130 FLUORESCENCE OF THE URANYL SALTS. 



are made up of very faint lines. But the first bands of the absorption 

 series i, j, and k fall at 2,083.8, 2,089.7, and 2,095.6, and it would seem, 

 therefore, that they might properly be looked upon as resulting from 

 the reversal of the final bands of the corresponding fluorescence series, 

 even though these bands escaped observation. 



The reciprocal wave-lengths for the principal absorption series are 

 given in table 43. Each series is lettered in such a way as to indicate 



TABLE 43. Series in the absorption spectrum of uranyl nitrate trihydrate [UO^NO^-^SH^O], 



b B= 2033.2 b =(2033.2) 2107.0 2180.8. 



c C= 2041.1 c = 2041.1 2112.7 2186.7. 



c' C"=? c'= 2043.3 2116.0 2189.7 2261.0. 



/' F'= 2058.5 /'= 2057.6 2129.0 2200.2 2271.7. 



G= 2070.7 0=2071.7 2142.7 2213.2 2285.7 2357.9. 

 h H= 2076.3 h =2076.5 2148.6 2220.6 2368.0. 



1 I =(2082.7) i = 2083.8 2154.5 2226.9 2297.8 2368.0. 

 j J =(2090.0) j= 2089.7 2162.0 2235.4 2307.9. 



k K =(2096.6) k = 2095.6 2166.7. 



I' L'=? l'= 2103.0 2173.4 2245.7 2317.5 



the fluorescence series with which it appears to be related, e. g., the 

 first band of series c is the reversal of the last band of series C. In 

 each case also the reciprocal wave-length is given for the last band of 

 the fluorescence series. The numbers in parentheses indicate bands that 

 were not observed, but would be expected to occur with the indicated 

 value of 1/X. 



It is to be observed that no absorption series were found which corre- 

 sponded to the fluorescence series A, D, E, and L. On the other hand, 

 no fluorescence series were observed to correspond with the absorption 

 series c' and I'. 



THE DIHYDRATE: UO 2 (N0 3 ) 2 +2H 2 0. 



Although the dihydrate has been made by several observers, the 

 crystalline form does not appear to have been studied. The crystals 

 used in this investigation were in most cases made by heating a tube 

 containing the crystallized trihydrate to a temperature somewhat 

 above 100 C. and passing through it a current of air which had been 

 run through a mixture of sulphuric acid and nitric acid and over 

 phosphorus pentoxide. The melted trihydrate slowly evaporated and 

 recrystallized as dihydrate without losing nitric acid. The tube was 

 then sealed up to prevent the entrance of moisture. The dihydrate 

 was also prepared synthetically by treating dry H 2 U0 4 with the 

 " monohydrate " nitric acid, the two being sealed in a glass tube and 

 allowed to react. The crystals obtained were in each case small, so 

 that the observations were made on a mass of crystals having no 

 systematic arrangement of the axes. 



Seventy-four bands were observed in the fluorescence spectrum, 61 

 of which fell into 12 constant-interval series of from 4 to 6 bands each. 

 The interval ranged from 87.6 in series F to 88.3 in series A, but in 

 most cases lay near the average of all, viz, 88. 1. 1 The values of I/A 



1 For series C, which contained two bands only, the interval was 87.2. 



