about one-eighth is made in this country, the
remainder being manufactured on the Continent. The total production of
alizarin corresponds in money value to about L2,000,000 per annum. One
pound of dry alizarin has the tinctorial power of 90 pounds of madder.
Seeing therefore that the raw material anthracene was at one time a waste
product, and that the quantity of alizarin produced in the factory
corresponds to nearly five pounds of 20 per cent. paste for one pound of
anthracene, it is not surprising that the artificial has been enabled to
compete successfully with the natural product.

The industrial history of anthracene is thus summarized. (See opposite.)

Anthracene
|
Anthraquinone
|
| } Sulpho-acid (Alizarin carmine)
|->Monosulpho-acid-->Alizarin----------} Purpurin
| } Nitro-alizarin-->Alizarin blue
|->[Greek: a]-Disulpho-acid-->Flavopurpurin |
| |
|->[Greek: b]-Disulpho-acid-->Anthrapurpurin |
Alizarin green.

The black, viscid residue left in the tar-still after the removal of the
anthracene oil is the substance known familiarly as pitch. From the
latter, after removal of all the volatile constituents, there is prepared
asphalte, which is a solution of the pitchy residue in the heavy tar-oils
from which all the materials used in the colour industry have been
removed. Asphalte is used for varnish-making, in the construction of hard
pavements, and for other purposes. A considerable quantity of pitch is
used in an industry which originated in France in 1832, and which is
still carried out on a large scale in that country, and to a smaller
extent in this and other tar-producing countries. The industry in question
is the manufacture of fuel from coal-dust by moulding the latter in
suitable machines with pitch so as to form the cakes known as "briquettes"
or "patent fuel." By this means two waste materials are disposed of in a
useful way--the pitch and the finely-divided coal, which could not
conveniently be used as fuel by itself. From two to three million tons of
this artificial fuel are being made annually here and on the Continent.

The various constituents of coal-tar have now been made to tell their
story, so far as relates to the colouring-matter