Newcastle─upon─Tyne, Sunderland, and Whitehaven. The particular places
whence they are obtained have the name of _collieries_, and the mines
from which they are dug are called _pits_. The deepest of these are in
Northumberland, and are worked at more than 900 feet below the surface
of the earth. At Newcastle there is a coal─pit near 800 feet in depth,
and which, at that depth, is wrought five miles horizontally, quite
across, and beneath the bed of the river Tyne, and under the adjacent
part of the county of Durham. At Whitehaven the mines are of great
depth, and are extended even under the sea, to places where there is
above them sufficient depth of water for ships of great burthen, and in
which the miners are able sometimes to hear the roaring of the water. On
the contrary, in some parts of Durham the coal lies so near the surface
of the earth that the wheels of carriages lay it open, and in such
quantity as to be sufficient for the use of the neighbourhood.
The beds of coal are of various thicknesses, from a few inches to
several feet; and in some places, it is found advantageous to work them
at a very great depth, although their thickness does not exceed four or
five feet. The thickest bed of English coal, of any extent, is that of
the main coal in Staffordshire, which measures about thirty feet. In
many places there are several beds above, and parallel to, each other,
separated by strata of slate, sandstone, and other minerals. Coal is
never found in chalk, and very rarely in limestone.
At Whitehaven, the principal entrance to the coalmine, both for men and
horses, is by an opening at the bottom of a hill, through a long passage
hewn in a rock. This, by a steep descent, leads to the lowest bed of
coal. The greatest part of the descent is through spacious galleries,
which intersect other galleries; all the coal having been cut away,
except large pillars, which, in deep parts of the mine, are three yards
high, and about twelve yards square at the base, such great strength
being there required to support the ponderous roof. There are three
distinct and parallel strata of coal, which lie at a considerable
distance above each other, and which have a communication by pits that
are sunk between them. These strata are not always regularly continued
in the same plane. The miners occasionally meet with veins of hard rock,
which interrupt their further progress, and, at such places, the earth,
on one side of the vein, appears to have sunk down, while that on the
opposite side has its ancient situation. These breaks the miners call
_dykes_ (4). When they come to one of them, their first care is to
discover whether the coal, in the part adjoining, be higher or lower
than that in which they have been working; or, to use their own terms,
whether it be cast down or cast up. For this purpose they examine
attentively the mineral strata on the opposite side, to see how far they
correspond with those which they have already passed through. If the
coal be cast down, they sink a pit to it: but if it be cast up, the
discovery of it is often attended with great labour and expense.
In general the entrance to coal mines is by perpendicular shafts, and
the coals and workmen are drawn up by machinery. As the mines frequently
extend to great distances, horizontally, beneath the surface of the
earth, peculiar care is necessary to keep them continually ventilated
with currents of fresh air, for the purpose, not only of affording to
the workmen a constant supply of that vital fluid, but also to expel
from the mines certain noxious exhalations which are sometimes produced
in them.
One of these, denominated _fire damp_, is occasioned by the generation
of hydrogen gas, or inflammable air (45). This gas, when mixed with the
common air of the atmosphere, explodes, with great violence, on the
approach of a lighted candle, or any other flame; and has, at different
times, occasioned the loss of many valuable lives. It is a singular
circumstance, that although it is immediately set on fire by a flame,
yet it cannot be kindled by red hot iron, nor by sparks produced from
the collision of flint and steel. Hence a machine was, some years ago,
adopted in the mines near Whitehaven and Workington, in which a wheel
formed of steel, and in shape somewhat like that of a razor─grinder, was
turned round with very rapid motion against a series of flints, and in
such manner as to yield to the miners sufficient light to carry on their
work in places where the flame of a candle would occasion the most
dreadful explosions. Sir Humphrey Davy has lately invented, for the use
of mines where this gas is prevalent, what is called a _safety lamp_.
This is a lamp enclosed in a wire cylinder, the interstices of which are
so extremely small as, whilst it gives light, will not explode the gas.
Another injurious exhalation in coal mines arises from the formation of
carbonic acid gas, or fixed air (26), and is called _choke damp_. It is
the property of inflammable air to rise to the upper parts; but this, on
account of its weight, occupies principally the lower parts of mines,
and occasions death by suffocation, though it is by no means so fatal as
the former. In some mines a prevention of injury arising from each of
these gases is attained, by ascertaining the particular crevices in the
coal from which they issue, confining them at those places within a
narrow space, and, if possible, conveying them out of the mines, through
long pipes, into the open air.
There is yet another danger attending coal mines which requires to be
provided against, and this is inundation. Many mines have been destroyed
by the flooding of water, which springs up within them. The modes by
which this was formerly extracted were extremely laborious, and, in
numerous instances, entirely inefficacious. By means, however, of the
fire or steam engines now in use, the quantity of water raised from
mines is perfectly astonishing. Four engines in one of the collieries at
Whitehaven discharge more than twenty hogsheads per minute, or upwards
of 30,000 hogsheads in every twenty─four hours.
The coal trade, which at present affords so important a nursery for our
seamen, and, in numerous other respects, yields advantages of the most
beneficial description to this country, was entirely unknown a few
centuries ago. Coals were not generally adopted as fuel until the
beginning of the reign of Charles I. They were, however, noticed in
documents anterior to the reign of Henry III., for, that monarch, in the
year 1234, renewed a charter, granted by his father, to the inhabitants
of Newcastle, by which they were permitted to dig coal upon payment of
100_l._ per annum. Coals had been introduced into London before 1306;
for in that year, the use of them as fuel was prohibited, from the
supposed tendency of their smoke to corrupt the air. About the beginning
of the sixteenth century, the best coals were sold in London at the rate
of 4_s._ 1_d._ per chaldron, and at Newcastle for no more than 2_s._
6_d._ During the ensuing century, however, they were received into such
general use, that, in 1648, on a scarcity of coal in London, many of the
poor are said to have died from want of fuel. The whole quantity of
coals imported into London has been estimated, on an average of four
years, ending in March, 1815, to amount to 1,170,000 chaldrons per
annum.
Some writers have imagined coal to be the remains of antediluvian
timber, which floated upon the waters of the deluge until several strata
of mineral substances had been formed: others conceive it to have been
antediluvian peat bog. It is called _pit coal_, from the circumstance
only of its being obtained from mines or pits; and, in London, for no
better reason than its having been conveyed thither by sea, it has the
name of _sea coal_.
Its uses as fuel are too extensively known to need here any
observations. By the distillation of coal an inflammable gas is
produced, which has of late been introduced for the lighting of
manufactories, and lighting several of the streets and shops of the
metropolis. This gas is conveyed by pipes, from the reservoir in which
it is collected, to great distances; and the light which it yields is
peculiarly brilliant and beautiful. It was at the foundery belonging to
Messrs. Boulton and Watts, at Birmingham, that the first public display
of _gas lights_ was made, in the year 1802, on the occasion of the
rejoicings for peace. In 1805 the cotton mills of Messrs. Phillips and
Lee, at Manchester, were lighted with gas, to the exclusion of lamps,
candles, and every other source of artificial light. In the beginning of
1816 it was estimated that, at the three gas─light stations, in
Peter─street, Westminster, Worship─street, and Norton Falgate, London,
twenty─five chaldrons of coals were used daily; and that these were
sufficient to supply with gas 125,000 large lamps. At the works in
Dorset─street, Fleet─street, the daily consumption of coal was about
three chaldrons, which afforded gas for 1,500 lamps.
The production of the _gas light_ is easily effected in miniature, by
putting common coal, pounded small, into the bowl of a tobacco─pipe, and
closely covering this with clay made into a stiff lute with water. When
the clay is dry, the bowl of the pipe must be put into the fire, and
there heated gradually. In a few minutes a stream of gas will issue from
the end of the pipe. This may be set on fire with a piece of paper, and
will burn with a bright flame. When the gas is no longer disengaged,
there will be found in the bowl of the pipe the remains of the coals, in
the form of coke.
It is estimated that one chaldron of good coals will afford from 17,000,
to 20,000 cubical feet of gas; and that one of the large burners in the
shops of London, consumes about four cubical feet per hour.
_Soot_ is produced from the smoke of burned coal, and is used as a
manure for cold, moist, and clayey meadows and pastures: and pounded
coal has been applied to the same purpose in some parts of the
Continent. By a process called charring, coal is divested of its humid,
acid, and bituminous particles, and is converted into a kind of cinder
called _coke_. This is employed in cases where intense heat is
requisite, as for the smelting of iron ore; and likewise where acid and
bituminous particles of coal would be detrimental, as in the drying of
malt.
What is usually termed _culm_ is the refuse or dusty coal, produced in
working the common coals. It contains much earthy matter, will not
kindle in an ordinary fire─place, but produces considerable heat and
flame in a furnace, where a strong current of air is introduced. In
England it is exempted from the high duty imposed on other coals, and is
sold at a very low price. It is used for burning lime, making salt, and
in steam engines.
219. _CANNEL COAL is of black colour, with little lustre, is not
laminar, but breaks in any direction, like pitch, and does not stain the
fingers._
This highly inflammable kind of coal is found abundantly in the
neighbourhood of Wigan, in Lancashire, where there is an entire stratum
of it about four feet in thickness. It is also found near Whitehaven, in
some of the pits at Newcastle, and in some parts of Scotland. Doubts
have been entertained respecting the name of this coal; but when it is
recollected that in Lancashire, whence it is chiefly brought, the word
candle is usually pronounced with the omission of the letter _d_, and
that, in many instances, the coal is used by the poor as a substitute
for candles, these will be immediately removed. In Scotland it has the
name of _parrot coal_.
No kind of coal takes fire so readily, nor burns with so cheerful and
brilliant a flame as this: and its not soiling the fingers, like pit
coal, renders the use of it peculiarly pleasant; but it does not cake,
and soon burns away. When first kindled, it crackles and splinters very
much; and, on this account, would be dangerous, were it not easily
prevented from so doing by being previously immersed for a little while
in water. Cannel coal has much the appearance of jet. It admits of being
turned in a lathe, and takes a good polish; and snuff─boxes and trinkets
made of it have in many instances been sold as jet (222). Of all the
kinds of coal that are used for gas─lights, none are said to be so
useful as this.
220. _STONE COAL, KILKENNY COAL, WELSH COAL, or GLANCE COAL, is of a
dark iron─black colour, with a metallic lustre and foliated texture; and
consists almost entirely of charcoal._
Unlike most other kinds of coal, this occurs both in stratified masses,
and in lumps, nested in clay. It is found in several countries of the
Continent, in Wales, Scotland, and near Kilkenny in Ireland.
When laid on burning coals, it becomes red hot, emits a blue lambent
flame in the same manner as charcoal; and is, at length, slowly
consumed, leaving behind a portion of red ashes. No smoke nor soot is
produced from this coal; but, on the contrary, it whitens the places
where the fume is condensed; and the effluvia which it gives out are
extremely suffocating.
This coal is chiefly used in the drying of malt.
221. _BOVEY COAL, BROWN COAL, or BITUMINOUS WOOD, is of brown colour,
and in shape exactly resembles the stems and branches of trees, but is
usually compressed. It is soft, somewhat flexible, and so light as
nearly to float when thrown into water._
The greatest abundance of this coal occurs at Bovey, near Exeter, from
which place it derives its name. The lowest stratum is worked at the
depth of seventy─five feet beneath the surface of the earth. It is also
found in Scotland, Ireland, and Germany.
As fuel, the Bovey coal is used only by the poorest classes of the
community, as, notwithstanding its burning with a clear flame, it emits
a sweetish but extremely disagreeable sulphureous gas, which is
injurious to the health of the inhabitants. It is principally used for
the burning of lime, and for the first baking of earthen ware.
222. _JET, or PITCH COAL, is a solid, black, and opaque mineral, harder
than coal, and found in detached_ _masses from an inch to seven or eight
feet in length, having a fine or regular structure, and a grain
resembling that of wood._
_It has sometimes been confounded with cannel coal (219), but it is
easily distinguished by its superior hardness: Jet cannot without
difficulty be scratched with a knife, whilst cannel coal may be marked
by the simple pressure of the nail._
The name of jet has been derived from Gages, a river of Lycia, whence
the ancients are said to have obtained this substance. It is frequently
cast ashore on the eastern coasts of England, together with pieces of
amber and curious pebbles, particularly near Lowestoft in Suffolk, and
in some parts of Yorkshire, where many persons employ their leisure in
searching for it, and forming it into various kinds of trinkets. Jet is
found in several countries of the Continent.
It is stated that in the district of Aude, in France, there are more
than 1,000 persons constantly employed in the fabrication of jet into
rosaries, buttons, ear─rings, necklaces, bracelets, snuff─boxes, and
trinkets of different kinds. Near fifty tons weight of it are annually
used for this purpose; and articles to the value of 18,000 livres are
said to be sold in Spain alone. In Prussia the amber diggers call it
_black amber_, because it is found accompanying that substance; and
because, like amber, it is faintly electric, or attracts feathers and
other light objects when rubbed. They manufacture it into various
ornamental articles, and sell these to ignorant persons, as black amber,
at a great price.
In different parts of the globe the trunks of trees, which have been
long buried, have passed into the state of jet; and, in almost all these
trees may be traced the distinctive characters of the species to which
they belong. They are more or less brittle, more or less unctuous,
according to the species, the degree of alteration, and the nature of
the soil. All of them have a smooth and glassy fracture, but all are not
adapted for the tool of the workman. When, for instance, the texture of
the tree presents only a mass of dry fibres, the jet obtained is dry and
brittle; and cannot be used in the forming of trinkets. But, if the
texture be unctuous the fibre acquires a considerable degree of
softness, is susceptible of being properly wrought, and receives a
perfect and beautiful polish.
A fictitious kind of jet is made of glass; and several varieties of
mineral pitch, and cannel coal, are imposed upon ignorant purchasers for
jet.
When jet is once set on fire it burns with a green flame, and continues
to burn for a considerable time, exhaling a strong bituminous smell. If
the heat be rendered greater, it melts.
GRAPHITE FAMILY.
223. _BLACK LEAD, or PLUMBAGO, is an inflammable mineral, which consists
of carbon, or charcoal (48), combined with iron, in the proportion of
about nine parts of the former to one of the latter._
_It is of dark iron─grey colour, with a strong metallic lustre, and so
soft that it is easily scratched with a knife. To the touch it is soft
and greasy; and, when handled, it stains the fingers. In weight it is
about twice as heavy as water._
The name of black lead has very improperly been given to this substance
from its appearance only, as it has no alliance whatever with lead. It
is usually found in kidney─shaped lumps of various size, and occurs in
several countries of Europe, but no where of such excellent quality as
in Borrowdale, Cumberland, where it has the name of _wadd_. The vein of
black lead lies between strata of slate, and is from eight to nine feet
thick. This mine is not opened more than once every three or four years,
the quantity thus obtained being found fully sufficient for the demand.
The only other mine of black lead in Britain is in Ayrshire, Scotland.
Artists in water─colours, if deprived of this mineral, would find great
difficulty in making their sketches; as the marks that are erroneously
made with it are more easily expunged than those of almost any other
substance. Hundreds of thousands of pencils are every year formed of
black lead. For this purpose the mineral is sawed into slender square
pieces. These are fixed into grooves, of the same shape, cut in cedar,
or some other soft wood; another piece of wood is then glued upon this,
and the whole is worked into a circular form. The finer kinds of black
lead are prepared for use by being boiled in oil before they are cut.
The coarser kinds, and the refuse of the sawings, are melted with
sulphur, and then cast into coarser pencils for carpenters. These may,
in general, be easily distinguished by their sulphureous smell. The
pencils that are manufactured in England are more esteemed on the
Continent than any others.
The powder produced in the sawing of pencils is employed for numerous
purposes. It is used for giving a bright gloss to cast─iron grates and
stoves, and defending them from rust, and from the action of fire. It
may also be advantageously applied to the inner surface of wooden
screws, to packing presses, the axles of various sorts of machines, to
slides, and other wood work, which are subject to friction. In this
respect it is far superior either to grease or soap. The makers of
razor─strops occasionally employ black lead in the composition which
they spread upon leather for the sharpening of razors; and, on the
Continent, it is sometimes used for blackening the hair. A coarser kind
of black lead is used for making the vessels that are used by chemists,
called crucibles.
RESIN FAMILY.
224. _AMBER is a substance usually of golden yellow colour,
semi─transparent, and of shining and somewhat resinous lustre. It is
occasionally seen of yellowish white colour, and nearly opaque._
The origin of amber is unknown. From the ants and other insects which it
frequently contains, there can be no doubt that it has once been in a
fluid state: and some writers have thought that it is a resinous juice,
gradually modified by the action of sulphuric acid (24); but this is
entirely conjecture. The ancients called it _electron_, and attributed
its formation to the sisters of Phaëton, who, lamenting the death of
their brother, were converted into poplar trees; these, it was said,
instead of tears, yielded every year this substance; which, issuing from
them in a fluid state, ran into the river, and there became hardened.
Amber is usually found in rounded and detached pieces, on the south
coast of the Baltic, on the eastern shores of England, and in small
quantity, on those of Sicily and the Adriatic; and a substance greatly
resembling it is occasionally found in gravel pits near London. The only
mines of amber at present known are in Prussia. These are worked in the
usual way, by shafts and galleries, to the depth of about 100 feet. The
amber is imbedded in a stratum of fossil wood, and occurs in rounded
pieces, from a few grains to three and even five pounds in weight. The
largest piece of amber ever known to be discovered in a detached state
was found near the surface of the ground, in Lithuania, about twelve
miles from the Baltic Sea. It weighed more than eighteen pounds, and was
deposited in the cabinet of the King of Prussia at Berlin. Very lately a
mass of amber, weighing thirteen pounds, was also found in Prussia. For
this piece 5000 dollars are said to have been offered; but the Armenian
merchants assert that it might have been sold in Constantinople for more
than 30,000 dollars.
Anterior to the discovery or general dispersion of precious stones from
India, amber was considered of great value as a jewel, and was employed
in all kinds of ornamental dresses. The ancient Romans were so partial
to this substance that Pliny, reprobating the great demand for it, says,
the Roman females would give larger sums for a puppet or figure in
amber, resembling a man or woman, however small its size, than they
would for the finest man or the most valiant soldier. Under the Emperor
Nero, persons were sent from Rome, for the purpose of collecting and
purchasing amber; and so much of it was at length obtained, that it was
used for ornamenting the nets and cordage employed in the theatres for
preventing the wild animals from approaching the populace there
assembled. It was likewise used to ornament the armour, the biers, and
funeral apparatus of such persons as were killed.
Amber is now chiefly in request by Greek and Armenian merchants, but it
is uncertain where they dispose of it. Some persons conjecture that it
is purchased by pilgrims previously to their journey to Mecca; and that,
on their arrival in that place, they burn it in honour of Mahomet.
The kind most in esteem is of a bright golden yellow colour. This is
occasionally manufactured into snuff─boxes, small vases, necklaces,
bracelets, cane─heads, and other ornamental articles, many of which are
purchased by the Turks, Russians, and Poles; but the general demand for
them has of late very much decreased. Some years ago the German artists
paid great attention to this substance; and many experiments were made
for the purpose of discovering means of removing its defects, and
improving its beauty. It is said that they possessed the art of
liquefying it to such a degree, that it could be run into moulds without
injuring its beauty; and that specimens of this liquefied amber are
preserved in the Electoral Cabinet at Dresden. There are still
considerable manufactories of amber at Stolpen, Konigsberg, Dantzic, and
Lubeck.
Amber, when wrought into ornaments, is first split on a leaden plate,
and then turned on a particular kind of whetstone. The polishing of it
is performed with chalk and water, or chalk and oil; and the work is
finished by rubbing the whole with clean flannel. Without great
attention it becomes very hot, and either flies into pieces, or takes
fire during the operation.
After having been roasted or melted, amber is readily soluble in oil,
and, in this state, constitutes the basis of several kinds of varnish.
It was formerly much used in medicine, but, in this respect, it is now
almost wholly neglected. Some persons, however, have still an absurd
notion that a collar or necklace of amber, tied round an infant’s neck,
will enable it to cut its teeth in safety. Oil of amber combined with
liquid ammonia constitutes a white soapy liquor called _eau─de─luce_.