed 

 that from the displacement of the bands he could recognize distinct sub- 

 stances or definite compounds. He showed that in the crystals we may 

 have, simultaneously, mixtures of different compounds and especially 

 basic salts. 



Demargay 5 studied the spectrum of didymium, and concluded that in 

 addition to praseodymium and neodymium there was probably present a 

 third element. In a subsequent investigation 6 he shows that neodymium 

 from entirely different minerals and sources always has the same spec- 

 trum, and concludes that it is a chemical element. 



Kriiss and Wilson 7 carried out an elaborate investigation on the absorp- 

 tion spectra of the rare earths. They concluded that we must assume the 

 existence of more than twenty elements in the various rare earth minerals. 



Bettendorff 8 carried out three investigations on the spectra of the 

 cerium and yttrium group, and Schottlander 8 made use of his spectro- 

 scopic studies and spectrophotometric work to characterize the various 

 rare earths. 



Boudouard 10 effected the separation of neodymium and praseodymium by 

 means of potassium sulphate instead of ammonium nitrate. The absorp- 

 tion spectra indicated a nearly complete separation from praseodymium. 



Scheele u did some very careful work on praseodymium in connection 

 with his determination of the atomic weight of that element, and later 12 

 in connection with the separation of praseodymium and neodymium. 



1 Lieb. Ann., 137, 1 (1886). 



2 Ann. Chim. Phys. (5), 30, 5 (1883). 



3 Ibid. (6), 14, 170 (1888). 



4 Ibid. (6), 14, 257 (1888). 



"Compt. rend., 102, 1551 (1886), 105, 276 (1887). 

 "Ibid., 126, 1040 (1898). 



7 Ber. d. deutsch. chem. Gesell., 20, 2134 (1887). 



8 Lieb. Ann., 256, 159^(1890); 263, 164 (1891); 270, 376 (1892). 



9 Ber. d. deutsch. chem. Gesell., 25, 569 (1892). 

 10 Compt. rend., 126, 900 (1898). 



"Ztschr. anorg. Chem., 17, 310 (1898). 



12 Ber. d. deutsch. chem. Gesell., 32, 409 (1899). 



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