64 THE ABSORPTION SPECTRA OF SOLUTIONS. 



sulphate aggregates. It is, however, surprising that these aggregates, if they 

 exist, are not broken up when the solution becomes very dilute. 



It is important that acid aggregates should be studied in the same way, 

 It is possible that these would break up more easily with increase in dilution 

 than the neutral aggregates apparently do. 



THE OXIDIZATION OF URANOUS SALTS BY NITRIC ACID. 



On account of the very great instability of uranous nitrate, it was ex- 

 pected that the addition of concentrated nitric acid to aqueous solutions of 

 the other uranous salts would cause their rapid oxidization. In the case of 

 uranous bromide, bromine was given off. In general, the addition of nitric 

 acid to an aqueous solution of uranous chloride causes the oxidization of that 

 salt, but if a large amount of nitric acid is added, the solution changes 

 from a very deep green to a light greenish-yellow, and the absorption spec- 

 trum shows that there is still a very considerable amount of uranous salt in 

 the solution; and the bands are quite different from those of neutral uranous 

 chloride. This uranous solution will remain for days, and seems to be quite 

 stable. 



A, plate 45, represents the absorption of a solution of uranous bromide 

 in water and methyl alcohol to which dilute nitric acid is added in increasing- 

 amounts. The addition of the nitric acid caused a slight increase in the trans- 

 mission in the ultra-violet, but this was quite small. The uranyl bands appear, 

 but are very weak. In strip 1 there is a band running from X 4200 to X 4400. 

 This is probably due to a water and alcohol band, the alcohol band being on 

 the red side. Apparently the alcohol band disappears, since the band nar- 

 rows rapidly on its red side, and then decreases slowly in intensity. The alco- 

 hol band at X 4650 has practically disappeared in the third strip. In strip 1 

 there is a weak, very diffuse band at X 4800, and a strong band at about X 4950. 

 As nitric acid is added these bands are replaced by a wide and strong region 

 of absorption, running from X 4600 to X 5000. The band X 5200 disappears. 

 The band X 5500 is shifted about 150 Angstrom units towards the violet. The 

 alcohol band running from about X 6000 to X 6300 narrows rapidly on its short 

 wave-length edge, disappears, and is replaced by a weak, diffuse band at about 

 X 6100. The red water bands increase and then gradually decrease in inten- 

 sity. When this decrease begins, the long wave-length band is much the 

 stronger of the two and indicates that the uranous bromide alcoholate and 

 the uranous bromide hydrate have both been changed to some uranous nitrate 

 hydrate, and that this compound is then oxidized to the uranyl salt. 



The addition of nitric acid to the aqueous solution of uranous sulphate 

 previously described produces a slow oxidization of the uranous into the ura- 

 nyl salt. This oxidization requires several minutes and would be a very good 

 reaction with which to study reaction velocity, the intensity of the absorp- 

 tion bands being determined by a radiomicrometric method. B, plate 46, is 

 a spectrograph of the oxidization produced by adding nitric acid to an aqueous 

 solution of uranous sulphate. Strip 5 is the absorption of the same solution 

 as that shown by strip 4, the only difference being that the solution had 

 been allowed to stand for several minutes. 



In the solution of uranous sulphate oxidized by nitric acid, the uranyl 

 bands are shifted slightly towards the violet, compared with the uranyl bands 



