88 ABSORPTION SPECTRA OF SOLUTIONS. 



The X4675 band of praseodymium chloride narrows towards the violet 

 about 20 a.u. with increase in dilution, while the broad band X5900, under 

 the same conditions, shows a narrowing of about 25 a.u. When more dilute 

 solutions are employed, none of the bands shows any change with dilution. 

 The changes in the two bands X4675 and X5900 with dilution are much less 

 than with the corresponding bands of neodymium. 



The two bands X4450 and X4650 of praseodymium nitrate widen about 20 

 a.u. with increase in concentration in very concentrated solutions. In the 

 more dilute solutions there is no change. 



The X4700 band of uranyl chloride shows marked widening with increase 

 in concentration, especially towards the red end of the spectrum. The 

 X4900 band also shades off rapidly towards the red end of the spectrum. 

 When more dilute solutions were used, both X4600 and X4700 gradually 

 widen with increase in concentration. 



The X4700 band of uranyl bromide widens uniformly with increase in the 

 concentration. When a more dilute solution was employed as the starting- 

 point, none of the bands changed with dilution. 



The absorption of concentrated solutions of uranyl nitrate is complete to 

 X4500. With increase in concentration this gradually recedes towards the 

 red, amounting to as much as 100 a.u. The X4700 band widens under the 

 conditions about 20 a.u. The sharp band X4875 widens slightly with 

 increase in concentration. 



In the more concentrated solutions of uranyl salts many of the bands 

 change with change in the dilution , while in the more dilute solutions there 

 is scarcely any change at all. 



The introduction of the radiomicrometer into this work converted it into a 

 quantitative study of the absorption spectra of solutions. The grating 

 spectroscope and photographic method were very efficient in locating the 

 positions of the absorption lines and bands from wave-lengths X2000 to 

 about X7600 ; and the photographic method gave some approximate idea as 

 to the intensities of the various lines and bands. This method is, however, 

 only roughly quantitative, and is very limited in the range of wave-lengths 

 to which it can be applied. 



The radiomicrometer provides us with a quantitative method for studying 

 the intensities of the various lines and bands, and also greatly extends the 

 range of wave-lengths that can be studied. In the earlier work with the 

 radiomicrometer much time and labor were expended in perfecting the 

 instrument, especially in constructing a sensitive radiomicrometer with a 

 short period. Dr. Guy accomplished this very successfully. 



The earlier work was practically limited to the study of the absorption 

 spectra of solutions of neodymium salts neodymium chloride, bromide, 

 nitrate, and acetate. 



The results were plotted in what is known as transmission curves, which 

 express the percentage transmission for the different wave-lengths. Solu- 

 tions of different concentrations of a given salt were studied, the depth of 



