13 Of winning the coal.

The cftablished price of boring in England is 5 s. per fathom for the firft five fathoms, 10 s. per fathom for the next five fathoms, and 158 per fathom for the next five fathoms; and fo continually increating 5 s. per fathom at the end of every five fathoms; the borer finding all kinds of boring inftruments, and taking his chance of the hardness of the ftrata, except above one foot in thickness of whin occur, when the former price ceafes, and he is paid per day.

It is exceedingly uncommon to meet with a ftratum of coal which is naturally dry, or whofe fubterranean fprings or feeders of water are fo very fmall as to require no other means than the labour of men to draw off or conduct them away; for it molt commonly happens, that the ftratum of coal, and the other ftrata adjacent, abound fo much in feeders of water, that, befor accefs can be had to the coal, fome other methods muk be purfued to drain or conduct away these feeders: therefore, after the deepest part of the coal is difcovered, the next confideration is of the best method of draining it, or, in the miner's language, of winning the coal.

If the coal lies in fuch an elevated fituation, that a part of it can be drained by a level brought up from the lower grounds, then that will be the moft natural method; but whether it be the most proper or not, depends upon certain circumftances. If the fituation of the ground be fuch, that the level would be of a great length, or have to come through very hard itrata, and the quantity of coal it would drain, or the profits expected to be produced by that coal, fhould be inadequate to the expence of carrying it up; in fuch cafe fome other method of winning might be more proper. Or fuppofe, in another cafe, it be found, that a level can be had to a coalery, which will coft L. 2000, and require five years to bring it up to the coal, and that it will drain 30 acres of coal when completed; yet if it be found that a fire engine, or fome other machine, can be erected on that coalery, for the fame fum of money, in one year, which will drain 50 acres of the fame coal, then this luft would be a more proper method than the level, because four years profit would be received by this method before any could come in by the other; and after the 30 acres drained by the level is all wrought, a machine of fome kind would nevertheless be neceifary to drain the remaining 20 acies: fo that erecting a machine at firft would be on all accounts the moit advisable.

Where a level can be drove, in a reafonable time, and at an adequate expence, to drain a fufficient tract of coal, it is then the most eligible method of winning; because the charge of upholding it is generally lefs than that of upholding fire-engines or other machines.

If a level is judged propereft after confideration of every neceffary circumftance, it may be begun at the place appointed in the manner of an open ditch, about three feet wide, and carried forward until it be about fix or feven feet deep from the furface, taking care to fecure the bottom and fides by timber-work or build

ing; after which it may be continued in the manner Coalery. of a mine about three feet wide, and three feet and a half high, through the folid ftrata, taking care all along to keep the bottom upon a level, and to fecure the roof, fides, and bottom, by timber or building, in all places where the ftrata are not itrong enough to fupport the incumbent weight, or where they are liable to decay by their expofure to the fresh air. If the mine has to go a very long way before it reach the coal, it may be neceffary to fink a fmall pit, for the convenience of taking out the ftones and rubbish produced in working the mine, as well as to fupply freth air to the workmen; and if the air fhould afterwards turn damp, then fquare wooden pipes made of dales clofely jointed (commonly called air-boxes), may be fixed in the upper part of the mine, from the pit-bottom all the way to the end of the mine, which will caufe a fufficient circulation of fresh air for the work

men; perhaps in a great length it will be found proper to fink another or more pits upon the mine, and by proceeding in this manner it may be carried forward until it arrive at the coal; and after driving a mine in the coal a few yards to one fide, the first coalpit may be funk.

tice Steam

If a level is found impracticable, or for particular reafons unadvifable; then a fire-engine*, or fome o-See ar ther machine, will be neceffary, which should be fixed upon the deepest part of the coal, or at leaft fo far engine. towards the dip as will drain a fufficient extent of coal, to continue for the time intended to work the coalery; and whether a fire-engine, or any other machine, is ufed, it will be of great advantage to have a partial level brought up to the engine-pit, if the fituation of the ground will admit it at a imall charge, in order to receive and convey away the water without drawing it fo high as to the furface: for if the pit was 30 fathoms deep to the coal, and if there was a partial level, which received the water five fathoms only below the furface, the engine by this means would be enabled to draw 1-6th part more water than without it; and if there were any feeders of water in the pit above this level, they might be conveyed into it, where they would be discharged without being drawn by the engine.

The engine-pit may be from feven to nine feet wide; and whether it be circular, oval, or of any other form, is not very material, provided it be fufficiently strong, though a circular fort is mott generally approved. -If any feeders of water are met with a few fathoms from the furface, it will be proper to make a circular or spiral cutting about one foot deep, and a little hollowed in the bottom, round the circumference of the pit, in order to receive and conduct the water down, without flying over the pit and incommoding the workmen. If the trata are of so tender or friable a nature as not to bear this opera tion, or if the water leaks through them, then it will be neceffary to infert in the forementioned cutting a circular piece of timber called a crib, hollowed in the fame manner to collect the water; and a fecond may be inferted two or three yards below the first, with a floping nitch down the wall or fide of the pit, to convey the water from the former into it; proceeding by fome of thefe methods until the pit is funk 15 or 20 fathoms; at which place it would be proper to fix a N 2

ciftern

Coalery. rooms, and to fupply fresh air to this new operation, a fmall mine might be drove from the room b, and a hole funk down upon the level roam ii; therefore, if the level mine ee was not drove fo far forward as to have all these operations completed before the rooms and other workings were intercepted by the dike, the working of the pit might ceafe until thefe new places were ready.

If there be two or three ftrata or feams of coal in the fame pit (as there often are) having only a ftratum of a few feet thick lying betwixt them, it is then material to obferve, that every pillar in the fecond feam be placed immediately below one in the firft, and every pillar in the third feam below one in the fecond; and in fuch a fituation the upper ftratum of coal ought to be firft wrought, or elfe all the three together: for it would be unfafe to work the lower one first, left the roof should break, and damage thofe lying

above.

It fometimes becomes neceffary to work the coal lying to the dip of the engine or the level; which coal is confequently drowned with water, and mult therefore be drained by fome means before it can be wrought. If the quantity of water proceeding from it be inconfiderable, it may then be drained by fmall pumps laid upon the pavement of the coal, and wrought by men or horfes, to raise the water up to the level of the engine-pit bottom: or if the feeders of water be more confiderable, and the fituation be fuitable, the working rod of thefe pumps might be connected with thofe in the engine-pit; by which means the water would be raifed up to the level; but if the quantity of water be very great; or if, from other circumftances, these methods may not be applicable; then the engine-pit may be funk as deep below the coal as may be neceffary, and a level stone mine drove from its bottom to the dip of the ftrata, until it interfect the ftratum of coal, from whence a new level mine might be worked, which would effectually drain it. Suppofe A B, fig. 8. to be a fection of the engine-pit; BC, the coal drained by the engine; BD, the coal to the dip of the engine intended to be drained; then if the engine-pit be funk deeper to E, a ftone mine may be wrought in the direction ED, until it interfect the coal at D, by which the water will have a free paffage to the engine, and the coal will be drained.

If there be another ftratum of coal lying at fuch a depth below the firtt as the engine-pit is intended to be funk to, the upper feam may in fome fituations be conveniently drained, by driving a mine in the lower feam of coal from E to F, and another in the upper one from B to D; and by boring a hole from D to F, the water will defcend to F, and, filling the mine EF, rife up to the engine-pit bottom at E, which is upon a level with D.

Whenever it is judged neceffary to work the pillars, regard must be had to the nature of the roof. If the roof is tender, a narrow room may be wrought through the pillar from one end to the other, leaving only a fhell of coal on each fide for fupporting the roof the time of working. Suppofe ABCD, fig. 7. to be a pillar of coal 18 feet long and 12 feet broad: if the roof is not frong, the room 1, 2, 3, 4, of eight feet wide, may be wrought up through that pillar, leaving a fhell of two feet thick on each fide; and if it can be

fafely done, a part of these fhells may also be wrought Coalery. away, by working two places through them as at 5 and 6. By this means very little of the coal will be loft; for two-thirds of the whole being obtained by the first working, and above two-thirds of the pillar by the fe cond working, the lofs upon the whole would not exceed one-tenth: but it may be observed, that fome pillars will not produce fo great a proportion, and perhaps others cannot be wrought at all; fo that, upon the whole, there may be about one-eighth, one-feventh, or in fome fituations one-fixth part of the coal loft. If the roof be hard and strong, then as much coal may be wrought off each fide and each end of the pillar as can be done with fafety, leaving only a fmall piece ftanding in the middle; and when the roof is very ftrong, fometimes feveral pillars may be taken entirely out, without any lots of coal: and in general this latt method is attended with lefs lofs, and produces larger coals, than the former. In all cafes it is proper to begin working thofe pillars firft which lie fartheft from the pit bottom, and to proceed working them regularly away towards the pit; but if there be a great number of pillars to the dip of the pit, it is the fafeft method to work thefe out before those to the rife of the pit are bega with.

There is no great difference in the weight of differ ent kinds of coals, the lighteft being about 74 pounds avoirdupois, and the heavicft about 79 pounds the cu-bic foot; but the moft ufual weight is 75 pounds the foot, which is 18 hundred weight and 9 pounds the cubic yard. The ftatute chalder is 53 hundred weight; or when meafured is as follows: 268:8 cubic inches to the Winchefter gallon; 4 gallons to the coal peck, about 3 pounds weight; 8 ccal pecks to the boll, about 247 pounds; and 24 bolls to the chalder, of 53 hundred weight. If one coal meafuring exactly a cubic yaıd (nearly equal to 5 bolls) be broken into pieces of a moderate fize, it will measure feven coal bolls and a half. If broken very small, it will meafure 9 bolls; which fhows, that the proportion of the weight to the meafure depends upon the fize of the coals; therefore accounting by weight is the moit rational method.

A TABLE of the weight and quantity of coal contained in one acre Scots meafure, allowing one fixth part to be loft below ground, in feams of the following thickneffes.

Coalery ced upon a fledge: a horfe by this means will bring out from four to eight hundred weight of coals at once, according to the quantity of the afcent or defcent. In fome coaleries they have accefs to the workings by a mine made for them, floping down from the furface of the earth to the coal; and where that convenience is wanting, they are bound into a net, and lowered down the pit. If the coal be not of fuch a height as to admit horses, and has a moderate rife like the laft, then men are employed to bring out the coals: they ufually draw a basket of four or five hundred weight of coals, fixed upon a small four-wheeled carriage. There are fome fituations in which neither horfes nor men can be properly ufed; particularly where the coal has a great degree of defcent, or where many dikes occur: in fuch a cafe the coals are beft brought out by women called bearers, who carry them in a kind of bafket upon their backs, ufually a hundred, or a hundred weight and a

15

Of crushes and fitte.

cul air.

A

half, at once.

When the coals are brought to the pit bottom, the baskets are then hooked on to a chain, and drawn up the pit by a rope to the furface, which is belt effected by a machine called a gin, wrought by horfes. There are other kinds of gins for drawing coals, fome wrought by water, others by the vibrating lever of a fire-engine; but either of thefe laft is only convenient in fome par ticular fituations, thofe wrought by horfes being in most general ufe. After the coals are got to the fur face, they are drawn a small distance from the pit, and laid in feparate heaps: the largeft coals in one heap, the finaller pieces called chews in another, and the culm or pan-coal in a feparate place.

There is an accident of a very dangerous nature to which all coaleries are liable, and which has been the ruin of feveral: it is called a crush, or a fitt. When the pillars of coal are left fo fmall as to fail, or yield under the weight of the fuperior frata; or when the pavement of the coal is fo foft as to permit the pillars to fink into it, which fometimes happens by the great weight that lies upon them; in either cafe the folid Aratum above the coal breaks and falls in, ciufhes the pillar to pieces, and clofeth up a great extent of the workings, or probably the whole coalery. As fuch an accident feldom comes on fuddenly, if it be perceived in the beginning, it may fometimes be ftopped by building large pillars of tone amongst the coal pillars: but if it has already made fome progrefs, then the best method is to work away as many of the coal pillars adjoining to the crush as may be fufficient to let the roof fall freely down; and if it makes a breach of the folid Arata from the coal up to the furface, it will very probably prevent the crush from proceeding any farther in that part of the coalery. If the crufh begins in the rife part of the coalery, it is more difficult to ftop it from proceeding to the dip, than it is to ftop it from going to the rife when it begins in a contrary part.

Another circumftance proper to be taken notice of is the foul or adulterated air fo often troublesome in coaleries. Of this there are two kinds: the black damp or flyth, which is of a fuffocating nature; and the inflammable or combustible damp. Without ftaying to inquire, in this place, into the origin and effects of thefe damps, it may be fufficient to obferve, that, in whatever part of any coalery a conftant fupply or a circulation of fresh air is wanting, there fome of

Plate

thefe damps exift, accumulate in a body, and become Coalery. noxious or fatal: and whenever there is a good circulation of fresh air, they cannot accumulate, being mixed with and carried away by the ftream of air as fast as they generate or exhale from the frata. Upon thefe principles are founded the feveral methods of ventilating a coalery. Suppofe the workings of the pits A and B (fig. 6.) to be obnoxious to the inflammable damps; if the communication was open betwixt the CXLII, two pits, the air which went down the pit A would proceed immediately along the mine a, and afcend out of the pit B; for it naturally takes the neare!t direction: fo that the air in all the workings would be ftag. nant; and they would be utterly inacceffible from the accumulation of the combuftible damp. In order to expel this, the air must be made to circulate through all the different rooms by means of collateral aircourfes made in this manner: The paffage or mine a must be clofed up or stopped by a partition of deals, or by a wall built with bricks or ftones, to prevent the air paffing that way. This building is called a flopping. There must also be toppings made in the thirlings 111, &c. betwixt the pillars ff, &c. which will direct the air up the mine ee, until it arrive at the innermoft thirling 2, which is to be left open for its paffage. There must alfo be stoppings made at the fide of the mine a at mm, and on both fides of the main headway BC at bb, &c. then returning to the innermoft thir ling 2, proceed to the third row of pillars, and build up the thirlings 22, &c. leaving open the thirling 3 for a paffage for the air; and proceeding on to the fifth row of pillars, build up in the fame manner the floppings 3 3, &c. leaving open 4 for an air course; and by proceeding in this manner to flop up the thirlings or paffages in every other row of pillars, the current of fresh air will circulate through and ventilate the whole workings, in the direction pointed to by the small arrows in the plan, clearing away all the damps and noxious vapours that may generate. When it is arrived at C, it is conduted across the main headway, and carried through the other part of the pit's workings in the fame manner, until it return through nn to the pit B where it afcends; and as the rooms advance farther, other toppings are regularly made.

In fome of thofe ftoppings, on the fides of the main headway, there must be doors to admit a paffage for the bringing out of the coals from the rooms to the pit, as at 55: thefe doors must be conftantly fhut, except at the time of paffing through them.

There are other methods of difpofing the toppings fo as to ventilate the pit; but none which will fo effectually difperfe the damps as that described above. If the damps are not very abundant, then the courfe of ftoppings 111, &c. in the level mine, and the others, at bbb, &c. in the main headway, without any others, may perhaps be fufficient to keep the pit clear. If at any time the circulation of the fresh air is not brifk enough, then a large lamp of fire may be placed at the bottom of the pit B, which, by rarefying the air there, will make a quicker circulation.

16

Moft of the larger coaleries fend their coals to the oflea ing fhips for the coafting trade or exportation; and, as the and f quantity is generally very large, it would take a greater ping le i3 number of carts than could conveniently be obtained at all times to carry them; befides the confiderable expence