1 



^8 INFRA-RED ABSORPTION SPECTRA. 



the shift at 3.3 fi is real will be discussed elsewhere. It will be suffi- 

 cient to notice that in mesitylene the 6.2 /* band is double (6.1S /x and 

 6.3 fj,) , so that with a smaller dispersion it would appear as one band, 

 with the maximum shifted. At 6.1 /x and 9.3 fi the bands are in common 

 with thiophene. The sample was labeled "free from thiophene," so 

 that this may be mere coincidence, rather than impurity. 



AnISOL. CeH^^-^CHa. (Fig. 78.) 



Here the benzene maximum is shifted from 3.25 ix to 

 ^CH 3-32/*' With the large spectrometer numerous small 

 I bands were detected in the transparent region from 4 to 



HC\^^^H ^ ^^ while the 6.8 /u, band was found double with maxima 

 " at 6.65 /x and 6.86 /x. The whole spectrum is composed of 



deep, narrow bands, which reminds us of the observation of Abney and 

 Festing that oxygen sharpens absorption bands. The strong band at 

 6.22 IX, which is only a slight depression in the benzene curve, is analo- 

 gous to the work of Liveing and Dewar,^ who found that mixtures of 

 metals (Mg and K) often showed lines not seen at all when these ele- 

 ments are taken separately. It also strengthens the belief, mentioned 

 elsewhere in this work, that many apparently new bands are not really 

 new, but that they are due to a condition in the molecule such that the 

 original vibrating ion is less damped by its neighbor. The spectrum 

 is entirely rearranged as compared with the original benzene spectrum. 



Ortho, Meta, and Para Xylenes. C8H4(CH3)2. (Figs. 81 to 83.) 



\Ortho\ \Meta\ \\Paj'a\ 



HC^ ^CH HC^ ^C-CH3 HC. JcW 



The three isomeric xylenes afford an example for investigating the 

 structure, as well as the question of bonding, in the molecule. As 

 found by Pauer^ for the ultra-violet, the spectrum is channeled, i. e., the 

 bands occur in groups, in the origins of 3.4, 6.7, 9.6, and 1.3 /a. The 

 first maximum for the three compounds occurs at 3.38 /x. They have 

 great similarity to 6 \x, where they begin to show the effect of structure. 

 At 6.8 ix they show great differences in the appearance of their curves. 

 Apparently the ortho is shifted the most, while the \>ara appears double. 

 This is best shown in the curves obtained with the large spectrometer. 



^Liveing & Dewar : Kayser's Spectroscopy, II, p. 251. 

 ^Pauer, loo cit. 



