twenty years after, viz., in 1885, this
had increased to no less than 159 millions, such were the giant strides
which the increase in consumption made.

In the return for 1892, this amount had farther increased to 181-1/2
millions of tons, an advance in eight years of a quantity more than equal
to the total raised in 1820, and in 1894 the total reached
199-1/2 millions; this was produced by 795,240 persons, employed in and
about the mines.

CHAPTER VIII.

THE COAL-TAR COLOURS.

In a former chapter some slight reference has been made to those
bye-products of coal-tar which have proved so valuable in the production
of the aniline dyes. It is thought that the subject is of so interesting
a nature as to deserve more notice than it was possible to bestow upon it
in that place. With abstruse chemical formulae and complex chemical
equations it is proposed to have as little as possible to do, but even
the most unscientific treatment of the subject must occasionally
necessitate a scientific method of elucidation.

The dyeing industry has been radically changed during the last half
century by the introduction of what are known as the _artificial_ dyes,
whilst the _natural_ colouring matters which had previously been the sole
basis of the industry, and which had been obtained by very simple
chemical methods from some of the constituents of the animal kingdom, or
which were found in a natural state in the vegetable kingdom, have very
largely given place to those which have been obtained from coal-tar, a
product of the mineralised vegetation of the carboniferous age.

The development and discovery of the aniline colouring matters were not,
of course, possible until after the extensive adoption of
house-gas for illuminating purposes, and even then it was many years
before the waste products from the gas-works came to have an appreciable
value of their own. This, however, came with the increased utilitarianism
of the commerce of the present century, but although aniline was first
discovered in 1826 by Unverdorben, in the materials produced by the dry
distillation of indigo (Portuguese, _anil_, indigo), it was not until
thirty years afterwards, namely, in 1856, that the discovery of the
method of manufacture of the first aniline dye, mauveine, was announced,
the discovery being due to the persistent efforts of Perkin, to whom,
together with other chemists working in the same field, is due the great
advance which has bee