Book: The Story of a Piece of Coal

E >> Edward A. Martin >> The Story of a Piece of Coal




The smoke nuisance is one which cuts at the very basis of our business
life. The cloud which, under certain atmospheric conditions, rests like a
pall over our great cities, will not even permit at times of a single ray
of sunshine permeating it. No one knows whence it rises, nor at what hour
to expect it. It is like a giant spectre which, having lain dormant since
the carboniferous age, has been raised into life and being at the call of
restless humanity; it is now punishing us for our prodigal use of the
wealth it left us, by clasping us in its deadly arms, cutting off our
brilliant sunshine, and necessitating the use in the daytime of
artificial light; inducing all kinds of bronchial and throat affections,
corroding telegraph and telephone wires, and weathering away the masonry
of public buildings.

The immense value to us of the coal-deposits which lie buried in such
profusion in the earth beneath us, can only be appreciated when we
consider the many uses to which coal has been put. We must remember, as
we watch the ever-extending railway ramifying the country in every
direction, that the first railway and the first locomotive ever built,
were those which were brought into being in 1814 by George Stephenson,
for the purpose of the carriage of coals from the Killingworth Colliery.
To the importance of coal in our manufactures, therefore, we owe the
subsequent development of steam locomotive power as the means of the
introduction of passenger traffic, and by the use of coal we are enabled
to travel from one end of the country to the other in a space of time
inconceivably small as compared with that occupied on the same journey in
the old coaching days. The increased rapidity with which our vessels
cross the wide ocean we owe to the use of coal; our mines are carried to
greater depths owing to the power our pumping-engines obtain from coal in
clearing the mines of water and in ensuring ventilation; the enormous
development of the iron trade only became possible with the increased
blast power obtained from the consumption of coal, and the very hulls and
engines of our steamships are made of this iron; our railroads and
engines are mostly of iron, and when we think of the extensive use of
iron utensils in every walk in life, we see how important becomes the
power we possess of obtaining the necessary fuel to feed the smelting
furnaces. Evaporation by the sun was at one time the sole means of
obtaining salt from seawater; now coal is used to boil the salt pans and
to purify the brine from the salt-mines in the triassic strata of
Cheshire. The extent to which gas is used for illuminating purposes
reminds us of another important product obtained from coal. Paraffin oil
and petroleum we obtain from coal, whilst candles, oils, dyes,
lubricants, and many other useful articles go to attest the importance of
the underground stores of that mineral which has well and deservedly been
termed the "black diamond."




CHAPTER VI.

HOW GAS IS MADE--ILLUMINATING OILS AND BYE-PRODUCTS.


Accustomed as we are at the present day to see street after street of
well-lighted thoroughfares, brilliantly illuminated by gas-lamps
maintained by public authority, we can scarcely appreciate the fact that
the use of gas is, comparatively speaking, of but recent growth, and
that, like the use of coal itself, it has not yet existed a century in
public favour. Valuable as coal is in very many different ways, perhaps
next in value to its actual use as fuel, ranks the use of the immediate
product of its distillation--viz., gas; and although gas is in some
respects waning before the march of the electric light in our day, yet,
even as gas at no time has altogether superseded old-fashioned oil, so we
need not anticipate a time when gas in turn will be likely to be
superseded by the electric light, there being many uses to which the one
may be put, to which the latter would be altogether inapplicable; for, in
the words of Dr Siemens, assuming the cost of electric light to be
practically the same as gas, the preference for one or other would in
each application be decided upon grounds of relative convenience, but
gas-lighting would hold its own as the poor man's friend. Gas is an
institution of the utmost value to the artisan; it requires hardly any
attention, is supplied upon regulated terms, and gives, with what should
be a cheerful light, a genial warmth, which often saves the lighting of a
fire.

The revolution which gas has made in the appearance of the streets, where
formerly the only illumination was that provided by each householder,
who, according to his means, hung out a more or less efficient lantern,
and consequently a more or less smoky one, cannot fail also to have
brought about a revolution in the social aspects of the streets, and
therefore is worthy to be ranked as a social reforming agent; and some
slight knowledge of the process of its manufacture, such as it is here
proposed to give, should be in the possession of every educated
individual. Yet the subjects which must be dealt with in this chapter are
so numerous and of such general interest, that we shall be unable to
enter more than superficially into any one part of the whole, but shall
strive to give a clear and comprehensive view, which shall satisfy the
inquirer who is not a specialist.

The credit of the first attempt at utilising the gaseous product of coal
for illumination appears to be due to Murdock, an engineer at Redruth,
who, in 1792, introduced it into his house and offices, and who, ten
years afterwards, as the result of numerous experiments which he made
with a view to its utilisation, made a public display at Birmingham on
the occasion of the Peace of Amiens, in 1802.

More than a century before, however, the gas obtained from coal had been
experimented upon by a Dr Clayton, who, about 1690, conceived the idea of
heating coal until its gaseous constituents were forced out of it. He
described how he obtained steam first of all, then a black oil, and
finally a "spirit," as our ancestors were wont to term the gas. This, to
his surprise, ignited on a light being applied to it, and he considerably
amused his friends with the wonders of this inflammatory spirit. For a
century afterwards it remained in its early condition, a chemical wonder,
a thing to be amused with; but it required the true genius and energy of
Murdock to show the great things of which it was capable.

London received its first instalment of gas in 1807, and during the next
few years its use became more and more extended, houses and streets
rapidly receiving supplies in quick succession. It was not, however, till
about the year 1820 that its use throughout the country became at all
general, St James' Park being gas-lit in the succeeding year. This is not
yet eighty years ago, and amongst the many wonderful things which have
sprung up during the present century, perhaps we may place in the
foremost rank for actual utility, the gas extracted from coal, conveyed
as it is through miles upon miles of underground pipes into the very
homes of the people, and constituting now almost as much a necessity of a
comfortable existence as water itself.

The use of gas thus rapidly extended for illuminating purposes, and to a
very great extent superseded the old-fashioned means of illumination.

[Illustration: FIG. 34.--Inside a Gas-Holder.]

The gas companies which sprang up were not slow to notice that, seeing
the gas was supplied by meter, it was to their pecuniary advantage "to
give merely the prescribed illuminating power, and to discourage the
invention of economical burners, in order that the consumption might
reach a maximum. The application of gas for heating purposes had not been
encouraged, and was still made difficult in consequence of the
objectionable practice of reducing the pressure in the mains during
daytime to the lowest possible point consistent with prevention of
atmospheric indraught."

The introduction of an important rival into the field in the shape of the
electric light has now given a powerful impetus to the invention and
introduction of effective gas-lamps, and amongst inventors of recent
years no name is, perhaps, in this respect so well known as the name of
Sugg. As long as gas retained almost the monopoly, there was no incentive
to the gas companies to produce an effective light cheaply; but now that
the question of the relative cheapness of gas and electricity is being
actively discussed, the gas companies, true to the instinct of
self-preservation, seem determined to show what can be done when gas is
consumed in a scientific manner.

In order to understand how best a burner should be constructed in order
that the gas that is burnt should give the greatest possible amount of
illumination, let us consider for a moment the composition of the gas
flame. It consists of three parts, (1) an interior dark space, in which
the elements of the gas are in an unconsumed state; (2) an inner ring
around the former, whence the greatest amount of light is obtained, and
in which are numerous particles of carbon at a white heat, each awaiting
a supply of oxygen in order to bring about combustion; and (3) an outer
ring of blue flame in which complete combustion has taken place, and from
which the largest amount of heat is evolved.

The second of these portions of the flame corresponds with the "reducing"
flame of the blow-pipe, since this part, if turned upon an oxide, will
reduce it, i.e., abstract its oxygen from it. This part also corresponds
with the jet of the Bunsen burner, when the holes are closed by which
otherwise air would mingle with the gas, or with the flame from a
gas-stove when the gas ignites beneath the proper igniting-jets, and
which gives consequently a white or yellow flame.

The third portion, on the other hand, corresponds with the "oxidising"
flame of the blow-pipe, since it gives up oxygen to bodies that are
thirsting for it. This also corresponds with the ordinary blue flame of
the Bunsen burner, and with the blue flame of gas-stoves where heat, and
not light, is required, the blue flame in both cases being caused by the
admixture of air with the gas.

Thus, in order that gas may give the best illumination, we must increase
the yellow or white space of carbon particles at a white heat, and a
burner that will do this, and at the same time hold the balance so that
unconsumed particles of carbon shall not escape in the way of smoke, will
give the most successful illuminating results. With this end in view the
addition of albo-carbon to a bulb in the gas-pipe has proved very
successful, and the incandescent gas-jet is constructed on exactly the
same chemical principle. The invention of burners which brought about
this desirable end has doubtless not been without effect in acting as a
powerful obstacle to the widespread introduction of the electric light.

Without entering into details of the manufacture of gas, it will be as
well just to glance at the principal parts of the apparatus used.

The gasometer, as it has erroneously been called, is a familiar object to
most people, not only to sight but unfortunately also to the organs of
smell. It is in reality of course only the gas-holder, in which the final
product of distillation of the coal is stored, and from which the gas
immediately passes into the distributing mains.

The first, and perhaps, most important portion of the apparatus used in
gas-making is the series of _retorts_ into which the coal is placed, and
from which, by the application of heat, the various volatile products
distil over. These retorts are huge cast-iron vessels, encased in strong
brick-work, usually five in a group, and beneath which a large furnace is
kept going until the process is complete. Each retort has an iron exit
pipe affixed to it, through which the gases generated by the furnace are
carried off. The exit pipes all empty themselves into what is known as
the _hydraulic main_, a long horizontal cylinder, and in this the gas
begins to deposit a portion of its impurities. The immediate products of
distillation are, after steam and air, gas, tar, ammoniacal liquor,
sulphur in various forms, and coke, the last being left behind in the
retort. In the hydraulic main some of the tar and ammoniacal liquor
already begin to be deposited. The gas passes on to the _condenser_,
which consists of a number of U-shaped pipes. Here the impurities are
still further condensed out, and are collected in the _tar-pit_ whilst
the gas proceeds, still further lightened of its impurities. It may be
mentioned that the temperature of the gas in the condenser is reduced to
about 60 deg. F., but below this some of the most valuable of the illuminants
of coal-gas would commence to be deposited in liquid form, and care has
to be taken to prevent a greater lowering of temperature. A mechanical
contrivance known as the _exhauster_ is next used, by which the gas is,
amongst other things, helped forward in its onward movement through the
apparatus. The gas then passes to the _washers_ or _scrubbers_, a series
of tall towers, from which water is allowed to fall as a fine spray, and
by means of which large quantities of ammonia, sulphuretted hydrogen,
carbonic acid and oxide, and cyanogen compounds, are removed. In the
scrubber the water used in keeping the coke, with which it is filled,
damp, absorbs these compounds, and the union of the ammonia with certain
of them takes place, resulting in the formation of carbonate of ammonia
(smelling salts), sulphide and sulphocyanide of ammonia.

[Illustration: FIG. 35.--Filling Retorts by Machinery.]

[Illustration: FIG. 36.--CONDENSERS.]

Hitherto the purification of the gas has been brought about by mechanical
means, but the gas now enters the "_purifier_," in which it undergoes a
further cleansing, but this time by chemical means.

[Illustration: FIG. 37.]

The agent used is either lime or hydrated oxide of iron, and by their
means the gas is robbed of its carbonic acid and the greater part of its
sulphur compounds. The process is then considered complete, and the gas
passes on into the water chamber over which the gas-holder is reared, and
in which it rises through the water, forcing the huge cylinder upward
according to the pressure it exerts.

The gas-holder is poised between a number of upright pillars by a series
of chains and pulleys, which allow of its easy ascent or descent
according as the supply is greater or less than that drawn from it by the
gas mains.

[Illustration: FIG. 38.]

When we see the process which is necessary in order to obtain pure gas,
we begin to appreciate to what an extent the atmosphere is fouled when
many of the products of distillation, which, as far as the production of
gas is concerned, may be called impurities, are allowed to escape free
without let or hindrance. In these days of strict sanitary inspection it
seems strange that the air in the neighbourhood of gas-works is still
allowed to become contaminated by the escape of impure compounds from the
various portions of the gas-making apparatus. Go where one may, the
presence of these compounds is at once apparent to the nostrils within a
none too limited area around them, and yet their deleterious effects can
be almost reduced to a minimum by the use of proper purifying agents, and
by a scientific oversight of the whole apparatus. It certainly behoves
all sanitary authorities to look well after any gas-works situated within
their districts.

Now let us see what these first five products of distillation actually
are.

Firstly, house-gas. Everybody knows what house-gas is. It cannot,
however, be stated to be any one gas in particular, since it is a
mechanical mixture of at least three different gases, and often contains
small quantities of others.

A very large proportion consists of what is known as marsh-gas, or light
carburetted hydrogen. This occurs occluded or locked up in the pores of
the coal, and often oozes out into the galleries of coal-mines, where it
is known as firedamp (German _dampf_, vapour). It is disengaged wherever
vegetable matter has fallen and has become decayed. If it were thence
collected, together with an admixture of ten times its volume of air, a
miniature coal-mine explosion could be produced by the introduction of a
match into the mixture. Alone, however, it burns with a feebly luminous
flame, although to its presence our house-gas owes a great portion of its
heating power. Marsh-gas is the first of the series of hydro-carbons
known chemically as the _paraffins_, and is an extremely light substance,
being little more than half the weight of an equal bulk of air. It is
composed of four atoms of hydrogen to one of carbon (CH_{4}).

Marsh-gas, together with hydrogen and the monoxide of carbon, the last of
which burns with the dull blue flame often seen at the surface of fires,
particularly coke and charcoal fires, form about 87 per cent. of the
whole volume of house-gas, and are none of them anything but poor
illuminants.

The illuminating power of house-gas depends on the presence therein of
olefiant gas (_ethylene_), or, as it is sometimes termed, heavy
carburetted hydrogen. This is the first of the series of hydro-carbons
known as the _olefines_, and is composed of two atoms of carbon to every
four atoms of hydrogen (C_{2}H_{4}). Others of the olefines are present
in minute quantities. These assist in increasing the illuminosity, which
is sometimes greatly enhanced, too, by the presence of a small quantity
of benzene vapour. These illuminants, however, constitute but about 6 per
cent. of the whole.

Added to these, there are four other usual constituents which in no way
increase the value of gas, but which rather detract from it. They are
consequently as far as possible removed as impurities in the process of
gas-making. These are nitrogen, carbonic acid gas, and the destructive
sulphur compounds, sulphuretted hydrogen and carbon bisulphide vapour. It
is to the last two to which are to be attributed the injurious effects
which the burning of gas has upon pictures, books, and also the
tarnishing which metal fittings suffer where gas is burnt, since they
give rise to the formation of oil of vitriol (sulphuric acid), which is
being incessantly poured into the air. Of course the amount so given off
is little as compared with that which escapes from a coal fire, but,
fortunately for the inmates of the room, in this case the greater
quantity goes up the chimney; this, however, is but a method of
postponing the evil day, until the atmosphere becomes so laden with
impurities that what proceeds at first up the chimney will finally again
make its way back through the doors and windows. A recent official report
tells us that, in the town, of St Helen's alone, sufficient sulphur
escapes annually into the atmosphere to finally produce 110,580 tons of
sulphuric acid, and a computation has been made that every square mile of
land in London is deluged annually with 180 tons of the same
vegetation-denuding acid. It is a matter for wonder that any green thing
continues to exist in such places at all.

The chief constituents of coal-gas are, therefore, briefly as
follows:--

/ (1) Hydrogen,
| (2) Marsh-gas (carburetted hydrogen or fire-damp),
| (3) Carbon monoxide,
| (4) Olefiant gas (ethylene, or heavy carburetted hydrogen), with
\ other olefines,
/ (5) Nitrogen,
| (6) Carbonic acid gas,
| (7) Sulphuretted hydrogen,
\ (8) Carbon bisulphide (vapour),

the last four being regarded as impurities, which are removed as far as
possible in the manufacture.

In the process of distillation of the coal, we have seen that various
other important substances are brought into existence. The final residue
of coke, which is impregnated with the sulphur which has not been
volatilised in the form of sulphurous gases, we need scarcely more than
mention here. But the gas-tar and the ammoniacal liquor are two important
products which demand something more than our casual attention. At one
time regarded by gas engineers as unfortunately necessary nuisances in
the manufacture of gas, they have both become so valuable on account of
materials which can be obtained from them, that they enable gas itself to
be sold now at less than half its original price. The waste of former
generations is being utilised in this, and an instance is recorded in
which tar, which was known to have been lying useless at the bottom of a
canal for years, has been purchased by a gas engineer for distilling
purposes. It has been estimated that about 590,000 tons of coal-tar are
distilled annually.

Tar in its primitive condition has been used, as every one is aware, for
painting or tarring a variety of objects, such as barges and palings, in
fact, as a kind of protection to the object covered from the ravages of
insects or worms, or to prevent corrosion when applied to metal piers.
But it is worthy of a better purpose, and is capable of yielding far more
useful and interesting substances than even the most imaginative
individual could have dreamed of fifty years ago.

In the process of distillation, the tar, after standing in tanks for some
time, in order that any ammoniacal liquor which may be present may rise
to the surface and be drawn off, is pumped into large stills, where a
moderate amount of heat is applied to it. The result is that some of the
more volatile products pass over and are collected in a receiver. These
first products are known as _first light oils_, or _crude coal-naphtha_,
and to this naphtha all the numerous natural naphthas which have been
discovered in various portions of the world, and to which have been
applied numerous local names, bear a very close resemblance. Such an one,
for instance, was that small but famous spring at Biddings, in
Derbyshire, from which the late Mr Young--Paraffin Young--obtained his
well-known paraffin oil, which gave the initial impetus to what has since
developed into a trade of immense proportions in every quarter of the
globe.

After a time the crude coal-naphtha ceases to flow over, and the heat is
increased. The result is that a fresh series of products, known as
_medium oils_, passes over, and these oils are again collected and kept
separate from the previous series. These in turn cease to flow, when, by
a further increase of heat, what are known as the _heavy oils_ finally
pass over, and when the last of these, _green grease_, as it is called,
distils over, pitch alone is left in the still. Pitch is used to a large
extent in the preparation of artificial asphalte, and also of a fuel
known as "briquettes."

The products thus obtained at the various stages of the process are
themselves subjected to further distillation, and by the exercise of
great care, requiring the most delicate and accurate treatment, a large
variety of oils is obtained, and these are retailed under many and
various fanciful names.

One of the most important and best known products of the fractional
distillation of crude coal-naphtha is that known as _benzene_, or
benzole, (C_{6}H_{6}). This, in its unrefined condition, is a light
spirit which distils over at a point somewhat below the boiling point of
water, but a delicate process of rectification is necessary to produce
the pure spirit. Other products of the same light oils are toluene and
xylene.

Benzene of a certain quality is of course a very familiar and useful
household supplement. It is sometimes known and sold as _benzene collas_,
and is used for removing grease from clothing, cleaning kid gloves, &c.
If pure it is in reality a most dangerous spirit, being very inflammable;
it is also extremely volatile, so much so that, if an uncorked bottle be
left in a warm room where there is a fire or other light near, its vapour
will probably ignite. Should the vapour become mixed with air before
ignition, it becomes a most dangerous explosive, and it will thus be seen
how necessary it is to handle the article in household use in a most
cautious manner. Being highly volatile, a considerable degree of cold is
experienced if a drop be placed on the hand and allowed to evaporate.

Benzene, which is only a compound of carbon and hydrogen, was first
discovered by Faraday in 1825; it is now obtained in large quantities
from coal-tar, not so much for use as benzene; is for its conversion, in
the first place, by the action of nitric acid, into _nitro-benzole,_ a
liquid having an odour like the oil of bitter almonds, and which is much
used by perfumers under the name of _essence de mirbane_; and, in the
second place, for the production from this nitro-benzole of the far-famed
_aniline_. After the distillation of benzene from the crude coal-naphtha
is completed, the chief impurities in the residue are charred and
deposited by the action of strong sulphuric acid. By further distillation
a lighter oil is given off, often known as _artificial turpentine oil_,
which is used as a solvent for varnishes and lackers. This is very
familiar to the costermonger fraternity as the oil which is burned in the
flaring lamps which illuminate the New Cut or the Elephant and Castle on
Saturday and other market nights.

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