128 INFRA-RED ABSORPTION SPECTRA. 



apart, the large absorption bands lie farthest toward the short wave- 

 lengths ; the meta has its bands in intermediate positions. 



The dielectric constants of a number of solvents and solutions have 

 been determined by Schlundt^ and by Eggers.^ They found that the 

 dielectric constants of C2N2, CH2(CN)2, and C2H4(CN)2 to be 2.52, 

 46.3, and 61.2, respectively, which would indicate that the dielectric 

 constant is dependent upon the comparative freedom of the cyanogen 

 radicals from each other. In general, however, they find that the 

 deleCtric of a substance is affected not only by the elements entering 

 into its decomposition, but also by the grouping of those elements in the 

 molecule. The dielectric constant decreases with increase in molecular 

 weight. Methyl, ethyl, amyl, and phenyl mustard oil have the respect- 

 ive dielectric constants, 17.9, 22, 17.3, and 8.5, so that evidently we gain 

 nothing in considering them in connection with the large band at 4.78 /*. 

 The value of the phenyl mustard oil is just about one-half that of the 

 others. 



These compounds were not examined for the 6.25 and 6.75 fx benzene 

 bands, because CCI4 has a large band at 6.5 /u., and the cell was opaque. 



It is to be noticed that these solids in solution are practically trans- 

 parent, except in the region of their absorption bands, which corresponds 

 to the results found for iodine in solution, as already mentioned. In 

 the present state of our knowledge of the subject it appears that a solid 

 in solution is far more transparent than in its undissolved state in the 

 infra-red, which seems a rather unusual condition that deserves further 

 inquiry. 



'Schlundt : Bull. Univ. of Wisconsin, 2, 353, 1901. 

 '^Eggers : Jour. Phys. Chem., viii, p. 14, 1904. 



