302 REPORT—1899, 
(3) Addition products of tertiary bases and salts.—Piperidine has no 
power of selective absorption ; this was predicted from the behaviour of 
benzene hexachloride, which also has no power of selective absorption. 
Tetra-hydro-quinoline, on the other hand, has still the power of selective 
absorption, and its spectrum shows one absorption band. 
(4) Primary and secondary aromatic bases or amido-derwatives and 
their salts.—Both ortho- and para-toluidine and their hydrochlorides show 
an absorption band. 
(5) The absorption spectra of ortho- and meta-xylene both show an 
absorption band ; that of para-xylene shows two absorption bands. 
These substances being, unlike other isomeric bodies formerly examined, 
free from oxygen, afford a means of estimating the differences in molecular 
absorption which is due to nothing more than the so-called relative 
functions of the compound radicals. 
The area enclosed by the curve of metaxylene appears to be the least, 
that of orthoxylene stands next, while that of paraxylene is the greatest. 
The following deductions were drawn from the investigations : 
1. When an atom of nitrogen is substituted for an atom of carbon in 
the benzene or naphthalene nucleus, the property of selective absorption is 
still retained. 
This had already been inferred from an examination of picoline.! 
2. When the condensation of the carbon and nitrogen im the molecule of 
a benzenoid compound or tertiary base is modified by the addition thereto 
of an atom of hydrogen to each atom of carbon and nitrogen, the power of 
selective absorption is destroyed. 
3. When the condensation of the carbon atoms in quinoline is modified 
by the combination therewith of four atoms of hydrogen, the intensity of the 
selective absorption is reduced but is not destroyed. 
4, Molecules of compounds—that is to say, molecules composed of dis- 
similar atoms—vibrate as wholes or units, and the fundamental vibrations 
give rise to secondary vibrations which stand in no visible relation to the 
chemical constituents of the molecule, whether these be atoms or smaller 
molecules. 
THE SPECTRA OF VARIOUS AROMATIC HyDROCARBONS AND 
SUBSTANCES DERIVED THEREFROM. 
Note on the Absorption Bands in the Spectrum of Benzene. 
(Hartiey and Dossie).” 
When benzene is examined with a wide slit, lenses of long focus, and 
a powerful spark, a remarkable feature is noticeable in the spectra photo- 
graphed. The absorption bands are seen to be degraded in the direction 
of the least refrangible rays, suggesting that the bands consist of groups 
of lines stronger and closer together on the more refrangible side ; weaker 
and wider apart on the less refrangible. Such were the conditions under 
which the first photographs were taken. By using a very powerful spark, 
but with an instrument of short focus and a narrow slit, the rays emitted 
by cadmium electrodes may be rendered sufficiently continuous to show 
1 Trans. Chem. Soc. vol. xli. p. 47, 1882. 
2 Trans. Chem. Soc. p. 695, 1898. 
