AS STUDIED BY MEANS OF THE RADIOMICROMETER. 37 



The concentration represented in fig. I 1 is 3.43 normal, in iig. 2 it is 0.857 

 normal, and in fig. 3 it is 0.427 normal. The depth of layer represented by 

 fig. 1 is 2.5 mm., by fig. 2 it is 10 mm., and by fig. 3 it is 20 mm. The con- 

 centration and depth of layer were thus varied so as to keep Nd constant. 



If the solvent plays no role in the absorption, the three sets of curves must 

 fall directly over one another, i. c, be identical, since the number of absorb- 

 ing parts in the path of the beam of light is kept constant. A comparison of 

 the curves shows that, in general, the more concentrated the solution the less 

 the transparency and the broader the absorption bands. In the more dilute 

 solution the intensity of the bands is greater. This comes out very clearly 

 in the red and infra-red region, where there is greater accuracy of measure- 

 ment. 



Take the three absorption bands, X730, X785, and X860. In curve 1 

 the minima of these bands are approximately 4, 9, and 33 per cent, while 

 the minima in curve 2 are much less. In fig. 2 the bands X730 and X785 

 reach the abscissa, which means that there is no transmission. At this dilu- 

 tion the band X860 has still considerable transparency, as will be seen by 

 the fact that it remains a considerable distance above the abscissa. The 

 band X860 does not reach the abscissa even at the dilution represented in 

 fig. 3. 



All of the bands manifest the above phenomena, the change in intensity 

 being greatest where the change in dilution is greatest, i. e.,from curve 1 to 

 curve 2. With increase in dilution the position of the middle of the band is 

 displaced toward the region of greater wave-length. 



Similar results were obtained with neodymium bromide, and these are 

 plotted in curves 4, 5, and 6. The concentrations and depths of layer were 

 varied so that the product of the two remained constant. The work with 

 the bromide was, therefore, done in terms of Beer's law. The concentra- 

 tions used were 1.66 normal, 0.415 normal, and 0.208 normal, the correspond- 

 ing depths of the solution being 2.5 mm., 10 mm., and 20 mm. We find here 

 the same general changes in the intensities of the bands as with the chloride. 

 The more dilute the solution the more intense and the narrower the band. 



This is shown by comparing figs. 4, 5, and 6. In fig. 4, which represents 

 the most concentrated solution of the three, the bands are the least intense. 

 In fig. 5 the opacity of two of the bands has become complete, shown by the 

 fact that these touch the abscissa. 



Neodymium nitrate was also studied and the results are plotted in curves 

 7, 8, and 9. The concentrations used were 2.95, 0.736, and 0.368 normal. 

 The depths of layer were 2.5 mm., 10 mm., and 20 mm. 



Band X570, curve 7, appears to be an exception to the general relation 

 pointed out above, connecting intensity and width of band with dilution. 

 This was the first band studied by means of the radiomicrometer, and com- 

 paratively small deflections were observed in this region of the spectrum. 



1 Our attention was drawn to the existence of these bands in the infra-red by Pfund, 

 who had already mapped them radiometrically for neodymium nitrate. 



