388 CARNEGIE INSTITUTION OF WASHINGTON. 



New Observations on the Luminescence of the Urantl Salts. 



When (in 1915) Professor H. L. Howes 1 described the remarkable changes 

 produced in the fluorescence spectra of frozen solutions of certain uranyl salts 

 upon cooling to the temperature of liquid air, it was suggested that the phe- 

 nomena were probably due to the formation of definite hydrates. Professor 

 F. E. E. Germann, 2 who took up the question from the point of view of the 

 physical chemist, has now succeeded in establishing the existence of at least 

 one such hydrate (U0 2 (N0 3 ) 2 . 24H 2 0), the temperature of formation of which, 

 — 35° C, corresponds to that of some of the most striking changes recorded 

 by Howes, whose explanation is thus confirmed. 



The complete mapping of the absorption spectra of uranyl salts has been 

 subject to unusual difficulties because of the opacity of these substances 

 in the ultra-violet. Dr. L. J. Boardman, 3 in an investigation just published, 

 has greatly extended the map of these spectra by means of the principle pre- 

 viously established by H. E. Howe, 4 that regions of the spectrum capable of 

 exciting fluorescence coincide as to wave-lengths with the absorption bands of 

 the fluorescing substance. The numerous bands thus mapped by Boardman 

 are new members of the absorption series previously known. Many of them 

 lie in the ultra-violet beyond the range of previous measurements; others are 

 hitherto undiscovered reversals of fluorescence bands. 



Within the present year, the relative brightness of many fluorescent ma- 

 terials has been quantitatively determined for the first time, 5 for which 

 purpose an optical pyrometer of the Morse type was calibrated to read in 

 millilamberts instead of temperatures. The two brightest substances thus 

 far tested are uran}d compounds, i. e., potassium uranyl sulphate, 35.2 milli- 

 lamberts; ammonium uranyl sulphate, 23.0 millilamberts. These are fol- 

 lowed by luciferin (Harvey) 16.0 millilamberts; synthetic willemites, 14.0 

 millilamberts, sidot blende; 10.9 millilamberts. 



Progress of the Work on Photo-active Cells. 



Under the direction of Professor C. C. Murdock further studies relating to 

 the photo-active cells have been in progress: 



Mr. K. F. Sun has developed a method for determining the variations in 

 electrolytic resistance and electrolytic capacity with temperature, concen- 

 tration, and applied potential difference. 



Mr. Irving Wolff has devised another method for the capacity of such high- 

 resistance cells by which it will be possible to find the change of capacity with 

 frequency. 



Miss Clara Cheney is working upon the migration ratio in the electrolyte 

 (rhodamin B) which is used in these photo-active cells. 



Miscellaneous Studies. 

 The investigations of Professor Frances G. Wick upon the kathodo-lumin- 

 escence of certain fluorites containing traces of the rare earths are nearly 

 completed and the results will soon be published. The interpretation of the 

 complicated spectra of these substances with their line-like bands has long 

 been a subject of controversy. 



i Howes: Physical Review (2), vol. vi, p. 192 (1915). 

 « Germann: Physical Review (2), vol. xix, p. 623 (1922). 

 'Boardman: Physical Review (2), vol. xx, p. 552 (1922). 

 4 Nichols: Proc. Am. Philos. Soc, vol. 56, p. 258 (1917). 

 6 Nichols: Science; vol. 55, p. 157 (1922). 



