344 REPORT—1899. 
bands when methy] is substituted for the amido group in such substances 
as chryséidine. 
Grebe! examined azo-colouring matters dissolved in sulphuric acid. 
By addition of carbon the bands shifted towards the red, OH and NH, 
cause the same displacement. The position of the substitution seems to 
have a regular influence on the position of the bands, and the extent of the 
shifting is about 20 micro-millimetres nearer to the red with « compounds 
of the naphthalene molecule than with the derivatives. The sulphonic 
acid group, it is stated, produces a displacement in the opposite direction, 
which in amount approximates to 40 micro-millimetres. 
Liebermann ? examined the spectra of alkyl derivatives of oxyanthra- 
quinones dissolved in cold strong sulphuric acid. The wave-lengths of 
bands measured are as follows :— 
— I II Til 
A A rn 
Alizarin . ‘ 3 5 ‘ <i 605 493 — 
Alizarin ethyl ester. 3 : =| 598 487 — 
Anthraflavic acid ; : it 495 463 _ 
Dimethyl ester ; : , ; 5OL 473 437 very feeble 
Diethyl ester . ‘ : : ; 504 477 439 ‘ 
Quinizarin ‘ P : ’ k 551 509 483 feeble 
Ethyl ester . : : ; : 564 520 484 ,, 
Diethyl ester . 4 : : 3 577 535 Ag4 
Iso-anthraflavic acid 4 : , — 540 494 not sharp 
Diethyl ester . , : ‘ 5 — 505 492 not sharp 
Flavo-purpurin : ; : 5 533 495 — 
Diethyl ester . ‘ ; ; : 542 50L — 
Anthragallol . : ‘ ; ; 525 492 — 
Ethylester . 5 : : ; — 515 Not sharp 
Diethyl ester . : : : : — 515 Not sharp 
Rufigallic acid : : : : 576 532 — 
Triethyl ester . ; . : : 579 545 
In this particular series again the alkyl radicals cause a shifting of 
the absorption bands towards the red. The extent of the shifting appears 
to be different in the different bands, and differs in the various substances. 
Girard and Pabst * carefully examined the absorption spectra of diazo 
colours such as Biebrich scarlet, congo red, ponceau, and chrysoidine, and 
illustrated their paper by drawings. The conclusions drawn from their 
observations were that homologous compounds, or compounds which are 
closely related in constitution, give similar absorption spectra. 1885. 
In 1887 H. W. Vogel* also examined the same class of colouring 
matters, and drew the following conclusions : 
(1) The substitution of methyl for hydrogen in diazobenzene shifts 
the position of the absorption bands towards the red end of the spectrum. 
The increase of wave-lengths is 10 millionths of a millimetre where the 
substitution takes place in the ortho- position, and 14 millionths of a 
millimetre in the case of the para- positions. 
1 Ber. vol. xxvi. p. 130, R, 1893; and Zeitschrift fiir physikalische Chemie, 
vol. x. p. 673. 
? Ber. vol. xxi. p. 2527, 1887. 
3° Comptes Rendus, vol. ci. pp. 157-160. 
* Sitzungsberichte d. preuss. Akad, d. Wiss. xw Berlin, vol, xxxiv. pp. 715-718. 
