gher homologues of phenol with various hydrocarbons and
basic compounds. It is the oil used for creosoting timber in the manner
already described; and among its other applications may be mentioned its
use as an illuminating agent and as a source of lampblack. In order to
burn the oil effectively as a source of light, a specially-constructed
burner is used, which is fed by a stream of oil raised from a reservoir at
its foot by means of compressed air, which also aids the combustion of the
oil. There is produced by this means a great body of lurid flame, which
is very serviceable where building or other operations have to be carried
on at night (see Fig. 10). For lampblack the oil is simply burnt in iron
pans set in ovens, and the sooty smoke conducted into condensing chambers.
The creosote oil constitutes more than 30 per cent. by weight of the
tar--the time may come when this fraction, like the light oil and carbolic
oil, may be found to contain compounds of value to the colour-maker or to
other branches of chemical manufacture.

[Illustration: FIG. 10.--VERTICAL BURNER FOR HEAVY COAL OIL BY THE LUCIGEN
LIGHT CO.]

[Illustration: FIG. 11.--THE MADDER PLANT (_Rubia tinctoria_).]

The utilization of the next fraction, anthracene oil, is one of the
greatest triumphs which applied chemical science can lay claim to since
the foundation of the coal-tar colour industry. This discovery dates from
1868, when it was shown by two German chemists, Graebe and Liebermann,
that the colouring-matter of madder was derived from the hydrocarbon
anthracene. Like indigo, madder may be regarded as one of the most ancient
of natural dye-stuffs. It consists of the powdered roots of certain plants
of the genus _Rubia_, such as _R. tinctoria_ (see Fig. 11), _R.
peregrina_, and _R. munjista_, which were at one time cultivated on an
enormous scale in various parts of Europe and Asia. It is estimated that
at the time of Graebe and Liebermann's discovery, 70,000 tons of madder
were produced annually in the madder-growing countries of the world. At
that time we were importing madder into this country at the rate of 15,000
to 16,000 tons per annum, at a cost of L50 per ton. In ten years the
importation had fallen to about 1600 tons, and the price to L18 per ton.
At the present time the cultivation of madder is practically extinct.

There is no better gauge of the practical utility of a scientific
discovery than the financial effect. In addition