522 Prof. E. 0. 0. Baly on 



relatively few substances exhibit fine-line absorption in thai 

 region. In the case of toluene and aniline the absorption 

 bands in the ultra-violet are resolved into fine lines, and in 

 both cases the principle holds good ; for the ultra-violet band 

 system of toluene can be calculated from the basis constants 

 of benzene and an aliphatic hydrocarbon, while those of 

 aniline can be calculated from the constants of ammonia and 

 benzene. 



The infra-red spectra of a number of saturated aliphatic 

 hydrocarbons have been measured by Coblentz, and they are 

 all strikingly similar. The compound which was examined 

 in a state of most probable purity was normal hexane. The 

 infra-red absorption of this substance is characterized by 

 three very strong bands at \ = 13*8/i, 6'86fi, and 3*43/4. The 

 wave-numbers of these are very nearly multiples of 4, and 

 the most probable values are l/\ = 72, 144, and 288, and the 

 corresponding wave-lengths 13*88, 6*94, and 3*47it. Since 

 these three bands are so intense in relation to all the others 

 of the aliphatic hydrocarbons, it may be concluded that a 

 second basis constant of 7*2 is present, of which the above 

 wave-numbers are multiples as well as of 4. The existence 

 of these two basis constants explains all the strong bands of 

 the saturated aliphatic hydrocarbons; and it is very interesting 

 to note that one of them (4) is the same as in the case of 

 benzene, which suggests that it is characteristic of the carbon 

 chain. 



That the basis constants act independently and that the 

 infra-red spectrum of a compound is due to the basis constants 

 of its radicles, can readily be seen from the following 

 examples. Myricyl alcohol shows very strong bands at 

 \ = 2*97, 3*43, 6'86, and 13*88/*. Of these there is no doubt 

 that the last three are due to the basis constants of the 

 hydrocarbon chain, while the first is due to those of water 

 (3'Ojj,). Again, triethylamine shows the hydrocarbon bands 

 at 3*43 and & m 86fju and also the ammonia bands at 6*1 

 and 9*3ytx. 



The infra-red spectrum of aniline shows strong bands at 

 2*97 and 6'1/jl, which are clearly due to the basis constants 

 of ammonia. It also shows the characteristic band of benzene 

 at 3*25 /x; but the 6*75 benzene band is now recorded at 

 6'68jjl, a somewhat remarkable shift. 



Owing to the complexity of the infra-red spectrum of 

 ammonia, it becomes very difficult directly to determine the 

 fundamental frequency of aniline, of which the central 

 frequencies of the ultra-violet bands are multiples. On the 





