X. THE FLUORESCENCE OF FROZEN SOLUTIONS. 



The fluorescence spectra of solutions generally consist of only one 

 or two very broad bands. Such bands undoubtedly possess component 

 bands in considerable number, but spectrum analysis often fails to 

 reveal them because of extensive overlapping. Chlorophyl in alcohol 

 possesses a series of absorption bands 1 which resemble the absorption 

 bands of the uranyl solutions. The very broad fluorescence band in 

 the orange and red probably consists of several components which 

 form a similar series. Anthracene in solution 2 presents a fluorescence 

 series of at least 4 bands which strongly resembles the series found in 

 the fluorescence spectra of uranyl solutions. 



Probably the first observer to note the fact that uranyl solutions 

 yield fluorescence spectra consisting of several bands was G. C. Stokes. 3 

 He states that "a solution of nitrate of uranium is decidedly sensi- 

 tive," i. e., fluorescent. Later, in the same paper, he writes "I have 

 observed seven of these bands arranged at regular intervals." E. 

 Becquerel, 4 in his monumental work on the uranyl salts, makes this 

 observation : 



" Certain solutions of the salts of uranium give, in the violet rays, a luminous 

 emission scarcely less brilliant than the crystals themselves .... several 

 [bands] appear to correspond to the bands given by the solid salts; the sul- 

 phate and the double sulphate of potassium and uranium are in this class." 



In the same year Hagenbach, 5 who was studying many fluorescence 

 materials, observed that the uranyl oxide in nitric acid shows 8 very 

 sharply outlined maxima in the fluorescence spectrum. Morton and 

 Bolton 6 studied the absorption of the uranyl solutions and noted the 

 fluorescence. These investigators were the first to recognize the 

 possibility of the existence of more than one hydrate of the same salt, 

 which, they state, "enables us to explain some discrepancies of authori- 

 ties on this point." Our present work has brought out the necessity, 

 of such a hypothesis. Jones and Strong, 7 following the same method 

 as Morton and Bolton, have published the most extensive data on the 

 absorption spectra, but their work does not include temperatures 

 below the freezing-point. 



This chapter contains the results of experiments which were de- 

 scribed in two papers, together with some additional data heretofore 

 unpublished. The first, a preliminary paper, 8 showed that the bands of 



1 Nichols and Merritt. Carnegie Inst. Wash. Pub. No. 130, p. 85. 1910. 



2 Louise MacDowell. Physical Review (1), 26, p. 155. 1908. 



3 Stokes. Philosophical Transactions, p. 463. 1852. 



4 E. Becquerel. Comptes Rendus, 75, p. 296. 1872. 



6 Hagenbach. Poggendorf Annalen, 146, p. 582. 1872. 



6 Morton and Bolton. Chemical News, pp. 113, 164. 1873. 



7 Carnegie Inst. Wash. Pub. No. 130. 



8 Nichols and Merritt. Physical Review (2), 3, p. 457. 1914. 



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