GENERAL DISCUSSION OF RESULTS. 141 



solution of uranous sulphate simply causes the g, h, and i bands to be shifted 

 about 20 Angstrom units to the violet. Similar changes are often produced 

 by adding salts containing the cation of the acid. For instance, it has been 

 found that the absorption spectra of uranyl chloride in a concentrated 

 aqueous solution of aluminium chloride, or zinc chloride, or hydrochloric 

 acid are very similar to that of uranyl and calcium chlorides in methyl 

 alcohol, or of uranyl chloride in ethyl alcohol. 



When nitric acid is added to an aqueous solution of uranous acetate, 

 it is found that the oxidation of the uranous salt does not occur when small 

 amounts of acid are added, but that in this case the uranous bands are 

 shifted to the violet. The uranyl bands pass through several stages and 

 change very greatly, indicating that the chemical reaction is quite complex. 



The absorption spectra of uranous salts usually show the uranyl 

 bands, and in some cases these are very strong. The question immediately 

 arises as to whether the uranyl bands are common both to the uranyl and 

 uranous salts. It seems probable that they are characteristic of only the 

 uranyl salts, although this is not certain. Uranous salts have been obtained 

 which show only a strong band appearing in about the same position as 

 that of the blue-violet uranyl band, and this indicates that the presence 

 of uranyl bands is due to the uranyl salt which has not been reduced. 

 In most of the changes of solvent and salt it has been found possible to 

 follow the individual uranyl bands throughout the reactions which took 

 place, and this seems to indicate that the absorption is due to a system of 

 some kind which preserves its entity throughout all these changes. 



The gradual shift of the absorption bands as one salt of a metal is trans- 

 formed into another salt by the addition of more and more free acid is very 

 important. 



The work already done in this laboratory on the absorption spectra 

 of solutions, in which about five thousand solutions have now been studied, 

 shows that anjr given series of absorption bands probably correspond to a 

 definite chemical condition of the dissolved substance. When a salt is 

 treated with a free acid the absorption bands of some of the salts shift grad- 

 ually over to the position occupied by the bands corresponding to the new 

 salt of the metal with the acid in question. In an example of this kind the 

 bands can be made to occupy any position between the initial and final posi- 

 tions, and it seems probable that when a salt of one acid is transformed in 

 this way into a salt of another acid, there is a whole series of intermediate 

 systems or compounds formed. These are, for the most part, too unstable 

 to be isolated by the methods at present at our disposal, but their action 

 on light makes their existence in solution highly probable. 



It is well known that our chemical equations represent, in general, only 

 the beginning and end of chemical reactions, and tell us nothing about the 

 intermediate stages of the reaction, which are, of course, the most interest- 

 ing parts of the reaction. The results obtained in this work make it 

 highly probable that chemical reactions may sometimes be much more com- 

 plex than would be indicated by the equations that we ordinarily use to express 

 them. When, for example, a nitrate is transformed into a sulphate, there 

 seems to be a series of intermediate systems nitrosulphates or sulpho- 



