124 



Mr. W. Crookes. 



[Feb. 17, 



Ytterbia from Professor Nilson, in the form of sulphate, refuses to 

 phosphoresce without the addition of lime. When lime is added it 

 only brings out traces of the phosphorescent bands of Gc, G/3, and Ga. 

 Evidently these are impurities. 



Ytterbia from M. de Marignac is identical with tha,t from M. Cleve, 

 as far as my examination can go. In sending me this ytterbia M. de 

 Marignac warned me that he was very far from thinking it pure. 



Yttrium. — During the fractionation of the higher fractions of 

 yttria ( + 6, 118 and 119), a very sharp green line sometimes makes 

 its appearance, situated between G(3 and G7 (approximate position on 

 the 1/X 2 scale, 325). It is very faint, and is not connected with the 

 orange line of SS, although it is as sharp. The yttria showing these 

 lines phosphoresces of a transparent golden -yellow colour, the 

 fractions at the other end phosphorescing yellowish green. 



I have previously described the action of a large number of bodies 

 on the phosphorescence of samarium.* The experiments resulting in 

 the following observations were tried at about the same time. I will 

 describe them in alphabetical order. Unless otherwise mentioned all 

 the mixtures were in the form of anhydrous sulphates. 



Yttrium 5 per cent., aluminium 95 per cent., gives a good yttria 

 spectrum ; the blue line of Ga, is very distinct, and the double green 

 of GrjS is well divided. In the phosphoroscope the G/3 and Ga. lines 

 first appear simultaneously, then the GB line.. 



Yttrium 99*5 per cent., bismuth 0*5 per cent. — The spectrum is 

 bright, and on close examination a trace of samarium green, G7, is to 

 be detected forming a wing to the Gc line. In the phosphoroscope 

 the citron line of GB entirely disappears and the samarium double 

 green line, which out of the phosphoroscope is almost obscured by the 

 great brightness of Gc8, now appears distinctly, together with the green 

 G/3 line. Yttrium 95 per cent., bismuth 5 per cent., gives the usual 

 yttria spectrum. ~No GB line appears in the phosphoroscope at any 

 speed. At first only the G 3 line is seen, and next the Ga line appears, 

 as in yttria. On gradually increasing the percentage of bismuth the 

 spectrum of yttria grows fainter, until with 95 per cent, of bismuth 

 the phosphorescence is bad and the spectrum faint. 



Yttrium 5 per cent., cadmium 95 per cent., gives a brilliant phos- 

 phorescence, but the spectrum is almost continuous. In the phos- 

 phoroscope a faint concentration of light is seen in the green, which 

 becomes sharper as the speed increases. 



The action of calcium on the phosphorescence of yttrium has 

 already been described. 



Yttrium and cerium. — Cerium has the effect of deadening the 



* " On Radiant Matter Spectroscopy. Part 2 — Samarium." 'Phil. Trans.,' 1885, 

 Part II (pp. 710-722). 



