SUMMARY AND GENERAL DISCUSSION OF RESULTS. 97 



before it is oxidized to the uranyl condition. Neutral uranous salts in solu- 

 tion, when heated to 80 or 90, form a black precipitate; but if some free 

 acid is present (or in the case of uranous chloride if other chlorides are present) 

 the uranous salts are much more stable. 



(6) Aggregates form compounds with solvents in many cases (for example, 

 various uranous aggregates in water and methyl alcohol) that are as charac- 

 teristic as those formed by the pure neutral salt. As yet no work has been 

 done on the effect of temperature and concentration on solvate aggregates. 



(7) In discussing the differences in the chemical properties of aggregates 

 mention will be made of the reduction and oxidization of uranium salts. It 

 is probable that many other chemical properties differ very much for the 

 various aggregates, but as this work has been mainly concerned with the 

 reduction and the oxidization of the salts, only these properties will be con- 

 sidered. As some of the methods used in the reduction of the uranyl salts 

 are in themselves of considerable interest, they will be taken up in more 

 detail than would otherwise be done. 



The method employed for the preparation of the uranous salts for work 

 on absorption spectra has been that described by Jones and Strong. 1 Under 

 these conditions it is possible to obtain quite concentrated solutions of the 

 chloride, the bromide, and the sulphate. No aqueous solution of uranous 

 nitrate could be obtained, although small amounts would be formed when the 

 hydrogen was first liberated from the acid, but in a very short time the uranous 

 nitrate was oxidized. 



The most concentrated solution of any uranous salt thus far obtained 

 is that of the chloride. Uranyl chloride is dissolved in ether (the solution 

 forms three distinct, unmiscible layers, the concentration of uranyl chloride 

 in each being different). To this solution is added a small amount of zinc 

 and concentrated hydrochloric acid. The uranous chloride formed is insoluble 

 in ether and accumulates in the dark oily liquid at the bottom of the vessel. 

 Layers of this liquid 1 mm. thick are almost opaque. The reduction of 

 uranyl chloride in isobutyl alcohol is very similar to that in ether. 



When hydrochloric acid and zinc are added to a solution of uranyl nitrate 

 a considerable amount of a uranous salt is formed, although it is quickly 

 oxidized again. This is true even when quite large amounts of hydrochloric 

 acid are present. A much more complete spectrographic study of the reduc- 

 tion of uranyl aggregates should be made, as it would probably lead to some 

 knowledge as to how the oxygen atoms are removed from the uranyl group 

 and the influence the other atoms and molecules of the aggregate have upon 

 this reduction. 



(8) Oxidization reactions also indicate very clearly that different aggre- 

 gates apparently possess different properties, although the action of the other 

 salts or acids present in the solution may modify the action of the oxidizing 

 agent. However this may be, it is found that uranous acid aggregates require 

 a great deal more of the oxidizing agent, especially when this is hydrogen 

 peroxide, than do the neutral aggregates. 



(9) Assuming the presence of aggregates, it is important to know what 

 effect dilution has upon their composition. It would be supposed that the 

 aggregates would break down at high dilution. To test this supposition the 



1 Phil. Mag., 19, 566 (1910) 



