ion
of an amidic into a pyridine group. We may speak of the amido-group as
being "pyridised" in such processes. Thus alizarin blue, which is formed
by heating nitro-alizarin with glycerin and sulphuric acid, results from
the pyridisation of the nitro-group. By an analogous method Doebner and v.
Miller prepared a homologue of quinoline (quinaldine) in 1881, by the
action of sulphuric acid and a certain modification of aldehyde known as
paraldehyde on aniline.

Quinoline and its homologue quinaldine have been utilized as sources of
colouring-matters. A green dye-stuff, known as quinoline green, was
formerly made by the same method as that employed for producing the
phosgene colours by Caro and Kern's process (p. 106). The phthalein of
quinaldine was introduced by E. Jacobsen in 1882 under the name of
quinoline yellow, a colouring-matter which forms a soluble sulpho-acid by
the action of sulphuric acid.

To return to coal-tar pharmaceutical preparations. At the present time
seven distinct derivatives of quinoline, all formed by pyridising the
amido-group in aniline, amido-phenols, &c., are known in medicine under
such names as kairine, kairoline, thalline, and thermifugine. The mode of
preparation of these compounds cannot be entered into here, Kairine, the
first of the artificial alkaloids, is a derivative of hydroxy-quinoline,
which was discovered in 1881 by Otto Fischer. All these quinoline
derivatives have the property of lowering the temperature of the body in
certain kinds of fevers, and may therefore be considered as the first
artificial products coming into competition with the natural alkaloid,
quinine. There is reason for believing that the latter alkaloid, the most
valuable of all febrifuges, is related to the quinoline bases, so that if
its synthesis is accomplished--as may certainly be anticipated--we shall
have to look to coal-tar as a source of the raw materials.

Another valuable artificial alkaloid, discovered in 1883 by Ludwig Knorr,
claims aniline as a point of departure. When aniline and analogous bases
are diazotised, and the diazo-salts reduced in the cold with a very gentle
reducing agent, such as stannous chloride, there are formed certain basic
compounds, containing one atom of nitrogen and one atom of hydrogen more
than the original base. These bases were discovered in 1876 by Emil
Fischer, and they are known as hydrazines, the particular compound thus
obtained from aniline being phenylhydrazine