1885.] On Radiant Matter Spectroscopy. 417 



phosphorescent spectrum in the radiant matter tube, but became im- 

 mediately endowed with this property by admixture with some other 

 substance, which substance likewise by itself had no power of phos- 

 phorescing with a discontinuous spectrum. 



" x " in Cerite. 



In the corresponding yttrium research I was aided materially by 

 the fact that the sought-for earth did not give an absorption spectrum. 

 This enabled me to throw out a large number of obscurely known 

 elements, and I therefore early endeavoured to ascertain whether the 

 supposed new earth, x, did or did not give an absorption spectrum. 

 Gradually it was noticed that whenever the didymium absorption 

 bands were strong the orange band spectrum was also particularly 

 brilliant. Moreover, amongst the earths previously enumerated as 

 mixed with lime in the quest for x, I have mentioned that some of 

 them gave the orange band spectrum with increased intensity ; the 

 earths of the cerium group were the most noteworthy, and these 

 considerations made it probable that here would be found the 

 location of x. 



Analysis of Cerite. 



The cerium group consists of cerium, lanthanum, didymium, and 

 samarium. 



The first necessity was to get the earths ceria, lanthana, and the 

 mixture hitherto called didymia, in a pure state, for my so-called 

 pure earths of this group all showed the orange band in more or less 

 degree. 



The separation from each other of ceria, lanthana, didymia, and 

 samaria is a most laborious process, and the amounts of these earths, 

 obtainable in anything like a pure state, is small, compared with the 

 mass of material worked up. Full particulars are given in the paper 

 as to the method adopted to obtain each of them in a state of purity. 



Ceria. 



The eerie oxide obtained was almost pure white. A considerable 

 thickness of a strong solution did not show a trace of absorption 

 spectrum. The atomic weight of the metal was taken and yielded 

 the number 141*1. 



The eerie oxide gave no orange baud spectrum in the radiant 

 matter tube, either with or without the addition of lime. 



Lanthana. 



Lanthana is more difficult to purify than ceria. Long after the 

 lanthana appeared pure, it gave in the radiant matter tube a good 



