12 INFRA-RED ABSORPTION SPECTRA. 



The amyl alcohol was yellow in color for the i. 6-meter cell, but color- 

 less for a small thickness. 



ULTRA-VIOLET. 



Soret and Rillet/ using a fluorescent ocular, examined different thick- 

 nesses of ethyl, butyl, and amyl nitrates, and found that, to completely 

 absorb certain cadmium lines used, it required the least thickness of 

 amyl nitrate, while greater thicknesses were required for the butyl and 

 ethyl, which is interpreted that with increasing molecular weight the 

 absorption increases toward the longer wave-lengths. The benzene 

 derivatives have been investigated by Pauer,^ by photography. The 

 benzene spectrum consists of four groups of bands. In the xylenes 

 and aniline the original benzene spectrum seems crowded together and 

 shifted toward the visible spectrum. For the liquid state the bands lie 

 farther toward the visible spectrum than for the vapor phase, so that 

 " if we consider each liquid body as a solution in itself, then Kundt's 

 law holds for shift of the band with increase in molecular weight of the 

 solvent." This seems to be giving the broadest possible interpretation 

 of this law. In toluene the substitution of a CHg group has not merely 

 destroyed the arrangement of the lines found for benzene, but the new 

 spectrum consists of a series of double lines, not regularly distributed. 

 The isomeric xylenes are of the most interest. The ortho has scarcely 

 any bands, while the meta has three and the para has five bands, which 

 show no regularity. The results show that the arrangement of the 

 atoms has a great influence on the absorption spectra, just as previously 

 found by Hartley.^ 



In the benzene spectrum Pauer observed several groups of lines in 

 which the " constant difference " of the vibration numbers is 98. He 

 observed that the absorption spectra of vapors show lines or groups of 

 lines which become bands in the liquid condition. Traces of benzene 

 in the air were sufficient to show the four strong groups of lines. He 

 also found that for nitro- or amido-benzene the bands shift toward the 

 longer wave-lengths (to the red), while Kriiss found exactly the oppo- 

 site (to the violet). The question whether this is a real shift will be 

 discussed in connection with the present investigation. 



Martens* examined the spectrum of a number of transparent non- 

 conducting elements (e. g., C. P. S. CI. Se. Br. I.) and found that the 

 wave-length corresponding to the principal absorption band in the ultra- 



*Soret & Rillet ; Compt. Rend., 89, p. 147, 1879. 

 ^Pauer : Ann. der Physik (3), 61, p. 363, 1897. 

 ^Hartley : Phil. Trans., 170, p. 270, 1879. 

 *Martens : Ann. der Physik (4), 6, p. 603, 1901. 



