92 ABSORPTION SPECTRA OF SOLUTIONS. 



intensity of the light after passing through a depth of water equal to the 

 water in the solution in question. 



The absorption spectrum of neodymium chloride shows three pronounced 

 minima representing the three absorption bands with their centers near 

 X7300, X7950, and X8700, and less pronounced bands near X7150 and X9000. 

 The latter may be due in part to the solvent; for all four dilutions studied 

 the X7300 and X7900 bands show complete absorption over a considerable 

 range of wave-lengths. The minimum of band X8700 is gradually lowered 

 with increasing dilution. 



The maximum transmission of solutions of neodymium chloride occur 

 near X7600 and X8400, these solutions becoming almost completely trans- 

 parent beyond Ijjl, except for the absorption of the solvent of this region. It 

 seems that Beer's law holds, in general, for the infra-red absorption of solu- 

 tions of neodymium chloride. 



The minima in the curves for the more dilute solutions of neodymium 

 chloride are in about the same positions as those in the more concentrated 

 solutions, but the solutions being more dilute are more transparent; hence 

 the minima are not so pronounced. The maximal absorption occurs near 

 X7300 and X7900. The X8700 band has a minimum transmission of 64 per 

 cent. There is complete transmission in the regions X7200, X7600, X8300, 

 and X9300. The drop in all of the curves beyond 0.9/i is due to the absorp- 

 tion of the water. 



With further increase in the dilution of the solution, there is a lowering of 

 the maxima. The change is most pronounced in the X8700 band, and here 

 the absorption of the water is the most pronounced. The absorption of the 

 water together with the correction for slit- width may account for this change, 

 and Beer's law may hold for the dilute solutions of neodymium chloride 

 almost as well as for the more concentrated. 



Neodymium nitrate shows three minima at X7300, X7950, and X8750. 

 The nitrate bands are not as intense as those of the chloride, the solution of 

 the nitrate not being as concentrated as that of the chloride. The nitrate 

 bands, like those of the chloride, become more intense with increase in 

 dilution. The absorption of water becomes more and more pronounced 

 beyond 1/x. 



The minima for solutions of neodymium acetate fall at approximately the 

 same positions as with the chloride and nitrate. 



Solutions of neodymium acetate, as indicated by the photographic 

 method, show greater absorbing power than those of either the chloride or 

 nitrate. The X7000 band is slightly more intense in the acetate. The 

 more intense bands X7300 and X7950 show the same tendency to have their 

 minima lowered with increasing dilution. There is a rapid increase in the 

 absorption near X9500, due to the water present in the solution. 



Solutions of praseodymium salts are transparent in the infra-red as far as 

 1.5ju, except two very weak bands which fall in the midst of the intense water 

 bands. Praseodymium salts have two groups of bands, one in the green 



