34 THE ABSORPTION SPECTRA OF SOLUTIONS. 



these will be taken up under the effect of change in temperature on absorption 

 spectra. 



Hofmann and Kirmreuther 1 have examined the absorption spectra of 

 certain salts of erbium, using the reflection method, and find a very marked 

 similarity between the spectra of all of the salts investigated, although these 

 may be as different as the chloride and sulphide of erbium. For this reason 

 they conclude that the erbium bands are due to locked electrons and not to 

 saturated valency electrons. 



THE ABSORPTION OF SOLUTIONS OF CERTAIN NEODYMIUM SALTS. 



Previous work has shown us that neodymium and uranous salts show 

 characteristic solvent spectra better than any other colored salts. On account 

 of the sharpness of the neodymium bands, neodymium salts have been made 

 the object of especial study for the existence of solvent spectra. In many 

 cases it is known how the neodymium bands break up in a magnetic field, 

 and in general it is probably true that the absorption of salts of this element 

 has been studied more than that of any of the others. It seems, therefore, 

 probable that ultimately some knowledge of the forces within the solvate may 

 be learned, when it is found how the various neodymium bands are broken 

 up for the different kinds of solvates. In the following pages considerable 

 emphasis will be laid upon the finer structure of the neodymium bands for 

 solutions in the various solvents. A large field of investigation is open for the 

 study of the difference in the structure of these bands in solids and especially 

 in crystals. Only a few examples of the latter kind will be described here. 



In the description of the groups of neodymium absorption bands, the 

 following nomenclature will be used. This is done for the reason that each 

 one of these groups of bands possesses a characteristic structure for the various 

 solvents, and very often for different salts in the same solvent. While the 

 groups of bands do not change greatly in relative intensities, the finer bands 

 in each group show most extraordinary changes of this kind. The a group 

 includes bands .in the region X 3400 to X 3600; the /3 group the bands at 

 about X 4300; the y group from X 4600 to X 4800; the 8 group from X 5000 to 

 X 5400 ; the e group in the region X 5800 and the group at X 6300. In the 

 general discussion of results these groups will be compared under various 

 conditions of temperature, solvent, acid, etc. 



In the measurements of the wave-lengths of the neodymium bands, the 

 standard spark lines were photographed only in the ultra-violet, so that the 

 measurements of the long wave-length bands here given are not claimed to 

 be very accurate and are made largely for comparison. On the other hand, 

 the difference in wave-length of bands in the same group is much more accurate. 



In designating the groups of bands of the neodymium spectra, previous 

 workers started with the red end of the spectrum. This, however, is an un- 

 natural method of procedure when a grating is used, since the spectrograms 

 are all printed with the short wave-lengths on the left side, with the wave- 

 lengths increasing linearly as we pass towards the right. Moreover, it is very 

 doubtful if the ultra-violet absorption spectra of neodymium can be investi- 

 gated much farther in this region, so that this is the natural end of the spectrum 



1 Zeit. phys. Chem., 71, 312 (1910). 



