382 CARNEGIE INSTITUTION OF WASHINGTON. 



The Double Chlohides. 



A detailed study of the double chlorides has likewise been completed.^ 

 It has already been shown" that uranyl ammonium chloride possesses 

 a fluorescence spectrum in which each of the usual uranyl bands is 

 resolved (at +20°) into five components, and that each of these is 

 further resolved into doublets upon cooUng to —185°. It had been 

 shown further^ that this spectrum is completely polarized, the com- 

 ponents of each doublet being capable of separation at +20°, so that 

 we have two complete fluorescence spectra and absorption spectra 

 polarized at right angles to one another and systematically related. 



These studies have now been extended to include uranyl potassium 

 chloride, uranyl rubidium chloride, and uranyl csesium chloride, all of 

 which (like the uranyl ammonium chloride) crystallize in pleochroic, 

 tricUnic plates and have spectra resolved at +20° and completely polar- 

 ized. The similarity of the spectra of these four salts is remarkable, 

 all having the same number of bands, similarly arranged in groups of 

 five and forming homologous series with a constant frequency interval. 



The interval is very nearly the same for all series and for all the salts, 

 with indications of a barely determinable diminution of interval with 

 increase in the molecular weight. The spectrum of each salt is thus an 

 almost exact repUca of that of the others, but slightly displaced in 

 wave-length, the order from red towards violet being K, NH4, Rb, Cs. 



The Effect of Crystalline Form. 



To determine whether the structure of the uranyl spectra depends 

 upon crystalline fonn it was necessary to compare two substances of 

 the same chemical composition but crystallographically distinct. 

 Uranyl ainmonium nitrate affords opportunity for such a comparison, 

 since it crystalHzes in two different systems — orthorhombic from 

 aqueous solution and trigonal from the acid — in both cases without 

 water of crystalUzation. 



The two spectra, which have been mapped by Doctors Howes and 

 Wilber,^ differ in the most striking manner as regards the position of 

 the groups, their structure, and the character of the resolution when 

 cooled to Uquid air. 



Doctors Howes and Wilber^ have also completed an instructive 

 investigation of the fluorescence of several forms of the uranyl sodium 

 phosphates, a study of especial interest in this connection because 

 these substances range from crystalUne powders to semi-fluid masses 

 of varying viscosity. It is found that only the dry, powdered forms 

 have spectra which resolve on cooling. All viscous forms, which are 

 solutions in varying amounts of free phosphoric acid, retain the broad 



'Nichols and Howes, Physical Review (2), vm, p. .SG4 (1916). 

 'Nichols and Merritt, Physical Review (2), vi, p. 358 (1916). 

 'Nichols and Howes, Proc. Nat. Acad. Sci., vol. i, p. 444 (1915). 

 ^Howes and Wilber, Physical Review (forthcoming). 

 *Howe9 and Wilber. Physical Review (2), vii, p. 395. 



