exploded in the higher part of the workings. It would be cruel to attach blame to the persons concerned in managing the colliery where these fatal events occurred. We are informed by a person, whose veracity cannot be doubted, "that this mine was considered by the workmen a model of perfection in the purity of its air and orderly arrangements." And we are informed, that, at the time the second explosion took place," the current of atmospheric air was so strong, that it was difficult for the workmen to keep their candles from being blown out by it;" if, however, under circumstances so favourable, and under careful management, such fearful accidents occur, the irresistible conviction flashes upon the mind, that the existing system of ventilation must be radically defective.

Your readers on a careful examination of the plan of the Felling colliery, will observe, that the workings are formed into a sort of double tube, which is called a double air course. They will likewise comprehend, that if a fall of the roof should shut up one of the branches of this tube near the upper end of the mine, the firedamp must rapidly accumulate in the choaked passage, while the ventilation would proceed as usual through the other. Now, if we suppose this passage to be 500 yards in length from the dip to the rise, six feet wide, and six feet high, we shall have a magazine of fire-damp containing at least 2,000 cubic yards. So much for the quantity of fire-damp which it is possible may accumulate in mines conducted on the present system.

Having thus converted the workings of a coal-mine into a tube, whether single, double, or treble; the next object of solicitude, under the present system of ventilation, is, to strengthen every part of this tube as much as possible. For this purpose, the lateral' openings are strongly and entirely stopped. In the Felling colliery we are told," that the stoppings are made of brick and lime, and are further strengthened on each side with a wall of stone." Now, if a violent explosion of fire-damp should occur in any part of this strongly fortified tube, the inevitable consequences must be, that if the stoppings stand the shock, the destructive blast must visit every ramification of the workings before it can get to either of the shafts; and if the stoppings give way, that those persons, whom the force of the explosion could not therefore reach, must be cut off from the possibility of escape. "But this," says Mr. Hodgson, speak ing of explosion, "though apparently the most terrible, is not the most destructive effect of these subterraneous thunderings. All the stoppings and trap-doors of the mine being blown down by the violence of the concussion, and the atmospheric current being for a short time entirely excluded from the workings, those that survived the discharge of the fire-damp are instantly suffocated by the after-damp, which immediately fills up the vacuum caused by the explosion." The existing system is therefore placed in a dilemma by this part of its arrangements, from which it will not be easily. extricated. In the mean time, while the strength of stoppings is considered as an essential principle in ventilation, the miner must

?

keep his spirits up with the hopes (too often fallacious!) that explo⚫sions may not often occur, and that when they do, they may be trifling; well knowing, that if a sufficient quantity of fire-damp takes fire, he must be blown to pieces in the first instance, or suffocated in the second.

The results then of the comparison which has been thus far pursued are: 1. That the proposed system of ventilation affords to the fire-damp every facility of making its escape. 2. Having so many other channels to escape by, it will take a considerable time to collect, in a passage which may be accidentally choaked. 3. By limiting the fire-damp, which can possibly accumulate, to a fixed quantity, we necessarily restrict in the same proportion its destructive effects if it should explode. 4. By affording to this limited quantity of fire-damp a free passage in every direction when it accidentally inflames, we prevent it from extending its ravages to distant quarters of the mine. This part of the subject may be here concluded by observing, that these important advantages will be in vain sought for in examining the arrangements of the existing system of ventilation.

There are still some points, the discussion of which, from their intimate connexion with the subject, it would be inconsistent with the objects of this paper to omit. After having described the mode of ventilating the Felling colliery, Mr. Hodgson goes on to say, "From this explanation it will easily be perceived, that the purity and wholesomeness of a coal-mine has no reference to its depth." This assertion appears to have been made without due consideration. In the first place, it is not attempted to be supported by facts, but by inconclusive reasoning. In the next place, it is at variance with numerous facts: and though an attempt has been made by an anonymous writer in the Philosophical Magazine, to evade the application of these facts, this writer must submit to be told," (as he phrases it,) that evidence of this kind can never be superseded by any species of reasoning, while the facts themselves are unassailed.

From the constitution of carbureted hydrogen gas, it is evident, that we cannot retain it at the surface of the earth, much less at any considerable depth below that surface, but by absolute force; hence this gas can never exist in a coal-mine, but in a state of compression, more or less forcible, from the moment it is evolved, until it is liberated by ascending into the atmosphere. But we know that atmospheric pressure increases as we descend below the surface of the earth, in the same proportion as it diminishes. when we ascend above it. The degree of compression in which firedamp is held below ground must, therefore, be regulated by the depth of the mine. But we also know, that compression is one of the principal conditions of explosion, and that the more forcible the compression, the more violent the explosion, and vice versa. Another remarkable fact, but well established, is, "that the workings of a colliery are often inaccessible with candles near the

297 downcast pit, called the first of the air; while they may be safely entered with any description of lights near the upcast pit, called the last of the air.*. The first of the air is the most dense, and as fluids are known to propagate pressure equally in every direction, it communicates its own degree of density to the fire-damp, with which it may meet in the neighbourhood of the downcast pit, thus fulfilling one of the conditions of explosion. This density will diminish as the mixture rises to the upcast shaft; it will also be diminished by the increase of temperature which it will gradually acquire by the way, and the air will consequently be deprived in a corresponding degree of the property of exploding. Until these, and other facts, can be otherwise explained, it may be taken for granted, that the deepest part of a coal-mine, or that part of it where the inflammable mixture is more forcibly compressed, is the most dangerous, and that of any number of mines, of unequal depths, affording the same quantities of fire-damp, the deepest must be the most dangerous.. This discussion may close here, with a quotation from a memoir by Grotthuss, which appeared in the Annales de Chimie, for April, 1812. It is peculiarly applicable, and may help to deter anonymous writers from hazarding unsupported opinions on the subject. Having, by the most satisfactory experiments ascertained the fact, that gaseous mixtures are more or less inflammable as the pressure upon them varies; "D'après cela," says he (page 41,)" il est très possible, qu'au fond des mines de sel à Cracovie, à Amsterdam, ou dans un autre ville basse, un mélange gazeux pourrait être enflammé, tandis qu'il ne serait plus inflammable, dans une ville tres-elevée comme à Quito dans l'Amerique Meridionale."

There is yet another cause of compression, which must produce effects proportioned to its intensity upon every species of air. which is found in coal-mines. This is the force, by which the current of air is induced, or accelerated, through the workings, from one end of a mine to the other; whether by exhaustion, or by the more common mode of rarefaction by the application of heat. The variations of atmospheric compression are wholly beyond our controul; but it seems probable, that the other species of force might be so regulated in its application, as to balance in some degree the effects of those variations. When the barometer sinks, vast quantitities of gas are liberated from every perpendicular fissure in the roof, in which it has been confined by the superior weight of the air.

Were the downcast shaft occasionally closed, a similar effect would follow, from the suspension of the force which induces the atmospheric current through the mine. A quantity of gas proportionate to the degree of force which held it in confinement, would be thus set at liberty, and would find its way to the upper

See a letter by Mr. John Buddle, in the first Report of the Society for pres yenting Accidents in Coal Mines, page 20.

part of the workings. The shutting of the downcast shaft for one quarter of an hour would in this manner clear the mine from a very considerable quantity of gas. The exhausting pump ought never to be omitted at the upcast shaft; vast quantities of firedamp might be extracted by it when the downcast shaft is shut; every stroke would extract a portion of the gas, and set another portion at liberty in the workings, ready to be swept out when the atmospheric current is again introduced. These operations, regularly performed, would go a great way in preventing the overwhelming discharges of fire-damp, which occur when the barometer suddenly sinks, after having been steady for some time, and which arise, not from an increased production or evolution of the gas, but from its sudden liberation from confinement. It ought also to be deeply impressed on the minds of viewers, and by them on the minds of workmen, to take care that no unnecessary holes or excavations be made in the roof of the mine. The collier ought to be made to understand, that even the mark of his pick in this part will contain, and retain, a portion of fire-damp, ready to expand into mischief at the first opportunity.

It appears from Mr. Dalton's experiments, that two gases, very considerably different in their specific gravities, as oxygen and hydrogen, will mix when confined together in a close vessel. It occurs to me that advantage might be taken of this fact in ventilation. A mine might be shut up for a few hours, until the mixture were completed. By then turning on the atmospheric current, the aerial contents of the workings would be hurried out before they had time to commix: which would have the effect of cleansing the mine of an enormous quantity of inflammable air. Why should not operations so simple, and so highly important, be executed on Sundays, while labour of other kinds is suspended?

From what has been said your readers will readily perceive that the power of complete ventilation has a certain and strongly marked limit. When, after every power of increasing the supply, or of accelerating the progress of atmospheric air, has been applied, the proportion of fire-damp discharged by the upcast shaft amounts to

th part of the whole quantity of air emitted by it; the ventilation of that mine must be incomplete, and the mine dangerous in the same degree. With due precaution, however, it may still continue to work, as allowance must be made for the effects of temperature and rarefaction; and because, being collected from distant quarters, the air at the bottom of the upcast shaft may be mixed to the dangerous point, while the other parts of the mine may be considerably below it. This, however, is a vast quantity of firedamp,; more, certainly, than is constantly discharged by any pit in existence; and if accidents do nevertheless frequently occur, long before the whole quantity evolved in the mine amounts to th part of what the shaft can discharge, they can only be referred to the imperfection of the system of ventilation pursued, in allowing the gas to accumulate, or by hindering it froni making its escape aš

fast as it is produced. It does not seem necessary to enter into any detailed account of the various contrivances in use for the purposes of producing, or quickening, a current of atmospheric air through the workings of coal-mines. It may be sufficient to say generally,. that they are simple and efficacious, and cannot therefore admit of much improvement. Those who may wish for minute details on this point are referred to Mr. Buddle's letter in the Report already quoted, which contains much useful information, and which is so much the more valuable, as it is the only thing of the kind before the public. They will not, however, be able to discover from it, that any one part of a coal-mine is higher than another; or that fire-damp possesses any other property than that of inflammability. They may likewise be startled on hearing from Mr. Buddle, (page 21,) that he considers the existing system of ventilation "to have arrived at an admirable degree of perfection ;" and that "on the strength of his own experience (page 22,) he freely hazards his opinion, that any further application of mechanical agency towards. preventing accidents in coal-mines (which are infested with firedamp in a high degree,) will be ineffectual." Mr. Buddle's experience ought to have guarded him against supposing further improvement impossible. When he himself has invented perhaps the greatest improvement in the system, viz. that of the swing door, which is both simple and ingenious, and which Mr. Buddle will perceive, if this should meet his eye, admits of a far more extensive application than he has made of it.

Your readers will find (page 21,) that "the improved system, (as it is called) was introduced into the collieries on the Tyne and Wear, about the year 1760, and has ever since continued in general use in collieries abounding with inflammable gas, without any rival method being thought of, or any improvement, except the mechanical auxiliaries detailed in the descriptions of sections three, four, five."*

This fact of itself will, in the opinion of many people, amount to a proof that there must now be room for improvement; this proof will be further strengthened by the recollection that almost all the knowledge we possess respecting gaseous fluids has been acquired since the year 1760. If any doubt should remain on this point, it will be entirely dissipated on finding that, notwithstanding the admirable perfection to which the improved system has arrived," its arrangements have not the slightest reference to the well-known levity of carbureted hydrogen gas.

Thus, Sir, have I endeavoured to place before your readers, in the plainest manner I could think of, a general outline of what I conceive to be a material improvement in the mode of ventilating coal-mines. I am persuaded that ventilation has at last become a

* These auxiliaries are merely different modes of accelerating the atmospheric current through the workings, by exhaustion and rarefaction of the air, The apparatus for which are all above ground.

་