42 THE ABSORPTION SPECTRA OF SOLUTIONS. 



e Group in Glycerol. The chloride gives the following bands: XX 5740 

 hazy, 5790, 5805, 5820, and 5850. 



Although the absorption spectra of the dry neodymium salts are very 

 different from one another, those of the aqueous solutions, especially when 

 dilute, are very much the same for the different salts. For concentrated 

 solutions the chloride is very similar to that of the bromide, but these are 

 quite different from the nitrate. 



The absorption spectra of neodymium chloride in methyl alcohol and in 

 ethyl alcohol are practically the same, and differ considerably from that of 

 the nitrate. The absorption bands of the nitrate in ethyl alcohol are, in 

 general, more diffuse than in methyl alcohol. 



The chloride is but slightly soluble in acetone. The absorption spectrum 

 of the nitrate in acetone is especially characterized by the weak and hazy 

 appearance of the bands. 



The absorption spectrum of neodymium chloride in glycerol is more like 

 that of the water spectrum, in that the bands are often very sharp and narrow. 



The absorption spectra of the chloride and nitrate in isobutyl alcohol 

 are quite different. The structure and distribution of the intensity of the 

 absorption in each group is entirely different. The center of gravity of the 

 absorption of each group is considerably farther to the red in the case of the 

 chloride, but the composition of the groups is so different for the two salts 

 that no relationship can be seen between them when the individual bands are 

 compared. These solutions would afford a very good example for the spectro- 

 photography of chemical actions in isobutyl alcohol at low temperatures. 



The above summary is made simply to give a few of the conclusions 

 reached in previous publications from this laboratory on absorption spectra, 

 and could be extended almost indefinitely. As the subject has not been studied 

 exhaustively, it is only given as typical of what should be done later. In the 

 present chapter the water, methyl and ethyl alcohols and glycerol solutions 

 were not taken up. For a further treatment the reader should refer to the 

 chapters that are to follow. On account of lack of time, the work on this 

 subject must be regarded as just begun. The following is the purpose of the 

 investigation. In the case of the uranyl bands it was found possible in many 

 instances to trace the bands by gradual changes from one salt to another. By 

 this means it was hoped to study chemical reactions in various solvents, to 

 find if a chemical reaction had the same effect on the uranyl bands under 

 different conditions. For a similar reason the neodymium spectrum has been 

 broken up into groups of bands, and it was proposed to study these minutely as 

 conditions were changed. The purpose here is to give a description of as many 

 characteristic groups as possible, and to correlate the groups that are alike. 

 It might be assumed, when the groups were constituted of the same bands with 

 the same relative intensity, sharpness, etc., that the physical and chemical 

 environment of the absorbing centers was the same, etc. Much more work 

 of the above kind remains to be done, especially with the rare earths already 

 described, erbium, holmium, etc. The absorption of the dry salts, the phos- 

 phorescent spectra, and the absorption spectra at low temperatures should 

 be obtained. This, naturally, brings us to the subject as it is presented in 

 the two chapters that follow. 



