128 



Mr. W. Crookes. 



[Feb. 17, 



strontia, or baryta, also affords a striking evidence of individuality 

 lime enhancing tlie residual glow, while strontia and baryta altogether 

 suppress it. 



Ge. — An earth phosphorescing with a yellow colour, and, in the 

 spectroscope, showing a sharp yellow line having a wave-length of 

 597. It is seen in the samarium spectrum as a sharp yellow line 

 superposed on a hazy double band. As I have already pointed out, 

 Ge fractionates out high up among the most basic earths, and gener- 

 ally accompanies lanthanum. In the phosphorescent spectrum of 

 lanthanum the line Ge is seen quite free from the lines of other 

 bodies. 



Gg. — An earth phosphorescing with a red light, showing in the 

 spectroscope a red line of wave-length 619. This body is always more 

 plentiful in yttrium obtained from samarskite and cerite than from 

 gadolinite, hielmite, and euxenite, and is almost absent in yttrium from 

 xenotime. G£ is of about intermediate basicity. Working with 

 samarskite yttria, Gg" becomes most brilliant after the line of G>j 

 has completely disappeared. Further fractionation causes the line 

 of G£ to fade out, and the citron and blue lines are then left. 



The phosphorescence of G£ is developed to a different extent 

 according to the metal with which the yttria is mixed. The order 

 (beginning with the substance having the greatest action) is zirco- 

 nium, tin, aluminium, bismuth, glucinum. 



Grj. — An earth phosphorescing with a deep red light, and showing 

 in the spectroscope a red line having a wave-length of 647. Like its 

 fellow red constituent, Grj occurs most plentifully in samarskite 

 yttrium, and scarcely at all in yttrium from hielmite, euxenite, and 

 cerite. It is the first of the strictly yttrium constituents to separate 

 out, on fractionation, at the most basic extremity, leaving Ga, G/3, Ge, 

 and G£\ In almost all samples of yttria, except wheu very highly 

 purified, Gij is seen very brilliantly, and by its side can be detected the 

 faint red band of samarium. In the phosphoroscope the line of Grj is 

 the last to appear when yttria alone is being observed ; strontia and 

 baryta enhance the residual glow of Gq, strontia in moderate 

 quantities bringing it out before that of G/3, while baryta brings it out 

 after G(3. 



So. — An earth giving in the spectroscope when phosphorescing a 

 very sharp orange line of wave-length 609. I have already* dis- 

 cussed the claims of this earth to be considered a separate entity. It 

 is not present in the rare earths from gadolinite, xenotime, monazite, 

 hielmite, euxenite, and arrhenite ; it is present in small quantity in 

 cerite, and somewhat more plentifully in samarskite. In samarskite 

 yttrium it concentrates at a definite part of the fractionation. Its 



* « Eoy. Soc. Froc.,' vol, 40, 1886, p. 540. 



