ABSORPTION SPECTRA AND CHEMICAL CONSTITUTION. 3A] 
the nature of the chemical reactions involved. The replacements of 
hydrogen by alkyls, nitroxyl, and amidogen was the subject of investiga- 
tion. The authors state that the subject had been partially investigated 
by Dunstan, Soret, and others, and appear to quote from the ‘ Pharm. 
Trans.’ vol. xi. p. 54. In attributing work of the kind to Dunstan they were 
in error, and this misstatement has been repeated by other authors in 
different publications. Their experiments were made upon indigo and its 
derivatives, m. methyl-indigo, m. oxymethyl-indigo, ethyl-indigo, mono- 
brom-indigo, dibrom-indigo, amido-indigo, and dibrom-amido-indigo, and 
show that the alkyl and oxyalkyl radicals shift the absorption bands 
towards the red, and that oxymethyl and ethyl exert a similar influence 
to methyl and ethyl, but are stronger in effect. An atom of bromine 
causes but little change, but the introduction of a second atom is equal in 
effect to « methyl group. It is stated that nitroxyl- and amido-groups 
have a reverse effect. 
Note on the above-mentioned papers.—No accurate conclusions of a 
general character can be drawn from observations on a part of the 
spectrum such as was in this case made with a molecule of complex 
structure like indigo. It is necessary to take into account the effect on 
the ultra-violet, and undoubtedly there the effect of NO, is to shift the 
bands towards the red, and that of NH, is the same when the molecule 
into which these radicals enter is a simple one like benzene. 
This is shown in the diagrams of Hartley and Huntington.! Com- 
pare benzene, aniline, with ortho- and para-nitraniline, phenol with ortho- 
nitrophenol and para-nitrophenol.? 
Kriiss and Giconomides examined (1883) solutions of indigo and its 
derivatives, with a view to decide whether the replacement of hydrogen 
by CH, C,.H;, NH., NO,, Br., &c., has a regular influence on the absorp- 
tion spectrum of the compound. Derivatives of fluorescein and _ rosolic 
acid were examined by Kriiss subsequently, with the result that the view 
previously put forward, namely, that the replacement of hydrogen in the 
benzene-ring or in the side chain. by alkyl or oxyalkyl radicals and bro- 
mine, caused a shifting of the absorption bands towards the less refrangible 
end of the spectrum, whilst the introduction of an NH, or NO, has the 
opposite effect. The shifting of the bands increases in proportion to the 
number of substituted hydrogen atoms, when the same elements or radi- 
cals are analogously introduced. 
In the case of alkyl radicals this also has been shown by Hartley and 
Huntington. Compare the plates of benzene, methyl-benzene, trimethyl- 
benzene, ethyl-benzene,? also pyridine and picoline (Hartley). It is par- 
ticularly to be noted in the case of the general absorption and in the more 
pronounced intensity of the bands, which,. however, do not, in the case of 
alkyl radicals, greatly alter throughout all dilutions in mere position, 
Ueber innere Molekularbewegung.4 By G. Kriss. 
On the basis of the velocity of light, taken as 299,000 kilometres per 
second, Kriiss calculated the oscillation frequencies in the principal absorp- 
1 Phil. Trams. 1879. 
* G. Kriiss, Ber. vol. xviii. 1426-1433; J. Chem. Soc, Abs. p, 949, 1885, 
3 Phil. Trans. 1879. 
4 Bar, vol. xviii, pp. 2686-21, 1885, 
