as formed. This is now manufactured under the name of "new blue," or
other designations, and is largely used for producing an indigo-blue shade
on cotton prepared with a suitable mordant. The discovery of this
colouring-matter gave an impetus to further discoveries in the same
direction. It was found that nitrosodimethylaniline reacted in a similar
way with other phenolic or with amidic compounds. In 1881 Koechlin
introduced an analogous dye-stuff prepared by the action of the same
nitroso-compound on gallic acid. Gallocyanin, as it is called, imparts a
violet blue shade to mordanted cotton. Other colouring-matters of the same
group are in use; some of them, like "new blue," being derivatives of
naphthalene. These compounds all belong to a series of which the parent
substance is constructed on a type similar to azine; it contains a
nitrogen and oxygen atom linking together the hydrocarbon residues, and is
therefore known as "oxazine." The researches of Nietzki in 1888 first
established the true constitution of the oxazines.

Closely related to this group is a colouring-matter introduced by Koechlin
and Witt in 1881 under the name of "indophenol." It is prepared in the
same way as the azines of the "neutral red" group; viz. by the action of
nitrosodimethylaniline on alpha-naphthol, or by oxidizing
amidodimethylaniline in the presence of alpha-naphthol. Indophenol belongs
to that group of blue compounds formed as intermediate products in the
manufacture of azines, as mentioned in connection with "neutral red." But
while these intermediate blues resulting from the oxidation of a diamine
in the presence of another amine are unstable, and pass readily into red
azines, indophenol is stable, and can be used for dyeing and printing in
the same way as indigo. The shades which it produces are very similar to
this last dye, but for certain practical reasons it has not been able to
compete with the natural dye-stuff.

The story of naphthalene is summarized in the schemes on pp. 164, 165.

Light Oil:

Benzene->Disulpho-acid-->Resorcinol.[6]
\
\-->Nitrobenzene} } Sulphanilic acid.[7]
} Aniline} Amidoazobenzene and sulpho-acid.[7]
} } Nitrosodimethylaniline[8] and
} } amidodimethylaniline.[8]
} Sulpho-acid-->Amidosulpho-acid-->Amidophenol
} and et