572 Absorption Spectra of Uranous and Uranyl Compounds, 



During this change the uranous acetate bands gradually dis- 

 appear, while very marked changes occur in the uranyl bands. 

 The resulting spectrum is not the same as that of uranyl 

 nitrate dissolved in water containing free nitric acid, but is 

 probably due to a different compound. The shifting bands 

 may correspond to the formation of a number of intermediate 

 compounds. 



It seems highly probable that the uranyl and uranous 

 bands are due to systems of absorbers in the uranium atom, 

 and that the effect of change of salt or solvent is to change 

 the electromagnetic field in which these absorbers vibrate. 

 Each frequency should thus be traced while external changes 

 about the uranium atom are taking place, and in many cases 

 this has been done. For instance, the vibrator producing 

 the d band consists of a system which can absorb three dif- 

 ferent frequencies, as is shown in the case of uranous chloride 

 in acetone and hydrochloric acid. The c band in this case 

 is doubled. Uranyl nitrate in nitric acid, to which hydro- 

 chloric acid is added, gives the c and d bands as a single 

 band. It would be very interesting to know how this c-d 

 band breaks up at low temperature. 



To summarize the results thus far obtained with uranous 

 and uranyl salts, we find that when the solvent or the salt is 

 changed, or acids or foreign salts added, the absorption spectra 

 are greatly modified. This modification is of two kinds : The 

 existence of characteristic bands for each state of the uranium 

 salt; or a gradual shift of the bands. When one salt of 

 uranium is transformed into another salt there is usually 

 a gradual shifting of the one series of bands into the series 

 corresponding to the second salt, and in this way a number of 

 relationships between the uranous and the uranyl bands have 

 been discovered. 



Uranous salts in different solvents show very different 

 absorption bands, and the solvents in question either have 

 practically no absorption or absorb only in the ultra-violet. 

 We regard this as evidence for the sol\ate theory proposed 

 in this laboratory, which says that there is some kind of 

 union between the solvent and the dissolved substance. It 

 is difficult to see how the different solvents could affect the 

 absorbers unless they combine in some way with them. 



Physical-Chemical Laboratory, 



Johns Hopkins University. 



January 1910. 



