A Manual of the Chemistry of the Carbon Compounds

•153 TBS CHEMISTRY OF
Crude coal-gas contains hydrogen, marsh-gas, and other paraffins,
olefines, acetylene, vapour of benzene, and other volatile hydrocarbons,
carbon monoxide and dioxide, carbon disulphide, hydrogen
sulphide, &c.
The liquid products separate, on standing, into two layers. The
aqueous solution obtained from coal contains chiefly ammonia, whilst
that from wood contains methyl alcohol, acetic acid, and other fatty
acids, methyl acetate, dimethyl ketone, dimethylaoetal, &c.
The composition of the dark oily layer, or tar, is very varying and
complicated. The following bodies have been found in different kinds
of tar:—
(1.) Paraffins occur chiefly in tar which has been obtained from
bodies containing a relatively large quantity of hydrogen, such as
cannel and boghead-coal.
(2.) Olefines exist also principally in the same kinds of tar.
(3.) Hydrocarbon of the acetylene.series.
(4.) Benzene and methylated benzenes.
(6.) Naphthalene, acenaphthene, phenanthrene, anthracene, pyrene,
dbrysene, retena
(6.) Phenol, oread, and homologues.
Wood-tar contains also pyrocatechin and homologues, as well aa
their methyl-ethers (creosote).
(7.) Aniline, toluidine, and homologous bases.
(8.) Ficoline and leucoline-hases.
The formation of these different bodies is partly explained by the
following oleervations.
When a carbon-compound burns in a limited supply of air, there is
always some acetylene formed, and such an incomplete combustion
takes place ab tho beginning of the dry distillation. On exposing
acetylene to a dull-red heat it undergoes polymerization, and yields
benzene, styrolene, and other products, among which hydrogen and
naphthalene have been observed.
At a bright-red heat, acetylene is resolved into hydrogen and carbon,
but at the time some marsh-gas, ethene and naphthalene are
produced.
Acetylene and hydrogen combine at a dull-red heat with the formation
of ethane and ethene.
When benzene is exposed to a bright-Ted heat it yields dipheayl,
diphenyl-benzene, and other hydrocarbons.
Toluene produces, under the same conditions, marsh-gas, benzene,
naphthalene, anthracene, &e.
The xylenes and pseudocumene yield similar products, and the
different hydrocarbons thus formed undergo further transformations
by acting on each other at a high temperature.