Of the Cost of Coal Mining
The Coal Question: Of the Cost of Coal Mining
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Historical E-Book: The Coal Question: An Inquiry Concerning the Progress of the Nation, and the Probable Exhaustion of Our Coal-Mines
Author: William Stanley Jevons
Edition Used: London: Macmillan and Co., 1866. (Second edition, revised)
First Published: 1865
Chapter IV
The difficulty and cost of winning and working coal-mines form an aspect of the question that obviously contains the solution of the whole. In a free industrial system, such as we are developing and assisting to spread, everything is a question of cost. We have heard of moral and physical impossibilities, but we ought to be aware that there are also commercial impossibilities. We must ask, in undertaking a work, not whether it can be done, or is physically possible, but whether it will pay to do it—whether it is commercially possible. The works of the two Brunels were, in a mechanical point of view, at least as successful and wonderful as those of the Stephensons; but, commercially speaking, they were disastrous failures, which no one would have undertaken had the consequences been seen. Commerce and industry cannot be carried on but by gain—by a return exceeding the outlay. Now, in coal-mining, we must discriminate the physical and commercial possibility. The second presupposes the first, but does not follow from it. The question is a twofold one:—Firstly, is it physically possible to drive our coal-mines to the depth of 4,000, 5,000, or 6,000 feet? and, secondly, is it commercially possible when in other parts of the world coal (The Coal Question: Of the Cost of Coal Mining) is yet being worked in the light of day? The very existence of Britain, as a great nation, is bound up in these questions.
Now I apprehend that there is not the least danger of our reaching any fixed limit of deep mining, where physical impossibility begins. In mines already 2,000 or 2,500 feet deep, there is no special difficulty felt in going deeper. But we must consider the matter a little, because the Quarterly Review has confidently asserted that 2,500 feet is the limit,[1] and Mr. Hull, after an express inquiry into the matter, thinks that 4,000 may be taken as the limit.[2] It has often been suggested that the increase of temperature of the earth's crust as we descend into it will prove an insuperable obstacle, and Mr. Hull and others have been inclined to hold, that beyond a depth of 4,000 or 5,000 feet the temperature will entirely prevent further sinking.
The increase of temperature varies in different mines from one degree in 35 to one degree in 88 feet. The increase in the deep Monkwearmouth Pit was one degree for 60 feet; but the observations of Mr. Astley in the sinking of the Dukinfield Deep Pit showed an average increase of one degree in 83 feet, nearly the lowest rate known. If with Mr. Hull we take one degree in 70 feet as a safe average rate of increase, we easily form the following table, starting from the depth of 50 feet from the surface, at which depth in this country an uniform temperature of about 50° Fahr. is found to exist.
| Depth in feet |
Increase of temperature of rock |
Actual temperature of rock |
|---|---|---|
| 50 | 0° | 50° |
| 1,000 | 14° | 64° |
| 2,000 | 28° | 78° |
| 3,000 | 42° | 92° |
| 4,000 | 56° | 106° |
| 5,000 | 71° | 121° |
The air in mines, independently of the rock, is also warmer than at the surface, owing to its greater density; for just as in ascending a mountain the barometer falls and the air grows rare and cold, so in descending a mine the barometer rises and the air grows warmer. The barometer, roughly speaking, varies about an inch for every 1,000 feet of elevation, and the temperature about one degree for every 300 feet. On these data, the following table is roughly calculated:—
| Depth in feet |
Height of Barometer |
Increase of temperature of air |
Actual temperature of air |
|---|---|---|---|
| 0 | 30·0 | 0° | 50° |
| 1,000 | 31·0 | 3° | 53° |
| 2,000 | 32·0 | 7° | 57° |
| 3,000 | 33·0 | 10° | 60° |
| 4,000 | 34·0 | 13° | 63° |
| 5,000 | 35·0 | 17° | 67° |
If air, then, of the temperature of 50° at the surface descend 5,000 feet, it will acquire the temperature of 67°. The [[rock]s] at that depth will have the temperature of 121°, and will therefore warm the air as it circulates through the mine up to their own temperature. But Mr. Hull has fallen into a very evident mistake in adding together the increments of temperature of the air and rocks. He makes the temperature, for instance, at a depth of 4,000 feet, to be 120°·08 as follows:—
| Invariable temperature of surface... | 50°·5 |
| Increase due to depth... | 56°·42 |
| Increase due to density of air... | 13°·16 |
| Resulting temperature (sum)... | 120°·08 |
On the contrary, even at 5,000 feet deep, the temperature will not exceed 121°, the temperature of the rock, and at 4,000 feet it will not exceed 106°. It may be reduced, too, by plentiful ventilation, or by letting out in the mine air compressed and cooled at the surface, as is done in the new coal-cutting machines. Now, as men can work at temperatures exceeding 100°, we are not likely to encounter the physical limit of sinking on this account.
But the cost of sinking and working deep pits is quite another matter. The growing temperature will enervate, if it does not stop the labourers. Thus it is stated[3] that in one Cornish mine men work in an atmosphere varying from 110° to 120° Fahr. But then they work only for twenty minutes at a time, with nearly naked bodies, and cold water frequently thrown over them. They sometimes lose eight or ten pounds in weight during a day's work. Much increased ventilation will be a matter of expense and difficulty; the hardening of the coal and rocks will render hewing more costly; creeps and subsidences of the strata will be unavoidable, and will crush a large portion of the coal or render it inaccessible; while explosions, fires, floods, and the hundred unforeseen accidents and disappointments to which mining is always subject, will lie as a burden on the whole enterprise, a risk which no assurance company will venture upon. In addition to these special difficulties, the whole capital and current expenditure of the mine naturally grows in a higher proportion than the depth. The sinking of the shaft becomes a long and costly matter; both the capital thus sunk has to be redeemed and interest upon it paid. The engine powers for raising water, [[coal]s], miners, &c., increase, and, beyond all, the careful ventilation and management of the mine render a large staff of mechanics, viewers, and attendants indispensable.
Much may be done by working larger areas from the same shaft; by forming consolidated companies for economical drainage; by perfecting machinery, and organizing labour to contend with the growing cost. But increased areas and distances of working, though comparatively diminishing the capital expense of the shafts and works above ground, will increase the current expenses of drainage, ventilation, and general maintenance.
A full analysis of the detailed accounts of a number of collieries of various depths would throw great light on this question, and might go far to solve the question of England's future career. But private commercial accounts are shrouded in such impenetrable closeness, that no individual inquirers can hope to gain the use of them. Even the several Parliamentary Committees, in their prolonged inquiries into the coal trade some thirty years ago, were continually frustrated by Mr. Buddle and other mining engineers, who declined to communicate information known to them professionally and confidentially. The investigation of such a subject might perhaps be best undertaken by a Committee of the British Association, or some other learned Society.
An account of the South Hetton Colliery establishment, a recent and well-arranged mine, throws light on this subject. It is published in a little work of the Traveller's Library,[4] remarkable for the amount of information it contains on the subject of coal.
Of 529 men employed in or about the colliery, 140 only are hewers of coal, representing the productive power of the establishment. We may divide the staff as follows:—
| Hewers of coal... | 140 |
| Putters, screeners, &c... | 227 |
| Employed in administration and maintenance of mine... | 123 |
| Boys, variously employed... | 39 |
The "putters," "screeners," and others, to the number of 227, are occupied in pushing the coal along the tramways from the hewer to the shaft; in raising it to the surface; screening it, and removing the stones, and, finally, loading it into the railway waggon or ship's hold. They represent, as it were, the trading part of the community, while the administration represents the government; consisting of a manager, viewers, engineers, clerks, and a surgeon; with a great number of joiners, sawyers, enginewrights, smiths, masons, carters, waggon-wrights, and common labourers, as well as ventilators, shifters, foremen, and others of responsible duties underground; all occupied in keeping the mine, the ventilation, machinery, engines, and the works generally, in repair.
Now, if coal were quarried at the surface, and wheeled straight away, each hewer would scarcely require more than one subsidiary labourer. In a deep mine we find that nearly three subsidiary labourers are required, so that four only accomplish what two would do at the surface, to say nothing of the timber and other materials consumed, and the great capital sunk in the shaft, engines, and works of the deep mine.
As mines become deeper and more extended, the system of management necessary to facilitate the working and diminish the risk of accidents, must become more and more complicated. The work is not of a nature to be made self-acting, and capable of execution by machinery. Even in the West Ardsley Colliery, belonging to the patentees of the coal-cutting machine, who naturally carry out its use to the utmost possible extent, this machine is found[5] to diminish the staff only ten per cent. The labour saved is only that of twenty-seven hewers, while other branches of the staff must be rather increased than diminished. So different, too, are the conditions of coal-mining, that in many collieries the use of coal-cutting machines is perhaps impracticable.
The deeper a mine the more fiery it in general becomes. Carburetted gas, distilled from the coal in the course of geological ages, lies pent up in the fissures at these profound depths, and is ever liable to blow off and endanger the lives of hundreds of persons. It was supposed that George Stephenson and Sir H. Davy had discovered a true safety lamp. But, in truth, this very ingenious invention is like the compass that Sir Thomas More describes in his Utopia as given to a distant people. It gave them such confidence in navigation that they were "farther from care than danger."
No lamp has been made, or, perhaps, can be made, that will prevent accidents when a feeder of gas is tapped, or a careless miner opens his lamp, or a drop of water cracks a heated glass, or a boy stumbles and breaks his lamp. The miner's lamp, in fact, is never a safety lamp, except when carefully used in a perfectly ventilated mine. Long experience shows that perfect ventilation is the only sure safeguard against explosion. But it is no easy matter to ventilate near a hundred miles of levels, inclines, stalls, and goaves in a fiery mine.
The amount of drainage required in deepening our mines is another point of the greatest importance. The coal-measures themselves, containing many beds of clay and shale, are dry enough in general, except where interrupted by faults which allow the water to penetrate. Thus, the lower parts of deep mines will in general be dry enough, but the passage through the overlying Permian and New Red Sandstone beds may often be extremely costly, or almost impossible.
"In all the sinkings through the Magnesian Limestone, feeders of water, more or less considerable, are met with at a certain distance from the surface, derived not so much by percolation through the mass of the rock—for this can obtain to a small extent only—but collected in and coming off the numerous gullets and fissures which everywhere intersect and divide the mass of strata. If the shaft be not drained by pumping or otherwise, the water from these feeders rises to a point which remains, save in exceptional cases, constant.... Immediately underlying the limestone is a bed of sandstone of very variable thickness, which, when exposed to the action of the atmosphere, disintegrates rapidly, and has hence acquired its local name of 'friable yellow sandstone.' It is in sinking through this bed of rapidly decomposing sandstone that such great engineering difficulties have been encountered, owing to the enormous quantity of water which in some cases is met with, more especially if the bed be thick and much below the level of saturation."
"A very full account of the sinking of the Murton Winning is given by Mr. Potter.[6]...Nearly 10,000 gallons of water per minute were pumped out of this bed by engines exceeding in the aggregate 1,500 horse-power. The circumstances which favour the remarkable accumulation of water in the limestone, and the rapidity with which it is drained off into pits sunk through it, are due to several causes, some of which are peculiar to this formation, and perhaps to this district. They are:—
- "1. The arrangement of the beds of stratification.
- "2. The contour of the country.
- "3. The permeability of this formation to water."[7]
In the sinking of Pemberton's Pit at Monkwearmouth, a stratum of freestone sand at the base of the Magnesian Limestone poured 3,000 gallons of water per minute into the sinking. And when this flood of water had been overcome by an engine of 180 or 200 horse-power, and had been "tubbed back," a new "feeder" was met at the depth of 1,000 feet, requiring fresh pumps, and an additional outlay of money.[8] The shaft was commenced in May, 1826; it was continued for eight and a half years before the first workable coal was reached; and it was only in April, 1846, twenty years afterwards, that the enterprise was proved successful by the winning of the "Hutton Seam." The South Hetton and Great Hetton pits were also very costly, difficult winnings, on account of the quicksands and irruptions of water. And the winning of a pit at Haswell, in the county of Durham, through the Magnesian Limestone and the underlying sand, was found impracticable for a like reason, in spite of engines capable of raising 26,700 tons of water per diem.[9]
In the continuous working of pits, even where "tubbing" is used to keep the water out of the shaft as much as possible, the quantity of water is not unusually seven or eight times as great as that of the coal raised. At the Friar's Goose Colliery, near Gateshead, 6,000 tons of water are raised from the mine every day, about twenty times as much as the weight of the coal extracted. In some, such as Percy Main and Wylam collieries, it reaches thirty times the weight of the coal.
Now, when it becomes necessary to sink, not only through the Magnesian Limestone, but through the New Red Sandstone, in order to reach new supplies of coal, may not the water be found overpowering? Mr. Hull, in a valuable paper "On the New Red Sandstone and Permian Formations, as Sources of Water-supply for Towns,"[10] has noticed the extremely porous and absorbent nature of the New Red Sandstone. "Rain rapidly sinks into it, leaving a dry soil," and "under and around all the towns built on this formation (or on the Permian) there lie natural reservoirs of pure water." Now, when we come to sink two or three thousand feet through such formations, may not the water prove an insuperable obstacle?
A question of secondary importance concerns the limit of thinness of workable coal seams. This is, of course, a question of the cost of mining. It is found that, at the present price of coal, it is not profitable to work seams of less than 18 or 24 inches thickness. The reason is obvious. In working a four-foot seam little rock has to be mined, since the spaces from which the coal has been removed furnish the levels and communications of the mine. In working a two-foot seam, however, large quantities of rock have to be removed in addition to the coal, and while the cost is hardly less than in a four-foot seam, the produce of coal is only one half. A one-foot seam, again, would be worked at a very great cost, and would furnish less than one fourth of the produce of a four-foot seam. Either the larger seam must yield extraordinary profits, or else the thinner seam cannot be worked.
In estimates of existing coal, 24 or 18 inches is taken as the limit of workable seams; how will this limit be affected by probable changes in the conditions of coal-mining? A considerable advance in the price of coal will, of course, enable thinner seams to be worked with profit. Thus, to some extent, the rise of prices will be slackened. The higher the price rises, the more thoroughly will the coal-measures be worked, and the more coal becomes workable. As, however, the high price of coal constitutes the evil of exhaustion, the dreaded results are only somewhat mitigated, not prevented. And it would be wholly erroneous to suppose that when once the thicker seams of a coal district have been worked out, we can readily, at a future time, work out the thinner seams, when the increased price of coal warrants it. For it must be observed, that a very large part of the cost of mining consists in the cost of draining, ventilation, and maintenance of the shaft, and works at the bank, which we may call the general mining expenses. Now, when these expenses are undertaken for the purpose of working a thick and valuable seam, it is often possible to work thin seams of 18 or 24 inches without any considerable increase in the general expenses. In short, the thick seam pays the general expenses of the mine as well as its own cost of hewing, while it is sufficient if the thin seam leaves a small profit on the expenses of hewing only. But the price of coal must rise in a very extreme degree, that an unworked thin seam should, at a future time, pay the general costs of drainage, ventilation, and maintenance, as well as the cost of hewing.
The same is true of immense masses of coal left underground during the former working of mines, as small or crushed coal, as pillars and barriers, or as outlying portions rendered difficult to mine by faults, or other mining troubles. If such portions of coal could not pay for removal when the mine was in full working efficiency, they cannot pay the whole costs of restoring and maintaining the mine in a workable condition, not at least until the price of coal has risen manifold.
All then that we can hope from thin seams, or abandoned coal, is a retardation of the rise of price after a considerable rise has already taken place. This will hardly prevent the evils apprehended from exhaustion.
Nor will the use of the coal-cutting machine much affect this question. By reducing the cost of hewing and the waste of coal in the "kirving," or cut made by the hewer, it will, undoubtedly, to some extent, allow thinner seams to be worked. At the same time, it will not affect the cost of removing large masses of profitless rock, which is essential in working thin seams, nor the general cost of the maintenance of the mine. If seams of 18 inches are now occasionally workable, the coal-cutting machine may reduce the limit a few inches; but it is evident that seams of less than 12 inches could never be worked while the price of coal remained at all tolerable.
Coal-mining is a fair fight with difficulties, and just as the balance inclines between the difficulties and the powers we possess to overcome them, will the cost of coal and the prospects of this country oscillate. What we can do to cheapen extraction, indeed, is chiefly effected by turning the powers of coal against itself, by multiplying steam power to pump and wind, and cut and draw the coal. But then the greater part of the work within the colliery is of a kind that cannot be executed by machinery, just as the building of houses, or the digging of holes, never has been, and scarcely can be, done by machinery.
But be the difficulties what they may, we would have ingenuity and energy enough to overcome them, were the question one of a simple absolute amount of difficulty. But in reality we must consider our mines not by themselves, but in comparison with those of other countries. Our main branches of iron industry grew up at places like Wednesbury, in South Staffordshire, "where there being but little earth lying over the measure of coal, the workmen rid off the earth and dig the coal under their feet, and carry it out in wheelbarrows, there being no need for windlass, rope, or corf."[11]
Our industry will certainly last and grow until our mines are commonly sunk 2,000 or 3,000, or even 4,000 feet deep. But when this time comes, the States of North America will still be working coal in the light of day, quarrying it in the banks of the Ohio, and running it down into boats alongside. The question is, how soon will our mines approach the limit of commercial possibility, and fail to secure us any longer that manufacturing supremacy on which we are learning to be wholly dependent?
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