76 



ABSOKPTION SPECTRA OF A NUMBER OF SALTS 



with when working with aqueous solutions at greater wave-lengths than l/x. 

 Even over the range of wave-lengths at which we have worked, it is seen 

 that the absorption due to water is a disturbing factor. 



Table 15. Trans?nissions of Neodymium Acetate Solutions. 



PRASEODYMIUM CHLORIDE. 



Solutions of praseodymium salts are not of great interest from our stand- 

 point, in those regions beyond the visible part of the spectrum. It was 

 found that such solutions were transparent in the infra-red end of the spec- 

 trum as far as 1.5, except two very weak bands which fall just in the midst of 

 the intense water-bands. Since, at this point, a very thin layer of water is 

 almost completely opaque, it is evident that it would be impossible to study 

 aqueous solutions in this region, especially dilute solutions. 



As shown by the photographic plate, praseodymium salts possess two 

 groups of bands in the visible spectrum, one in the green near X4600 and 

 another near X5900. Since the amount of energy at the former wave-length 

 is so very small, the width of slits necessary to be used was too large to give 

 satisfactory results. Such bands could, of course, be detected, but the 

 deflections of the instrument at this part of the spectrum are very small, 

 and, hence, relatively large errors would occur in making the readings. 



For these reasons we have confined our attention to a careful study of the 

 one band which has its center near X5900. Table 16 gives the observed 

 transmissions for the four dilutions of solutions of praseodymium chloride. 



