182 FLUORESCENCE OF THE URANYL SALTS. 



conducting material. The Dewar bulb was fastened to an adjustable 

 support H, and the mounting could be submerged in the liquid air 

 to various depths by raising or lowering the bulb by means of a cord R. 



Fluorescence was excited by the rays from a carbon arc A. The 

 light passed successively through a water-cell W, a large short-focused 

 condenser C, and a solution of ammonio-copper sulphate B. This 

 solution absorbed all of the exciting light of a wave-length greater 

 than 0.4780 fj,, so that the fluorescent light, which entered the colli- 

 mator slit S of the spectrometer, could be viewed on a black back- 

 ground. A small resistance coil T was inserted in a glass tube, which 

 was always placed in the middle of the solution. The temperatures 

 were recorded on a Callender recorder. The massive copper block M 

 served to reduce the vertical temperature gradient in the frozen solu- 

 tion to less than 1 per centimeter. It made the apparatus rather slow 

 in responding to changes, but afforded an excellent control of tempera- 

 ture. 



The salts were carefully weighed and "normal" solutions were 

 prepared. 1 Acid solutions were made by adding a definite volume of 

 the commercial concentrated acid to a definite volume of a water 

 solution of known concentration. 



Although readings were taken and tables made in units of wave- 

 length, the diagrams of spectra are plotted on an arbitrary scale of 

 frequencies, i. e., I/JJL X 10 3 . 



URANYL SULPHATE IN AQUEOUS SOLUTION. 



The uranyl sulphate in water, upon excitation with the carbon arc, 

 yields 4 bands at +20 C.; but when cooled 6 bands are visible, the 

 new bands being of longer wave-lengths. This phenomenon increase 

 of intensity with cooling is a very fortunate one, for otherwise the 

 study of the more dilute solutions would be limited to the lowest 

 temperatures. In table 108 will be found the bands of the 1/1, 1/10, 

 1/100, and 1/1000 normal aqueous solutions. In the spectrum of the 

 1/1 normal solution band 7 is at 0.4927 IJL at +20, which is of interest 

 because the crystalline salt was found to give a fluorescence band at 

 0.4925. 2 



If a reasonable error is assumed, these bands may be considered to 

 be coincident. In this region they are approximately 75 A.U. in width; 

 hence measurements were taken on the crest rather than on the middle 

 of the band, the crests being located slightly nearer the violet edge. 



The absorption spectrum 3 of the normal solution presents a band in 

 this region at 0.4910, which is 17 A.U. nearer the violet than the fluores- 



1 The term "normal" solution, as used in this paper, means one which contains the same num- 

 ber of grams of solute to the liter of solvent as the number which represents the molecular weight 

 of the particular salt dissolved. 



2 Nichols and Merritt. Physical Review (1), 33, p. 354. 1911. 



3 Jones and Strong. Carnegie Inst. Wash. Pub. No. 130, p. 109. 



