16 A STUDY OF THE ABSORPTION SPECTRA. 



METHOD OF ATTACKING THE PROBLEM OF EMISSION AND 



ABSORPTION SPECTRA. 



The method of attacking the above problem will be to study the effect 

 on the spectra of a body produced by changing the physical and chemical 

 conditions about the light absorbers or emitters within as wide ranges as 

 possible. Some of the possible changes that can be made are as follows: 

 Take, for instance, the uranyl group U0 2 . We can find the effect upon 

 the absorption bands produced (1) by diluting the solution, (2) by changing 

 the acid radical to which the uranyl group is united, (3) by changing the 

 solvent and using mixtures of solvents, (4) by adding other salts (like 

 aluminium chloride), or (5) by adding acids of the same kind as that of the 

 salt of the uranyl group. The effect (6) of adding foreign salts and acids 

 at the same time and then varying the solvent, or the temperature, can 

 also be tried. In this way a very large number of very interesting things 

 can be tested. In most of these changes Ic will be kept constant. 



In the above example the temperature (7), the external pressure (8), 

 the electric field (9), and the magnetic field (10) can be changed between 

 wide limits. The latter effect is a very important one. For example, in 

 aqueous solution neodymium salts give a large number of fine bands, in 

 glycerol there are quite a number of new bands replacing the " water " 

 bands, and in the alcohols there are various " alcohol " bands. At low 

 temperatures these bands become very fine and it is quite possible to detect 

 the Zeeman effect. Now it seems quite probable that a "glycerol " band 

 and an " alcohol " band that seem to replace each other as the solvent is 

 changed are both due to the same vibrator. If the Zeeman effect is the 

 same in both cases it would be a strong argument in favor of the above 

 theory. A case that will soon be described is very important. It was 

 found that the wave-lengths of certain neodymium lines in a pure aqueous 

 solution did not change when the temperature was raised from to 90. 

 If, however, calcium chloride was added, then on raising the temperature 

 the above bands were shifted to the red. A very interesting and important 

 investigation is whether the Zeeman effect on the band would be affected 

 by the presence of substances like calcium chloride. 



To be compared with the above changes are changes in the absorption 

 spectra of the crystals of the salt (1 1) as affected by water of crystallization, 

 or by the presence of foreign substances, or as affected by the polarization 

 (12) or direction of passage of light through the crystal. The absorption 

 spectra (13) of the anhydrous powder at different temperatures, etc., should 

 be found. The phosphorescent spectrum (14) should be studied in this 

 connection, especially as affected by the mode of stimulation (X-rays, 

 cathode rays, heating, or monochromatic light of different wave-lengths). 

 The temperature, electric or magnetic field could be changed about the 

 phosphorescing body. The effect of change of state (15) should be tried if 

 this is possible, also any possible changes of valency of the atoms (16) com- 

 posing the body investigated. It is very important that these suggested 

 modes of attack should be extended throughout the whole range of wave- 

 lengths. 



