_Classification of Pit-coal, and maximum quantity of gas, obtainable
from different kinds of Coal._
We have stated already that pitcoal is in this country the cheapest
crude natural production from which carburetted hydrogen gas can be
obtained in the large way. It is that which yields it in abundance, and
which can with the least trouble and expence be subjected to the
operation it has to undergo for the production of the gas.[3] Nature has
dealt this mineral out to us, with an unsparing hand, and has provided
mines of coal which seem to defy the power of man to exhaust.
[3] Other Substances from which carburetted hydrogen gas, may be
economically obtained, are animal and vegetable oil, tar, both
vegetable and coal tar; pitch, resin, the essential oils obtainable
from vegetable and from coal tar, and the compact species of turf. On
this subject we shall speak hereafter.
The principal coal mines in England are those near Newcastle and
Whitehaven. The town of Newcastle stands on beds of coal which extend to
a considerable distance round the place, and which as far as concerns
many hundred generations after us, may be pronounced inexhaustible.
Pitcoal like all other bituminous substances is composed of a fixed
carbonaceous base in the state of bitumen, united to a small portion of
earthy and saline matter, which constitute the ashes left behind when
the coal is burnt. The proportions of these parts differ considerably in
different kinds of coal; and according to the prevalence of one or other
of them, so the coal is more or less combustible, passing by various
shades from the most inflammable coal into blind coal, Kilkenny coal, or
stone coal, and lastly into a variety of earthy, or stony substances,
which although they are inflammable do not merit the appellation of
coal.
All the varieties of coal used in this country for fuel may be divided
into the following classes.
The first class comprehends those varieties which are chiefly composed
of bitumen only, which take fire easily, and burn briskly with a strong
and yellowish white blaze, which do not swell or cake on the fire, and
require no stirring, which produce no slag, and by a single combustion
are reduced to light white ashes. Some of this species of coal when
suddenly heated crackle and split into pieces, especially if laid on the
fire in the direction of the cross fracture of their laminæ.
Cannel coal, deserves to be placed at the head of this class; next to
this, we may rank all those descriptions of coal known in the London
market by the names of Hartley, Cowper’s Main, Tanfield Moor, Eighton
Main, Blythe, and Pont Tops. It also includes the sort of coals found in
several parts of Scotland, called Splent coal, and some of those raised
on the Western Coast of England.
Most of the coals raised in Staffordshire ought likewise to be classed
among this species of coal, but the line of distinction between these,
and the classes subsequently named, cannot be accurately drawn.
The following table exhibits the maximum quantity of gas obtainable from
the first class of coal.[4]
[4] Own Experiments, made at the Royal Mint Gas-Works.
One Chaldron of Coal, produces Cubic feet of Gas.
Scotch Cannel coal 19,890
Lancashire Wiggan coal 19,608
Yorkshire Cannel coal,
(Wakefield) 18,860
Staffordshire coal,[5]
First variety,[6] 9,748
Second variety, 10,223
Third variety, 10,866
Fourth variety, 9,796
Gloucestershire coal,[7]
First variety, (Forest of Dean, High Delph) 16,584
Second variety, (Low Delph) 12,852
Third variety, (Middle Delph) 12,096
Newcastle coal,
First variety, (Hartley) 16,120
Second variety, (Cowper’s High Main) 15,876
Third variety, (Tanfield Moor) 16,920
Fourth variety, (Pontops) 15,112
[5] They require a much higher temperature, than is necessary for the
decomposition of Newcastle coal.
[6] For the maximum quantity of gas produced from this and the three
succeeding varieties of coal, I am indebted to J. Gostling, Esq.
Proprietor of the Birmingham Gas Works.
[7] Most varieties afford a porous, and very friable coke.
The second class of coal, comprehends all those varieties which contain
a less quantity of bitumen, and a larger quantity of carbon than the
first class. They burn with a flame less bright and of a more yellowish
colour, and the last portion of flame they are capable of yielding is
always of a lambent blue colour, they become soft after having laid on
the fire for some time, swell in bubbles and pass into a state of
semi-fusion, they then cohere and coke, puff up and throw out tubercular
scoriæ, with a hissing noise, accompanied with small jets of flame.
In consequence of the agglutination and tumefaction, the passage of air,
if this sort of coal be burnt in an open grate, is interrupted, the fire
burns as it is called hollow, and would become extinguished if the top
of the coal were not from time to time broken into with the poker.
The coke formed from this species of coal is more compact than that
produced from the first sort of coal, and is well calculated for
standing the blast of bellows in metallurgical operations. In respect to
weight the second class of coal is considerably heavier than those of
the first class, the difference amounts to not less than from
twenty-eight pounds to thirty-three pounds in the sack of coal. A
chaldron of some varieties of this class of coal, if the coals are in
large lumps, weighs upwards of twenty-eight hundred weight.
The usual denomination by which the second class of coal is known in the
London market, is that of _strong burning coal_. The following varieties
are sufficiently known, Russel’s Walls-End; Bewick’s and Craister’s
Walls-End; Brown Walls-End, Wellington Main, Temple Main, Heaton Main,
Killingsworth Main, Percy Main, Benton Main, and some varieties of the
Swansea coal.
The smaller kinds of coal of this class are preferred by smiths, because
they stand the blast well. They make a caking fire so as to form a kind
of hollow, space or oven, as the workmen call it. Some varieties abound
in pyrites, and others are intersected with thin layers of slate and
lime-stone. They require more heat for being carbonized than the first
class, and the fluid obtained from it by distillation, contains a
considerable portion of carbonate, sulphate, and hydrosulphuret of
ammonia. They are well calculated for the production of coal gas; the
coke which they produce is not very brittle, and will bear moving from
place to place, without crumbling into dust.
The following table exhibits the maximum quantity of gas obtainable from
the second class of coal.[8]
[8] Own Experiments, made at the Royal Mint Gas-Works.
One Chaldron of Coal, produces Cubic feet of Gas.
Newcastle coal,
First variety, (Russel’s Wall’s End) 16,876
Second variety, (Bewick and Craister’s Wall’s End) 16,897
Third variety, (Heaton Main) 15,876
Fourth variety, (Killingsworth Main) 15,312
Fifth variety, (Benton Main) 14,812
Sixth variety, (Brown’s Wall’s End) 13,600
Seventh variety, (Mannor Main) 12,548
Eighth variety, (Bleyth) 12,096
Ninth variety, (Burdon Main) 13,608
Tenth variety, (Wears Wall’s End) 14,112
Eleventh variety, (Eden Main) 9,600
Twelfth variety, (Primrose Main) 8,348
The third and last class of coals includes those which are destitute of
bitumen, being chiefly composed of carbon in a peculiar state of
aggregation, evidently combined chemically with much earthy matter.
Coals of this class require a still higher temperature to become ignited
than any of the former classes, they emit little or no smoke. When laid
on a fire they burn away with a feeble lambent flame, indeed some
varieties give no flame at all, but burn merely with a red glow,
somewhat like charcoal, and at length become consumed without caking.
They leave a small portion of heavy ashes.
When submitted to distillation they afford little or no tar; of a
consistence almost resembling pitch, and a gaseous fluid chiefly
composed of gaseous oxide carbon and hydrogen gas. It is scarcely
necessary to add that they are altogether unfit to be employed for the
manufacture of coal gas. The Kilkenny, Welch, and stone or hard coal
belong to this class. They require a strong draught when burnt in an
open fire-grate, and the large quantity of gaseous oxide of carbon which
they furnish during their combustion is extremely offensive. This is
particularly the case with Kilkenny coal. The Welch stone or hard coal
is better adapted for culinary purposes, and there is reason to believe
that this species of coal might be rendered useful in the smelting of
iron ore, by a slight modification in the metallurgic process employed
for extracting the metal from its ore, but to eradicate prejudice, and
to alter established practices is a work which nothing but time can
effect. This species of coal is sent all over the kingdom; it is well
calculated for the operations of drying malt and hops, and its small
coal or culm has been found a more economical fuel, than Newcastle and
Sunderland coals, for the burning of lime and bricks, and for all other
processes where no blazing fuel is required.
The following table exhibits the maximum quantity of gas obtainable from
this class of coals.
One Chaldron of Coal, produces Cubic feet of Gas.
Welch coal. First variety, from
Tramsaren, near Kidwelly,[9] 2,116
Second variety, from the yard vein at the same place 1,656
Third variety, from Blenew, near Llandillo 1,416
Fourth variety, from Rhos, near Ponty Barren 1,272
Fifth variety, from the Vale of Gwendrath 1,292
Sixth variety, from ditto 1,486
[9] The coal for these Experiments was supplied gratuitously, to the
Gas Works of the Royal Mint, by Sir W. Paxton of Middleton Hall.
When we consider the before mentioned varieties of coal in an economical
point of view, as fuel to be used in the gas-light process, for heating
the retorts, it appears from a series of experiments that have been made
under my direction, that the second class of coal comprehending those
varieties which contain a larger quantity of carbon than bitumen (p.
45,) afford the most economical fuel, they act less on the grate bars,
and fire bricks of the furnace than those varieties which take fire
easily and burn briskly with a strong blaze. A mixture of Welch Stone
coal, and Newcastle coal forms an excellent economical fuel, where an
intense glowing fire is required.