1909.] OF VARIOUS SALTS IN SOLUTION. 219 



can be made are as follows : Take for instance the' uranyl group 

 UO,. We can find the effect upon the absorption bands produced 

 (i) by diluting the solution, (2) by changing the acid radicle to 

 which the uranyl group is united, (3) by changing the solvent and 

 using mixtures of solvents, (4) by adding other salts (like alumin- 

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

 the salt of the uranyl group. The effect 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 examples 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 im- 

 portant. It was found that certain neodymium lines in a pure water 

 solution did not have their wave-length changed when the tempera- 

 ture was changed from 0° 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 this band would be affected by the 

 presence of bodies like calcium chloride. 



To be compared with the above changes are changes in the 

 absorption spectra of the crystals of the salt (11) 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 



