oluble /
| Diph. Blue /
| /
------------------------------------------------ /
| | | /
Crystal Violet, Methyl Violet | /
Auramine, & and Green Malachite
other Phosgene dyes Green series

From benzene and toluene alone about forty distinct colouring-matters of
the rosaniline group are sent into commerce. The relationship of those
compounds to each other and to their generating substances is not easy to
grasp by those to whom the facts are presented for the first time. The
scheme on page 107 shows these relationships at a glance.

The colouring-matters derived from these two hydrocarbons are far from
being exhausted. During the oxidation of aniline for the production of
mauve--which colouring-matter, it may be mentioned, is no longer made--a
red compound is formed as a by-product. This was isolated by Perkin in
1861, and studied scientifically by Hofmann and Geyger, who established
its composition in 1872, the dye being at that time manufactured under the
name of "saffranine." It appears to have been first introduced about 1868.
The conditions of formation of this dye were at first imperfectly
understood, but the problem was attacked by chemists and technologists,
and the first point of importance resulting from their work was that
saffranine was derived from one of the toluidines present in the
commercial aniline. To record the various steps in this chapter of
industrial chemistry would take us beyond the scope of the present work.
In addition to the chemists named, Caro, Bindschedler, and others
contributed to the technology, while the scientific side of the matter was
first taken up by Nietzki in 1877, by Otto Witt in 1878, and by Bernthsen
in 1886. It is to the work of these chemists, and especially to that of
Witt, that we owe our present knowledge of the constitution of this and
allied colouring-matters. Space will not admit of our traversing the
ground, although to chemists it is a line of investigation full of
interest; it will be sufficient to say that by 1886 these investigators
had accomplished for these colouring-matters what the Fischers had done
for the rosaniline group--they established their constitution, and showed
that they were