140 



A STUDY OF THE ABSORPTION SPECTRA. 



of sulphuric acid on the sulphate; acetic acid on the acetate; or hydro- 

 chloric acid, calcium, or aluminium chloride on the chloride. In general 

 the presence of these foreign reagents causes the uranyl bands to become more 

 intense and, in most cases, narrower. The action of all the above reagents 

 except nitric acid is to cause the uranyl bands to be shifted towards the red. 

 Nitric acid, however, causes large shifts towards the violet. The above 

 reagents have a similar effect on the corresponding uranous bands. 



The explanation of the above effects seems possible by supposing that 

 aggregates are formed. In the case of neodymium salts the effect of the 

 above reagents is very small, and nitric acid, instead of causing the 

 neodymium nitrate bands to become narrower, stronger, and to be shifted 

 towards the violet, simply causes the bands to become much more diffuse. 

 The other reagents cause the neodymium bands to become diffuse, weaker, 

 and to broaden somewhat towards the red. 



In addition to trying the effect of acids upon uranium salts of the same 

 acid, spectrum photographs were made of the effect produced by adding acids 

 to different uranyl, uranous, and neodymium salts. Uranyl nitrate was 

 treated with sulphuric, hydrochloric, and acetic acids; uranyl and uranous 

 acetates with various acids; various uranous salts and neodymium acetate 

 with nitric acid. These salts and acids were selected, since they showed 

 the greatest spectroscopic changes. Especially interesting are the spec- 

 trograms made by treating uranous salts with nitric acid. 



The spectrophotographs of chemical reactions show, invariably) that the 

 changes produced in the spectra as one salt is transformed into another are 

 gradual, whereas in changing the solvent this is not the case. For instance, 

 when uranyl nitrate is transformed into uranyl sulphate, the uranyl nitrate 

 bands gradually shift into the sulphate position. The same effect is produced 

 when solutions are made containing different amounts of uranyl nitrate 

 and uranyl sulphate. Further addition of sulphuric acid causes the bands 

 to shift still more. An example is given where to a small amount of a 

 solution of uran}d nitrate in nitric acid a large amount of sulphuric acid 

 is added. 



1 Narrow. 



2 Double. 



It will be seen that the shifts in these cases are quite large, and the 

 moving together of the / and g bands is especially remarkable. The chem- 

 ical changes studied thus far spectroscopically have been in most cases 

 confined to aqueous solutions. Changes effected in other solvents are usu- 

 ally smaller. For instance, the addition of sulphuric acid to a glycerol 



