THORITE. 167 



ducts are obtained of still greater purity ; and by re- 

 peating this mode of treatment seve'ral times, nitrate 

 of erbium is ultimately obtained containing no appre- 

 ciable quantity of yttrium. 



Pure erbia obtained by ignition of the nitrate or 

 oxalate, has a faint rose-red color (not yellow, as stated 

 by Mosander). It does not melt at the strongest white 

 heat, but aggregates to a spongy mass, glowing with an 

 intense green light; which, when examined by the 

 spectroscope, exhibits a continuous spectrum inter- 

 sected by a number of bright bands. Solutions of 

 erbium-salts, on the other hand, give an absorption- 

 spectrum exhibiting dark bands, and the points of 

 maximum intensity of the light bands in the emis- 

 sion-spectrum of glowing erbia coincide exactly in 

 position with the points of greatest darkness in the 

 absorption-spectrum. The position of these bands is 

 totally different from those in the emission and ab- 

 sorption-spectra of didymium ; in fact there is not a 

 single line of the erbium-spectrum which corresponds 

 with that of didymium. 



89. THORITE.* 

 ThO 2 ,Si0 2 -f2HO. 



The finely-powdered mineral gelatinizes entirely 

 with concentrated hydrochloric acid. The solution is 

 evaporated to dryness, the silica filtered off, the filtrate 

 highly concentrated by evaporation, and mixed with 



* This black, amorphous mineral, from Lovb'n, near Brevig in 

 Norway, is taken here, without regard to its rarity, as an example 

 of a compound of thoria, in order to direct attention to the detec- 

 tion of this earth, which must certainly occur more frequently. 

 The orange-colored orangite of Brevig has a similar composition. 



