n made in the chemical knowledge of the carbon,
hydrogen, and oxygen compounds. Scientists appeared to work along two
planes; there were those who discovered certain chemical compounds in the
resulting products of reactions in the treatment of _existing_
vegetation, and there were those who, studying the wonderful constituents
in coal-tar, the product of a _past_ age, immediately set to work to find
therein those compounds which their contemporaries had already
discovered. Generally, too, with signal success.

The discovery of benzene in 1825 by Faraday was followed in the course of
a few years by its discovery in coal-tar by Hofmann. Toluene, which was
discovered in 1837 by Pelletier, was recognised in the fractional
distillation of crude naphtha by Mansfield in 1848. Although the method
of production of mauveine on a large scale was not accomplished until
1856, yet it had been noticed in 1834, the actual year of its recognition
as a constituent of coal-tar, that, when brought into contact with
chloride of lime, it gave brilliant colours, but it required a
considerable cheapening of the process of aniline manufacture before the
dyes commenced to enter into competition with the old natural dyes.

The isolation of aniline from coal-tar is expensive, in consequence of
the small quantities in which it is there found, but it was discovered by
Mitscherlich that by acting upon benzene, one of the early distillates of
coal-tar, for the production of nitro-benzole, a compound was produced
from which aniline could be obtained in large quantities. There were thus
two methods of obtaining aniline from tar, the experimental and the
practical.

In producing nitrobenzole (nitrobenzene), chemically represented as
(C_{6}H_{5}NO_{2}), the nitric acid used as the reagent with benzene, is
mixed with a quantity of sulphuric acid, with the object of absorbing
water which is formed during the reaction, as this would tend to dilute
the efficiency of the nitric acid. The proportions are 100 parts of
purified benzene, with a mixture of 115 parts of concentrated nitric acid
(HNO_{3}) and 160 parts of concentrated sulphuric acid. The mixture is
gradually introduced into the large cast-iron cylinder into which the
benzene has been poured. The outside of the cylinder is supplied with an
arrangement by which fine jets of water can be made to play upon it in
the early stages of the reaction which follows, and at the end of from
eight to ten hours t