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XIII. The Absorption Spectra of the Vapours of Benzene and its Homologues , at 
Different Temperatures and Pressures , and of Solutions of Benzene. 
By Walter Noel Hartley, D.Sc., F.R.S., Royal College of Science, Dublin. 
Received August 15,—Read December 12, 1907. 
[Plates 32-33.] 
Introduction. 
The absorption spectrum of benzene in a state of vapour and in solution was 
photographed by W. A. Miller (‘Phil. Trans.,’ 1862, vol. 152, II., pp. 861-887). It 
was also photographed by me in 1880 (‘J. Chem. Soc.,’ 1881, vol. 39, p. 153; 1882, 
vol. 41 ; 1885, vol. 47, pp. 685-757), with the instrument and by the method 
described in the ‘Scientific Proceedings of the Royal Dublin Society’ in 1881 
(vol. iii., p. 93, IS^ew Series) and ‘ J. Society of Arts,’ 1885. For these investigations 
a molecular weight in milligrammes was employed to test the molecular absorption of 
the hydrocarbon, but the quantity of vapour was too large even at low temperatures, 
and the temperature, as since ascertained, was in other experiments too high to admit 
of the numerous absorption bands being observed, although a series of bands had been 
photographed from very dilute solutions of benzene in alcohol. The continuous rays 
which accompany the lines in the emission spectrum of the strongly condensed spark 
of cadmium were found to afford the best source of light in the region of short wave¬ 
lengths. 
J. Pauer, in 1897 (‘ Wiedemann’s Annalen,’ vol. 61, p. 363), also used the 
cadmium spectrum precisely in the same manner for a more complete investigation of 
benzene and its homologues, but his experiments were not quantitative, although he 
compared the same substances in the states of vapour, of liquid, and in solution at a 
temperature of 20° C. He accurately measured 29 different narrow bands charac¬ 
teristic of the spectrum of the vapour of benzene. More recently this work has been 
repeated by Wilhelm Friederichs (‘ Zeitschrift f. Wissenschaftl. Photographie,’ 
1905, vol. 3, p. 154) and by Leonard Grebe ( loc. cit., 1905, p. 363). 
Friederichs used a quartz vacuum-tube containing hydrogen as a source ol 
continuous rays; while Grebe used the continuous spectrum described by Konen, 
vol. ccviii.—a 439. 3 p 2 26.10.08 
