INVESTIGATION WITH A ROCK-SALT PRISM. 83 



13.25 jLt. This is the only compound studied that has such a spectrum 

 composed chiefly of fine lines. The vibration of the benzene nucleus at 

 3.25, 6.25, and 6.75 fx has not been obliterated. The 4.45 fj. band is to 

 be found at 4.38 /x in CHoCN and C0H5CN, while it is shifted to 4.8/1 in 

 phenyl mustard oil, CgHsNCS, which should be noticed in connection 

 with this compound. But few compounds have been found which have 

 so many absorption bands at from 3 to 6/t, The large spectrometer 

 was very useful in determining them with certainty. The contrast 

 between the curve for this compound and the one for CgH-Cl is very 

 marked. In the latter the substitution of a CI atom has not affected 

 the 3.25 fi (6.25 ix) and 6.75 /x bands of benzene, but beyond this point 

 the absorption bands at 9.3 /x. are much deeper, while at 13.25 fx the band 

 is broad and shallow. On the other hand the substitution of the CN- 

 group has caused a narrowing of all bands except the one at 13.25 fx, 

 which is unusually strong. The spectrum of this compound shows that 

 the numerous shallow bands in other compounds are not always due to 

 the small dispersion used, but that the actual width of the lines must 

 also be considered. 



DiPHENYL. (C6H5)2. 



Diphenyl, as the structural formula shows, consists of two benzene 

 rings. It is made by passing benzene vapor through red-hot tubes, 

 the heat causing it to polymerize into this larger molecule. The sub- 

 stance itself is a solid, of large lamellar crystals, which melt at 71°. It 

 was of great interest to study this compound in connection with benzene. 

 The results were somewhat disappointing on account of the difficulty, 

 always experienced with crystalline solids, in obtaining a film that was 

 smooth and continuous and at the same time thin enough to be trans- 

 parent. This one shows great opacity, but this is probably due to scat- 

 tering of the transmitted energy. The film was continuous and 0.12 

 mm. in thickness. No marked bands are to be found in this curve 

 except at 7.3 fx and 9.3 fx. Only a few — the least conspicuous — bands of 

 benzene are common with diphenyl, e. g., 10.2 /t. 



This compound was studied in solution in CCl^ (Appendix IV), 

 where it was found that the 3.25 ix benzene band occurs in its usual 

 place and its usual intensity. It is quite transparent, showing that in 

 the solid film the opacity is due to the scattering of the energy. 



Naphthalene and azobenzene were also studied. They have the 

 3.25 IX benzene band, showing that the vibration of the benzene nucleus 

 still exists. 



