128 



FLUORESCENCE OF THE URANYL SALTS. 



THE TRIHYDRATE: UO 2 (NO 3 )2+3H 2 O. 



The trihydrate crystallizes in the triclinic system with the axial 

 ratios a : b : c = 1.2542 : 1 : 0. 70053. l The crystals were grown by 

 evaporating the nitric-acid solution in a desiccator over caustic potash 

 and sulphuric acid or over calcium chloride. To obtain large crystal 

 plates the bottom of a dish 6 cm. in diameter was covered with the 

 solution to a depth of about 2 mm. and the solution was "seeded" 

 near the center. A cover was then placed over the solution with a 

 small opening at the center, so that evaporation took place directly 

 over the crystal. The trihydrate was also obtained in the form of a 

 fine powder by efflorescence of the hexahydrate crystals in dry air. 

 Although most of the observations recorded below were made with 

 single crystals, a few measurements were made, with concordant results, 

 on the powder. In the fluorescence spectrum visual observations only 

 were made. In the absorption spectrum the measurements were in 

 most cases photographic. 



6 H ,0 



J A 1 

 3^0 



fl 1 ^ 



H i 



L 'A B C D 

 2^0 



1 



F T H 



I . I I 



J K L 



I 1.1 



M 'A BCD E FG'HIJ KLM 



ANHYDROUS 



i9'oo 



FIG. 78. One group of bands from the fluorescence spectrum of each of the salts studied. The 

 spectrum of the hexahydrate contains 7 such groups; that of the trihydrate, 6; the dihy- 

 drate, 5; and the anhydrous salt, 3. 



The fluorescence spectrum of the trihydrate was found to consist of 

 63 bands, of which 55 fell into 12 constant-interval series of from 3 to 

 6 bands each. The intervals for the different series ranged from 86.5 

 to 87.5, the average being 86.8. The reciprocal wave-lengths are given 

 in table 42. The numbers in parentheses refer to absorption bands 

 which seem to fall into the fluorescence series. The relative intensities 



1 Wyrouboff. Sur quelques composes deruranium, Bull. Soc. Francaise Mineral, 32, 349-350. 1909. 



