66 



ABSORPTION SPECTRA OF A NUMBER OF SALTS 



The work in the visible region of the spectrum was limited by the slit- 

 widths necessary to be used, which has been mentioned and discussed above. 

 We have rather chosen a limited portion of the infra-red, over which we 

 could work without altering either the intensity of the light or the slit-width, 

 which was in all cases 0.2 mm. 



The curves representing table 12 are given in figs. 18 to 21 inclusive. 

 The percentages of transmission are plotted as ordinates, while the wave- 

 lengths are given as abscissse. An examination of these curves shows three 

 pronounced minima, representing the three absorption bands, with their 

 centers near X7300, 1 X7950, and X8700, and less-marked bands near X7150 

 and X9000. The latter of these small bands is possibly due in part to the 



absorption of the solvent; but since its intensity does not increase markedly 

 with dilution, it is more probably a doublet. Considering the curves repre- 

 senting all four dilutions, we see that the X7300 and X7900 bands show com- 

 plete absorption over a considerable range of wave-lengths, and any change 

 in intensity could not be very noticeable. The X8700 band, however, has 

 its minima gradually lowered as we pass from curve 18 to curve 21, i, e., in 

 the direction of increasing dilution. This phenomenon has been noted else- 

 where in this monograph, and a possible explanation of it based upon a 

 theory of resonance suggested. A closer and more exact study has shown 

 that, although the phenomenon is a real one, yet it is probable that it may 



1 The wave-lengths in the above and following tables are given, in general, to only 

 three places. 



