VIII. THE ACETATES. 



The uranyl acetates afford a broader field for investigation than the 

 chlorides or nitrates, the spectra of which have been considered in 

 previous chapters. 



In addition to two forms of the single acetate UO 2 (C 2 H 3 02)2, we have 

 the double salts of all the alkali metals except caesium; the double salts 

 of calcium, barium, strontium, magnesium, zinc, lead, silver, and 

 manganese; the triple salt NaMg UO 2 (C 2 H 3 2 ) 5 . 



In the fluorescence spectra of the acetates, as in the case of all 

 uranyl salts thus far studied, the broader bands observed at room 

 temperature are resolved into groups when the substance is excited 

 at the temperature of liquid air, and the constitution of these groups, 

 which repeat themselves at regular intervals from the red to the region 

 in the blue, where absorption begins to replace fluorescence, is very 

 similar in the acetates to that of the groups in the spectra of the com- 

 pounds already discussed. 



THE SINGLE ACETATE. 



Two distinct varieties of this salt were available for observation 

 the finely powdered anhydrous form, U0 2 (C 2 H 3 2 ) 2 , and the crystalline 

 form, U0 2 (C 2 H 3 2 )2.H 2 O. 



The spectra of the two are very similar in appearance; each being 

 characterized by two strong, well-defined series forming a set of doub- 

 lets. They are easily distinguished, however, by the widely different 

 location of the doublets. In the spectrum of the anhydrous variety 

 these occur near the group centers of the alkaline double salts, whereas 

 in the crystalline form they fall nearly midway between these groups. 



The strong series of the crystalline salt, which we have denoted as 

 E and F, frequently appear in greatly reduced intensity in the spectra 

 of the double salts, due doubtless to the presence of traces of the single 

 acetate. The strong doublets C and D of the anhydrous acetate, 

 if they ever appear in the spectra of the double salts, would be more 

 difficult to detect, as they would overlap bands in the groups of the 

 latter. 



Wave-lengths and frequencies of these two forms of uranyl acetate 

 are given in tables 54 and 55. Intensities are designated as very strong 

 (vs), strong (s), medium (m), dim (d), very dim (vd), and very very 

 dim (wd). 



STUDIES OF A SINGLE GROUP. 



Since the acetates, like the chlorides and nitrates discussed in pre- 

 vious chapters, have spectra consisting of similar recurring groups, 

 it is convenient and sufficient, in the study of the structure of the 

 ensemble of the fluorescence, to consider a single group. For this 



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