86 



A STUDY OF THE ABSORPTION SPECTRA. 



a, b, c, d, etc. For instance, shifts in the position of the bands, a, b, c, etc., 

 due to relative changes in the intensity of the components, may be observed 

 when the frequency of none of the component bands has been changed at all. 

 Becquerel ' found that the position and intensity of the absorption 

 bands of a crystal depend on the direction in which the light traversed the 

 crystal. To study this phenomenon of absorption he cut sections of crystals 

 in three different directions. One section was cut parallel to the optic axes 

 that cut each other obliquely ("axe moyen "), one section perpendicular 

 to the bisector of the acute angle (" bissectrice aigue"), and another section 

 perpendicular to the bisector of the obtuse angle (" bissectrice obtuse "). 

 Crystals of uranyl nitrate belong to the orthorhombic type. Becquerel 

 measured the wave-lengths of the three bands, a, b, c, for the different 

 sections. 



URANYL NITRATE. 



The wave-lengths of the absorption bands of crystals of the double 

 chloride of uranyl and potassium were as follows: 



Bissectrice aigue . . 



Axe moyen 



Bissectrice obtuse , 



Bissectrice aigue. . 



Axe moyen 



Bissectrice obtuse 



X 5047 



X 5007 

 A 5000 

 X 5000 



X 4905 



X 4935 to X 4920 

 X 4953 to X 4910 



X 4957 



A 4869 

 A 4869 



X 4843 

 A4826 



A 4783 

 A4783 



A 4741 

 X 4741 

 X 4741 



X 4702 

 X 4702 



Knoblauch ' investigated the effect of change of concentration on the 

 absorption spectra of various uranyl salts. He kept the amount of salt 

 in the path of the beam of light constant but varied the concentration 

 between wide limits. In the case of uranyl nitrate, U0 2 (N0 3 ) 2 .6H 2 0, he 

 compared the absorption of solutions having concentrations about 1.1 

 normal (c x ) and 0.0033 normal (c 2 ) (c t : c. = 3428 : 1). If the molecules 

 of uranyl nitrate had acted like the molecules of a gas, the concentrated 

 solution would have exerted a pressure of 25.4 atmospheres and the dilute 

 solution y^g atmosphere. For both solutions the a (X 4920-4850) and the 

 b (X 4780-4680) bands appeared in the same position. With uranyl acetate, 

 U0 2 (C 2 H;j02)22H 2 0, a change in concentration of c t : c 2 = 446 : 1 did not 

 cause any shift in the a {X 4940-4870) or the b (X 4820-4730) bands. The 

 position of the edge of the ultra-violet absorption was the same for both 

 concentrations. The absorption bands were found to be more intense for 

 the dilute solution. Uranyl chloride in concentrations c t : c 2 = 2500 : 1 



1 Loc. cit. 



