e, and which is
related to quinoline in the same way that anthracene is related to
naphthalene. The three hydrocarbons are comparable with the three bases,
which may be regarded as derived from them in the same manner that
pyridine is derived from benzene--

Benzene ... ... ... Pyridine
Naphthalene ... ... Quinoline
Anthracene ... ... ... Acridine

Some of these bases and their homologues are found in the evil-smelling
oil produced by the destructive distillation of bones (Dippel's oil, or
bone oil), and the group is frequently spoken of as the pyridine group.
The colouring-matter described as phosphine, obtained as a by-product in
the manufacture of magenta (p. 94), is a derivative of acridine, and a
yellow colouring-matter discovered by Rudolph in 1881, and obtained by
heating the acetyl derivative of aniline with zinc chloride, is a
derivative of a homologue of quinoline. This dye-stuff, known as
"flavaniline," is no longer made; but it is interesting as having led to
the discovery of the constitution of phosphine by O. Fischer and Koerner in
1884.

The antipyretic medicines which we have first to consider are derivatives
of quinoline. This base was discovered in coal-tar by Runge in 1834, and
was obtained by Gerhardt in 1842 by distilling cinchonine, one of the
cinchona alkaloids, with alkali. Now it is of interest to note that the
quinoline of coal-tar is of no more use to the technologist than the
aniline; these bases are not contained in the tar in sufficient quantity
to enable them to be separated and purified with economical advantage. If
the colour industry had to depend upon this source of aniline only, its
development would have been impossible. But as chemistry enabled the
manufacturer to obtain aniline in quantity from benzene, so science has
placed quinoline at his disposal. This important discovery was made in
1880 by the Dutch chemist Skraup, who found that by heating aniline with
sulphuric acid and glycerin in the presence of nitrobenzene, quinoline is
produced. The nitrobenzene acts only as an oxidizing agent; the
amido-group of the aniline is converted into a group containing carbon,
hydrogen, and nitrogen, _i.e._ the pyridine group. The discovery of
Skraup's method formed the starting-point of a series of syntheses, which
resulted in the formation of many products of technical value. In all
these syntheses the fundamental change is the same, viz. the convers