16 



THE ABSORPTION SPECTRA OF SOLUTIONS. 



tion coefficient varies somewhat for every solvent. In the same solvent the 

 extinction coefficient usually increases as radicals are added to the dissolved 

 substance, increasing its molecular weight. Hantzsch 1 furnishes evidence 

 which shows the presence of solvates and molecular aggregates in the case of 

 nitrohydroquinone dimethyl ether. 



An interesting investigation has been made by Kalandek. 2 Resonators 

 will emit electromagnetic waves of different wave-lengths, depending on the 

 index of refraction of the liquid in which they are vibrating. Kalandek inves- 

 tigated the effect of different solvents on the period of various resonators, 

 and also on the positions of the absorption bands of a large number of organic 

 compounds. In general, the relations were not very close. It would be very 

 interesting, however, to carry these investigations into the infra-red. 



The Absorption Spectra of Benzene and Its Derivatives. 



Benzene and several of its derivatives show selective absorption in the 

 ultra-violet. Generally the absorption spectra of organic compounds consist 

 of very wide, diffuse bands. The absorption bands of gaseous benzene, on the 

 other hand, are very fine. Benzene in solution shows seven absorption bands 

 between X 2330 and X 2710, and in the gaseous state about 30 bands. Pauer, 3 

 Friedrichs, 4 Grebe, and Hartley 6 have investigated several of the benzene 

 compounds. The bands in the gaseous state are much finer and usually more 

 numerous than in solution or in the solid state. 



Both the vapor and solution bands are shifted to the red when CI, Br, 

 CH 3 , etc., are substituted for hydrogen. The shift is generally greater the 

 greater the molecular weight of the radical. The bands of benzene shifted in 

 this way are the ones that are common to benzene, toluene, ethylbenzene, 

 and hydroxy xylene, and are unaffected by temperature and pressure. Hartley 

 gives the following wave-lengths for benzene: 



As far as investigated, the substitution products of benzene have much less 

 characteristic spectra than the spectrum of benzene itself. It would be very 

 interesting to know whether the shift of the bands is gradual as the state is 

 changed or as different radicals are added. 



Anthracene has the following bands: 



1 Ber. d. chem. Ges., 40, 1556 (1907). 

 2 Phys. Zeit, 9, 128 (1908). 



3 Wied. Ann., 61, 363 (1897). 



4 Z. wiss. Phot., 3, 154 (1905). 

 6 Ibid., 3, 363 (1905). 



8 Journ. Chem. Soc., 77, 839 (1900). Phil. Trans., 208, A, 475-528 (1908). 



