. Carnegie Institution of Washington publication. 26 FLUORESCENCE OF THE URANYL SALTS. light. The observed distribution of energy would correspond with the actual distribution only in case an excessively thin layer of the sub- stance is excited—so thin that the absorption of the light emitted is neg- ligible. As a matter of fact, the band lying to the violet side of the maximum is in a region where the absorption is considerable, while the brightest band and those lying to the red are in the region where the absorption is small. The constancy of the ratio in the case of the lower curves, and t
. Carnegie Institution of Washington publication. 26 FLUORESCENCE OF THE URANYL SALTS. light. The observed distribution of energy would correspond with the actual distribution only in case an excessively thin layer of the sub- stance is excited—so thin that the absorption of the light emitted is neg- ligible. As a matter of fact, the band lying to the violet side of the maximum is in a region where the absorption is considerable, while the brightest band and those lying to the red are in the region where the absorption is small. The constancy of the ratio in the case of the lower curves, and the small variation of the ratio shown by the upper curves, are therefore entirely consistent with the view that the observed variations are the result of absorption, and that the first effect of excitation, whatever may be the wave-length of the exciting light, is to produce all of the bands with a definite and constant intensity distribution. .30 .40^. .30 .40 FIG. 18. FIG. 19. Relative intensities of the brightest fluorescence bands of uranyl nitrate (fig. 18) and uranyl- potassium sulphate (fig. 19). The intensity of the brightest band is put equal to 10. The upper curve in each figure refers to the band lying next to the brightest toward the violet. The lower curve refers to the band toward the red. Abscissae give the wave-length of the exciting light. (See table 11.) The observations recorded in the foregoing paragraphs all tend to indicate that the fluorescence spectrum of a uranyl salt is a homo- geneous complex. The envelope is single-crested and has the form typical of a simple band. Neither its position nor form is modified by changing the mode of excitation. To test this conclusion we have made many experiments under widely varying conditions, especially in the way of selective and monochromatic excitation of the resolved spectra, where it should be possible to observe critically the disappearance or enhancement of single narrow components of groups of series. The
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