THE ACETATES. 



163 



units from the terminating absorption band mentioned above, des- 

 ignated as e in accordance with convention used in previous papers. 



An excellent example of this type of change from fluorescence to 

 absorption is afforded by the spectrum of barium uranyl acetate 

 (fig. 87) . Here an exact reversal of band Eg 1 occurs and the strong 

 absorption band e, which takes the place of E in that group, is 85 

 frequency units from the first member of the strong e series which 

 extends toward the ultra-violet with the usual absorption interval 

 of 70 units. Displaced reversals F, G, and H also occur an indica- 

 tion of the probably complex structure of these bands. The corre- 

 sponding absorption bands are likewise 85 units from the first members 

 of the/', g', and h f series of the absorption spectrum. 



There is almost as notable a resemblance between the absorption 

 spectra of this class as between their fluorescence spectra. The resolu- 

 tion is, however, not so good, and all the members of the various series 

 are not so easily located. Almost without exception the bands which 

 can be observed are definitely related, in the manner just described, 

 to the fluorescence series. 



(2) The single acetates U0 2 (C 2 H 3 2 ) 2 and U02(C 2 H 3 2 )2+2H 2 0; 

 double acetates of Mg, Mn, Pb. 



Here the absorption system (interval 70 =*=) distinctly overlaps the 

 fluorescence system extending into the region of groups 8 and 7 beyond, 

 without change of interval. 



FIQ. 87. 



The various series of absorption bands located in our visual and 

 photographic studies of the acetates are contained in tables 85 to 97 

 inclusive. Frequencies and average intervals are given for each salt, 

 the series being designated as usual by small letters, which indicate 

 their relation to fluorescence series denoted by the corresponding 

 capital letter. The three examples of bands or series not thus related 

 to visible fluorescence are indicated by means of the Greek letter 7. 



1 This band Eg may appear either as fluorescence or as absorption according to the conditions 

 of illumination, etc. It is commonly seen as fluorescence in the spectrum of the zinc uranyl 

 acetate and as absorption in the spectra of other salts of this class. 



