94 THE ABSORPTION SPECTRA OF SOLUTIONS. 



(6) From the above examples it must be remembered that because the 

 absorption spectra of a salt in two different solvents prove to be very much 

 the same, this fact is not an argument that no solvation exists in the two cases. 



(7) The values of x and y probably have a very considerable effect on the 

 nature of the solvates, but even under these conditions the little work that has 

 been done indicates, for cases where y has a value, i.e., where there are other 

 salts, or the acid corresponding to the given salt is present, that we still have 

 the constants a, b, etc., although these may have a different value from what 

 they have when y = 0. 



(8) Very little work has been done on the change in the persistency of 

 solvate bands when foreign salts are added to the solution. The addition of 

 aluminium and calcium chlorides to solutions of colored chlorides seems to 

 increase the persistency of the alcohol bands relative to the water bands. 



(9) The selective action of foreign salts on solvates is shown very strik- 

 ingly by the addition of oxidizing agents to solutions of uranous salts in 

 water and alcohol. Substances like potassium and calcium nitrates and 

 sodium perchlorate cause the water bands to decrease very greatly in inten- 

 sity. The alcohol bands, on the other hand, seem to remain of about the 

 same intensity. Whether this is due to the oxidization of the hydrate or 

 simply to a decrease in its persistency, can not always be stated. Some cases 

 indicate that selective oxidization takes place. The oxidization of hydrogen 

 peroxide affects water and alcohol bands in the same way. 



(10) In many cases the solubility of a salt like uranous bromide is much 

 less after alcohol has been added to the water than before. Sometimes pre- 

 cipitates form when a second solvent is added, and in some cases the filtrate 

 shows the presence of only one solvate, whereas before the precipitate was 

 formed both solvates were present. This may be denoted as selective solvate 

 precipitation. 



(11) The effect of rise in temperature changes the relative intensity of 

 the solvate bands of a solution. A very marked example of this kind is a 

 solution of uranous chloride in a mixture of water and ethyl alcohol in such 

 proportions as to show the water and alcohol bands of the same intensity at 

 ordinary room temperatures. Heat the solution to about 80 C. and the 

 water bands practically disappear, leaving only the uranous alcohol bands in 

 the spectrum. 



(12) Whether or not there is a dynamic equilibrium of solvates is not 

 certain, but the selective action of foreign salts, the effect of changing the 

 relative quantities of the solvents and of changing the temperature, would 

 lead us to believe that there is some interchange of solvates going on. The 

 velocity of reactions of this kind may, however, be comparatively slow. 



THE URANYL AND URANOUS BANDS. 



The uranyl spectrum consists of some twelve bands starting from X 5000 

 and runs into the ultra-violet. Starting with the long wave-length band 

 they have been designated by the letters a, b, c, etc. These bands form a series, 

 the distance between the bands decreasing with the wave-length. The uranous 

 bands do not form any series, and resemble the uranyl bands only in their 

 general appearance. The uranium bands are quite wide and diffuse as com- 

 pared with the erbium and neodymium bands. A considerable amount of 



