In an article which appeared in this _Journal_ in August 1876, entitled
_The Age of the World_, we endeavoured to explain how coal was
produced, and how it might be regarded simply as stored-up heat and
light, derived from the sun ages ago.
Apart from the varied uses of coal in its ordinary state, we owe an
immense deal to the products which by chemical means we obtain from it;
and it is our purpose in this paper to briefly review these products,
and to shew how we have adapted them to our several wants.
The manufacture of gas is undoubtedly the most important feature in
the modern history of coal. Natural reservoirs of inflammable air
exist in many parts of the world, and have in many cases been turned
to profitable account. In China, for instance, the evaporation of
salt has for many years been carried on by the heat obtained by the
combustion of gas which issues from the ground. Streets and buildings
there have also been lighted by the same means. In our own country
too, such eruptions of natural gas—which have generally manifested
themselves during the operation of well-boring—have not been uncommon.
But the gas so obtained is not the same as that which we get from the
distillation of coal, although it forms one of its chief constituents.
It is commonly called marsh-gas, from its constant presence in bogs
and places where decaying vegetable matter abounds. The treacherous
Will o’ the Wisp owes its origin to this gas. It also issues in large
quantities from coal-beds, and diluted with air forms the dreadful
compound called ‘fire-damp.’
The first recorded experiment relating to the production of true
coal-gas was as early as the year 1660, when a country clergyman
distilled some coal, collected the gas in bladders, and burnt it from
a jet, for the amusement of his friends. Although this very suggestive
experiment was communicated to the Royal Society, no action seems to
have been taken upon it until the beginning of the present century,
when the matter seems to have attained a more practical form. At this
time one or two factories in Manchester and Birmingham were for the
first time lighted with gas. The idea of illuminating an entire town
by means of a chemical vapour seems to have met with much ridicule,
and it was found necessary to employ lecturers to go about the country
to shew people how such an apparent impossibility could be carried
out. However, in spite of much opposition, part of London was lighted
by gas in 1812; and three years later, Paris adopted the same system.
The delay in the acceptance of gas-making among the industrial arts
was no doubt largely due to the expressed opinion of several eminent
chemists and others, who considered that such a mode of lighting our
towns could never be realised, because of the supposed danger which it
involved. Modern experience teaches us that it is at once the cheapest
as well as the safest mode of illumination that we can as yet command.
In the manufacture of gas, the coal is placed in iron retorts, which
are subjected to a high temperature for about six hours, when the
operation is finished, and the retorts are ready for a fresh charge.
A residue of nearly pure carbon, in the form of coke, remains in the
retort, whilst the varied products of the distillation are carried off
by pipes into suitable receptacles. For the sake of convenience, we
will at present name only three of these products—ammoniacal liquor,
tar, and the gas itself. The first is the principal source of ammonia,
one of the most useful substances known. It may be almost said of
ammonia, as it has been remarked of sulphuric acid, that the prosperity
of a country may be known by the quantity which it consumes. It is used
by colour-makers, calico-printers, and in the manufacture of most of
the textile fabrics; in cleansing and extracting grease from various
kinds of cloth, in the preparation of leather, in galvanising iron, and
in pewtering. The chemist would be almost helpless without its aid;
whilst in medicine it is used in about twenty different forms as a
most valuable stimulant. It is almost needless to say that ammonia was
in general use long before the era of gas-manufacture, for life could
hardly go on without it. In fact its very name is derived from its
manufacture hundreds of years ago from animal refuse in a district of
Libya where the deity Jupiter Ammon was worshipped. The old alchemists
too obtained it from the distillation of deer’s horns; hence one
preparation of it is still called spirit of hartshorn. There are many
other sources of ammonia, for its presence in nature is universal; but
all have sunk into insignificance since the gas-works have yielded such
plentiful supplies.
Coal-tar in its crude state is not of very great importance, its use
being confined to such rough work as the water-proofing of boats and
the painting of outhouses and the like. But in the hands of the chemist
its applications cannot be lightly regarded, in fact its distillation
is of sufficient importance to form a distinct branch of trade. In this
process coal-tar is separated into three different products—naphtha
(which in a rectified state is the benzol of commerce); heavy or
creosote oil, which is used almost exclusively for the preservation of
railway sleepers; and the residue pitch. The last is of great use to
shipbuilders, and has more recently found employment in the preparation
of asphalt roofing and paving. But naphtha is by far the most important
of the three substances, if it were only for its use as a solvent for
both india-rubber and gutta-percha. No doubt, failing this, other
solvents for caoutchouc would have been found; but naphtha is a
particularly cheap and effective menstruum for the purpose; and when we
consider the varied uses to which india-rubber and gutta-percha are now
applied—from elastic hosiery to submarine cables—we must acknowledge
that naphtha is a valuable addition to our manufacturing resources.
It is a significant circumstance that the date of the introduction
of manufactured india-rubber (by Mr Mackintosh) follows the general
adoption of gas-lighting by only a few years. Previous to this,
india-rubber was imported merely as a curiosity, its first use being to
obliterate pencil-marks, for which purpose it was once advertised in
London at the modest price of six shillings per square inch.
Besides its use as a solvent, benzol is of particular importance in
yielding, when treated with nitric acid, a substance called aniline.
The discovery of aniline is one of the most remarkable triumphs of
chemistry, as applied to the advancement of a manufacturing industry.
(Before the date of coal-tar it was obtained from indigo, and the
name it bears is the Portuguese for that colour.) The production of
aniline caused quite a revolution in the various trades which are
dependent in any way upon the colour-manufacturer; for lithographers,
paper-stainers, calico-printers, and especially dyers, owe their most
brilliant tints to its aid. The various dyes which are now commonly
retailed for household use are also derived from the same source.
Aniline is an almost colourless liquid, of a peculiar vinous odour,
which after exposure to the air, changes to a dark resinous matter.
The treatment which it undergoes in producing the various colours (and
nearly every colour of the rainbow can now be obtained from it), is of
too complicated a nature to be of any interest to the general reader.
Magenta, the advent of which some years back many of our readers
will remember, was the first aniline dye which appeared. The other
colours have followed in quick succession, nearly all of them being
the subjects of one or more patents. It is questionable whether all
these colours are strictly permanent; but it is a pleasing thought that
the hues which in one form or another existed at a period long before
mankind had a place in nature, are now reproduced for man’s delight and
benefit.
Another very important product of gas-tar is carbolic acid, which is
also largely employed for dyeing purposes. Its value as a disinfectant
is too well known to need recapitulation here; but we may mention
that its use as a preventive of disease was most abundantly proved
during the last epidemic among our cattle. It is in general use in
our hospitals, not only as a disinfectant, but also as an antiseptic
both in the dressing of wounds and in the treatment of various skin
diseases. Carbolic acid also yields a substance called picric acid,
which, on account of its explosive properties when combined with
potassium, has been proposed as a substitute for gunpowder. There are
many other substances derived from the distillation of coal-tar, but at
present they are only of interest to the experimental chemist.
A ton of coals will produce a chaldron of coke, twelve gallons of tar,
ten gallons of ammoniacal liquor, and nearly ten thousand feet of gas.
A consideration of these figures, with a due regard to what we have
said as to the value of the various chemical products obtained by
distillation, will enable our readers to understand why gas companies
can shew such good balance-sheets. Much has been written as to the
possible exhaustion, after one or two centuries, of the British
coal-fields. This is a question upon which it is next to impossible
to form any reliable opinion. Should the coal-supply actually fail,
it is more than probable that as science is extended, a new source of
light and heat may be developed. A cheap and ready means of producing
electricity, as we have in a former article endeavoured to shew, would
at once solve the problem, and it is within the bounds of reason that
to this agency the future races of the earth will look for the two most
common necessaries of existence.