70 THE ABSORPTION SPECTRA OF SOLUTIONS. 



loses its greenish-yellow color and becomes slightly clouded, the solution being 

 of a pale-white color. At the same time an almost black solution is formed, 

 whose volume is about the same as that of the hydrochloric acid added. 

 Further addition of hydrochloric acid results in the ester solution becoming 

 of a darkish-green color, while a small amount of the very deeply colored, 

 oil-like solution still remained at the bottom of the solution. 



SELECTIVE REDUCTION OF URANYL AGGREGATES. 



The met hod employed for the preparation of uranous salts for work on their 

 absorption spectra has usually been to add an acid corresponding to that of the 

 uranyl salt,, and some zinc. There would be present in the solution of the 

 uranous salt the corresponding zinc salt. It is possible, under these conditions, 

 to obtain fairly concentrated solutions of uranous chloride, uranous bromide, 

 and uranous sulphate. It does not seem, by this method, to be possible to 

 obtain uranous nitrate in stable condition. A small amount of uranous 

 nitrate is formed, but it is very quickly oxidized again. Dilute aqueous 

 solutions of uranous acetate can be obtained by this method. 



The most concentrated solution of any uranous salt thus far obtained 

 is that of uranous chloride. A considerable volume of a solution of uranyl 

 chloride in ether was prepared; to this was added a small amount of concen- 

 trated hydrochloric acid and zinc. The uranous chloride formed is nearly 

 insoluble in the ether, and collects in a dark, oily liquid at the bottom of the 

 vessel. 



The action of certain acids on the uranyl salts is peculiar. As has been 

 stated, the addition of nitric acid and zinc to a uranyl chloride solution did 

 not result in the formation of any uranous salt, although the absorption 

 spectra would probably have shown very little effect on the uranyl chloride 

 bands produced by the addition of nitric acid. The sulphate would probably 

 have been a better uranyl salt to use in this connection, because the uranyl 

 sulphate bands are harder to change to the nitrate bands then the uranyl 

 chloride bands are. To a uranyl chloride solution containing some free hydro- 

 chloric acid were then added, as before, some nitric acid and zinc. In this case 

 some uranous salt was produced, but it was quite unstable and was quickly 

 oxidized again. 



On the other hand, to an aqueous solution of uranyl chloride were added 

 some hydrochloric acid and zinc. A uranous salt was formed, but in a few 

 minutes this was transformed back into the uranyl condition again. This is 

 rather unexpected, since it would be thought that the uranous salt would be 

 in the condition of the chloride, and the chloride is quite stable. To an aqueous 

 uranyl nitrate solution were then added a large amount of concentrated hydro- 

 chloric acid and a little zinc. The solution turns green during the first few 

 minutes and then goes over to the uranyl state, although hydrogen gas i^ 

 being rapidly evolved. Very little could be done with the bromides along this 

 line on account of the liberation of bromine. It would be very interesting 

 to find how much the uranyl bromide bands are changed before the bromine 

 gas is evolved, since this would give the condition of the aggregate when it is 

 broken up and bromine evolved. 



