THE DIDYMIUMS. 353 



Bauer's little known determinations* were also made by the synthesis 

 of the sulphate. They have corroborative value and are as follows : 



Per cent. Di.fi.^. At. Wt. Di. 



58.285 143-56 



58. 100 142.40 



58.133 142.64 



58.098 142-38 



In 1885 all of the foregoing determinations were i)ractically brushed 

 aside by Auer von Welsbach,! who by the most laborious fractionations 

 proved that the so-called "didymia"was really a mixture of oxides, 

 whose metals he names neodidymium and praseodidymium, names 

 which are now commonly shortened into neodymium and praseodymium. 

 One of these metals gives deep rose-colored salts, the other forms green 

 compounds, and the difference of color is almost as strongly marked as 

 in the cases of cobalt and nickel. Their atomic weights, determined by 

 the sulphate method, are given b}^ Welsbach a — 



Pr = 143.6 

 Nd= 140.8 



No further details as to these determinations are cited, and whether 

 they rest upon = 16, SO3 = 80, or = 15.96 is uncertain. Fuller deter- 

 minations are evidently needed. 



* Freiburg Inaugural Dissertation, iSSt. 

 t Monatsh. Cheni., 6. 490. 18S5. 



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