The Story of a Piece of Coal
by
Edward A. Martin
Part 2 out of 3
form of the pit is circular, but elliptical and rectangular pits are also
in use. On the Continent polygonal-shaped shafts are not uncommon, all of
them, of whatever shape, being constructed with a view to resist the
great pressure exerted by the rock around.
[Illustration: FIG. 31.--Engine-House and Buildings at head of a
Coal-Pit.]
If there be one of these shafts at one end of the mine, and another at a
remote distance from it, a movement of the air will at once begin, and a
rough kind of ventilation will ensue. This is, however, quite
insufficient to provide the necessary quantity of air for inhalation by
the army of workers in the coal-mine, for the current thus set up does
not even provide sufficient force to remove the effete air and impurities
which accumulate from hundreds of perspiring human bodies.
It is therefore necessary to introduce some artificial means, by which a
strong and regular current shall pass down one shaft, through the mine in
all its workings, and out at the other shaft. This is accomplished in
various ways. It took many years before those interested in mines came
thoroughly to understand how properly to secure ventilation, and in
bygone days the system was so thoroughly bad that a tremendous amount of
sickness prevailed amongst the miners, owing to the poisonous effects of
breathing the same air over and over again, charged, as it was, with more
or less of the gases given off by the coal itself. Now, those miners who
do so great a part in furnishing the means of warming our houses in
winter, have the best contrivances which can be devised to furnish them
with an ever-flowing current of fresh air.
Amongst the various mechanical appliances which have been used to ensure
ventilation may be mentioned pumps, fans, and pneumatic screws. There is,
as we have said, a certain, though slight, movement of the air in the two
columns which constitute the upcast and the downcast shafts, but in order
that a current may flow which shall be equal to the necessities of the
miners, some means are necessary, by which this condition of almost
equilibrium shall be considerably disturbed, and a current created which
shall sweep all foul gases before it. One plan was to force fresh air
into the downcast, which should in a sense push the foetid air away by
the upcast. Another was to exhaust the upcast, and so draw the gases in
the train of the exhausted air. In other cases the plan was adopted of
providing a continual falling of water down the downcast shaft.
These various plans have almost all given way to that which is the most
serviceable of all, namely, the plan of having an immense furnace
constantly burning in a specially-constructed chamber at the bottom of
the upcast. By this means the column of air above it becomes rarefied
under the heat, and ascends, whilst the cooler air from the downcast
rushes in and spreads itself in all directions whence the bad air has
already been drawn. On the other hand, to so great a state of perfection
have ventilating fans been brought, that one was recently erected which
would be capable of changing the air of Westminster Hall thirty times in
one hour.
Having procured a current of sufficient power, it will be at once
understood that, if left to its own will, it would take the nearest path
which might lie between its entrance and its exit, and, in this way,
ventilating the principal street only, would leave all the many
off-shoots from it undisturbed. It is consequently manipulated by means
of barriers and tight-fitting doors, in such a way that the current is
bound in turn to traverse every portion of the mine. A large number of
boys, known as trappers, are employed in opening the doors to all comers,
and in carefully closing the doors immediately after they have passed, in
order that the current may not circulate through passages along which it
is not intended that it should pass.
The greatest dangers which await the miners are those which result, in
the form of terrible explosions, from the presence of inflammable gases
in the mines. The great walls of coal which bound the passages in mines
are constantly exuding supplies of gas into the air. When a bank of coal
is brought down by an artificial explosion, by dynamite, by lime
cartridges, or by some other agency, large quantities of gas are
sometimes disengaged, and not only is this highly detrimental to the
health of the miners, if not carried away by proper ventilation, but it
constitutes a constant danger which may at any time cause an explosion
when a naked light is brought into contact with it. Fire-damp may be
sometimes heard issuing from fiery seams with a peculiar hissing sound.
If the volume be great, the gas forms what is called a _blower_, and this
often happens in the neighbourhood of a fault. When coal is brought down
in any large volume, the blowers which commence may be exhausted in a few
moments. Others, however, have been known to last for years, this being
the case at Wallsend, where the blower gave off 120 feet of gas per
minute. In such cases the gas is usually conveyed in pipes to a place
where it can be burned in safety.
In the early days of coal-mining the explosions caused by this gas soon
received the serious attention of the scientific men of the age. In the
_Philosophical Transactions of the Royal Society_ we find a record of a
gas explosion in 1677. The amusing part of such records was that the
explosions were ascribed by the miners to supernatural agencies. Little
attention seemed to have been paid to the fact, which has since so
thoroughly been established, that the explosions were caused by
accumulations of gas, mixed in certain proportions with air. As a
consequence, tallow candles with an exposed flame were freely used,
especially in Britain. These were placed in niches in the workings, where
they would give to the pitman the greatest amount of light. Previous to
the introduction of the safety-lamp, workings were tested before the men
entered them, by "trying the candle". Owing to the specific gravity of
fire-damp (.555) being less than that of air, it always finds a lodgement
at the roofs of the workings, so that, to test the condition of the air,
it was necessary to steadily raise the candle to the roof at certain
places in the passages, and watch carefully the action of the flame. The
presence of fire-damp would be shown by the flame assuming a blue colour,
and by its elongation; the presence of other gases could be detected by
an experienced man by certain peculiarities in the tint of the flame.
This testing with the open flame has almost entirely ceased since the
introduction of the perfected Davy lamp.
The use of candles for illumination soon gave place in most of the large
collieries to the introduction of small oil-lamps. In the less fiery
mines on the Continent, oil-lamps of the well-known Etruscan pattern are
still in use, whilst small metal lamps, which can conveniently be
attached to the cap of the worker, occasionally find favour in the
shallower Scotch mines. These lamps are very useful in getting the coal
from the thinner seams, where progress has to be made on the hands and
feet. At the close of the last century, as workings began to be carried
deeper, and coal was obtained from places more and more infested with
fire-damp, it soon came to be realised that the old methods of
illumination would have to be replaced by others of a safer nature.
It is noteworthy that mere red heat is insufficient in itself to ignite
fire-damp, actual contact with flame being necessary for this purpose.
Bearing this in mind, Spedding, the discoverer of the fact, invented what
is known as the "steel-mill" for illuminating purposes. In this a toothed
wheel was made to play upon a piece of steel, the sparks thus caused
being sufficient to give a moderate amount of illumination. It was found,
however, that this method was not always trustworthy, and lamps were
introduced by Humboldt in 1796, and by Clanny in 1806. In these lamps the
air which fed the flame was isolated from the air of the mine by having
to bubble through a liquid. Many miners were not, however, provided with
these lamps, and the risks attending naked lights went on as merrily as
ever.
In order to avoid explosions in mines which were known to give off large
quantities of gas, "fiery" pits as they are called, Sir Humphrey Davy in
1815 invented his safety lamp, the principle of which can be stated in a
few words.
If a piece of fine wire gauze be held over a gas-jet before it is lit,
and the gas be then turned on, it can be lit above the gauze, but the
flame will not pass downwards towards the source of the gas; at least,
not until the gauze has become over-heated. The metallic gauze so rapidly
conducts away the heat, that the temperature of the gas beneath the gauze
is unable to arrive at the point of ignition. In the safety-lamp the
little oil-lamp is placed in a circular funnel of fine gauze, which
prevents the flame from passing through it to any explosive gas that may
be floating about outside, but at the same time allows the rays of light
to pass through readily. Sir Humphrey Davy, in introducing his lamp,
cautioned the miners against exposing it to a rapid current of air, which
would operate in such a way as to force the flame through the gauze, and
also against allowing the gauze to become red-hot. In order to minimise,
as far as possible, the necessity of such caution the lamp has been
considerably modified since first invented, the speed of the ventilating
currents not now allowing of the use of the simple Davy lamp, but the
principle is the same.
During the progress of Sir Humphrey Davy's experiments, he found that
when fire-damp was diluted with 85 per cent. of air, and any less
proportion, it simply ignited without explosion. With between 85 per
cent. and 89 per cent. of air, fire-damp assumed its most explosive form,
but afterwards decreased in explosiveness, until with 94-1/4 per cent. of
air it again simply ignited without explosion. With between 11 and 12 per
cent. of fire-damp the mixture was most dangerous. Pure fire-damp itself,
therefore, is not dangerous, so that when a small quantity enters the
gauze which surrounds the Davy lamp, it simply burns with its
characteristic blue flame, but at the same time gives the miner due
notice of the danger which he was running.
[Illustration: FIG. 32.--Gas Jet and Davy Lamp.]
With the complicated improvements which have since been made in the Davy
lamp, a state of almost absolute safety can be guaranteed, but still from
time to time explosions are reported. Of the cause of many we are
absolutely ignorant, but occasionally a light is thrown upon their origin
by a paragraph appearing in a daily paper. Two men are charged before the
magistrates with being in the possession of keys used exclusively for
unlocking their miners' safety-lamps. There is no defence. These men know
that they carry their lives in their hands, yet will risk their own and
those of hundreds of others, in order that they may be able to light
their pipes by means of their safety-lamps. Sometimes in an unexpected
moment there is a great dislodgement of coal, and a tremendous quantity
of gas is set free, which may be sufficient to foul the passages for some
distance around. The introduction or exposure of a naked light for even
so much as a second is sufficient to cause explosion of the mass; doors
are blown down, props and tubbing are charred up, and the volume of
smoke, rushing up by the nearest shaft and overthrowing the engine-house
and other structures at the mouth, conveys its own sad message to those
at the surface, of the dreadful catastrophe that has happened below.
Perhaps all that remains of some of the workers consists of charred and
scorched bodies, scarcely recognisable as human beings. Others escape
with scorched arms or legs, and singed hair, to tell the terrible tale to
those who were more fortunately absent; to speak of their own sufferings
when, after having escaped the worst effects of the explosion, they
encountered the asphyxiating rush of the after-damp or choke-damp, which
had been caused by the combustion of the fire-damp. "Choke-damp" in very
truth it is, for it is principally composed of our old acquaintance
carbonic acid gas (carbon dioxide), which is well known as a
non-supporter of combustion and as an asphyxiator of animal life.
It seems a terrible thing that on occasions the workings and walls
themselves of a coal-mine catch fire and burn incessantly. Yet such is
the case. Years ago this happened in the case of an old colliery near
Dudley, at the surface of which, by means of the heat and steam thus
afforded, early potatoes for the London market, we are told, were grown;
and it was no unusual thing to see the smoke emerging from cracks and
crevices in the rocks in the vicinity of the town.
From fire on the one hand, we pass, on the other, to the danger which
awaits miners from a sudden inrush of water. During the great coal strike
of 1893, certain mines became unworkable in consequence of the quantity
of water which flooded the mines, and which, continually passing along
the natural fractures in the earth's crust, is always ready to find a
storage reservoir in the workings of a coal-mine. This is a difficulty
which is always experienced in the sinking of shafts, and the shutting
off of water engages the best efforts of mining engineers.
Added to these various dangers which exist in the coal-mine, we must not
omit to notice those accidents that are continually being caused by the
falling-in of roofs or of walls, from the falling of insecure timber, or
of what are known as "coal-pipes" or "bell-moulds." Then, again, every
man that enters the mine trusts his life to the cage by which he descends
to his labour, and shaft accidents are not infrequent.
The following table shows the number of deaths from colliery accidents
for a period of ten years, compiled by a Government inspector, and from
this it will be seen that those resulting from falling roofs number
considerably more than one-third of the whole.
-------------------------------------------------------------------
| Causes of Death. | No. of | Proportion |
| | Deaths. | per cent. |
-------------------------------------------------------------------
| Deaths resulting from fire-damp | | |
| explosions | 2019 | 20.36 |
| | | |
| Deaths resulting from falling | | |
| roofs and coals | 3953 | 39.87 |
| | | |
| Deaths resulting from shaft | | |
| accidents | 1710 | 17.24 |
| | | |
| Deaths resulting from miscellaneous | | |
| causes and above ground | 2234 | 22.53 |
| |------------|------------|
| | 9916 | 100.00 |
------------------------------------------------------------------|
Every reader of the daily papers is familiar with the harrowing accounts
which are there given of coal-mine explosions.
This kind of accident is one, which is, above all, associated in the
public mind with the dangers of the coal-pit. Yet the accidents arising
from this cause number but 20 per cent. of those recorded, and granted
there be proper inspection, and the use of naked lights be absolutely
abolished, this low percentage might still be considerably reduced.
A terrific explosion occurred at Whitwick Colliery, Leicestershire, in
1893, when two lads were killed, whilst a third was rescued after a very
narrow escape. The lads, it is stated, _were working with naked lights_,
when a sudden fall of coal released a quantity of gas, and an immediate
explosion was the natural result. Accidents had been so rare at this pit
that it was regarded as particularly safe, and it was alleged that the
use of naked lights was not uncommon.
This is an instance of that large number of accidents which are
undoubtedly preventable.
An interesting commentary on the careless manner in which miners risk
their lives was shown in the discoveries made after an explosion at a
colliery near Wrexham in 1889. Near the scene of the explosion an
unsecured safety lamp was found, and the general opinion at the time was
that the disaster was caused by the inexcusable carelessness of one of
the twenty victims. Besides this, when the clothing of the bodies
recovered was searched, the contents, taken, it should be noted, with the
pitmen into the mines, consisted of pipes, tobacco, matches, and even
keys for unlocking the lamps. It is a strange reflection on the manner in
which this mine had been examined previous to the men entering upon their
work, that the under-looker, but half an hour previously, had reported
the pit to be free from gas.
Another instance of the same foolhardiness on the part of the miners is
contained in the report issued in regard to an explosion which occurred
at Denny, in Stirlingshire, on April 26th, 1895. By this accident
thirteen men lost their lives, and upon the bodies of eight of the number
the following articles were found; upon Patrick Carr, tin matchbox half
full of matches and a contrivance for opening lamps; John Comrie, split
nail for opening lamps; Peter Conway, seven matches and split key for
opening lamps; Patrick Dunton, split nail for opening lamps; John Herron,
clay pipe and piece of tobacco; Henry M'Govern, tin matchbox half full of
matches; Robert Mitchell, clay pipe and piece of tobacco; John Nicol,
wooden pipe, piece of tobacco, one match, and box half full of matches.
The report stated that the immediate cause of the disaster was the
ignition of fire-damp by naked light, the conditions of temperature being
such as to exclude the possibility of spontaneous combustion. Henry
M'Govern had previously been convicted of having a pipe in the mine. With
regard to the question of sufficient ventilation it continued:--"And we
are therefore led, on a consideration of the whole evidence, to the
conclusion that the accident cannot be attributed to the absence of
ventilation, which the mine owners were bound under the Mines Regulation
Act and the special rules to provide." The report concluded as follows:--
"On the whole matter we have to report that, in our opinion, the
explosion at Quarter Pit on April 26th, 1895, resulting in the loss of
thirteen lives, was caused by the ignition of an accumulation or an
outburst of gas coming in contact with a naked light, 'other than an open
safety-lamp,' which had been unlawfully kindled by one of the miners who
were killed. In our opinion, the intensity of the explosion was
aggravated, and its area extended, by the ignition of coal-dust."
We have mentioned that accidents have frequently occurred from the
falling of "coal-pipes," or, as they are also called, "bell-moulds." We
must explain what is meant by this term. They are simply what appear to
be solid trunks of trees metamorphosed into coal. If we go into a
tropical forest we find that the woody fibre of dead trees almost
invariably decays faster than the bark. The result is that what may
appear to be a sound tree is nothing but an empty cylinder of bark. This
appears to have been the case with many of the trees in coal-mines, where
they are seen to pierce the strata, and around which the miners are
excavating the coal. As the coaly mass collected around the trunk when
the coal was being formed, the interior was undergoing a process of
decomposition, while the bark assumed the form of coal. The hollow
interior then became filled with the shale or sandstone which forms the
roof of the coal, and its sole support when the coal is removed from
around it, is the thin rind of carbonised bark. When this falls to
pieces, or loses its cohesion, the sandstone trunk falls of its own
weight, often causing the death of the man that works beneath it. Sir
Charles Lyell mentions that in a colliery near Newcastle, no less than
thirty _sigillaria_ trees were standing in their natural position in an
area of fifty yards square, the interior in each case being sandstone,
which was surrounded by a bark of friable coal.
[Illustration: Fig. 33--Part of a trunk of _Sigillaria_, showing the thin
outer carbonised bark, with leaf-scars, and the seal-like impressions
where the bark is removed.]
The last great danger to which we have here to make reference, is the
explosive action of a quantity of coal-dust in a dry condition. It is
only now commencing to be fully recognised that this is really a most
dangerous explosive. As we have seen, large quantities of coal are formed
almost exclusively of _lepidodendron_ spores, and such coal is productive
of a great quantity of dust. Explosions which are always more or less
attributable to the effects of coal-dust are generally considered, in the
official statistics, to have been caused by fire-damp. The Act regulating
mines in Great Britain is scarcely up to date in this respect. There is a
regulation which provides for the watering of all dry and dusty places
within twenty yards from the spot where a shot is fired, but the
enforcement of this regulation in each and every pit necessarily devolves
on the managers, many of whom in the absence of an inspector leave the
requirement a dead letter. Every improvement which results in the better
ventilation of a coal-mine tends to leave the dust in a more dangerous
condition. The air, as it descends the shaft and permeates the workings,
becomes more and more heated, and licks up every particle of moisture it
can touch. Thorough ventilation results in more greatly freeing a mine of
the dangerous fire-damp, but the remedy brings about another disease,
viz., the drying-up of all moisture. The dust is thus left in a
dangerously inflammable condition, acting like a train of gunpowder, to
be started, it may be, by the slightest breath of an explosion. There is
apparently little doubt that the presence of coal-dust in a dry state in
a mine appreciably increases the liability of explosion in that mine.
So far as Great Britain is concerned, a Royal Commission was appointed by
Lord Rosebery's Government to inquire into and investigate the facts
referring to coal-dust. Generally speaking, the conclusion arrived at was
that fine coal-dust was inflammable under certain conditions. There was
considerable difference of opinion as to what these conditions were. Some
were of opinion that coal-dust and air alone were of an explosive nature,
whilst others thought that alone they were not, but that the addition of
a small quantity of fire-damp rendered the mixture explosive. An
important conclusion was come to, that, with the combustion of coal-dust
alone, there was little or no concussion, and that the flame was not of
an explosive character.
Coal-dust was, however, admittedly dangerous, especially if in a dry
condition. The effects of an explosion of gas might be considerably
extended by its presence, and there seems every reason to believe that,
with a suitable admixture of air and a very small proportion of gas, it
forms a dangerous explosive. Legislation in the direction of the report
of the Commission is urgently needed.
We have seen elsewhere what it is in the dust which makes it dangerous,
how that, for the most part, it consists of the dust-like spores of the
_lepidodendron_ tree, fine and impalpable as the spores on the backs of
some of our living ferns, and the fact that this consists of a large
proportion of resin makes it the easily inflammable substance it is.
Nothing but an incessant watering of the workings in such cases will
render the dust innocuous. The dust is extremely fine, and is easily
carried into every nook and crevice, and when, as at Bridgend in 1892, it
explodes, it is driven up and out of the shaft, enveloping everything
temporarily in dust and darkness.
In some of the pits in South Wales a system of fine sprays of water is in
use, by which the water is ejected from pin-holes pricked in a series of
pipes which are carried through the workings. A fine mist is thus caused
where necessary, which is carried forward by the force of the ventilating
current.
A thorough system of inspection in coal-mines throughout the world is
undoubtedly urgently called for, in order to ensure the proper carrying
out of the various regulations framed for their safety. It is extremely
unfortunate that so many of the accidents which happen are preventable,
if only men of knowledge and of scientific attainments filled the
responsible positions of the overlookers.
CHAPTER V.
EARLY HISTORY--ITS USE AND ITS ABUSE.
The extensive use of coal throughout the civilised world for purposes of
heating and illumination, and for the carrying on of manufactures and
industries, may be regarded as a well-marked characteristic of the age in
which we live.
Coal must have been in centuries past a familiar object to many
generations. People must have long been living in close proximity to its
outcrops at the sides of the mountains and at the surface of the land,
yet without being acquainted with its practical value, and it seems
strange that so little use was made of it until about three centuries
ago, and that its use did not spread earlier and more quickly throughout
civilised countries.
A mineral fuel is mentioned by Theophrastus about 300 B.C., from which it
is inferred that thus early it was dug from some of the more shallow
depths. The Britons before the time of the Roman invasion are credited
with some slight knowledge of its industrial value. Prehistoric
excavations have been found in Monmouthshire, and at Stanley, in
Derbyshire, and the flint axes there actually found imbedded in the layer
of coal are reasonably held to indicate its excavation by neolithic or
palaeolithic (stone-age) workmen.
The fact that coal cinders have been found on old Roman walls in
conjunction with Roman tools and implements, goes to prove that its use,
at least for heating purposes, was known in England prior to the Saxon
invasion, whilst some polygonal chambers in the six-foot seam near the
river Douglas, in Lancashire, are supposed also to be Roman.
The Chinese were early acquainted with the existence of coal, and knew of
its industrial value to the extent of using it for the baking of
porcelain.
The fact of its extensive existence in Great Britain, and the valuable
uses to which it might be put, did not, however, meet with much notice
until the ninth century, when, owing to the decrease of the
forest-area, and consequently of the supply of wood-charcoal therefrom,
it began to attract attention as affording an excellent substitute for
charcoal.
The coal-miner was, however, still a creation of the future, and even as
peat is collected in Ireland at the present day for fuel, without the
laborious process of mining for it, so those people living in
coal-bearing districts found their needs satisfied by the quantity of
coal, small as it was, which appeared ready to hand on the sides of the
carboniferous mountains. Till then, and for a long time afterwards, the
principal source of fuel consisted of vast forests, amidst which the
charcoal-burners, or "colliers" as they were even then called, lived out
their lonely existence in preparing charcoal and hewing wood, for the
fires of the baronial halls and stately castles then swarming throughout
the land. As the forests became used up, recourse was had more and more
to coal, and in 1239 the first charter dealing with and recognising the
importance of the supplies was granted to the freemen of Newcastle,
according them permission to dig for coals in the Castle fields. About
the same time a coal-pit at Preston, Haddingtonshire, was granted to the
monks of Newbattle.
Specimens of Newcastle coal were sent to London, but the city was loth to
adopt its use, objecting to the innovation as one prejudicial to the
health of its citizens. By the end of the 16th century, two ships only
were found sufficient to satisfy the demand for stone-coal in London.
This slow progress may, perhaps, have been partially owing to the
difficulties which were placed in the way of its universal use. Great
opposition was experienced by those who imported it into the metropolis,
and the increasing amount which was used by brewers and others about the
year 1300, caused serious complaints to be made, the effect of which was
to induce Parliament to obtain a proclamation from the King prohibiting
its use, and empowering the justices to inflict a fine on those who
persisted in burning it. The nuisance which coal has since proved itself,
in the pollution of the atmosphere and in the denuding of wide tracts of
country of all vegetation, was even thus early recognised, and had the
efforts which were then made to stamp out its use, proved successful,
those who live now in the great cities might never have become acquainted
with that species of black winter fog which at times hangs like a pall
over them, and transforms the brightness of day into a darkness little
removed from that of night. At the same time, we must bear in mind that
it is universally acknowledged that England owes her prosperity, and her
pre-eminence in commerce, in great part, to her happy possession of wide
and valuable coal-fields, and many authorities have not hesitated to say,
that, in their opinion, the length of time during which England will
continue to hold her prominent position as an industrial nation is
limited by the time during which her coal will last.
The attempt to prohibit the burning of coal was not, however, very
successful, for in the reign of Edward III. a license was again granted
to the freemen of Newcastle to dig for coals. Newcastle was thus the
first town to become famous as the home of the coal-miner, and the fame
which it early acquired, it has held unceasingly ever since.
Other attempts at prohibition of the article were made at various times
subsequently, amongst them being one which was made in Elizabeth's reign.
It was supposed that the health of the country squires, who came to town
to attend the session of Parliament, suffered considerably during their
sojourn in London, and, to remedy this serious state of affairs, the use
of stone-coal during the time Parliament was sitting was once more
prohibited.
Coal was, however, by this time beginning to be recognised as a most
valuable and useful article of fuel, and had taken a position in the
industrial life of the country from which it was difficult to remove it.
Rather than attempt to have arrested the growing use of coal, Parliament
would have been better employed had it framed laws compelling the
manufacturers and other large burners to consume their own smoke, and
instead of aiming at total prohibition, have encouraged an intelligent
and more economical use of it.
In spite of all prohibition its use rapidly spread, and it was soon
applied to the smelting of iron and to other purposes. Iron had been
largely produced in the south of England from strata of the Wealden
formation, during the existence of the great forest which at one time
extended for miles throughout Surrey and Sussex. The discovery of coal,
however, and the opening up of many mines in the north, gave an important
impetus to the smelting of iron in those counties, and as the forests of
the Weald became exhausted, the iron trade gradually declined. Furnace
after furnace became extinguished, until in 1809 that at Ashburnham,
which had lingered on for some years, was compelled to bow to the
inevitable fate which had overtaken the rest of the iron blast-furnaces.
In referring to this subject, Sir James Picton says:--"Ironstone of
excellent quality is found in various parts of the county, and was very
early made use of. Even before the advent of the Romans, the Forest of
Dean in the west, and the Forest of Anderida, in Sussex, in the east,
were the two principal sources from which the metal was derived, and all
through the mediaeval ages the manufacture was continued. After the
discovery of the art of smelting and casting iron in the sixteenth
century, the manufacture in Sussex received a great impulse from the
abundance of wood for fuel, and from that time down to the middle of the
last century it continued to flourish. One of the largest furnaces was at
Lamberhurst, on the borders of Kent, where the noble balustrade
surrounding St Paul's Cathedral was cast at a cost of about L11,000. It
is stated by the historian Holinshed that the first cast-iron ordnance
was manufactured at Buxted. Two specialities in the iron trade belonged
to Sussex, the manufacture of chimney-backs, and cast-iron plates for
grave-stones. At the time when wood constituted the fuel the backs of
fire-places were frequently ornamented with neat designs. Specimens, both
of the chimney-backs and of the monuments, are occasionally met with.
These articles were exported from Rye. The iron manufacture, of course,
met with considerable discouragement on the discovery of smelting with
pit-coal, and the rapid progress of iron works in Staffordshire and the
North, but it lingered on until the great forest was cut down and the
fuel exhausted."
In his interesting work, "Sylvia," published in 1661, Evelyn, in speaking
of the noxious vapours poured out into the air by the increasing number
of coal fires, writes, "This is that pernicious smoke which sullies all
her glory, superinducing a sooty crust or furr upon all that it lights,
spoiling movables, tarnishing the plate, gildings and furniture, and
corroding the very iron bars and hardest stones with those piercing and
acrimonious spirits which accompany its sulphur, and executing more in
one year than the pure air of the country could effect in some hundreds."
The evils here mentioned are those which have grown and have become
intensified a hundred-fold during the two centuries and a half which have
since elapsed. When the many efforts which were made to limit its use in
the years prior to 1600 are remembered; at which time, we are informed,
two ships only were engaged in bringing coal to London, it at once
appears how paltry are the efforts made now to moderate these same
baneful influences on our atmosphere, at a time when the annual
consumption of coal in the United Kingdom has reached the enormous total
of 190 millions of tons. The various smoke-abatement associations which
have started into existence during the last few years are doing a little,
although very little, towards directing popular attention to the subject;
but there is an enormous task before them, that of awakening every
individual to an appreciation of the personal interest which he has in
their success, and to realise how much might at once be done if each were
to do his share, minute though it might be, towards mitigating the evils
of the present mode of coal-consumption. Probably very few householders
ever realise what important factories their chimneys constitute, in
bringing about air pollution, and the more they do away with the use of
bituminous coal for fuel, the nearer we shall be to the time when yellow
fog will be a thing of the past.
A large proportion of smoke consists of particles of pure unconsumed
carbon, and this is accompanied in its passage up our chimneys by
sulphurous acid, begotten by the sulphur which is contained in the coal
to the amount of about eight pounds in every thousand; by sulphuretted
hydrogen, by hydro-carbons, and by vapours of various kinds of oils,
small quantities of ammonia, and other bodies not by any means
contributing to a healthy condition of the atmosphere. A good deal of the
heavier carbon is deposited along the walls of chimneys in the form of
soot, together with a small percentage of sulphate of ammonia; this is as
a consequence very generally used for manure. The remainder is poured out
into the atmosphere, there to undergo fresh changes, and to become a
fruitful cause of those thick black fogs with which town-dwellers are so
familiar. Sulphuretted hydrogen (H_{2}S) is a gas well known to students
of chemistry as a most powerful reagent, its most characteristic external
property being the extremely offensive odour which it possesses, and
which bears a strong resemblance to that of rotten eggs or decomposing
fish. It tarnishes silver work and picture frames very rapidly. On
combustion it changes to sulphurous acid (SO_{2}), and this in turn has
the power of taking up from the air another atom of oxygen, forming
sulphuric acid (SO_{3} + water), or, as we more familiarly know it, oil
of vitriol.
Yet the smoke itself, including as it does all the many impurities which
exist in coal, is not only evil in itself, but is evil in its influences.
Dr Siemens has said:--"It has been shown that the fine dust resulting
from the imperfect combustion of coal was mainly instrumental in the
formation of fog; each particle of solid matter attracting to itself
aqueous vapour. These globules of fog were rendered particularly
tenacious and disagreeable by the presence of tar vapour, another result
of imperfect combustion of raw fuel, which might be turned to better
account at the dyeworks. The hurtful influence of smoke upon public
health, the great personal discomfort to which it gave rise, and the vast
expense it indirectly caused through the destruction of our monuments,
pictures, furniture, and apparel, were now being recognised."
The most effectual remedy would result from a general recognition of the
fact that wherever smoke was produced, fuel was being consumed
wastefully, and that all our calorific effects, from the largest furnace
to the domestic fire, could be realised as completely, and more
economically, without allowing any of the fuel employed to reach the
atmosphere unburnt. This most desirable result might be effected by the
use of gas for all heating purposes, with or without the additional use
of coke or anthracite. The success of the so-called smoke-consuming
stoves is greatly open to question, whilst some of them have been
reported upon by those appointed to inspect them as actually accentuating
the incomplete combustion, the abolition of which they were invented to
bring about.
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.
By distillation of the _heavy oils_, carbolic acid and commercial
_anthracene_ are produced, and by a treatment of the residue, a white and
crystalline substance known as _naphthalin_ (C_{10}H_{8}) is finally
obtained.
Thus, by the continued operation of the chemical process known as
fractional distillation of the immediate products of coal-tar, these
various series of useful oils are prepared.
The treatment is much the same which has resulted in the production of
paraffin oil, to which we have previously referred, and an account of the
production of coal-oils would be very far from satisfactory, which made
no mention of the production of similar commodities by the direct
distillation of shale. Oil-shales, or bituminous shales, exist in all
parts of the world, and may be regarded as mineral matter largely
impregnated by the products of decaying vegetation. They therefore
greatly resemble some coals, and really only differ therefrom in degree,
in the quantity of vegetable matter which they contain. Into the subject
of the various native petroleums which have been found--for these
rock-oils are better known as petroleums--in South America, in Burmah
(Rangoon Oil), at Baku, and the shores of the Caspian, or in the United
States of America, we need not enter, except to note that in all
probability the action of heat on underground bituminous strata of
enormous extent has been the cause of their production, just as on a
smaller scale the action of artificial heat has forced the reluctant
shale to give up its own burden of mineral oil. However, previous to
1847, although native mineral oil had been for some years a recognised
article of commerce, the causes which gave rise to the oil-wells, and the
source, probably a deep-seated one, of the supply of oil, does not appear
to have been well known, or at least was not enquired after. But in that
year Mr Young, a chemist at Manchester, discovered that by distilling
some petroleum, which he obtained from a spring at Riddings in
Derbyshire, he was able to procure a light oil, which he used for burning
in lamps, whilst the heavier product which he also obtained proved a most
useful lubricant for machinery. This naturally distilled oil was soon
found to be similar to that oil which was noticed dripping from the roof
of a coal-mine. Judging that the coal, being under the influence of heat,
was the cause of the production of the oil, Mr Young tested this
conclusion by distilling the coal itself. Success attended his endeavour
thus to procure the oil, and indelibly Young stamped his name upon the
roll of famous men, whose industrial inventions have done so much towards
the accomplishment of the marvellous progress of the present century.
From the distillation he obtained the well-known Young's Paraffin Oil,
and the astonishing developments of the process which have taken place
since he obtained his patent in 1850, for the manufacture of oils and
solid paraffin, must have been a source of great satisfaction to him
before his death, which occurred in 1883.
Cannel coal, Boghead or Bathgate coal, and bituminous shales of various
qualities, have all been requisitioned for the production of oils, and
from these various sources the crude naphthas, which bear a variety of
names according to some peculiarity in their origin, or place of
occurrence, are obtained. Boghead coal, also known as "Torebanehill
mineral," gives Boghead naphtha, while the crude naphtha obtained from
shales is often quoted as shale-oil. In chemical composition these
naphthas are closely related to one another, and by fractional
distillation of them similar series of products are obtained as those we
have already seen as obtained from the crude coal-naphtha of coal-tar.
In the direct distillation of cannel-coal for the production of paraffin,
it is necessary that the perpendicular tubes or retorts into which the
coal is placed be heated only to a certain temperature, which is
considerably lower than that applied when the object is the production of
coal-gas. By this means nearly all the volatile matters pass over in the
form of condensible vapours, and the crude oils are at once formed, from
whence are obtained at different temperatures various volatile ethers,
benzene, and artificial turpentine oil or petroleum spirit. After these,
the well-known safety-burning paraffin oil follows, but it is essential
that the previous three volatile products be completely cleared first,
since, mixed with air, they form highly dangerous explosives. To the fact
that the operation is carried on in the manufactories with great care and
accuracy can only be attributed the comparative rareness of explosions of
the oil used in households.
After paraffin, the heavy lubricating oils are next given off, still
increasing the temperature, and, the residue being in turn subjected to a
very low temperature, the white solid substance known as paraffin, so
much used for making candles, is the result. By a different treatment of
the same residue is produced that wonderful salve for tender skins, cuts,
and burns, known popularly as _vaseline_. Probably no such
widely-advertised remedial substance has so deserved its success as this
universally-used waste product of petroleum.
We have noticed the fact that in order to procure safety-burning oils, it
is absolutely necessary that the more volatile portions be completely
distilled over first. By Act of Parliament a test is applied to all oils
which are intended for purposes of illumination, and the test used
consists of what is known as the flashing-point. Many of the more
volatile ethers, which are highly inflammable, are given off even at
ordinary temperatures, and the application of a light to the oil will
cause the volatile portion to "flash," as it is called. A safety-burning
oil, according to the Act, must not flash under 100 deg. Fahrenheit open
test, and all those portions which flash at a less temperature must be
volatilised off before the residue can be deemed a safe oil. It seems
probable that the flashing-point will sooner or later be raised.
One instance may be cited to show how necessary it is that the native
mineral oils which have been discovered should have this effectual test
applied to them.
When the oil-wells were first discovered in America, the oil was obtained
simply by a process of boring, and the fountain of oil which was bored
into at times was so prolific, that it rushed out with a force which
carried all obstacles before it, and defied all control. In one instance
a column of oil shot into the air to a height of forty feet, and defied
all attempts to keep it under. In order to prevent further accident, all
lights in the immediate neighbourhood were extinguished, the nearest
remaining being at a distance of four hundred feet. But in this crude
naphtha there was, as usual, a quantity of volatile spirit which was
being given off even at the temperature of the surrounding atmosphere.
This soon became ignited, and with an explosion the column of oil was
suddenly converted into a roaring column of fire. The owner of the
property was thrown a distance of twenty feet by the explosion, and soon
afterwards died from the burns which he had received from it. Such an
accident could not now, however, happen. The tapping, stopping, and
regulating of gushing wells can now be more effectually dealt with, and
in the process of refining; the most inflammable portions are separated,
with a result that, as no oil is used in the country which flashes under
100 deg. F. open test, and as our normal temperature is considerably less
than this, there is little to be feared in the way of explosion if the
Act be complied with.
When the results of Mr Young's labours became publicly known, a number of
companies were started with the object of working on the lines laid down
in his patent, and these not only in Great Britain but also in the United
States, whither quantities of cannel coal were shipped from England and
other parts to feed the retorts. In 1860, according to the statistics
furnished, some seventy factories were established in the United States
alone with the object of extracting oil from coal and other mineral
sources, such as bituminous shale, etc. When Young's patent finally
expired, a still greater impetus was given to its production, and the
manufacture would probably have continued to develop were it not that
attention had, two years previously, been forcibly turned to those
discoveries of great stores of natural oil in existence beneath a
comparatively thin crust of earth, and which, when bored into, spouted
out to tremendous heights.
The discovery of these oil-fountains checked for a time the development
of the industry, but with the great production there has apparently been
a greatly increased demand for it, and the British industry once again
appears to thrive, until even bituminous shales have been brought under
requisition for their contribution to the national wealth.
Were it not for the nuisance and difficulty experienced in the proper
cleaning and trimming of lamps, there seems no other reason why mineral
oil should not in turn have superseded the use of gas, even as gas had,
years before, superseded the expensive animal and vegetable oils which
had formerly been in use.
Although this great development in the use of mineral oils has taken
place only within the last thirty years, it must not be thought that
their use is altogether of modern invention. That they were not
altogether unknown in the fifth century before Christ is a matter of
certainty, and at the time when the Persian Empire was at the zenith of
its glory, the fires in the temples of the fire-worshippers were
undoubtedly kept fed by the natural petroleum which the districts around
afforded. It is thought by some that the legend which speaks of the fire
which came down from heaven, and which lit the altars of the
Zoroastrians, may have had its origin in the discovery of a hitherto
unknown petroleum spring. More recently, the remarks of Marco Polo in his
account of his travels in A.D. 1260 and following years, are particularly
interesting as showing that, even then, the use of mineral oil for
various purposes was not altogether unknown. He says that on the north of
Armenia the Greater is "Zorzania, in the confines of which a fountain is
found, from which a liquor like oil flows, and though unprofitable for
the seasoning of meat, yet is very fit for the supplying of lamps, and to
anoint other things; and this natural oil flows constantly, and that in
plenty enough to lade camels."
From this we can infer that the nature of the oil was entirely unknown,
for it was a "liquor like oil," and was also, strange to say,
"unprofitable for the seasoning of meat"! In another place in Armenia,
Marco Polo states that there was a fountain "whence rises oil in such
abundance that a hundred ships might be at once loaded with it. It is not
good for eating, but very fit for fuel, for anointing the camels in
maladies of the skin, and for other purposes; for which reason people
come from a great distance for it, and nothing else is burned in all this
country."
The remedial effects of the oil, when used as an ointment, were thus
early recognised, and the far-famed vaseline of the present day may be
regarded as the lineal descendent, so to speak, of the crude medicinal
agent to which Marco Polo refers.
The term asphalt has been applied to so many and various mixtures, that
one scarcely associates it with natural mineral pitch which is found in
some parts of the world. From time immemorial this compact, bituminous,
resinous mineral has been discovered in masses on the shores of the Dead
Sea, which has in consequence received the well-known title of Lake
Asphaltites. Like the naphthas and petroleums which have been noticed,
this has had its origin in the decomposition of vegetable matter, and
appears to be thrown up in a liquid form by the volcanic energies which,
are still believed to be active in the centre of the lake, and which may
be existent beneath a stratum, or bed, of oil-producing bitumen.
In connection with the formation of this substance, the remarks of Sir
Charles Lyell, the great geologist, may well be quoted, as showing the
transformation of vegetable matter into petroleum, and afterwards into
solid-looking asphalt. At Trinidad is a lake of bitumen which is a mile
and a half in circumference. "The Orinoco has for ages been rolling down
great quantities of woody and vegetable bodies into the surrounding sea,
where, by the influence of currents and eddies, they may be arrested, and
accumulated in particular places. The frequent occurrence of earthquakes
and other indications of volcanic action in those parts, lend countenance
to the opinion that these vegetable substances may have undergone, by the
agency of subterranean fire, those transformations or chemical changes
which produce petroleum; and this may, by the same causes, be forced up
to the surface, where, by exposure to the air, it becomes inspissated,
and forms those different varieties of earth-pitch or asphaltum so
abundant in the island."
It is interesting to note also that it was obtained, at an ancient
period, from the oil-fountains of Is, and that it was put to considerable
use in the embalming of the bodies of the Egyptians. It appears, too, to
have been employed in the construction of the walls of Babylon, and thus
from very early times these wonderful products and results of decayed
vegetation have been brought into use for the service of man.
Aniline has been previously referred (p. 135) to as having been prepared
from nitro-benzole, or _essence de mirbane_, and its preparation, by
treating this substance with iron-filings and acetic acid, was one of the
early triumphs of the chemists who undertook the search after the unknown
contained in gas-tar. It had previously been obtained from oils distilled
from bones. The importance of the substance lies in the fact that, by the
action of various chemical reagents, a series of colouring matters of
very great richness are formed, and these are the well-known _aniline
dyes_.
As early as 1836, it was discovered that aniline, when heated with
chloride of lime, acquired a beautiful blue tint. This discovery led to
no immediate practical result, and it was not until twenty-one years
after that a further discovery was made, which may indeed be said to have
achieved a world-wide reputation. It was found that, by adding bichromate
of potash to a solution of aniline and sulphuric acid, a powder was
obtained from which the dye was afterwards extracted, which is known as
_mauve_. Since that time dyes in all shades and colours have been
obtained from the same source. _Magenta_ was the next dye to make its
appearance, and in the fickle history of fashion, probably no colours
have had such extraordinary runs of popularity as those of mauve and
magenta. Every conceivable colour was obtained in due course from the
same source, and chemists began to suspect that, in the course of time,
the colouring matter of dyer's madder, which was known as _alizarin_,
would also be obtained therefrom. Hitherto this had been obtained from
the root of the madder-plant, but by dint of careful and well-reasoned
research, it was obtained by Dr Groebe, from a solid crystalline coal-tar
product, known as _anthracene_, (C_{12}H_{14}). This artificial alizarin
yields colours which are purer than those of natural madder, and being
derived from what was originally regarded as a waste product, its cost of
production is considerably cheaper.
We have endeavoured thus far to deal with (1) gas, and (2) tar, the two
principal products in the distillation of coal. We have yet to say a few
words concerning the useful ammoniacal liquor, and the final residue in
the retorts, _i.e._, coke.
The ammoniacal liquor which has been passing over during distillation of
the coal, and which has been collecting in the hydraulic main and in
other parts of the gas-making apparatus, is set aside to be treated to a
variety of chemical reactions, in order to wrench from it its useful
constituents. Amongst these, of course, _ammonia_ stands in the first
rank, the others being comparatively unimportant. In order to obtain
this, the liquor is first of all neutralised by being treated with a
quantity of acid, which converts the principal constituent of the liquor,
viz., carbonate of ammonia (smelling salts), into either sulphate of
ammonia, or chloride of ammonia, familiarly known as sal-ammoniac,
according as sulphuric acid or hydrochloric acid is the acid used. Thus
carbonate of ammonia with sulphuric acid will give sulphate of ammonia,
but carbonate of ammonia with hydrochloric acid will give sal-ammoniac
(chloride of ammonia). By a further treatment of these with lime, or, as
it is chemically known, oxide of calcium, ammonia is set free, whilst
chloride of lime (the well-known disinfectant), or sulphate of lime
(gypsum, or "plaster of Paris" ), is the result.
Thus:
Sulphate of ammonia + lime = plaster of Paris + ammonia.
or,
Sal-ammoniac + lime = chloride of lime + ammonia.
Ammonia itself is a most powerful gas, and acts rapidly upon the eyes. It
has a stimulating effect upon the nerves. It is not a chemical element,
being composed of three parts of hydrogen by weight to one of nitrogen,
both of which elements alone are very harmless, and, the latter indeed,
very necessary to human life. Ammonia is fatal to life, producing great
irritation of the lungs.
It has also been called "hartshorn," being obtained by destructive
distillation of horn and bone. The name "ammonia" is said to have been
derived from the fact that it was first obtained by the Arabs near the
temple of Jupiter Ammon, in Lybia, North Africa, from the excrement of
camels, in the form of sal-ammoniac. There are always traces of it in the
atmosphere, especially in the vicinity of large towns and manufactories
where large quantities of coal are burned.
Coke, if properly prepared, should consist of pure carbon. Good coal
should yield as much as 80 per cent. of coke, but owing to the
unsatisfactory manner of its production, this proportion is seldom
yielded, whilst the coke which is familiar to householders, being the
residue left in the retorts after gas-making, usually contains so large a
proportion of sulphur as to make its combustion almost offensive. No
doubt the result of its unsatisfactory preparation has been that it has
failed to make its way into households as it should have done, but there
is also another objection to its use, namely, the fact that, owing to the
quantity of oxygen required in its combustion, it gives rise to feelings
of suffocation where insufficient ventilation of the room is provided.
Large quantities of coke are, however, consumed in the feeding of furnace
fires, and in the heating of boilers of locomotives, as well as in
metallurgical operations; and in order to supply the demand, large
quantities of coal are "coked," a process by which the volatile products
are completely combusted, pure coke remaining behind. This process is
therefore the direct opposite to that of "distillation," by which the
volatile products are carefully collected and re-distilled.
The sulphurous impurities which are always present in the coal, and which
are, to a certain extent, retained in coke made at the gas-works,
themselves have a value, which in these utilitarian days is not long
likely to escape the attention of capitalists. In coal, bands of bright
shining iron pyrites are constantly seen, even in the homely scuttle, and
when coal is washed, as it is in some places, the removal of the pyrites
increases the value of the coal, whilst it has a value of its own.
The conversion of the sulphur which escapes from our chimneys into
sulphuretted hydrogen, and then into sulphuric acid, or oil of vitriol,
has already been referred to, and we can only hope that in these days
when every available source of wealth is being looked up, and when there
threatens to remain nothing which shall in the future be known as
"waste," that the atmosphere will be spared being longer the receptacle
for the unowned and execrated brimstone of millions of fires and
furnaces.
CHAPTER VII.
THE COAL SUPPLIES OF THE WORLD.
As compared with some of the American coal-fields, those of Britain are
but small, both in extent and thickness. They can be regarded as falling
naturally into three principal areas.
The northern coal-field, including those of Fife, Stirling, and Ayr
in Scotland; Cumberland, Newcastle, and Durham in England; Tyrone
in Ireland.
The middle coal-field, all geologically in union, including those of
Yorkshire, Derbyshire, Shropshire, Staffordshire, Flint, and
Denbigh.
The southern coal-field, including South Wales, Forest of Dean,
Bristol, Dover, with an offshoot at Leinster, &c., and Millstreet,
Cork.
Thus it will be seen that while England and Scotland are, in comparison
with their extent of surface, bountifully supplied with coal-areas, in
the sister island of Ireland coal-producing areas are almost absent. The
isolated beds in Cork and Tipperary, in Tyrone and Antrim, are but the
remnants left of what were formerly beds of coal extending the whole
breadth and length of Ireland. Such beds as there remain undoubtedly
belong to the base of the coal-measures, and observations all go to show
that the surface suffered such extreme denudation subsequent to the
growth of the coal-forests, that the wealth which once lay there, has
been swept away from the surface which formerly boasted of it.
On the continent of Europe the coal-fields, though not occupying so large
a proportion of the surface of the country as in England, are very far
from being slight or to be disregarded. The extent of forest-lands still
remaining in Germany and Austria are sufficing for the immediate needs of
the districts where some of the best seams occur. It is only where there
is a dearth of handy fuel, ready to be had, perhaps, by the simple
felling of a few trees, that man commences to dig into the earth for his
fuel. But although on the continent not yet occupying so prominent a
position in public estimation as do coal-fields in Great Britain, those
of the former have one conspicuous characteristic, viz., the great
thickness of some of the individual seams.
In the coal-field of Midlothian the seams of coal vary from 2 feet to 5
feet in thickness. One of them is known as the "great seam," and in spite
of its name attains a thickness only of from 8 to 10 feet thick. There
are altogether about thirty seams of coal. When, however, we pass to the
continent, we find many instances, such as that of the coal-field of
Central France, in which the seams attain vast thicknesses, many of them
actually reaching 40 and 60 feet, and sometimes even 80 feet. One of the
seams in the district of St. Etienne varies from 30 to 70 feet thick,
whilst the fifteen to eighteen workable seams give a thickness of 112
feet, although the total area of the field is not great. Again, in the
remarkable basin of the Saone-et-Loire, although there are but ten beds
of coal, two of them run from 30 to 60 feet each, whilst at Creusot the
main seam actually runs locally to a thickness varying between 40 and 130
feet.
The Belgian coal-field stretches in the form of a narrow strip from 7 to
9 miles wide by about 100 miles long, and is divided into three principal
basins. In that stretching from Liege to Verviers there are eighty-three
seams of coal, none of which are less than 3 feet thick. In the basin of
the Sambre, stretching from Namur to Charleroi, there are seventy-three
seams which are workable, whilst in that between Mons and Thulin there
are no less than one hundred and fifty-seven seams. The measures here are
so folded in zigzag fashion, that in boring in the neighbourhood of Mons
to a depth of 350 yards vertical, a single seam was passed through no
less than six times.
Germany, on the west side of the Rhine, is exceptionally fortunate in the
possession of the famous Pfalz-Saarbruecken coal-field, measuring about 60
miles long by 20 miles wide, and covering about 175 square miles. Much of
the coal which lies deep in these coal-measures will always remain
unattainable, owing to the enormous thickness of the strata, but a
careful computation made of the coal which can be worked, gives an
estimate of no less than 2750 millions of tons. There is a grand total of
two hundred and forty-four seams, although about half of them are
unworkable.
Beside other smaller coal-producing areas in Germany, the coal-fields of
Silesia in the southeastern corner of Prussia are a possession unrivalled
both on account of their extent and thickness. It is stated that there
exist 333 feet of coal, all the seams of which exceed 2-1/2 feet, and
that in the aggregate there is here, within a workable depth, the
scarcely conceivable quantity of 50,000 million tons of coal.
The coal-field of Upper Silesia, occupying an area about 20 miles long by
15 miles broad, is estimated to contain some 10,000 feet of strata, with
333 feet of good coal. This is about three times the thickness contained
in the South Wales coal-field, in a similar thickness of coal-measures.
There are single seams up to 60 feet thick, but much of the coal is
covered by more recent rocks of New Red and Cretaceous age. In Lower
Silesia there are numerous seams 3-1/2 feet to 5 feet thick, but owing to
their liability to change in character even in the same seam, their value
is inferior to the coals of Upper Silesia.
When British supplies are at length exhausted, we may anticipate that
some of the earliest coals to be imported, should coal then be needed,
will reach Britain from the upper waters of the Oder.
The coal-field of Westphalia has lately come into prominence in
connection with the search which has been made for coal in Kent and
Surrey, the strata which are mined at Dortmund being thought to be
continuous from the Bristol coal-field. Borings have been made through
the chalk of the district north of the Westphalian coal-field, and these
have shown the existence of further coal-measures. The coal-field extends
between Essen and Dortmund a distance of 30 miles east and west, and
exhibits a series of about one hundred and thirty seams, with an
aggregate of 300 feet of coal.
It is estimated that this coal-field alone contains no less than 39,200
millions of tons of coal.
Russia possesses supplies of coal whose influence has scarcely yet been
felt, owing to the sparseness of the population and the abundance of
forest. Carboniferous rocks abut against the flanks of the Ural
Mountains, along the sides of which they extend for a length of about a
thousand miles, with inter-stratifications of coal. Their actual contents
have not yet been gauged, but there is every reason to believe that those
coal-beds which have been seen are but samples of many others which will,
when properly worked, satisfy the needs of a much larger population than
the country now possesses.
Like the lower coals of Scotland, the Russian coals are found in the
carboniferous limestone. This may also be said of the coal-fields in the
governments of Tula and Kaluga, and of those important coal-bearing
strata near the river Donetz, stretching to the northern corner of the
Sea of Azov. In the last-named, the seams are spread over an area of
11,000 square miles, in which there are forty-four workable seams
containing 114 feet of coal. The thickest of known Russian coals occur at
Lithwinsk, where three seams are worked, each measuring 30 feet to 40
feet thick.
An extension of the Upper Silesian coal-field appears in Russian Poland.
This is of upper Carboniferous age, and contains an aggregate of 60 feet
of coal.
At Ostrau, in Upper Silesia (Austria), there is a remarkable coal-field.
Of its 370 seams there are no less than 117 workable ones, and these
contain 350 feet of coal. The coals here are very full of gas, which even
percolates to the cellars of houses in the town. A bore hole which was
sunk in 1852 to a depth of 150 feet, gave off a stream of gas, which
ignited, and burnt for many years with a flame some feet long.
The Zwickau coal-field in Saxony is one of the most important in Europe.
It contains a remarkable seam of coal, known as Russokohle or soot-coal,
running at times 25 feet thick. It was separated by Geinitz and others
into four zones, according to their vegetable contents, viz.:--
1. Zone of Ferns.
2. Zone of Annularia and Calamites.
3. Zone of Sigillaria.
4. Zone of Sagenaria (in Silesia), equivalent to the culm-measures of
Devonshire.
Coals belonging to other than true Carboniferous age are found in Europe
at Steyerdorf on the Danube, where there are a few seams of good coal in
strata of Liassic age, and in Hungary and Styria, where there are
tertiary coals which approach closely to those of true Carboniferous age
in composition and quality.
In Spain there are a few small scattered basins. Coal is found overlying
the carboniferous limestone of the Cantabrian chain, the seams being from
5 feet to 8 feet thick. In the Satero valley, near Sotillo, is a single
seam measuring from 60 feet to 100 feet thick. Coal of Neocomian age
appears at Montalban.
When we look outside the continent of Europe, we may well be astonished
at the bountiful manner in which nature has laid out beds of coal upon
these ancient surfaces of our globe.
Professor Rogers estimated that, in the United States of America, the
coal-fields occupy an area of no less than 196,850 square miles.
Here, again, it is extremely probable that the coal-fields which remain,
in spite of their gigantic existing areas, are but the remnants of one
tremendous area of deposit, bounded only on the east by the Atlantic, and
on the west by a line running from the great lakes to the frontiers of
Mexico. The whole area has been subjected to forces which have produced
foldings and flexures in the Carboniferous strata after deposition. These
undulations are greatest near the Alleghanies, and between these
mountains and the Atlantic, whilst the flexures gradually dying out
westward, cause the strata there to remain fairly horizontal. In the
troughs of the foldings thus formed the coal-measures rest, those
portions which had been thrown up as anticlines having suffered loss by
denudation. Where the foldings are greatest there the coal has been
naturally most altered; bituminous and caking-coals are characteristic of
the broad flat areas west of the mountains, whilst, where the contortions
are greatest, the coal becomes a pure anthracite.
It must not be thought that in this huge area the coal is all uniformly
good. It varies greatly in quality, and in some districts it occurs in
such thin seams as to be worthless, except as fuel for consumption by the
actual coal-getters. There are, too, areas of many square miles in
extent, where there are now no coals at all, the formation having been
denuded right down to the palaeozoic back-bone of the country.
Amongst the actual coal-fields, that of Pennsylvania stands
pre-eminent. The anthracite here is in inexhaustible quantity, its output
exceeding that of the ordinary bituminous coal. The great field of which
this is a portion, extends in an unbroken length for 875 miles N.E. and
S.W., and includes the basins of Ohio, Maryland, Virginia, Kentucky, and
Tennessee. The workable seams of anthracite about Pottsville measure in
the aggregate from 70 to 207 feet. Some of the lower seams individually
attain an exceptional thickness, that at Lehigh Summit mine containing a
seam, or rather a bed, of 30 feet of good coal.
A remarkable seam of coal has given the town of Pittsburg its name. This
is 8 feet thick at its outcrop near the town, and although its thickness
varies considerably, Professor Rogers estimates that the sheet of coal
measures superficially about 14,000 square miles. What a forest there
must have existed to produce so widespread a bed! Even as it is, it has
at a former epoch suffered great denudation, if certain detached basins
should be considered as indicating its former extent.
The principal seam in the anthracite district of central Pennsylvania,
which extends for about 650 miles along the left bank of the Susquehanna,
is known as the "Mammoth" vein, and is 29-1/2 feet thick at Wilkesbarre,
whilst at other places it attains to, and even exceeds, 60 feet.
On the west of the chain of mountains the foldings become gentler, and
the coal assumes an almost horizontal position. In passing through Ohio
we find a saddle-back ridge or anticline of more ancient strata than the
coal, and in consequence of this, we have a physical boundary placed upon
the coal-fields on each side.
Passing across this older ridge of denuded Silurian and other rocks, we
reach the famous Illinois and Indiana coal-field, whose
coal-measures lie in a broad trough, bounded on the west by the uprising
of the carboniferous limestone of the upper Mississippi. This limestone
formation appears here for the first time, having been absent on the
eastern side of the Ohio anticline. The area of the coal-field is
estimated at 51,000 square miles.
In connection with the coal-fields of the United States, it is
interesting to notice that a wide area in Texas, estimated at 3000 square
miles, produces a large amount of coal annually from strata of the
Liassic age. Another important area of production in eastern Virginia
contains coal referable to the Jurassic age, and is similar in fossil
contents to the Jurassic of Whitby and Brora. The main seam in eastern
Virginia boasts a thickness of from 30 to 40 feet of good coal.
Very serviceable lignites of Cretaceous age are found on the Pacific
slope, to which age those of Vancouver's Island and Saskatchewan River
are referable.
Other coal-fields of less importance are found between Lakes Huron and
Erie, where the measures cover an area of 5000 square miles, and also in
Rhode Island.
In British North America we find extensive deposits of valuable
coal-measures. Large developments occur in New Brunswick and Nova Scotia.
At South Joggins there is a thickness of 14,750 feet of strata, in which
are found seventy-six coal-seams of 45 feet in total thickness. At Picton
there are six seams with a total of 80 feet of coal. In the lower
carboniferous group is found the peculiar asphaltic coal of the Albert
mine in New Brunswick. Extensive deposits of lignite are met with both in
the Dominion and in the United States, whilst true coal-measures flank
both sides of the Rocky Mountains. Coal-seams are often encountered in
the Arctic archipelago.
The principal areas of deposit in South America are in Brazil, Uruguay,
and Peru. The largest is the Candiota coal-field, in Brazil, where
sections in the valley of the Candiota River show five good seams with a
total of 65 feet of coal. It is, however, worked but little, the
principal workings being at San Jeronimo on the Jacahahay River.
In Peru the true carboniferous coal-seams are found on the higher ground
of the Andes, whilst coal of secondary age is found in considerable
quantities on the rise towards the mountains. At Porton, east of
Truxillo, the same metamorphism which has changed the ridge of sandstone
to a hard quartzite has also changed the ordinary bituminous coal into an
anthracite, which is here vertical in position. The coals of Peru usually
rise to more than 10,000 feet above the sea, and they are practically
inaccessible.
Cretaceous coals have been found at Lota in Chili, and at Sandy Point,
Straits of Magellan.
Turning to Asia, we find that coal has been worked from time to time at
Heraclea in Asia Minor. Lignites are met with at Smyrna and Lebanon.
The coal-fields of Hindoostan are small but numerous, being found in all
parts of the peninsula. There is an important coal-field at Raniganj,
near the Hooghly, 140 miles north of Calcutta. It has an area of 500
square miles. In the Raniganj district there are occasional seams 20 feet
to 80 feet in thickness, but the coals are of somewhat inferior quality.
The best quality amongst Indian coals has come from a small coal-field of
about 11 square miles in extent, situated at Kurhurbali on the East
Indian Railway. Other coal-fields are found at Jherria and on the Sone
River, in Bengal, and at Mopani on the Nerbudda. Much is expected in
future from the large coal-field of the Wardha and Chanda districts, in
the Central Provinces, the coal of which may eventually prove to be of
Permian age.
The coal-deposits of China are undoubtedly of tremendous extent, although
from want of exploration it is difficult to form any satisfactory
estimate of them. Near Pekin there are beds of coal 95 feet thick, which
afford ample provision for the needs of the city. In the mountainous
districts of western China the area over which carboniferous strata are
exposed has been estimated at 100,000 square miles. The coal-measures
extend westward to the Mongolian frontier, where coal-seams 30 feet thick
are known to lie in horizontal plane for 200 miles. Most of the Chinese
coal-deposits are rendered of small value, either owing to the
mountainous nature of the valleys in which they outcrop, or to their
inaccessibility from the sea. Japan is not lacking in good supplies of
coal. A colliery is worked by the government on the island of Takasima,
near Nagasaki, for the supply of coals for the use of the navy.
The British possession of Labuan, off the island of Borneo, is rich in a
coal of tertiary age, remarkable for the quantity of fossil resin which,
it contains. Coal is also found in Sumatra, and in the Malayan
Archipelago.
In Cape Colony and Natal the coal-bearing Karoo beds are probably of New
Red age. The coal is reported to be excellent in quantity.
In Abyssinia lignites are frequently met with in the high lands of the
interior.
Coal is very extensively developed throughout Australasia. In New South
Wales, coal-measures occur in large detached portions between 29 deg. and 35 deg.
S. latitude. The Newcastle district, at the mouth of the Hunter river, is
the chief seat of the coal trade, and the seams are here found up to 30
feet thick. Coal-bearing strata are found at Bowen River, in Queensland,
covering an area of 24,000 square miles, whilst important mines of
Cretaceous age are worked at Ipswich, near Brisbane. In New Zealand
quantities of lignite, described as a hydrous coal, are found and
utilised; also an anhydrous coal which may prove to be either of
Cretaceous or Jurassic age.
We have thus briefly sketched the supplies of coal, so far as they are
known, which are to be found in various countries. But England has of
late years been concerned as to the possible failure of her home supplies
in the not very distant future, and the effects which such failure would
be likely to produce on the commercial prosperity of the country.
Great Britain has long been the centre of the universe in the supply of
the world's coal, and as a matter of fact, has been for many years
raising considerably more than one half of the total amount of coal
raised throughout the whole world. There is, as we have seen, an
abundance of coal elsewhere, which will, in the course of time, compete
with her when properly worked, but Britain seems to have early taken the
lead in the production of coal, and to have become the great universal
coal distributor. Those who have misgivings as to what will happen when
her coal is exhausted, receive little comfort from the fact that in North
America, in Prussia, in China and elsewhere, there are tremendous
supplies of coal as yet untouched, although a certain sense of relief is
experienced when that fact becomes generally known.
If by the time of exhaustion of the home mines Britain is still dependent
upon coal for fuel, which, in this age of electricity, scarcely seems
probable, her trade and commerce will feel with tremendous effect the
blow which her prestige will experience when the first vessel, laden with
foreign coal, weighs anchor in a British harbour. In the great coal
lock-out of 1893, when, for the greater part of sixteen weeks scarcely a
ton of coal reached the surface in some of her principal coal-fields, it
was rumoured, falsely as it appeared, that a collier from America had
indeed reached those shores, and the importance which attached to the
supposed event was shown by the anxious references to it in the public
press, where the truth or otherwise of the alarm was actively discussed.
Should such a thing at any time actually come to pass, it will indeed be
a retribution to those who have for years been squandering their
inheritance in many a wasteful manner of coal-consumption.
Thirty years ago, when so much small coal was wasted and wantonly
consumed in order to dispose of it in the easiest manner possible at the
pitmouths, and when only the best and largest coal was deemed to be of
any value, louder and louder did scientific men speak in protest against
this great and increasing prodigality. Wild estimates were set on foot
showing how that, sooner or later, there would be in Britain no native
supply of coal at all, and finally a Royal Commission was appointed in
1866, to collect evidence and report upon the probable time during which
the supplies of Great Britain would last.
This Commission reported in 1871, and the outcome of it was that a period
of twelve hundred and seventy-three years was assigned as the period
during which the coal would last, at the then-existing rate of
consumption. The quantity of workable coal within a depth of 4000 feet
was estimated to be 90,207 millions of tons, or, including that at
greater depths, 146,480 millions of tons. Since that date, however, there
has been a steady annual increase in the amount of coal consumed, and
subsequent estimates go to show that the supplies cannot last for more
than 250 years, or, taking into consideration a possible decrease in
consumption, 350 years. Most of the coal-mines will, indeed, have been
worked out in less than a hundred years hence, and then, perhaps, the
competition brought about by the demand for, and the scarcity of, coal
from the remaining mines, will have resulted in the dreaded importation
of coal from abroad.
In referring to the outcome of the Royal Commission of 1866, although the
Commissioners fixed so comparatively short a period as the probable
duration of the coal supplies, it is but fair that it should be stated
that other estimates have been made which have materially differed from
their estimate. Whereas one estimate more than doubled that of the Royal
Commission, that of Sir William Armstrong in 1863 gave it as 212 years,
and Professor Jevons, speaking in 1875 concerning Armstrong's estimate,
observed that the annual increase in the amount used, which was allowed
for in the estimate, had so greatly itself increased, that the 212 years
must be considerably reduced.
One can scarcely thoroughly appreciate the enormous quantity of coal that
is brought to the surface annually, and the only wonder is that there are
any supplies left at all. The Great Pyramid which is said by Herodotus to
have been twenty years in building, and which took 100,000 men to build,
contains 3,394,307 cubic yards of stone. The coal raised in 1892 would
make a pyramid which would contain 181,500,000 cubic yards, at the low
estimate that one ton could be squeezed into one cubic yard.
The increase in the quantity of coal which has been raised in succeeding
years can well be seen from the following facts.
In 1820 there were raised in Great Britain about 20 millions of tons. By
1855 this amount had increased to 64-1/2 millions. In 1865 this again had
increased to 98 millions, whilst 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 been made in the chemical knowledge of the carbon,
hydrogen, and oxygen compounds. Scientists appeared to work along two
planes; there were those who discovered certain chemical compounds in the
resulting products of reactions in the treatment of _existing_
vegetation, and there were those who, studying the wonderful constituents
in coal-tar, the product of a _past_ age, immediately set to work to find
therein those compounds which their contemporaries had already
discovered. Generally, too, with signal success.
The discovery of benzene in 1825 by Faraday was followed in the course of
a few years by its discovery in coal-tar by Hofmann. Toluene, which was
discovered in 1837 by Pelletier, was recognised in the fractional
distillation of crude naphtha by Mansfield in 1848. Although the method
of production of mauveine on a large scale was not accomplished until
1856, yet it had been noticed in 1834, the actual year of its recognition
as a constituent of coal-tar, that, when brought into contact with
chloride of lime, it gave brilliant colours, but it required a
considerable cheapening of the process of aniline manufacture before the
dyes commenced to enter into competition with the old natural dyes.
The isolation of aniline from coal-tar is expensive, in consequence of
the small quantities in which it is there found, but it was discovered by
Mitscherlich that by acting upon benzene, one of the early distillates of
coal-tar, for the production of nitro-benzole, a compound was produced
from which aniline could be obtained in large quantities. There were thus
two methods of obtaining aniline from tar, the experimental and the
practical.
In producing nitrobenzole (nitrobenzene), chemically represented as
(C_{6}H_{5}NO_{2}), the nitric acid used as the reagent with benzene, is
mixed with a quantity of sulphuric acid, with the object of absorbing
water which is formed during the reaction, as this would tend to dilute
the efficiency of the nitric acid. The proportions are 100 parts of
purified benzene, with a mixture of 115 parts of concentrated nitric acid
(HNO_{3}) and 160 parts of concentrated sulphuric acid. The mixture is
gradually introduced into the large cast-iron cylinder into which the
benzene has been poured. The outside of the cylinder is supplied with an
arrangement by which fine jets of water can be made to play upon it in
the early stages of the reaction which follows, and at the end of from
eight to ten hours the contents are allowed to run off into a storage
reservoir. Here they arrange themselves into two layers, the top of which
consists of the nitrobenzene which has been produced, together with some
benzene which is still unacted upon. The mixture is then freed from the
latter by treatment with a current of steam. Nitrobenzene presents itself
as a yellowish oily liquid, with a peculiar taste as of bitter almonds.
It was formerly in great demand by perfumers, but its poisonous
properties render it a dangerous substance to deal with. In practice a
given quantity of benzene will yield about 150 per cent of nitrobenzene.
Stated chemically, the reaction is shown by the following equation:--
C_{6}H_{6} + HNO_{3} = C_{6}H_{5}NO_{2}, + H_{2}O
(Benzene) (Nitric acid) (Nitrobenzene) (Water).
The water which is thus formed in the process, by the freeing of one of
the atoms of hydrogen in the benzene, is absorbed by the sulphuric acid
present, although the latter takes no actual part in the reaction.
From the nitrobenzene thus obtained, the aniline which is now used so
extensively is prepared. The component atoms of a molecule of aniline are
shown in the formula C_{6}H_{5}NH_{2}. It is also known as phenylamine or
amido-benzole, or commercially as aniline oil. There are various methods
of reducing nitrobenzene for aniline, the object being to replace the
oxygen of the former by an equivalent number of atoms of hydrogen. The
process generally used is that known as Bechamp's, with slight
modifications. Equal volumes of nitrobenzene and acetic acid, together
with a quantity of iron-filings rather in excess of the weight of the
nitrobenzene, are placed in a capacious retort. A brisk effervescence
ensues, and to moderate the increase of temperature which is caused by
the reaction, it is found necessary to cool the retort. Instead of acetic
acid hydrochloric acid has been a good deal used, with, it is said,
certain advantageous results. From 60 to 65 per cent. of aniline on the
quantity of nitrobenzene used, is yielded by Bechamp's process.
Stated in a few words, the above is the process adopted on all hands for
the production of commercial aniline, or aniline oil. The details of the
distillation and rectification of the oil are, however, as varied as they
can well be, no two manufacturers adopting the same process. Many of the
aniline dyes depend entirely for their superiority, on the quality of the
oil used, and for this reason it is subject to one or more processes of
rectification. This is performed by distilling, the distillates at the
various temperatures being separately collected.
When pure, aniline is a colourless oily liquid, but on exposure rapidly
turns brown. It has strong refracting powers and an agreeable aromatic
smell. It is very poisonous when taken internally; its sulphate is,
however, sometimes used medicinally. It is by the action upon aniline of
certain oxidising agents, that the various colouring matters so well
known as aniline dyes are obtained.
Commercial aniline oil is not, as we have seen, the purest form of
rectified aniline. The aniline oils of commerce are very variable in
character, the principal constituents being pure aniline, para- and
meta-toluidine, xylidines, and cumidines. They are best known to the
colour manufacturer in four qualities--
(_a_) Aniline oil for blue and black.
(_b_) Aniline oil for magenta.
(_c_) Aniline oil for safranine.
(_d_) _Liquid toluidine.
From the first of these, which is almost pure aniline, aniline black is
derived, and a number of organic compounds which are further used for the
production of dyes. The hydrochloride of aniline is important and is
known commercially as "aniline salt."
The distillation and rectification of aniline oil is practised on a
similar principle to the fractional distillation which we have noticed as
being used for the distillation of the naphthas. First, light aniline
oils pass over, followed by others, and finally by the heavy oils, or
"aniline-tailings." It is a matter of great necessity to those engaged in
colour manufacture to apply that quality oil which is best for the
production of the colour required. This is not always an easy matter, and
there is great divergence of opinion and in practice on these points.
The so-called aniline colours are not all derived from aniline, such
colouring matters being in some cases derived from other coal-tar
products, such as benzene and toluene, phenol, naphthalene, and
anthracene, and it is remarkable that although the earlier dyes were
produced from the lighter and more easily distilled products of
coal-tar, yet now some of the heaviest and most stubborn of the
distillates are brought under requisition for colouring matters, those
which not many years ago were regarded as fit only to be used as
lubricants or to be regarded as waste.
It is scarcely necessary or advisable in a work of this kind to pursue
the many chemical reactions, which, from the various acids and bases,
result ultimately in the many shades and gradations of colour which are
to be seen in dress and other fabrics. Many of them, beautiful in the
extreme, are the outcome of much careful and well-planned study, and to
print here the complicated chemical formulae which show the great changes
taking place in compounds of complex molecules, or to mention even the
names of these many-syllabled compounds, would be to destroy the purpose
of this little book. The Rosanilines, the Indulines, and Safranines; the
Oxazines, the Thionines: the Phenol and Azo dyes are all substances which
are of greater interest to the chemical students and to the colour
manufacturer than to the ordinary reader. Many of the names of the bases
of various dyes are unknown outside the chemical dyeworks, although each
Back to Full Books
|