ABSORPTION SPECTRA AND CHEMICAL CONSTITUTION, 349 
Rays are then transmitted to near N, or !/d 2780, after which there is but 
little absorption with ;},th of a molecule, and that lies at about !/\ 3900. 
Chrysoidine hydrochloride, C,H; * N : N -C;H,(NH,),, 2HCi. 
Comparing chrysoidine with azobenzene the rate of the vibrations is 
much reduced, and their amplitude is increased. There is, with ,1,th of a 
molecule, complete absorption beyond '/A 1800 ; what appears below this 
point is an absorption band, apparently the principal band of azobenzene 
modified by being extended from !/A 1800 to !/A 2890, or near O, but 
with ,},th of a molecule all absorption practically ceases. 
The absorption of the following azobenzene and azonaphthalene deri- 
vatives has also been examined :— 
Bismarck Brown, ; 
NH,° C,H,’ N: N : C,;H;(NH,),. 
Tropeolin O., 
NaSO;°C,H,:N : N:C,H;(OH),. 
Helianthin, 
HSO;:C,H,:N:N-+C,H,:-N(CH;).. 
Benzene-azo-(-naphtholdisulphonie acid, 
C,H;:N:N-C,,.H,(HSO,), : OH,. 
Sulpho-xylene-azo-[3-naphtholdisulphonic acid, 
HSO; -C,H,:N: N-+C,,H,(HSO;), :-OH,. 
Cumene-azo-3-naphtholdisulphonic acid, 
C,H,,°N : N:C,,H,(HSO;),: OH,. 
Phenyl-azo-phenyl-B-naphtholsulphonic acid (Croceine Scarlet), 
C,H;:N:N-C,H,:-N: N -C,)H,;(HSO;) -OH,. 
Biebrich Scarlet, 
NaSO; -C,H,:N : N'C;H,(NaSO;):N : N-C,,)H, * OH,. 
In these substances the amplitude of the vibrations is virtually the 
same as in chrysoidine, and the character of their curves is similar, though 
no two are alike. These substances are very varied as regards the hydro- 
carbon radicals from which they are derived. It follows, therefore, that 
the nitrogen is largely concerned in the development of the colours, and 
that the hydrocarbon radicals are of comparatively small importance so 
long as they are benzenoid in character. 
Sodium a-naphthol-azophenylsulphonate, 
OH, -C,,H,:N:N ‘C,H, ‘SO;Na. 
(Tropzolin 000 No. 1). 
Sodium (-naphthol-azo-phenylsulphonate, 
OH, -C,,H,:N: N-C,H,:°SO,Na. 
(Tropzolin 000 No. 2). 
Although these two bodies are isomeric, and only differ in that the first 
