THE NITRATES AND PHOSPHATES. 



125 



U0 2 (N0 3 ) a +6H a O 



U0 2 (N0 3 ) 



bands, while ordinates give the number of times each interval occurred. 

 The range of possible error in the location of each band is arbitrarily 

 assumed to be 2 units. Thus for a frequency interval 32 (abscissa) the 

 ordinate is 10. This means that 10 pairs of bands were found for which 

 the interval lay between 31 and 33. 



It is evident from the chart that certain intervals occur with much 

 greater frequency than would be expected if the bands were distributed 

 at random, and this is most conspicuously true of the interval 86. It 

 will be noted that the curve also shows lesser maxima for several other 

 frequency intervals: e. g., 8, 16, 70, 78, and 94. These intervals corre- 

 spond to the spacing of the bands in the successive groups which make 

 up the spectrum. 



On account of the fact that large, clear 

 crystals could be obtained, the hexahydrate 

 offered an especially favorable case for the 

 study of the absorption spectrum. Obser- 

 vations were made with a number of dif- 

 ferent crystals ranging in thickness from a 

 few tenths of a millimeter to 3 or 4 mm. 

 The averages given in table 41 are in many 

 cases based upon 15 or more independent 

 measurements. In the case of the band at 

 2,148.7, for example, 17 measurements of 

 wave-length were made, of which 3 were 

 discarded because of the unsatisfactory 

 character of the negatives. In the 14 

 measurements used in forming the average, 

 the reciprocal wave-length ranged from 

 2,147.8 to 2,149.6, most of the values lying 

 close to the average. In other cases the 

 wave-length is much more uncertain. The 

 extremely faint band at 2,536.4, for example, 

 was observed on only two negatives, while the dim, broad band at 

 2,720.3 was observed only once. The reliability of the recorded average 

 has been estimated in each case and is indicated in the table. 



A study of the absorption spectrum shows that an interval of about 

 71 between bands is of relatively frequent occurrence. (See the lower 

 curve, fig. 77.) In several instances definite series exist with this con- 

 stant interval. The values of I/A for the bands forming these series are 

 given in table 41. 



The two series e and / begin with reversible bands. Thus, the first 

 band of series e, at I/A = 2,058. 6, can not be distinguished in position 

 from the last band, I/A = 2,058.5, of the fluorescence series E, while the 

 first band, 1 /A = 2,061.9, of series /is coincident with the band 2,061.7 of 



U0 2 (N0 3 )2+6HO 

 ABSORPTIO.N 



FIG. 77. Frequency of occurrence 

 of different intervals between 

 bands. Abscissae show the in- 

 tervals (1 division 10); ordi- 

 nates show the number of timea 

 the interval occurs (1 division 

 -10). 



