thirling next the foreheads _f_, _h_, and _m_, _fig._ 860., and moves
through the thirling which is nearest to the face of every board and
room, the emission of fire-damp is frequently so abundant from the coaly
strata, that the miners dare not proceed forwards more than a few feet
from that aerial circulation, without hazard of being burned by the
combustion of the gas at their candles. To guard against this accident,
temporary shifting brattices are employed. These are formed of deal,
about 3/4 of an inch thick, 3 or 4 feet broad, and 10 feet long; and are
furnished with cross-bars for binding the deals together, and a few
finger loops cut through them, for lifting them more expeditiously, in
order to place them in a proper position. Where inflammable air abounds,
a store of such brattice deals should be kept ready for emergencies.
[Illustration: 861]
The mode of applying these temporary brattices, or deal partitions, is
shown in the accompanying figure (_fig._ 861.), which shows how the air
circulates freely through the thirling _d_, _d_ before the brattices are
placed. At _b_ and _c_, we see two heading boards or rooms, which are so
full of inflammable air as to be unworkable. Props are now erected near
the upper end of the pillar _e_, betwixt the roof and pavement, about
two feet clear of the sides of the next pillar, leaving room for the
miner to pass along between the pillar side and the brattice. The
brattices are then fastened with nails to the props, the lower edge of
the under brattice resting on the pavement, while the upper edge of the
upper is in contact with the roof. By this means any variation of the
height in the bed of coal is compensated by the overlap of the brattice
boards; and as these are advanced, shifting brattices are laid close to,
and alongside of, the first set. The miner next sets up additional props
in the same parallel line with the former, and slides the brattices
forwards, to make the air circulate close to the forehead where he is
working; and he regulates the distance betwixt the brattice and the
forehead by the disengagement of fire-damp and the velocity of the
aerial circulation. The props are shown at _d d_, and the brattices at
_f_, _f_. By this arrangement the air is prevented from passing directly
through the thirling _a_, and is forced along the right-hand side of the
brattice, and, sweeping over the wall face or forehead, returns by the
back of the brattice, and passes through the thirling _a_. It is
prevented, however, from returning in its former direction by the
brattice planted in the forehead _c_, whereby it mounts up and
accomplishes its return close to that forehead. Thus headways and boards
are ventilated till another thirling is made at the upper part of the
pillar. The thirling _a_ is then closed by a brick stopping, and the
brattice boards removed forward for a similar operation.
[Illustration: 862]
When blowers occur in the roof, and force the strata down, so as to
produce a large vaulted excavation, the accumulated gas must be swept
away; because, after filling that space, it would descend in an unmixed
state under the common roof of the coal. The manner of removing it is
represented in _fig._ 862., where _a_ is the bed of coal, _b_ the
blower, _c_ the excavation left by the downfall of the roof, _d_ is a
passing door, and _e_ a brattice. By this arrangement the aerial current
is carried close to the roof, and constantly sweeps off or dilutes the
inflammable gas of the blower, as fast as it issues. The arrows show the
direction of the current; but for which, the accumulating gas would be
mixed in explosive proportions with the atmospheric air, and destroy the
miners.
[Illustration: 863]
There is another modification of the ventilating system, where the
air-courses are traversed across; that is, when one air-course is
advanced at right angles to another, and must pass it in order to
ventilate the workings on the further side. This is accomplished on the
plan shown in _fig._ 863., where _a_ is a main road with an air-course,
over which the other air-course _b_, has to pass. The sides of this air
channel are built of bricks arched over so as to be air-tight, and a
gallery is driven in the roof strata as shown in the figure. If an
air-course, as _a_, be laid over with planks made air-tight, crossing
and recrossing may be effected with facility. The general velocity of
the air in these ventilating channels is from 3 to 4 feet per second, or
about 2-1/2 miles per hour, and their internal dimensions vary from 5 to
6 feet square, affording an area of from 25 to 36 square feet.
[Illustration: 864]
Mr. Taylor’s hydraulic air-pump, formerly described, p. 839., deserves
to be noticed among the various ingenious contrivances for ventilating
mines, particularly when they are of moderate extent. _a_ is a large
wooden tub, nearly filled with water, through whose bottom the
ventilating pipe _b_ passes down into the recesses of the mine. Upon the
top of _b_, there is a valve _e_, opening upwards. Over _b_, the
gasometer vessel is inverted in _a_, having a valve also opening
outwards at _d_. When this vessel is depressed by any moving force, the
air contained within it is expelled through _d_; and when it is raised,
it diminishes the atmospherical pressure in the pipe _b_, and thus draws
air out of the mine into the gasometer; which cannot return on account
of the valve at _e_, but is thrown out into the atmosphere through _d_
at the next descent.
The general plan of distributing the air, in all cases, is to send the
first of the current that descends in the downcast shaft among the
horses in the stables, next among the workmen in the foreheads, after
which the air, loaded with whatever mixtures it may have received, is
made to traverse the old wastes. It then passes through the furnace with
all the inflammable gas it has collected, ascends the upcast shaft, and
is dispersed into the atmosphere. This system, styled _coursing the
air_, was invented by Mr. Spedding of Cumberland. According to the
quantity of the fire-damp, the coursing is conducted either up one room,
and returned by the next alternately, through the whole extent of the
works, or it passes along 2 or 3 connected rooms, and returns by the
same number.
[Illustration: 865]
This admirable system has received the greatest improvements from the
mining engineers of the Newcastle district, and especially from Mr.
Buddle of Wallsend. His plan being a most complete scale of ventilation,
where the aerial current is made to sweep every corner of the workings,
is shown in _fig._ 865.; in which _a_ represents the downcast, and _b_
the upcast shaft. By pursuing the track of the arrows, we may observe
that the air passes first along the two rooms _c_, _d_, having free
access to each through the walls, but is hindered from entering into the
adjoining rooms by the stoppings which form the air-courses. It sweeps
along the wall faces of the rooms _c_, _d_, and makes a return down the
rooms _e_, _f_, but is not allowed to proceed further in that direction
by the stoppings _g_, _h_. It then proceeds to the foreheads _i_, _k_,
and single courses all the rooms to the foreheads _l_, _m_; from this
point it would go directly to the upcast pit _b_, were it not prevented
by the stopping _n_, which throws it again into double coursing the
rooms, till it arrives at _o_, whence it goes directly to the furnace,
and ascends the shaft _b_. The lines across each other represent the
passing doors; and these may be substituted in any place for a passage
where there is a stopping. The stopping _p_, near the bottom of the
downcast shaft, is termed a main stopping; because if it were removed,
the whole circulation would instantly cease, and the air, instead of
traversing in the direction of the arrows, would go directly from the
downcast pit _a_, to the upcast pit _b_, along the gallery _q_. Hence
every gallery and room of the workings would be laid _dead_, as it is
termed, and be immediately filled with fire-damp, which might take fire
either at the workmen’s candles, or at the furnace next the upcast shaft
_b_. Thus also a partial stagnation in one district of the colliery,
would be produced by any of the common stoppings being accidentally
removed or destroyed, since the air would thereby always pursue the
nearest route to the upcast pit. Main stoppings are made particularly
secure, by strong additional stone buildings, and they are set up at
different places, to maintain the main air courses entire in the event
of an explosion; by which precautions great security is given to human
life. This system of ventilation may be extended to almost any distance
from the pit-bottom, provided the volume of fresh air introduced be
adequate to dilute sufficiently the fire-damp, so that the mixture shall
not reach the explosive point. The air, by this management, ventilates
first one panel of work, and then other panels in succession, passing
onwards through the barriers or panel walls, by means of galleries, as
in _fig._ 843., by the principle either of single, double, or triple
coursing, according to the quantity of gas in the mine.
In ventilating the very thick coal of Staffordshire, though there is
much inflammable air, less care is needed than in the north of England
collieries, as the workings are very roomy, and the air courses of
comparatively small extent. The air is conducted down one shaft, carried
along the main roads, and distributed into the sides of work, as shown
in _fig._ 848. A narrow gallery, termed the air-head, is carried in the
upper part of the coal, in the rib walls, along one or more of the
sides. In the example here figured, it is carried all round, and the air
enters at the bolt-hole _e_. Lateral openings, named spouts, are led
from the air-head gallery into the side of work; and the circulating
stream mixed with the gas in the workings, enters by these spouts, as
represented by the arrows, and returns by the air-head at _g_, to the
upcast pit.
When the fire-damp comes off suddenly in any case, rendering the air
foul and explosive at the foreheads, if no other remedy be found
effectual, the working of the coal must be suspended, and a current of
air sent directly from the fresh in-going stream, in order to dilute the
explosive mixture, before it reaches the furnace. This is termed
_skailing the air_; for otherwise the gas would kindle at the furnace,
and flame backwards, like a train of gunpowder, through all the windings
of the work, carrying devastation and death in its track. By _skailing_
the air, however, time is given for running forward with water, and
drowning the furnace. A cascade of water from the steam engine pumps is
then allowed to fall down the pit, the power of which through a fall of
500 or 600 feet, is so great in carrying down a body of air, that it
impels a sufficient current through every part of the workings. The
ventilation is afterwards put into its usual train at leisure.
In collieries which have been worked for a considerable time, and
particularly in such as have goaves, creeps, or crushed wastes, the
disengagement of the fire-damp from these recesses is much influenced by
the state of atmospheric pressure. Should this be suddenly diminished,
as shown by the fall of the barometer, the fire-damp suddenly expands
and comes forth from its retirement, polluting the galleries of the mine
with its noxious presence. But an increase of barometric pressure
condenses the gases of the mine, and restrains them within their
sequestered limits. It is therefore requisite that the coal-viewer
should consult the barometer before inspecting the subterraneous
workings of an old mine, on the Monday mornings, in order to know what
precautions must be observed in his personal survey.
The catastrophe of an explosion in an extensive coal-mine is horrible in
the extreme. Let us imagine a mine upwards of 100 fathoms deep, with the
workings extended to a great distance under the surrounding country,
with machinery complete in all its parts, the mining operations under
regular discipline, and railways conducted through all its
ramifications; the stoppings, passing doors, brattices, and the entire
economy of the mine, so arranged that every thing moves like a well
regulated machine. A mine of this magnitude at full work is a scene of
cheering animation, and happy industry; the sound of the hammer resounds
in every quarter, and the numerous carriages, loaded or empty, passing
swiftly to and fro from the wall faces to the pit bottom, enliven the
gloomiest recesses. At each door a little boy, called a trapper, is
stationed, to open, and shut it. Every person is at his post, displaying
an alacrity and happiness pleasingly contrasted with the surrounding
gloom. While things are in this merry train, it has but too frequently
happened that from some unforeseen cause, the ventilation has partially
stagnated, allowing a quantity of the fire-damp to accumulate in one
space to the explosive pitch; or a blower has suddenly sprung forth, and
the unsuspecting miner entering this fatal region with his candle, sets
the whole in a blaze of burning air, which immediately suffocates and
scorches to death every living creature within its sphere, while
multitudes beyond the reach of the flame are dashed to pieces by the
force of the explosion, rolling like thunder along the winding
galleries. Sometimes the explosive flame seems to linger in one
district for a few moments; then gathering strength for a giant effort,
it rushes forth from its cell with the violence of a hurricane, and the
speed of lightning, destroying every obstacle in its way to the upcast
shaft. Its power seems to be irresistible. The stoppings are burst
through, the doors are shivered into a thousand pieces; while the
unfortunate miners, men, women, and boys, are swept along with an
inconceivable velocity, in one body, with the horses, carriages, corves,
and coals. Should a massive pillar obstruct the direct course of the
aerial torrent, all these objects are dashed against it, and there
prostrated or heaped up in a mass of common ruin, mutilation, and death.
Others are carried directly to the shaft, and are either buried there
amid the wreck, or are blown up and ejected from the pit mouth. Even at
this distance from the explosive den, the blast is often so powerful,
that it frequently tears the brattice walls of the shaft to pieces, and
blows the corves suspended in the shaft as high up into the open air as
the ropes will permit. Not unfrequently, indeed, the ponderous
pulley-wheels are blown from the pit-head frame, and carried to a
considerable distance in the bosom of a thick cloud of coals and
coal-dust brought up from the mine by the fire-damp, whose explosion
shakes absolutely the superincumbent solid earth itself with a mimic
earthquake. The dust of the ruins is sometimes thrown to such a height
above the pit as to obscure the light of the sun. The silence which
succeeds to this awful turmoil is no less formidable; for the
atmospheric back-draught, rushing down the shaft, denotes the
consumption of vital air in the mine, and the production of the
deleterious choke-damp and azote.
Though many of the miners may have escaped by their distance in the
workings from the destructive blast and the fire, yet their fate may
perhaps be more deplorable. They hear the explosion, and are well aware
of its certain consequences. Every one anxious to secure his personal
safety, strains every faculty to reach the pit-bottom. As the lights are
usually extinguished by the explosion, they have to grope their way in
utter darkness. Some have made most marvellous escapes, after clambering
over the rubbish of fallen roofs, under which their companions are
entombed; but others wandering into uncertain alleys, tremble lest they
should encounter the pestilential airs. At last they feel their power,
and aware that their fate is sealed, they cease to struggle with their
inevitable doom; they deliberately assume the posture of repose, and
fall asleep in death. Such has been too often the fate of the hardy and
intelligent miners who immure themselves deep beneath the ground, and
venture their lives for the comfort of their fellow-men; and such
frequently is the ruinous issue of the best ordered and most prosperous
mining concerns.
In such circumstances the mining engineers or coal viewers have a
dangerous and difficult duty to perform. The pit into which they must
descend as soon as possible, is rendered unsafe by many causes; by the
wrecks of loose timber torn away by the eruption, or by the unrespirable
gases; by the ignition perhaps of a portion of the coal itself, or by
the flame of a blower of fire-damp; either of which would produce
violent and repeated explosions whenever the gas may again accumulate to
the proper degree. Such a predicament is not uncommon, and it is one
against which no human skill can guard. Yet even here, the sense of
duty, and the hope of saving some workmen from a lingering death by
wounds or suffocation, lead this intrepid class of men to descend amid
the very demons of the mine.
As soon as the ventilation is restored by temporary brattices, the
stoppings and doors are rebuilt in a substantial manner, and the
workings are resumed with the wonted activity. From an inspection of
_fig._ 864., p. 1029, it is obvious that the stability of the main
stopping _p_, is an important point; for which reason it is
counterforted by strong walls of stone, to resist the explosive force of
fire-damp.
When it is known that fire exists in the wastes, either by the burning
of the small coal-dust along the roads, or from the ignition of the
solid coal by a blower of gas, the inspection of the mine is
incomparably more hazardous, as safety cannot be insured for an instant;
for if the extrication of gas be great, it rapidly accumulates, and
whenever it reaches the place where the fire exists, a new explosion
takes place. There have been examples of the most furious detonations
occurring regularly after the interval of about an hour, and being thus
repeated 36 times in less than two days, each eruption appearing at the
pit mouth like the blast of a volcano. It would be madness for any one
to attempt a descent in such circumstances. The only resource is to moat
up the pit, and check the combustion by exclusion of atmospheric air, or
to drown the workings by letting the water accumulate below ground.
When fire exists in the wastes, with less apparent risk of life, water
is driven upon it by portable fire-extinguishing engines, or small
cannon are discharged near the burning coal, and the concussion thus
produced in the air sometimes helps to extinguish the flame.
Since the primary cause of these tremendous catastrophes is the
accension of the explosive gases by the candle of the miner, it has been
long a desideratum to procure light of such a nature as may not possess
the power of kindling the fire-damp. The train of light producible from
the friction of flint and steel, by a mechanism called _a steel mill_,
has been long known, and afforded a tolerable gleam, with which the
miners were obliged to content themselves in hazardous atmospheres.
It consists of a small frame of iron, mounted with a wheel and pinion,
which give rapid rotation to a disk of hard steel placed upright, to
whose edge a piece of flint is applied. The use of this machine entailed
on the miner the expense of an attendant, called the miller, who gave
him light. Nor was the light altogether safe, for occasionally the
ignited shower of steel particles attained to a sufficient heat to set
fire to the fire-damp.
At length the attention of the scientific world was powerfully attracted
to the means of lighting the miner with safety, by an awful catastrophe
which happened at Felling Colliery, near Newcastle, on the 25th May,
1812. This mine was working with great vigour, under a well-regulated
system of ventilation, set in action by a furnace and air-tube, placed
over a rise pit in elevated ground. The depth of winning was above 100
fathoms; 25 acres of coal had been excavated, and one pit was yielding
at the rate of 1700 tons per week. At 11 o’clock in the forenoon the
night shift of miners was relieved by the day shift; 121 persons were in
the mine, at their several stations, when, at half-past 11, the gas
fired, with a most awful explosion, which alarmed all the neighbouring
villages. The subterraneous fire broke forth with two heavy discharges
from the dip-pit, and these were instantly followed by one from the
rise-pit. A slight trembling, as from an earthquake, was felt for about
half a mile round the colliery, and the noise of the explosion, though
dull, was heard at from 3 to 4 miles’ distance. Immense quantities of
dust and small coal accompanied these blasts, and rose high into the
air, in the form of an inverted cone. The heaviest part of the ejected
matter, such as corves, wood, and small coal, fell near the pits; but
the dust borne away by a strong west wind fell in a continuous shower a
mile and a half from the pit. In the adjoining village of Heworth it
caused a darkness like that of early twilight, covering the roads where
it fell so thickly that the footsteps of passengers were imprinted in
it. The heads of both shaft-frames were blown off, their sides set on
fire, and their pulleys shattered to pieces. The coal-dust ejected from
the rise-pit into the horizontal part of the ventilating tube, was about
3 inches thick, and speedily burnt to a cinder; pieces of burning coal,
driven off the solid stratum of the mine, were also blown out of this
shaft. Of the 121 persons in the mine at the time of the explosion, only
32 were drawn up the pit alive, 3 of whom died a few hours after the
accident. Thus no less than 92 valuable lives were instantaneously
destroyed by this pestilential fire-damp. The scene of distress among
the relatives at the pit mouth was indescribably sorrowful.
Dr. W. Reid Clanny, of Sunderland, was the first to contrive a lamp
which might burn among explosive air without communicating flame to the
gas in which it was plunged. This he effected, in 1813, by means of an
air-tight lamp, with a glass front, the flame of which was supported by
blowing fresh air from a small pair of bellows through a stratum of
water in the bottom of the lamp, while the heated air passed out through
water by a recurved tube at top. By this means the air within the lamp
was completely insulated from the surrounding atmosphere. This lamp was
the first ever taken into a body of inflammable air in a coal-mine, at
the exploding point, without setting fire to the gas around it. Dr.
Clanny made another lamp upon an improved plan, by introducing into it
the steam of water generated in a small vessel at the top of the lamp,
heated by the flame. The chief objection to these lamps is their
inconvenience in use.
Various other schemes of safe-lamps were offered to the miner by
ingenious mechanicians, but they have been all superseded by the
admirable invention of Sir H. Davy, founded on his fine researches upon
flame. The lamp of Davy was instantly tried and approved of by Mr.
Buddle and the principal mining engineers of the Newcastle district. A
perfect security of accident is therefore afforded to the miner in the
use of a lamp which transmits its light, and is fed with air, through a
cylinder of wire gauze; and this invention has the advantage of
requiring no machinery, no philosophical knowledge to direct its use,
and is made at a very cheap rate.
In the course of a long and laborious investigation on the properties of
the fire-damp, and the nature and communication of flame, Sir H. Davy
ascertained that the explosions of inflammable gases were incapable of
being passed through long narrow metallic tubes; and that this principle
of security was still obtained by diminishing their length and diameter
at the same time, and likewise diminishing their length, and increasing
their number, so that a great number of small apertures would not pass
an explosion, when their depth was equal to their diameter. This fact
led him to trials upon sieves made of wire-gauze, or metallic plates
perforated with numerous small holes; and he found it was impossible to
pass explosions through them.
The apertures in the gauze should never be more than 1-20th of an inch
square. In the working models sent by Sir H. to the mines, there were
748 apertures in the square inch, and the wire was about the 40th of an
inch diameter. The cage or cylinder of wire gauze should be made by
double joinings, the gauze being folded over in such a manner as to
leave no apertures. It should not be more than two inches in diameter;
or in large cylinders the combustion of the fire-damp renders the top
inconveniently hot; and a double top is always a proper precaution,
fixed at a distance of about half an inch above the first top. The gauze
cylinder should be fastened to the lamp by a screw of 4 or 5 turns. All
joinings in the lamp should be made with hard solder; and the security
depends upon the condition, that no aperture exists in the apparatus
larger than in the wire gauze.
The forms of the lamp and cage, and the mode of burning the wick, may be
greatly diversified; but the principle which ensures their safety must
be strictly attended to. See LAMP OF DAVY, SAFETY LAMP, and VENTILATION.
The state of the air in coal mines, from very early periods till the
discovery of the safe-lamp, was judged of by the appearances exhibited
by the flame of a candle; and this test must in many circumstances be
still had recourse to. When there is merely a defect of atmospheric
oxygen, the air being also partially vitiated by a little carbonic acid,
either from choke-damp or the lungs and candles of the miners, the
lights burn with a very dull flame, the tallow ceases to melt in the cup
formed round the wick, till the flame flickers and expires. In this case
the candle may be kept burning by slanting it more or less towards a
horizontal position, which causes the tallow to melt with the edge of
the flame. The candle is thus rapidly wasted, however; and therefore an
oil lamp is preferable, as it continues to burn where a candle would be
extinguished. The candles of the collier are generally small, with a
very small wick; such being found to produce a more distinct flame than
candles of a large size with a thick wick.
In trying the quality of the air by the flame of a candle, the wick must
be trimmed by taking off the snuff, so as to produce a clear, distinct,
and steady-burning flame. When a candle thus trimmed is looked at in
common air, a distinct and well-defined cone of flame is seen, of a fine
sky-blue at the bottom next the wick, and thence of a bright yellow to
the apex of the cone. Besides this appearance, there is another,
surrounding the cone, which the brightness of the flame prevents the eye
from discerning. This may be seen by placing one of the hands expanded
as a screen betwixt the eyes and the candle, and at the distance of
about an inch, so that the least point of the apex of the yellow flame
may be seen, and no more. By this method, a top, as the miners term it,
will be distinctly observed close to the apex of the yellow flame, from
an eighth to a quarter of an inch in length. This top is of a
yellowish-brown colour, and like a misty haze. This haze is seen not
only on the top, but it extends downwards and surrounds the flame fully
half way, about a twentieth of an inch in thickness; here it assumes a
violet colour, which passes into a beautiful blue at the bottom next the
wick. The test of the state of the air in mines, or “trying the candle,”
as practised by miners, depends entirely on the appearance which this
haze assumes in shape and colour at the top of the flame. In fact, this
top has distinct appearances when burning in atmospheric air, carbonated
air, azotized air, or fire-damp air; displaying many modifications,
according to the proportions of the various admixtures.
When azote or carbonic acid abounds, the top is frequently an inch or
two in length, of a decided brown colour, and the flame is short and
dim. When they are still more copious, the flame goes out, and the
miners immediately retire.
When inflammable air is imagined to exist in considerable quantity, the
miner trims his candle, and advances with cautious step, holding the
candle with the left hand, and screening the flame with the right; and
as the fire-damp floats in the upper part of the gallery next the roof,
he holds the candle as low as he can, and keeping his eye fixed on the
tip, he moves forwards. If the gas be small in quantity, he may reach
the forehead without observing any material change in his light. But if
in his advance he perceives the tip to elongate, and take a bluish-gray
colour, he is put on his guard, and steps on with much caution; and if
the tip begins to spire, he drops down on one knee, and holding the
candle near the pavement, gradually raises it up, and watches the change
it undergoes as it approaches the roof. If the gas be copious, the flame
elongates into a sharp spire, as well as the top. It is in general
reckoned dangerous when the tip changes from the bluish-gray to a fine
blue colour, accompanied with minute luminous points, which pass rapidly
upwards through the flame and top. When the symptoms are manifestly
dangerous, a sudden movement of the hands or body is liable to produce
ignition by agitation of the fire-damp. The experienced miner therefore
slowly and cautiously lowers his candle to the pavement, and then
turning round, effects his retreat slowly, or slips up his right hand
and extinguishes the flame with his finger and thumb. Should he venture
too far, and approach the body of gas in an explosive condition, the tip
of the candle rapidly elongates, and the whole rises in a sharp spire
several inches in length; and then the whole surrounding atmosphere is
in a blaze, an explosion ensues, and destructive ravage is the
consequence, to an extent proportioned to the quantity of fire-damp. See
SAFETY LAMP, and VENTILATION.
This _trying the candle_ is a delicate operation, requiring much
practical sagacity, where the lives of so many men, and the welfare of
the whole establishment, are at stake. Almost every colliery, after
having been worked for some time, gives a peculiar top to the candle;
so that while in one mine liable to fire-damp an explosion will take
place with a top less than an inch long, in another mine the top may be
two inches high, and yet the air be considerably under the point of
accension. These differences depend on several particulars. If the gas
has not passed through a long course of ventilation, and is little mixed
with air, it will ignite with a very short top; while on the other hand,
a gas which has run through a ventilation of 20 or 30 miles may cause
the production of a long top without hazard. It is hence obvious, that
skilful experience, and thorough practical knowledge, are the only sure
guides in these cases.
[Illustration: 866 867]
We shall now describe briefly the modern modes of working coals
a-dipping of, and deeper than, the engine-pit bottom. One of these
consists in laying a working pump barrel with a long wind-bore at the
bottom of the downset mine, furnished with a smooth rod working through
a collar at the top of the working barrel. At one side of this, near the
top, a kneed pipe is attached, and from it pipes are carried to the
point of delivery, either at the engine-pit bottom or day level, as
represented in _fig._ 866. The spears are worked sometimes by rods
connected with the machinery at the surface; in which case the spears,
if very long, are either suspended from swing or pendulum rods, or move
on friction rollers. But since the action of the spears, running with
great velocity the total length of the engine stroke, very soon tears
every thing to pieces, the motion of the spears underground has been
reduced from 6 or 8 feet, the length of the engine stroke, to about 15
inches; and the due speed in the pump is effected by the centering of a
beam, and the attachment of the spears to it, as represented in _fig._
867., where _a_ is the working barrel, _b_ the beam centered at _c_,
having an arc-head and martingale sinking-chain. The spears _d_ are
fastened by a strong bolt, which passes through the beam; and there are
several holes, by means of which the stroke in the pumps can be
lengthened or shortened at convenience. The movement of the spears is
regulated by a strong iron quadrant or wheel at the bottom.
In level-free coals, these pumps may be worked by a water-wheel,
stationed near the bottom of the pit, impelled by water falling down the
shaft, to be discharged by the level to the day (day-level).
But the preferable plan of working under-dip coal, is that recently
adopted by the Newcastle engineers; and consists in running a mine
a-dipping of the engine-pit, in such direction of the dip as is most
convenient; and both coals and water are brought up the rise of the coal
by means of high-pressure engines, working with a power of from 30 to 50
pounds on the square inch. These machines are quite under command, and,
producing much power in little space, they are the most applicable for
underground work. An excavation is made for them in the strata above the
coal, and the air used for the furnace under the boiler, is the returned
air of the mine ventilation. In the dip-mine a double tram-road is laid;
so that while a number of loaded corves are ascending, an equal number
of empty ones are going down. Although this improved method has been
introduced only a few years back, under-dip workings have been already
executed more than an English mile under-dip of the engine-pit bottom,
by means of three of these high-pressure engines, placed at equal
distances in the under-dip mine. It may hence be inferred, that this
mode of working is susceptible of most extensive application; and in
place of sinking pits of excessive depth upon the dip of the coal, at an
almost ruinous expense, much of the under-dip coal will in future be
worked by means of the actual engine-pits. In the Newcastle district,
coals are now working in an engine-pit 115 fathoms deep under-dip of the
engine-pit bottom, above 1600 yards, and fully 80 fathoms of
perpendicular depth more than the bottom of the pit.
[Illustration: 868]
If an engine-pit be sunk to a given coal at a certain depth, all the
other coals of the coal-field, both above and below the coal sunk to,
can be drained and worked to the same depth, by driving a level
cross-cut mine, both to the dip and rise, till all the coals are
intersected, as represented in _fig._ 868., where A is the engine-pit
bottom reaching to the coal _a_; and _b_, _c_, _d_, _e_, _f_, coals
lying above the coal _a_; the coals which lie below it, _g_, _h_, _i_;
_k_ is the forehead of the cross-cut mine, intersecting all the lower
coals; and _l_, the other forehead of the mine, intersecting all the
upper coals.
[Illustration: 869
1. First stage of active creep.
2. Second do.
3. Third do.
4. Fourth do.
5. The metal ridge closed, and the creep beginning to settle.
6. The creep settled, the metal ridges being closely compressed, and
supporting the roof.]
In the “Report from the select committee of the House of Lords,
appointed to take into consideration the state of the coal trade in the
United Kingdom,” printed in June, 1829, under the head of Mr. Buddle’s
evidence we have an excellent description of the nature and progress of
creeps, which we have adverted to in the preceding account. The annexed
_fig._ 869. exhibits the creep in all its progressive stages, from its
commencement until it has completely closed all the workings, and
crushed the pillars of coal. The section of the figures supposes us
standing on the level of the different galleries which are opened in the
seam. The black is the coal pillars between each gallery; when these are
weakened too much, or, in other words, when their bases become too
narrow for the pavement below, by the pressure of the incumbent
stratification they sink down into the pavement, and the first
appearance is a little curvature in the bottom of each gallery: that is
the first symptom obvious to sight; but it may generally be heard before
it is seen. The next stage is when the pavement begins to open with a
crack longitudinally. The next stage is when that crack is completed,
and it assumes the shape of a metal ridge. The next is when the metal
ridge reaches the roof. The next stage is when the peak of the metal
ridge becomes flattened by pressure, and forced into a horizontal
direction, and becomes quite close; just at this moment the coal pillars
begin to sustain part of the pressure. The next is when the coal pillars
take part of the pressure. The last stage is when it is dead and
settled; that is, when the metal or factitious ridge, formed by the
sinking of the pillar into the pavement, bears, in common with the
pillars of coal on each side, the full pressure, and the coal becomes
crushed or cracked, and can be no longer worked, except by a very
expensive and dangerous process. _Fig._ 869.
The quantity of coals, cinders, and culm shipped coastways, and exported
from the several ports of the United Kingdom in the year 1837, was
8,204,301 tons; in 1836, the quantity was 7,389,272 tons, being an
increase of 815,029 tons, or 11·03 per cent. in favour of 1837.
The following TABLE shows the separate proportions of this quantity
supplied by England and Wales, Scotland, and Ireland:--
+-----------------+---------+---------+--------------------------+
| | 1836. | 1837. | Increase. |
+-----------------+---------+---------+--------------------------+
| | Tons. | Tons. | Tons. |
|England and Wales|6,757,937|7,570,254|812,317 or 12·02 per cent.|
|Scotland | 624,308| 626,532| 2,204 0·36 |
|Ireland | 7,027| 7,515| 488 6·94 |
| +---------+---------+--------------------------+
| Total |7,389,272|8,204,301|815,029 or 11·03 per cent.|
+-----------------+---------+---------+--------------------------+
PITCOAL, COKING OF. See also CHARCOAL.
[Illustration: 870]
_Fig._ 870. represents a _schachtofen_, or pit-kiln, for coking coals in
Germany. _a_ is the lining (_chemise_), made of fire-bricks; the
enclosing walls are built of the same material; _b_, _b_, is a cast-iron
ring covered with a cast-iron plate _c_. The floor of the kiln is
massive. The coals are introduced, and the coke taken out, through a
hole in the side _d_; during the process it is bricked up, and closed
with an iron door. In the surrounding walls are 4 horizontal rows of
flues _e_, _e_, _e_, _e_, which are usually iron pipes; the lowest row
is upon a level with the floor of the kiln; and the others are each
respectively one foot and a half higher than the preceding. Near the top
of the shaft there is an iron pipe _f_, of from 8 to 10 inches in
diameter, which allows the incoercible vapours generated in the coking
to escape into the condenser, which consists either of wood or brick
chambers. For kindling the coal, a layer of wood is first placed on the
bottom of the kiln.
The coking of small coal is performed upon vaulted hearths, somewhat
like bakers’ ovens, but with still flatter roofs. Of such kilns, several
are placed alongside one another each being an ellipse deviating little
from a circle, so that the mouth may project but a small space. The
dimensions are such, that from 10 to 12 cubic feet of coal-culm may be
spread in a layer 6 inches deep upon the sole of the furnace. The top of
the flat arch of fire brick should be covered with a stratum of loam and
sand.
[Illustration: 871 872]
_Figs._ 871. and 872. represent such a kiln as is mounted at Zabrze, in
Upper Silesia, for coking small coal. _Fig._ 871. is the ground plan;
_fig._ 872. the vertical section in the line of the long axis of _fig._
871. _a_, is the sand-bed of the hearth, under the brick sole; _b_, is
the roof of large fire-bricks; _c_, the covering of loam; _d_, the top
surface of sand; _e_, the orifice in the front wall, for admission of
the culm, and removal of the coke, over the sloping stone _f_. The flame
and vapours pass off above this orifice, through the chimney marked _g_,
or through the aperture _h_, into a lateral chimney. _i_, is a bar of
iron laid across the front of the door as a fulcrum to work the iron
rake upon. A layer of coals is first kindled upon the hearth, and when
this is in brisk ignition, it is covered with the culm in successive
sprinklings. When the coal is sufficiently coked, it is raked out, and
quenched with water.
[Illustration: 873 874]
_Fig._ 873. represents a simple coking _meiler_ or _mound_, constructed
in a circular form round a central chimney of loose bricks, towards
which small horizontal flues are laid among the lumps of coals. The
sides and top are covered with culm or slack, and the heap is kindled
from certain openings towards the circumference. _Fig._ 874. represents
an oblong _meiler_, sometimes made 100 or 150 feet in length, and from
10 to 12 in breadth. The section in the middle of the figure shows how
the lumps are piled up; the wooden stakes are lifted out when the heap
is finished, in order to introduce kindlings at various points; and the
rest of the meiler is then covered with slack and clay, to protect it
from the rains. A jet of smoke and flame is seen issuing from its left
end.
[Illustration: 875 876 877]
An excellent range of furnaces for making a superior article of coke,
for the service of the locomotive engines of the London and Birmingham
Railway Company, has been recently erected at the Camden Town station;
consisting of 18 ovens in two lines, the whole discharging their
products of combustion into a horizontal flue, which terminates in a
chimney-stalk, 115 feet high. _Fig._ 875. is a ground plan of the
elliptical ovens, each being 12 feet by 11 internally, and having 3 feet
thickness of walls. _a_, _a_, is the mouth, 3-1/2 feet wide outside,
and about 2-3/4 feet within. _b_, _b_, are the entrances into the flue;
they may be shut more or less completely by horizontal slabs of
fire-brick, resting on iron frames, pushed in from behind, to modify the
draught of air. The grooves of these damper-slabs admit a small stream
of air to complete the combustion of the volatilized particles of soot.
By this means the smoke is well consumed. The flue _c_, _c_, is 2-1/2
feet high, by 21 inches wide. The chimney _d_, at the level of the flue,
is 11 feet in diameter inside, and 17 outside; being built from an
elegant design of Robert Stephenson, Esq. (See CHIMNEY.) _d_, _d_, are
the keys of the iron hoops, which bind the brickwork of the oven. _Fig._
876. is a vertical section in the line A, B, of _fig._ 875. showing, at
_b_, _b_, and _e_, _e_, the entrances of the different ovens into the
horizontal flue; the direction of the draught being indicated by the
arrows. _f_, _f_, is a bed of concrete, upon which the whole
furnace-range is built, the level of the ground being in the middle of
that bed. _g_, is a stauncheon on which the crane is mounted: (see
_fig._ 877.) _h_ is a section of the chimney wall, with part of the
interior to the left of the strong line. _Fig._ 877. is a front
elevation of two of these elegant coke-ovens; in which the bracing hoops
_i_, _i_, _i_, are shown; _k_, _k_, are the cast-iron doors,
strengthened outside with diagonal ridges; each door being 5-1/2 feet
high, by 4 feet wide, and lined internally with fire-bricks. They are
raised and lowered by means of chains and counterweights, moved by the
crane _l_.
Each alternate oven is charged, between 8 and 10 o’clock every morning,
with 3-1/2 tons of good coals. A wisp of straw is thrown in on the top
of the heap, which takes fire by the radiation from the dome (which is
in a state of dull ignition from the preceding operation), and inflames
the smoke then rising from the surface, by the re-action of the hot
sides and bottom upon the body of the fuel. In this way the smoke is
consumed at the very commencement of the process, when it would
otherwise be most abundant. A neighbour of the above coking ovens,
having lately indicted them as a nuisance, procured, _secundum artem_, a
parcel of affidavits from sundry chemical and medical men. Two of the
former, who had not entered the premises, but had espied the outside of
the furnaces’ range at some distance, declared that “the coking process,
as performed at the ovens, is a species of distillation of coal”! How
rashly do unpractical theorists affirm what is utterly unfounded, and
mislead an unscientific judge! That the said coking process is in no
respect a species of distillation, but a complete combustion of the
volatile principles of the coal, will be manifest from the following
description of its actual progress. The mass of coals is first kindled
at the surface, as above stated, where it is supplied with abundance of
atmospheric oxygen; because the doors of the ovens in front, and the
throat-vents behind, are then left open. The consequence is, that no
more smoke is discharged from the top of the chimney, at this the most
sooty period of the process, than is produced by an ordinary kitchen
fire. In these circumstances, the coal gas, or other gas, supposed to be
generated in the slightly heated mass beneath, cannot escape destruction
in passing up through the bright open flame of the oven. As the coking
of the coal advances most slowly and regularly from the top of the heap
to the bottom, only one layer is affected at a time, and in succession
downwards, while the surface is always covered with a stratum of redhot
cinders, ready to consume every particle of carburetted or sulphuretted
hydrogen gases which may escape from below. The greatest mass, when
calcined in this downward order, cannot emit into the atmosphere any
more of the above-mentioned gases than the smallest heap; and therefore
the argument raised on account of the magnitude of the operations, is
altogether fallacious.
The coke being perfectly freed from all fuliginous and volatile matters
by a calcination of upwards of 40 hours, is cooled down to moderate
ignition by sliding in the dampers, and sliding up the doors, which had
been partially closed during the latter part of the process. It is now
observed to form prismatic concretions, somewhat like a columnar mass of
basalt. These are loosened by iron bars, lifted out upon shovels
furnished with long iron shanks, which are poised upon swing chains with
hooked ends, and the lumps are thrown upon the pavement, to be
extinguished by sprinkling water upon them from the rose of a
watering-can; or, they might be transferred into a large chest of
sheet-iron set on wheels, and then covered up. Good coals thus treated,
yield 80 per cent. of an excellent compact glistening coke; weighing
about 14 cwt. per chaldron.
The loss of weight in coking in the ordinary ovens is usually reckoned
at 25 per cent.; and coal, which thus loses one-fourth in weight, gains
one-fourth in bulk.
Labourers who have been long employed at rightly-constructed coke ovens,
seem to enjoy remarkably good health.
PITTACALL, is one of the 6 curious principles detected in wood-tar by
Reichenbach. It is a dark-blue solid substance, somewhat like indigo,
assumes a metallic fiery lustre on friction, and varies in tint from
copper to golden. It is void of taste and smell, not volatile;
carbonizes at a high heat without emitting an ammoniacal smell; is
soluble or rather very diffusible in water; gives a green solution with
a cast of crimson, in sulphuric acid, with a cast of red blue, in
muriatic acid, and with a cast of aurora red, in acetic acid. It is
insoluble in alkalis. It dyes a fast blue upon linen and cotton goods,
with tin and aluminous mordants.
PLASTER; see MORTAR.
PLASTER OF PARIS; see GYPSUM.
PLATED MANUFACTURE. (_Fabrique de plaqué_, Fr.; _Silber plattirung_,
Germ.) The silver in this case is not applied to ingots of pure copper,
but to an alloy consisting of copper and brass, which possesses the
requisite stiffness for the various articles.
The furnace used for melting that alloy, in blacklead crucibles, is a
common air-furnace, like that for making brass.
The ingot-moulds are made of cast iron, in two pieces, fastened
together; the cavity being of a rectangular shape, 3 inches broad, 1-1/2
thick, and 18 or 20 long. There is an elevated mouth-piece or gate, to
give pressure to the liquid metal, and secure solidity to the ingot. The
mould is heated, till the grease with which its cavity is besmeared,
merely begins to smoke, but does not burn. The proper heat of the melted
metal for casting, is when it assumes a bluish colour, and is quite
liquid. Whenever the metal has solidified in the mould, the wedges that
tighten its rings are driven out, lest the shrinkage of the ingot should
cause the mould to crack. See BRASS.
The ingot is now dressed carefully with the file on one or two faces,
according as it is to be single or double plated. The thickness of the
silver plate is such as to constitute one fortieth of the thickness of
the ingot; or when this is an inch and a quarter thick, the silver plate
applied is one thirty-second of an inch, being by weight a pound troy of
the former, to form 8 to 10 pennyweights of the latter. The silver,
which is slightly less in size than the copper, is tied to it truly with
iron wire, and a little of a saturated solution of borax is then
insinuated at the edges. This salt melts at a low heat, and excludes the
atmosphere, which might oxidize the copper, and obstruct the union of
the metals. The ingot thus prepared is brought to the plating furnace.
The furnace has an iron door with a small hole to look through; it is
fed with cokes, laid upon a grate at a level with the bottom of the
door. The ingot is placed immediately upon the cokes, the door is shut,
and the plater watches at the peep-hole the instant when the proper
soldering temperature is attained. During the union of the silver and
copper, the surface of the former is seen to be drawn into intimate
contact with the latter, and this species of _riveting_ is the signal
for removing the compound bar instantly from the furnace. Were it to
remain a very little longer, the silver would become alloyed with the
copper, and the plating be thus completely spoiled. The adhesion is, in
fact, accomplished here by the formation of a film of true silver-solder
at the surfaces of contact.
The ingot is next cleaned, and rolled to the proper thinness between
cylinders as described under MINT; being in its progress of lamination
frequently annealed on a small reverberatory hearth. After the last
annealing, the sheets are immersed in hot dilute sulphuric acid, and
scoured with fine Calais sand; they are then ready to be fashioned into
various articles.
In plating copper wire, the silver is first formed into a tubular shape,
with one edge projecting slightly over the other; through which a redhot
copper cylinder being somewhat loosely run, the silver edges are closely
pressed together with a steel burnisher, whereby they get firmly united.
The tube thus completed, is cleaned inside, and put on the proper copper
rod, which it exactly fits. The copper is left a little longer than its
coating tube, and is grooved at the extremities of the latter, so that
the silver edges, being worked into the copper groove, may exclude the
air from the surface of the rod. The compound cylinder is now heated
redhot, and rubbed briskly over with the steel burnisher in a
longitudinal direction, whereby the two metals get firmly united, and
form a solid rod, ready to be drawn into wire of any requisite fineness
and form; as flat, half-round, fluted, or with mouldings, according to
the figure of the hole in the draw-plate. Such wire is much used for
making bread-baskets, toast-racks, snuffers, and articles combining
elegance with lightness and economy. The wire must be annealed from time
to time during the drawing, and finally cleaned, like the plates, with
dilute acid.
Formerly the different shaped vessels of plated metal were all fashioned
by the hammer; but every one of simple form is now made in dies struck
with a drop-hammer or stamp. Some manufacturers employ 8 or 10 drop
machines.
[Illustration: 878 879 880 881]
_Fig._ 878. and 879. are two views of the stamp. A is a large stone, the
more massy the better; _b_, the anvil on which the die _e_ is secured by
four screws, as shown in the ground plan, _fig._ 880. In _fig._ 878., _a
a_ are two upright square prisms, set diagonally with the angles opposed
to each other; between which the hammer or drop _d_ slides truly, by
means of nicely fitted angular grooves or recesses in its sides. The
hammer is raised by pulling the rope _f_, which passes over the pulley
_c_, and is let fall from different heights, according to the impulse
required. Vessels which are less in diameter at the top and bottom than
in the middle, must either be raised by the stamp in two pieces, or
raised with a hand hammer. The die is usually made of _cast_ steel. When
it is placed upon the anvil, and the plated metal is cut into pieces of
proper size, the top of the die is then surrounded with a lute made of
oil and clay, for an inch or two above its surface; and the cavity is
filled with melted lead. The under face of the stamp-hammer has a plate
of iron called the _licker-up_ fitted into it, about the area of the
die. Whenever the lead has become solid, the hammer is raised to a
certain height, and dropped down upon it; and as the under face of the
licker-up is made rough like a rasp, it firmly adheres to the lead, so
as to lift it afterwards with the hammer. The plated metal is now placed
over the die, and the hammer mounted with its lead is let fall
repeatedly upon it, till the impression on the metal is complete. If the
vessel to be struck, be of any considerable depth, two or three dies may
be used, of progressive sizes in succession. But it occasionally happens
that when the vessel has a long conical neck, recourse must be had to an
auxiliary operation, called _punching_. See the embossing punches,
_fig._ 881. These are made of cast steel, with their hollows turned out
in the lathe. The pieces _a_, _b_ are of lead. The punching is performed
by a series of these tools, of different sizes, beginning with the
largest, and ending with the least. By this means a hollow cone, 3 or 4
inches deep, and an inch diameter, may be raised out of a flat plate.
These punches are struck with a hand hammer also, for small articles, of
too great delicacy for the drop. Indeed it frequently happens that one
part of an article is executed by the stamp, and another by the hand.
[Illustration: 882 883]
Cylindrical and conical vessels are mostly formed by bending and
soldering. The bending is performed on blocks of wood, with wooden
mallets; but the machine so much used by the tin-smiths, to form their
tubes and cylindric vessels (see the end section, _figs._ 882. and
883.), might be employed with advantage. This consists of 3 iron rollers
fixed in an iron frame. A, B, C, are the three cylinders, and _a_, _b_,
_c_, _d_, the riband or sheet of metal passed through them to receive
the cylindrical or conical curvature. The upper roller A can be raised
or lowered at pleasure, in order to modify the diameter of the tube; and
when one end of the roller is higher than the other, the conical
curvature is given. The edges of the plated cylinders or cones are
soldered with an alloy composed of silver and brass. An alloy of silver
and copper is somewhat more fusible; but that of brass and silver
answers best for plated metal, the brass being in very small proportion,
lest the colour of the plate be affected. Calcined borax mixed with
sandiver (the salt skimmed from the pots of crown glass) is used along
with the alloy, in the act of soldering. The seam of the plated metal
being smeared with that saline mixture made into a pap with water, and
the bits of laminated solder, cut small with scissors, laid on, the seam
is exposed to the flame of an oil blowpipe, or to that of charcoal urged
by bellows in a little forge-hearth, till the solder melts and flows
evenly along the junction. The use of the sandiver seems to be, to
prevent the iron wire that binds the plated metal tube from being
soldered to it.
[Illustration: 884 885 886 887 888]
Mouldings are sometimes formed upon the edges of vessels, which are not
merely ornamental, but give strength and stiffness. These are fashioned
by an instrument called a _swage_, represented in _figs._ 884. and 885.
The part A lifts up by a joint, and the metal to be _swaged_ is placed
between the dies, as shown in the figures; the tail _b_ being held in
the jaws of a vice, while the shear-shaped hammer rests upon it. By
striking on the head A, while the metal plate is shifted successively
forwards, the beading is formed. In _fig._ 884. the tooth _a_ is a guide
to regulate the distance between the bead and the edge. A similar effect
is produced of late years in a neater and more expeditious manner by the
rollers, _figs._ 886. 887. _Fig._ 888. is a section to show the form of
the bead. The two wheels _a_, _a_, _fig._ 886., are placed upon axes,
two of which are furnished with toothed pinions in their middle; the
lower one being turned by the handle, gives motion to the upper. The
groove in the upper wheel corresponds with the bead in the lower, so
that the slip of metal passed through between them assumes the same
figure.
The greatest improvement made in this branch of manufacture, is the
introduction of silver edges, beads and mouldings, instead of the plated
ones, which from their prominence had their silver surface speedily worn
off, and thus assumed a brassy look. The silver destined to form the
ornamental edgings is laminated exceedingly thin; a square inch
sometimes weighing no more than 10 or 12 grains. This is too fragile to
bear the action of the opposite steel dies of the swage above described.
It is necessary, therefore, that the sunk part of the die should be
steel, and the opposite side lead, as was observed in the stamping; and
this is the method now generally employed to form these silver
ornaments. The inside shell of this silver moulding is filled with soft
solder, and then bent into the requisite form.
The base of candlesticks is generally made in a die by the stamp, as
well as the neck, the dish part of the nozzle or socket, and the tubular
stem or pillar. The different parts are united, some with soft and
others with hard solder. The branches of candlesticks are formed in two
semi-cylindrical halves, like the feet of tea-urns. When an article is
to be engraved on, an extra plate of silver is applied at the proper
part, while the plate is still flat, and fixed by burnishing with great
pressure over a hot anvil. This is a species of welding.
The last finish of plated goods is given by burnishing-tools of
bloodstone, fixed in sheet-iron cases, or hardened steel, finely
polished.
The ingots for lamination might probably be plated with advantage by the
delicate pressure process employed for silvering copper wire.
The total value of the plate, plated ware, jewellery, and watches,
exported in the year 1836, was 338,889_l._; but the value of the plated
goods is not given in the tables of revenue. M. Parquin, the greatest
manufacturer of plated goods in Paris (or France, for this business is
monopolized by the capital), who makes to the value of 700,000 francs
per annum, out of the 1,500,000 which, he says, is the whole internal
consumption of the kingdom, states that the internal consumption of the
United Kingdom amounts 30,000,000, or 20 times, that of France! He adds,
that our common laminated copper costs 26 sous the pound, while theirs
costs 34. Their plated goods are fashioned, not in general with stamps,
but by the pressure of tools upon wood moulds in the turning-lathe,
which is a great economy of capital to the manufacturer. There are
factories at Birmingham which possess a heavy stock of 300,000 different
die-moulds. See STAMPING OF METALS.
PLATINA-MOHR. The following easy method of preparing igniferous black
platinum, proposed thirty years ago by Descotils, has been recently
recommended by M. Dobereiner:--
Melt platina ore with double its weight of zinc, reduce the alloy to
powder, and treat it first with dilute sulphuric acid, and next with
dilute nitric acid, to oxidize and dissolve out all the zinc, which,
contrary to one’s expectations, is somewhat difficult to do, even at a
boiling heat. The insoluble black-gray powder contains some osmiuret of
iridium, united with the crude platinum. This compound acts like simple
platina-black, after it has been purified by digestion in potash lye,
and washing with water. Its oxidizing power is so great, as to transform
not only the formic acid into the carbonic, and alcohol into vinegar,
but even some osmic acid, from the metallic osmium. The above powder
explodes by heat like gunpowder.
When the platina-_mohr_ prepared by means of zinc is moistened with
alcohol, it becomes incandescent, and emits osmic acid; but if it be
mixed with alcohol into a paste, and spread upon a watch-glass, nothing
but acetic acid will be disengaged; affording an elegant means of
diffusing the odour of vinegar in an apartment.
PLATINUM, is a metal of a grayish-white colour, resembling in a good
measure polished steel. It is harder than silver, and of about double
its density, being of specific gravity 21. It is so infusible, that no
considerable portion of it can be melted by the strongest heats of our
furnaces. It is unchangeable in the air and water; nor does a white heat
impair its polish. The only acid which dissolves it, is the
nitro-muriatic; the muriate or chloride thus formed, affords, with pure
ammonia or sal ammoniac, a triple salt in a yellow powder, convertible
into the pure metal by a red heat. This character distinguishes platinum
from every other metal.
_Native Platinum._--In the natural state it is never pure, being alloyed
with several other metals. It occurs only under the form of grains,
which are usually flattened, and resemble in shape the gold _pepitas_.
Their size is in general less than linseed, although in some cases they
equal hempseed, and, occasionally, peas. One piece brought from Choco,
in Peru, and presented to the Cabinet of Berlin, by M. Humboldt, weighs
55 grammes = 850 grains, or nearly 2 oz. avoirdupois. The greatest lump
of native platinum known, till of late years, was one in the Royal
Museum of Madrid, which was found in 1814 in the gold mine of Condoto,
province of Novita, at Choco. Its size is greater than a Turkey’s egg,
(about 2 inches one diameter, and 4 inches the other,) and its weight
760 grammes, = 24 oz. or fully 2 lbs. troy. See _infrà_.
The colour of the grains of native platinum is generally a grayish
white, like tarnished steel. The cavities of the rough grains are often
filled with earthy and ferruginous matters, or sometimes with small
grains of black oxide of iron, adhering to the surface of the platinum
grains. Their specific gravity is also much lower than that of forged
pure platinum; varying from 15 in the small particles, to 18·94 in M.
Humboldt’s large specimen. This relative lightness is owing to the
presence of iron, copper, lead, and chrome; besides its other more
lately discovered metallic constituents, palladium, osmium, rhodium, and
iridium.
Its main localities in the New Continent, are in the three following
districts:--
1. At Choco, in the neighbourhood of Barbacoas, and generally on the
coasts of the South Sea, or on the western slopes of the Cordillera of
the Andes, between the 2nd and the 6th degrees of north latitude. The
gold-washings that furnish most platinum, are those of Condoto, in the
province of Novita; those of Santa Rita, or Viroviro, of Santa Lucia, of
the ravine of Iro, and Apoto, between Novita and Taddo. The deposit of
gold and platinum grains is found in alluvial ground, at a depth of
about 20 feet. The gold is separated from the platinum by picking with
the hand, and also by amalgamation; formerly, when it was imagined that
platinum might be used to debase gold, the grains of the former metal
were thrown into the rivers, through which mistaken opinion an immense
quantity of it was lost.
2. Platinum grains are found in Brazil, but always in the alluvial lands
that contain gold, particularly in those of Matto-Grosso. The ore of
this country is somewhat different from that of Choco. It is in grains,
which seem to be fragments of a spongy substance. The whole of the
particles are nearly globular, exhibiting a surface formed of small
spheroidal protuberances strongly cohering together, whose interstices
are clean, and even brilliant.
This platinum includes many small particles of gold, but none of the
magnetic iron-sand or of the small zircons which accompany the Peruvian
ore. It is mixed with small grains of native palladium, which may be
recognised by their fibrous or radiated structure, and particularly by
their chemical characters.
3. Platinum grains are found in Hayti, or Saint Domingo, in the sand of
the river Jacky, near the mountains of Sibao. Like those of Choco, they
are in small brilliant grains, as if polished by friction. The sand
containing them is quartzose and ferruginous. This native platinum
contains, like that of Choco, chromium, copper, osmium, iridium,
rhodium, palladium, and probably titanium. Vauquelin could find no gold
among the grains.
Platinum has been discovered lately in the Russian territories, in the
auriferous sands of Kuschwa, 250 wersts from Ekaterinebourg, and
consequently in a geological position which seems to be analogous with
that of South America.
These auriferous sands are, indeed, almost all superficial; they cover
an argillaceous soil; and include, along with gold and platinum, debris
of dolerite (a kind of greenstone), protoxide of iron, grains of
corundum, &c. The platinum grains are not so flat as those from Choco,
but they are thicker; they have less brilliancy, and more of a leaden
hue. This platinum, by M. Laugier’s analysis, is similar in purity to
that of Choco; but the leaden-gray grains, which were taken for a
mixture of osmium and iridium, are merely an alloy of platinum,
containing 25 per cent. of these metals.
The mines of Brazil, Columbia, and Saint Domingo furnish altogether only
about 400 kilos. of platinum ore per annum; but those of Russia produce
above 1800 kilos. The latter were discovered in 1822, and were first
worked in 1824. They are all situated in the Ural mountains. The ore is
disseminated in an argillaceous sand, of a greenish-gray colour,
resulting from the disintegration of the surrounding rocks, and
constitutes from 1 to 3 parts in 4000 of the sand. Occasionally it has
been found in lumps weighing 8 kilogrammes (16 lbs.!), but it generally
occurs in blackish angular grains, which contain 70 per cent. of
platinum, and 3 to 5 of iridium. The ore of Goroblagodat is in small
flattened grains, which contain 88 per cent. of this precious metal. The
osmiure of iridium is found upon a great many points of the Urals,
throughout a space of 140 leagues, being a product accessory to the gold
washings. 32 kilogrammes of osmiure are collected there annually, which
contain upon an average 2 per cent. of platinum.
M. Vauquelin found nearly ten per cent. of platinum in an ore of
argentiferous copper, which was transmitted to him as coming from
Guadalcanal in Spain. This would be the only example of platinum
existing in a rock, and in a vein. As the same thing has not again been
met with, even in other specimens from Guadalcanal, we must delay
drawing geological inferences, till a new example has confirmed the
authenticity of the first.
Platinum has been known in Europe only since 1748, though it was noticed
by Ulloa in 1741. It was compared at first to gold; and was, in fact,
brought into the market under the name of white gold. The term platinum,
however, is derived from the Spanish word _plata_, silver, on account of
its resemblance in colour to that metal.
The whole of the platinum ore from the Urals is sent to St. Petersburg,
where it is treated by the following simple process:--
One part of the ore is put in open platina vessels, capable of
containing from 6 to 8 lbs., along with 3 parts of muriatic acid at 25°
B. and 1 part of nitric acid at 40°. Thirty of these vessels are placed
upon a sand-bath covered with a glazed dome with movable panes, which is
surmounted by a ventilating chimney to carry the vapours out of the
laboratory. Heat is applied for 8 or 10 hours, till no more red vapours
appear; a proof that the whole nitric acid is decomposed, though some of
the muriatic remains. After settling, the supernatant liquid is decanted
off into large cylindrical glass vessels, the residuum is washed, and
the washing is also decanted off. A fresh quantity of nitro-muriatic
acid is now poured upon the residuum. This treatment is repeated till
the whole solid matter has eventually disappeared. The ore requires for
solution from 10 to 15 times its weight of nitro-muriatic acid,
according to the size of its grains.
The solutions thus made are all acid; a circumstance essential to
prevent the iridium from precipitating with the platinum, by the water
of ammonia, which is next added. The deposit being allowed to form, the
mother waters are poured off, the precipitate is washed with cold water,
dried, and calcined in crucibles of platinum.
The mother-waters and the washings are afterwards treated separately.
The first being concentrated to one-twelfth of their bulk in glass
retorts, on cooling they let fall the iridium in the state of an
ammoniacal chloride, constituting a dark-purple powder, occasionally
crystallized in regular octahedrons. The washings are evaporated to
dryness in porcelain vessels; the residuum is calcined and treated like
fresh ore; but the platinum it affords needs a second purification.
For agglomerating the platinum, the spongy mass is pounded in bronze
mortars; the powder is passed through a fine sieve, and put into a
cylinder of the intended size of the ingot. The cylinder is fitted with
a rammer, which is forced in by a coining press, till the powder be much
condensed. It is then turned out of the mould, and baked 36 hours in a
porcelain kiln, after which it may be readily forged, if it be pure, and
may receive any desired form from the hammer. It contracts in volume
from 1-6th to 1-5th during the calcination. The cost of the manufacture
of platinum is fixed by the administration at 32 francs the Russian
pound; but so great a sum is never expended upon it.
For Dr. Wollaston’s process, see Phil. Trans. 1829, Part I.
Platinum furnishes most valuable vessels to both analytical and
manufacturing chemists. It may be beat out into leaves of such thinness
as to be blown about with the breath.
This metal is applied to porcelain by two different processes; sometimes
in a rather coarse powder, applied by the brush, like gold, to form
ornamental figures; sometimes in a state of extreme division, obtained
by decomposing its muriatic solution, by means of an essential oil, such
as rosemary or lavender. In this case, it must be evenly spread over the
whole ground. Both modes of application give rise to a steely lustre.
The properties possessed in common by gold and platinum, have several
times given occasion to fraudulent admixtures, which have deceived the
assayers. M. Vauquelin having executed a series of experiments to
elucidate this subject, drew the following conclusions:--
If the platinum do not exceed 30 or 40 parts in the thousand of the
alloy, the gold does not retain any of it when the parting is made with
nitric acid in the usual way; and when the proportion of platinum is
greater, the fraud becomes manifest, 1st by the higher temperature
required to pass it through the cupel, and to form a round button, 2, by
the absence of the lightning, fulguration, or coruscation; 3, by the
dull white colour of the button and its crystallized surface; 4, by the
straw-yellow colour which platinum communicates to the aquafortis in the
parting; 5, by the straw-yellow colour, bordering on white, of the
cornet, after it is annealed. If the platinum amounts to one fourth of
the gold, we must add to the alloy at least 3 times its weight of fine
silver, laminate it very thin, anneal somewhat strongly, boil it half an
hour in the first aquafortis, and at least a quarter of an hour in the
second, in order that the acid may dissolve the whole of the platinum.
Were it required to determine exactly the proportions of platinum
contained in an alloy of copper, silver, gold, and platinum, the amount
of the copper may be found in the first place by _cupellation_, then the
respective quantities of the three other metals may be learned by a
process founded, 1, upon the property possessed by sulphuric acid of
dissolving silver without affecting gold or platinum; and, 2, upon the
property of platinum being soluble in the nitric acid, when it is
alloyed with a certain quantity of gold and silver.
According to Boussingault, the annual product of Platinum in America
does not exceed 8-1/3 cwts. At Nischne-Tagilsk, in 1824, a lump of
native platinum weighing fully 10 lbs. was found; and in 1830, another
lump, of nearly double size, which weighed 35-3/4 Prussian marcs; fully
18 lbs. avoirdupoise.