supply the oxygen necessary to support combustion. It has, however, been observed Pea that the coals producing the greatest quantity of pyrites are not always the most subkeject to heat spontaneously, while it has also been noticed that the most inflammable

coals are those containing the largest proportions of oxygen; it has, consequently, been suggested that the more probable cause of spontaneous combustion may be the combination of oxygen with the carbon, under the influence of moisture, and which is accompanied by the generation of carbonic acid and a considerable amount of heat. In ever the coal mines of Silesia, where cases of spontaneous combustion are of frequent occurrence, numerous observations have demonstrated that this class of accidents need not be feared where the "roof" of the vein is either sandstone or conglomerate, nor near the outcrop, whatever the nature of the top rock may be; on the other hand, beds worked at a considerable depth, or even when moderately near the surface, but covered by a shale capable of being softened by moisture, are the most liable to spontaneous combustion. It was long considered in Silesia that the only means of preventing fires from this cause, consisted in sending all the fine coal, "waste," or "gob," out to the surface. This was often impracticable, expensive, and not always effectual; hence other means of Tattaining the same end were sought for. Since it is well known that combustion cannot exist when deprived of oxygen or air, one means of preventing spontaneous combustion consisted in isolating the working places, or goaf, by means of a heavy dry wall, or by two parallel walls filled in between with clay or other material packed hard, and sometimes a heavy pillar of coal was left for the same purpose. In each case, however, the weight of the superincumbent rocks almost invariably crushes the walls or pillars, and produces cracks or fissures, through which air, sufficient to sustain the slow combustion of the coal, can pass. This method has been employed with greater or less success in some of the mines in the centre of France, and in the thick seam of Staffordshire. It is evident that when used the greatest possible care must be taken to keep the fissures closed, which are found from time to time, so as to seal hermetically the space inclosed. But besides the practical difficulty in effecting this, the fact that these inclosed spaces generally fill with fire-damp, and therefore form veritable magazines of a substance far more dangerous than powder, and which, through the crushing of a wall or pillar, or the fall of a portion of the roof, may at any moment be brought in contact with the lights of the men working in fancied security in the neighboring roads or chambers, is a sufficient reason for condemning so dangerous a system as that of isolation of the "goaves" by "pack walls."

The spontaneous heating of coal is so slow a process that the increment of temperature is easily carried off by a moderately rapid current of air; we can thus prevent the temperature from ever rising to the point of ignition, by simply ventilating the " goaves;" this, then, is the exact opposite of the last method, and though much safer and fully as practical, yet very serious objections can be made to it. It is all but impossible, owing to falls, &c., to keep the "goaves" sufficiently open to maintain the necessary circulation of air, and the expense of clearing up falls and opening the old workings, where obstructed, is so great as to render this method impracticable in many cases. The system is, however, more or less successfully used in many mining districts in England, Silesia, &c. There now remains but one other method to describe, and it is by far the safest and most efficient in the prevention of danger by spontaneous combustion. It consists in filling or packing with earth and other material sent down from the surface the spaces from which the coal has been removed, and which the waste.of the mine does not fill. This method, though somewhat expensive in large seams which make but little waste, is assuredly the most effectual remedy, since it not only prevents the admission of air to the old workings, and therefore does away with the expense of ventilating them, but it prevents the falls of the roof, in which "blowers" are frequently opened, and renders impossible any accumulation of fire-damp, which is the great source of danger in the method of isolation by pack-walls, &c. Thus this method not only procures perfect immunity from danger by spontaneous combustion, but the system of mining of which it is the principal feature enables us to obtain all the coal of the vein. It is, therefore, not only the safest, but also, as regards the amount of coal obtained, the most economical, method now in use, and it is deservedly popular in Europe, and more especially in France, Belgium, and Germany, where it has been employed for a number of years, and has now taken the place of every other system in most of the coal mines.

Whatever precautions may have been taken to prevent fires, yet the carelessness, ignorance, and sometimes the malice of men are causes which cannot always be effectnally guarded against; hence we must be prepared to meet the danger of fire when it occurs, and to apply promptly the most suitable means for its extinction.

When a fire originates in coal or timber, every effort should be immediately made to extinguish it by throwing water on it either with buckets, or, better, with a fire engine; or where practicable, by tapping the column-pipe of the pump and leading the water through hose to the seat of the conflagration. In some cases the use of portable "fire extinguishers," (which generate carbonic acid gas,) such as are now found in every village of the land, may prove of great service. If the fire originates by the ignition

of a blower of fire-damp, efforts should be made with wet cloth, water, &c., to put out the flame; in some cases where these means failed, the flame has been extinguished by the concussion of the air, caused by discharging a cannon in the gallery where the fire exists. When the coal surrounding the "blower" has already become ignited it will in mediately re-ignite the fire-damp; so that this method can only be applied either where the blower is in rock or where it has not had time to thoroughly ignite the coal While these means are being applied, preparation should be made for erecting stoppings or dams, in view of the failure to extinguish the fire by the direct means; yet these should not be abandoned till there is no further possibility of success. When it is no longer possible to approach the fire near enough to throw water on it-that is, when the fire can no longer be kept under control-it becomes necessary to resort to other methods of extinction, viz:

By isolating the part of the mine on fire, and then applying extinguishing agents to the part inclosed. When this fails or becomes impracticable, there remains but one other method, viz:

By closing the entire mine, and applying the same extinguishing agents.

These agents are water, carbonic acid, and nitrogen gases, steam, or any other gas incapable of sustaining combustion; those mentioned being adopted on account of their effectiveness and small cost.

The isolation of a fire in a mine is effected by constructing walls or stoppings across all the galleries or other openings which connect this portion with the remainder of the mine. These stoppings are sometimes walls of brick or masonry, varying in thickness from twelve inches to six or eight feet; at other times two lighter parallel walls are built, and a current of air allowed to circulate between them in order to keep the inner wall cool, or else the space between the walls is filled in with clay and mine waste; while still another method is to make a stopping, several yards in thickness entirely of clay, waste, &c. In cases where it can be done without danger, a timber stopping or even a simple board bratticing can be adopted; the kind of stopping as well as its strength will depend on the position of the fire, its extent, the presence of absence of fire-damp, whether the stopping is intended to dam back water or not, and such like considerations, which under the enunciations of fixed dimension, are imprae ticable. The essential in every case is that the stopping should be air-tight, and that it should be constructed with the least possible delay, and at such a distance from the fire as to allow time for its completion, before the smoke and irrespirable gases produced by the fire can prevent the men from working.

Notwithstanding that the ventilation of the part on fire has been reduced to a minimum by the erection of temporary bratticing, &c., yet the combustion of the coal and wood produces such enormous volumes of irrespirable gases that the work of building the stoppings is one of great difficulty and danger, more particularly in mines producing fire-damp, where the danger from explosion is still greater than that from the gaseous products of combustion.

It is evident that the stoppings can be constructed with least difficulty by commenc ing with those on the "outside" of the fire, or the side from which the air proceeds to the fire, and afterward building those "inside" the fire, or where the air comes from the fire; yet in mines yielding fire-damp this method of proceeding is attended with great danger; the fire-damp mixing with the air confined between the stopping and the fire makes an explosive compound, which is carried forward toward the fire, where it ignites, and though it may not cause a fatal accident, yet it almost invariably throws down the stoppings by which it was sought to isolate the fires. As from one-tenth to one-seventh of its volume of carbonic acid, added to an explosive mixture of air and fire-damp, renders the latter entirely inexplosive, (a larger quantity renders it incapable of sustaining combustion,) and as the products of combustion are carbonic acid and nitrogen, it follows that by closing first the galleries on the side toward which the air from the fire goes, we prevent the danger of explosion by mixing carbonic acid with the air con tained between the stopping and the fire, and by throwing the smoke and irrespirable gases back or the fire, we go far toward extinguishing it. It is true it is a matter of great danger and difficulty to build stoppings between a fire and the "returns," but by the use of temporary bratticing and by commencing at a sufficient distance from the fire, it is often practicable, and it is always desirable. Where it is impossible to build the stoppings in this order then, when practicable, it would be advantageous to inject carbonic acid gas, or choke-damp, (through a pipe in the stopping,) from the moment the latter comes near completion, so that the air contained between the stopping and the fire may not become explosive. We speak, of course, of mines yielding fire-damp. Where carbonic acid is not available, it will sometimes be possible to inject steam, which will not only deaden the fire, but will, at least, diminish the intensity of the explo

sions.

The stoppings completed-and where there is no danger from explosion or need of inundating with water the part on fire, there is no necessity for making them heavywe proceed to fill the part inclosed with carbonic acid gas, with choke-damp, with steam, or with water. In the first case the carbonic acid can be manufactured eithe

H. Ex. Doc. 207 41

pure, or nearly so, by the use of any strong acid, such as sulphuric or muriatic acid and chalk, or limestone, or any of the carbonates of low price and easily decomposed. This gas is easiest prepared in a lead vessel, which is not attacked by the acid. Where the space to be filled is not great, some of the numerous patent fire-extinguishers might be found of service, as being quickly and easily brought into action. These methods have the advantage of supplying the gas at a low temperature, and thereby facilitating the cooling of the rocks after the flame is extinguished. If the circumstances are such as to make the use of choke-damp-that is, a mixture of carbonic acid and nitrogen-advisa bie, it can be produced in one of the furnaces of which drawings and particulars are given below. In either case, as carbonic acid and choke-damp are both heavier than air, it follows that the tube through which we admit these gases should be at the lowest, and that through which the air from the inclosed space is allowed exit should be at the highest attainable point of the isolated workings, and the admission of the gases should be continued till it is evident they have completely filled these works. This is easily proved by their instantly extinguishing lamps, burning tow, &c., at the outlet tube. The tubes should then be closed, leaving only a siphon or water-gauge to mark the difference in pressure between the inside and outside of the stoppings, and a place for the introduction of a thermometer used to note the variations in temperature, so as to know when it will be safe to open the stoppings. The greatest care should be taken to keep the stoppings air-tight; they should be frequently inspected, and where from any reason it is found desirable to "drown out" or inundate the part on fire, they should have a thickness proportionate to the head of water they will have to retain. When the fire has assumed greater dimensions, or when its position is such that it becomes dangerous or impossible to confine it by stoppings such as we have described, it becomes necessary to abandon the entire mine and to resort to closing the shafts. Even when it is decided to inundate the mine, it is always advisable to close the pit. whether the mine produce carburetted hydrogen (fire-damp) or not, since by so doing we deaden, at least, the combustion, and prevent, in a great measure, the damage always caused by the high temperature produced by a rapid combustion. The shaft should, therefore, be immediately closed hermetically, provision being made for openings through which a registering thermometer can be introduced, and a bent pipe, or siphon, containing water, to show the pressure behind the stopping, and prevent its becoming excessive, while at the same time it prevents the admission of fresh air. The closing of the shaft may be effected by hanging heavy pieces of timber, by means of chains, some distance down the shaft. On the platform thus made clay is thrown, and packs itself by the force of the fall, thus rendering the stopping perfectly air-tight. The tubes above mentioned should be inserted, and one siphon should be so arranged as to allow the water to flow down the shaft, instead of accumulating above the stopping. Where the pit is divided into a number of compartments, it be comes difficult to close it perfectly in this way. The mouth of the pit is then covered over with planks or iron doors, and clay, sand, &c., packed on this, every crevice being carefully closed. Great attention must be paid to this, more particularly in the case where it is desired to "smother out" the fire without the injection of steam or car bonic acid, otherwise a quantity of air may enter, which, though insufficient to maintam an active combustion, may yet suffice to support a slow fire, or, at least, greatly increase the time necessary for its complete extinction.

Where the mine does not produce fire-damp, there is no great danger in closing the pit, but if that gas is given off in any considerable quantity, the closing of the pit is sometimes attended with great danger, there being a certain time after the closing when the quantity of atmospheric air is sufficient to make an explosive mixture with the gas from the inine. After a time, the quantity of air, or rather oxygen, is diminished by that consumed by the fire itself, and the incombustible gases produced by the combustion, mixing with the fire and fire-damp, soon render the compound inexplo sive. In such mines it is highly desirable to inject steam alone, or, better, steam and carbonic acid, into the downcast from the earliest practicable moment, so as thereby to diminish, as far as possible, the chance of explosion during the operation of closing: and it should continue to be injected after the stopping is made till the mine is com pletely filled, which can be known by the air issuing from the upcast extinguishing a lighted lamp, &c. It is almost needless to add, that great care should be taken, and no open lights allowed near the shaft when there is any possibility of fire-damp exist ing in dangerous quantity. If the mine does not produce that gas, the immediate ad mission of choke damp is not so necessary, though it is always desirable as checking the spreading of the fire.

As the majority of tires occur from explosions of fire-damp, it follows that in most cases the air doors, bratticing, and other divisions necessary to guide the air current through the mine, are destroyed. It is then difficult to ascertain if the carbonic acid has gone into every part of the mine, or whether a large amount of air may not yet remain in the workings; this should be carefully considered in deciding on the means to be adopted to extinguish the fire, and also in fixing on the time for reopening the pit. Not a few of our fatal accidents occurring from explosions were caused by re

opening the mine too soon, or before the coal had time to cool down below the temperature at which it will ignite. In some cases, it may even be considered safest and most economical to fill the mine with water. This decision must be taken only after a careful consideration of the position of the fire, the amount of water needed to fill the works to the depth required, the time necessary to pump in that water, the nature of the roof and coal in the works, and the effect which a longer or shorter inundation would have on them, the facility for getting the water out, &c. The inundation of a mine is always an expensive expedient, and should only be adopted as a last resort; yet there are cases where it is undoubtedly the best method to adopt. Each case requires a special study, and the method which might be the most suitable in one may not be adapted to another. The great sources of expense in inundating a mine are the damage caused by the water remaining for any length of time in the works (with certain kinds of rocks-some slates and fire-clays especially,) the falls of roof, causing delay and expense, and the delay and cost of filling with and pumping out the water. And in coal subject to spontaneous combustion it not unfrequently happens that when the water has been pumped out, the wetting of the " gob," or waste," causes it to heat, and even to ignite, before the ventilation can be fully re-established. Every other means should in general be tried before inundating the mine, and the most efficient of these various means are the introduction of steam, carbonic acid, (choke-damp,) and after-damp, which is a mixture of nitrogen and carbonic acid. Steam is available at almost every mine, and is easily applied; it should be carried in pipes, and discharged as near the seat of the fire as possible, in order to prevent its condensation; it is a very efficient extinguishing agent, and from the facility with which it can be employed, it is now commencing to be much used; in many cases, a rubber hose, made especially for a steam hose, is all that is required to carry it for several hundred feet, and it will last as long as the occasion requires in most cases. The greatest disadvantage in the use of steam is its energetic action on some rocks, causing them to disintegrate and "fall;" but where the roof is such that it is not materially injured by steam, this is one of the most convenient, and it is always one of the most effective extinguishing agents we can use. Its action is limited to the expulsion of the air, and as it maintains a high temperature we are generally obliged to inject water, in order to cool the rocks sufficiently to allow the men to work, and also to prevent any possibility of reignition. The following example of its application will prove instructive: In 1857, at the St. Mathew mine, near St. Etienne, France, steam was injected after the mine had been on fire for eight days; this was continued for seventy hours, after which cold water was injected for three days, in order to cool the sides of the shaft, galleries, &c., previous to descending into the mine. The pit was then opened, and a current of air circulated while the men went down. After two days, however, the mine again caught fire, and it became again necessary to close the pit. Steam was then injected during twenty-four hours, and, after an intermission of eighteen hours, cold water was injected for twelve hours. The fire broke out a third time, and steam was admitted for eleven hours, then cold water, after which the men were enabled to enter, and extinguish the fire completely by throwing water on it. I believe the same process was employed at the Yellow Jacket and Kentuck mines, on the Comstock lode, which were on fire a few months ago.

The application of carbonic acid or choke-damp and after-damp is more complicated than that of steam, since the materials for its manufacture are not often on hand. The most usual method of manufacturing carbonic acid is by means of chalk or limestone, or any cheap carbonate easily decomposed, treated with one of the cheaper acids-as sulphuric, nitric, or hydrochloric. The gas produced in this way has the advantage of possessing a low temperature; it not only extinguishes the fire but tends to cool the rocks to a point below the temperature necessary for ignition. Portable machines, known as "fire extinguishers," are convenient means of manufacturing this gas where the quantity required is not very great, and they are to be found everywhere, at a small cost, and are always ready for use. Where the quantity of gas required is very large, as, for example, in filling a mine, one of the cheapest and most convenient methods of producing it is by the combustion of coke or charcoal in a furnace of suitable form, and, as it was the means adopted in the first application of "after-damp" or carbonic acid to the extinguishing of fires in mines, we will devote some space to it, especially as the credit of the invention is commonly misapplied. The first application was made by M. Jules Letoret, in Belgium, in the year 1844. Five years later (1849) we find the same principle applied in England by Goldsworthy Gurney, who takes credit himself for the invention, and is even at the present time credited with it by nearly all the English engineers. It is scarcely possible that Mr. Gurney could have been ignorant of M. Letoret's invention, for we find him perfectly "posted" on the application of his steam jet in the Belgian mines, about the same

time.

On the 15th of February, 1844, a fire occurred from an explosion of fire-damp in the No. 2 shaft, Agrappe colliery, near Mons, in Belgium; the pit was 1,171 feet deep, three veins at different levels being worked. Efforts were made to extinguish the fire by