URANIUM SALTS. 107 



Plate 71, A, represents the effect of rise in temperature on the absorp- 

 tion spectra of a ^ normal solution of uranyl nitrate. From the fact that 

 the uranyl nitrate bands have a shorter wave-length than the bands of the 

 other salts, it was thought that the effect of temperature might be different; 

 that at high temperatures all the bands might have the same positions. 

 The uranyl nitrate bands shift very little to the red, if they shift at all, for 

 changes in temperature of 90. The effect of temperature seems to be 

 independent of the temperature. 



Absorption Spectrum of Anhydrous Uranyl Nitrate. 



When it was first discovered that the uranyl nitrate "water " bands were 

 all shifted to the violet with reference to the band of the other uranyl salts in 

 water, as well as with reference to the uranyl nitrate bands in other solvents, 

 it was thought that possibly it was more hydrated than the other salts in 

 solution. The uranyl salts crystallized from aqueous solutions at ordinary 

 temperatures have the following composition: U0 2 (N0 3 ) 2 .6H 2 0, U0 2 S0 4 - 

 3H 2 0, U0 2 (CH 3 COO) 2 .2H 2 0, and U0 2 C1 2 .H 2 0. This fact would favor the 

 supposition that in solution the nitrate might be more hydrated than the 

 other salts. The fact that the absorption of the aqueous solution of the 

 nitrate and the crystallized salt was very much the same, as far as the posi- 

 tions of the uranyl bands is concerned, also seemed to favor this view. 



In this connection it was considered important to examine the absorp- 

 tion spectrum of the anhydrous uranyl nitrate. This salt was powdered 

 and placed in a closed glass tube just above the slit of the spectroscope. 

 The light of a Nernst glower was then focused upon the surface of the salt 

 nearest the slit and an exposure of about 3 hours made. In this way we 

 examine light that has penetrated a short distance into the powder and is 

 then diffusely reflected. 



The absorption spectrum was found to consist of quite a large number 

 of bands that seem quite different in many respects from those of the solu- 

 tion. The following are the approximate wave-lengths: U 4800, 4650, 4500, 

 4420, 4360, 4280, 4180 (broad), 4060 (broad), 3950 (broad), 3820 (broad), 

 3700 (narrow), and 3600 (narrow). The bands marked broad are from 50 

 to 60 Angstrom units wide and the narrow bands about 20 Angstrom units. 

 If the first band is the a band, then the bands of the anhydrous salt are to 

 the violet side of the corresponding bands of the crystals and of the solu- 

 tion. If it is the b band the opposite is the case. On account of the small- 

 ness of the intensity of the bands it could not be settled whether X 4800 is 

 the a or the b band. Further investigation of this point will be made. 



There are two difficulties in the above theory, difficulties for which no 

 explanation has thus far been suggested. In the work on the effect of rise 

 in temperature on the absorption spectrum it was found that the uranyl 

 nitrate bands did not shift to the red. On the other hand, the uranyl 

 sulphate and uranyl chloride bands were shifted to the red under the same 

 conditions. (In these cases aqueous solutions were investigated.) If the 

 uranyl nitrate bands owe their position to a large amount of hydration, it 

 would be expected that with rise in temperature they would be shifted 

 towards the red more than the bands of the sulphate and chloride. Another 



