THE ACETATES. 



149 



appear to have the same interval. The difference between the weighted 

 averages is much less than the uncertainties in the determination of 

 the intervals of the dim bands of the weaker series. 



TABLE 57. Uranyl acetate (crystalline; 2HiO). 



THE DOUBLE ACETATES. 



The fluorescence spectra of these salts have as a rule lower frequency 

 intervals than the two forms of single acetate. The average interval 

 is below 85, as compared with 85.7 for U02(C 2 H 3 02)22H 2 and 85.9 

 for the anhydrous single acetate. 



The group structure is in general less symmetrical than that of the 

 double chlorides or the double nitrates and precise comparisons are 

 therefore more difficult. 



Corresponding groups in the majority of cases, however, occupy very 

 nearly the same position in the spectrum, and the system of designating 

 the various bands employed in the discussion of the chlorides and 

 nitrates has been used. 



If we neglect some of the weaker outlying bands, the group structure 

 of several of the double acetates is found to consist of 4 nearly equi- 

 distant bands the wave-length of which is almost if not quite inde- 

 pendent of the metal which enters into the composition of the double 

 salt. The substances which most nearly conform to this type are the 

 double acetates containing lithium, potassium, calcium, and strontium. 



Manganese uranyl acetate differs from these only in the absence of 

 band B in some groups. (See fig. 83.) 



In the spectrum of the barium double acetate the groups are shifted 

 bodily toward the red about 5 frequency units. In the spectra of the 

 ammonium and rubidium salts band D is doubled. 



