t this naphtha contained. But science soon laid hands on the
materials furnished by the tar-distiller, and the naphtha was one of the
first products which was made to reveal the secret of its hidden treasures
to the scientific investigator. From this period science and industry
became indissolubly united, and the researches of chemists were carried
on hand-in-hand with the technical developments of coal-tar products.

[Illustration: FIG. 4.--Read Holliday's lamp for burning light coal-tar
oils. The oil is contained in the cistern _c_, from whence it flows down
the pipe, when the stopcock is opened, into the burner _a_. Below the
burner is a little cup, in which some of the oil is kept burning, and the
heat from this flame volatilizes the oil as it flows down the pipe, the
vapour thus generated issuing from the jets in the burner and there
undergoing ignition. The burner and cup are shown on an enlarged scale at
_a_ in the lower figure.]

In 1825 Michael Faraday discovered a hydrocarbon in the oil produced by
the condensation of "oil gas"--an illuminating gas obtained by the
destructive distillation of oleaginous materials. This hydrocarbon was
analysed by its illustrious discoverer, and named in accordance with his
results "bicarburet of hydrogen." In 1834 the same hydrocarbon was
obtained by Mitscherlich by heating benzoic acid with lime, and by Peligot
by the dry distillation of calcium benzoate. For this reason the compound
was named "benzin" by Mitscherlich, which name was changed into "benzol"
by Liebig. In this country the hydrocarbon is known at the present time as
benzene. Twenty years after Faraday's discovery, viz. in 1845, Hofmann
proved the existence of benzene in the light oils from coal-tar, and in
1848 Hofmann's pupil, Mansfield, isolated considerable quantities of this
hydrocarbon from the said light oils by fractional distillation. At the
time of these investigations no great demand for benzene existed, but the
work of Hofmann and Mansfield prepared the way for its manufacture on a
large scale, when, a few years later, the first coal-tar colouring-matter
was discovered by our countryman, W. H. Perkin.

It is always of interest to trace the influence of scientific discovery
upon different branches of industry. As soon as it had been shown that
benzene could be obtained from coal-tar, the nitro-derivative of this
hydrocarbon--_i.e._ the oily compound produced by the action of nitric
acid upon benzene