URANIUM SALTS. 



87 



showed three absorption bands, a (X 4950-4870), b (X 4820-4720), and c 

 (X 4650-4560). The bands were unaffected by dilution. 



Knoblauch considers that deviations from Beer's law must be due to 

 (1) a change in the molecular complex that constitutes the absorber; (2) a 

 chemical change such as hydrolysis or hydration; (3) dissociation; (4) 

 mutual actions which exist between the dissolved molecules in concentrated 

 solutions that do not occur in very dilute solutions. The experimental 

 results which he obtains for uranyl and eosin salts indicate that deviations 

 from Beer's law can not be explained as being due to dissociation. 



Hartley has made an interesting observation on uranyl nitrate, U0 2 - 

 (N0 3 ) 2 .6H 2 0. He finds on dissolving this crystalline nitrate in ether that 

 the water of crystallization does not act as ordinary water and mix with 

 the ether, but that it remains in combination with the uranyl nitrate. It 

 would be interesting to find the effect of change in temperature on this 

 water. In this connection it is very important to determine the trans- 

 ference numbers for the various uranyl, uranous, and neodymium salts in 

 different solvents and mixtures of these solvents. The amount of heat 

 absorbed or given off when salts containing a different number of molecules 

 of the solvent of crystallization are dissolved should also be determined. 

 These data are necessary in order that the facts obtained by spectrum 

 analysis may be properly interpreted. In the case of uranium or neodym- 

 ium it is probable that only a few of the atoms are concerned with the 

 absorption, and the condition of the great mass of the atoms may differ 

 very greatly from that of the few that are taking part in the absorption of 

 light. 



Deussen l has made a very complete examination of the absorption 

 spectra of various uranyl salts in different solvents and in mixtures of dif- 

 ferent solvents. Below are the wave-lengths measured by Deussen: 



The above wave-lengths of the bands do not agree very well with our 

 own measurements. For instance, the ethyl alcohol-bands are found to 

 have a greater wave-length than the water-bands. Deussen worked with 

 mixtures of all the above solvents and water. He obtained some very 

 remarkable results. For example, he finds that, as compared with a pure 

 aqueous solution of uranyl nitrate, in the 50 per cent ethyl alcohol solution 

 all the uranyl bands are shifted towards the red. When the solvent con- 



1 hoc. cit. 



