THE ACETATES. 



151 



A POSSIBLE RELATION TO THE METALLIC SPARK SPECTRA. 



It appears from the foregoing that any metal capable of forming a 

 double uranyl acetate modifies the constitution of the fluorescence 

 spectrum both as to the composition of the groups and 

 their location. Certain metals, such as lithium, potas- 

 sium, calcium, manganese, and strontium, produce one 

 and the same modification, irrespective of the metal which 

 is present. Other metals shift the group slightly (e. g., 

 barium) or vary slightly the relative distances between 

 neighboring bands without otherwise changing the struc- 

 ture of the group. The presence of still other metals, 

 such as sodium, magnesium, zinc, silver, and lead, results 

 in a considerable general shift and the introduction of 

 new series into the spectrum characteristic of the partic- 

 ular metal in question and existing only in the doublet 

 salt of which it forms a part. Some of these groups are 

 much more complex than the uniform type depicted in 

 figure 83. The others are accompanied by strong bands or 

 minor groups of bands lying outside the usual boundaries. 



One might imagine, to account for this type of spec- 

 trum, that in addition to the metal in combination as a 

 part of the double salt, there are in solution certain 

 other radiators. If these are uncombined particles of 

 the metal existing in a condition akin to the gaseous 

 state, one might expect a type of radiation, under exci- 

 tation, similar to that discovered by Wood 1 in sodium- 

 vapor; i. e., series of constant frequency made up of bands 

 instead of lines because of damping. One member of each 

 such series should coincide or nearly coincide with some 

 line in the arc or spark spectrum of the metal. 



Now, there are in fact various coincidences or approxi- 

 mations thereto close enough to bring lines of the 

 emission spectrum well within the brighter portion of 

 one of the fluorescence bands in question. In the spec- 

 trum of silver uranyl acetate, for example, there is a 

 strong series which does not coincide with any series in 

 the fluorescence spectra of the other acetates thus far 

 observed. One member of this series coincides with 

 the brightest visible line in the spark spectrum of silver 

 (Haschek 0.54655 /JL; frequency number 1,829.6). Our 

 reading of the corresponding band, made before we had 

 any suspicion of the possible relation here suggested, was 

 1,829.8. The rather bright line (0.51838) and the neigh- 

 boring doublet (0.51729-0.51675) in the spark spectrum 

 of magnesium correspond similarly to bands 1,928.9 and 

 1,934.4 of the fluorescence spectrum. 



FIG. 85. 



1 R. W. Wood. Physical Review (2), xi, p. 76. 



