54 



THE ABSORPTION SPECTRA OF SOLUTIONS. 



Phosphorescence of Praseodymium, Xeodymium, and Erbium in Calcium Oxide. 



vs. = very strong; w. = weak; m.=medium; dif. = diffuse; v-w. = very 

 weak; s. = strong; sn. = strong and narrow. 



The phosphorescence of compounds of the rare earths in other diluents 

 is much simpler than in calcium oxide : 



Phosphorescence of Praseodymium in Calcium Sulphate. 

 XX 5876, 6000, and 6100. 



Phosphorescence of Erbium in Calcium Sulphate. 

 XX 5220, 5435, 5535. 



Phosphorescence of Erbium in Calcium Fluoride. 

 XX 5170. 5200, 5250, 5310, 5400, 5465 strong, 5510 strong, 5620. 



By using monochromatic light or homogeneous cathode rays of different 

 velocities, it might be possible to excite only certain related bands and not 

 the whole absorption spectrum. This might apply especially to the uranium 

 salts. On the other hand, the presence of the diluent might preclude any 

 possibility of this kind. The recent work of Wood and Franck 1 on the effect 

 of the presence of helium on the resonance of iodine vapor would lead to a 

 conclusion of this kind. A study of the fluorescence of sodium, potassium, 

 mercury, and iodine vapor shows that the intensity of the emitted light is 

 greatly reduced if air or some other inert gas is present. The effectiveness 

 of a gas in destroying fluorescence appears to increase with the molecular 

 weight. In the case of the fluorescence of anthracene, Elston found that hydro- 

 gen and nitrogen had very little effect, while oxygen and carbon dioxide had 

 a very great effect. 



Warburg 2 has shown that the current obtained from the negative point 

 discharge is much greater in nitrogen, helium, argon, and hydrogen when the 

 last traces of oxygen 3 have been removed. To explain this Warburg assumed 



1 Phil. Ma^., 21, 309, 314 (1910). 



- Ann. d. Phys., 40, 1 (1896). 



3 J. Franck: Yerh. der deutsch. phys. Ges., July (1910). 



