544 SCIENCE PROGRESS 



carbons. — Victor Henri {Jonrn. Phys. et Radium, 1922, [vi], 3, 

 181-211 ; and C.R., 1922, 175, 421) has effected a considerable 

 improvement in the technique of the measurement of the 

 adsorption bands of organic substances. The ultraviolet 

 spectrum of benzene has been measured at vapour pressures 

 ranging from o-oi to 65 mm. At the low pressures, the 

 adsorption bands are resolved into a series of narrow bands 

 about 0'i5A apart, and these fuse into wider bands on passing 

 a certain limiting pressure. More than 350 bands have been 

 counted. It is shown that the adsorption of ultraviolet light 

 by benzene obeys the same laws as the band spectra of simple 

 di- or tri-atomic molecules. The application of the Bohr theory 

 to the band spectra permits of their classification into four 

 series, each band being given by an equation of the form 

 \l\ = h-B + na- [pb + p'^b^) + a{m^ - q"), in which A, B, a, b, 

 b^, and a are constants and n, p, m, and q whole numbers. 

 The coefficients deduced from the results of the ultraviolet 

 absorption may be employed for the calculation of the infrared 

 absorption spectra of benzene. The terms A and B are due to 

 electronic movements and do not enter into the frequency of 

 the infrared adsorption bands, for which a simple formula is 

 deduced, il\ = an — bp. The calculated and experimental values 

 are in satisfactory agreement. The ultraviolet spectra of 

 liquid benzene and its solutions, whilst very similar to that of 

 the vapour, show a slight shift towards longer wave lengths. 

 The displacement does not bear any relation to the dielectric 

 constant of the solvent. The fluorescent spectrum of liquid 

 benzene consists of six bands, which are excited by mono- 

 chromatic light of wave lengths lying between the benzene 

 absorption bands D, E, F, G, and H ; the lines corresponding 

 to the Aj and B absorption bands do not excite any fluorescence. 

 The fluorescent bands are displaced towards the red, with 

 respect to the absorption bands. 



For naphthalene a similar absorption spectra has been 

 found to that observed with benzene. In all seventeen bands 

 were measured between 3207 and 2563, and one band in the 

 extreme ultraviolet. The absorption curve is displaced towards 

 the red, with respect to that of benzene, and the adsorption is 

 ten times stronger and the number of bands more numerous 

 than in the case of benzene. The influence of the solvent on 

 the spectra of the two substances is the same in both 

 cases. 



Stewart and Marsh {Nature, 1923, 111, 115) have succeeded 

 in obtaining the luminescence spectrum of benzene, by subject- 

 ing benzene vapour to the action of the waves from a Tesla 

 transformer. At low pressures a regular spectrum is obtained, 

 composed of a series of band groups. These emission bands 



