gases, and at that time recent accidents had been occasioned by explosions in spite of safety lamps. The test was therefore repeated, still more publicly, upon some sixty lamps of various patterns, and it was found that only the old-fashioned Davy, and one other, the name of which escapes us, would retain the flame. Those lamps were found to be particularly dangerous which possessed separate openings below for the admission of air to support the flame.

These experiments indicate the same conclusion as was lately arrived at by English investigators, namely, that the strength of the draught of inflammable gases through à safety lamp has much to do with the degree of its security. The Zwickau lamp may have been unusually faulty in construction, rather than principle; but this fact, though it might lessen the importance of these special experiments, could not alter the general bearing of both practice and theory on the question of the safety of all lamps. The principle involved is that of the rapid conduction and radiation of heat by the wire of the gauze surrounding the flame. Before the burning gas can pass through the meshes, it is said, so much of its heat will have been abstracted, and radiated away in all directions, that it will fall below the temperature of ignition or explosion. Now, this depends upon the amount of heat communicated to the wire in a given time. The wire may get hot faster than it can grow cool again, and if this increase of temperature is carried to a white heat, the gas outside will be set on fire. But the amount of heat given to the wire in a certain time depends again on the amount of burning gas that passes through it in that time, and hence it is clear that a strong current of gas may overheat the wire and cause an explosion. The Davy lamp is not constructed to favor a strong current. Indeed, one complaint of it has been the feebleness of the light, from insufficient air. It appears, however, that attempts to remedy this deficiency are fraught with peril. We desire to call the attention of engineers to the great simplicity and conclusiveness of the test above described, and to urge that it be at once applied to the lamps of every mine. There can be no harm in knowing whether the lamps will do what is claimed for them. It is true that common illuminating gas forms with common air a more explosive mixture than does the fire-damp of mines; but the severity of this test ought to be nothing against it, so long as any lamp can be found to bear it.

In the general dissatisfaction with the use of safety lamps, which spread through the Zwickau district after the experiments alluded to, a new and bold plan was suggested, and has been carried out in several cases with the best success. This was nothing more nor less than to burn naked lights in great numbers wherever inflammable gases made their appearance. Some of the workings presented, under this system, an unwonted appearance. In one case, the fire-damp could be heard streaming out of the fissures of the coal, with that peculiar humming sound which the miners know so well and fear so greatly; the innumerable lights carried each a long blue tip-the usual signal of danger-yet no harm occurred. The gases were quietly consumed as fast as they entered the mine, and the illumination was carefully kept up, night and day, Sundays and between shifts, that no opportunity was given for an accumulation of explosive material.

The great difficulty of this plan is its direct injurious effect on ventilation. The stationary lights with which the mine is crowded, in addition to those carried by the workmen themselves, must necessarily use up a good deal of oxygen, and produce a good deal of carbonic acid. But this is an evil which can be combated in other ways and, at all

events, it is preferable to the danger of explosion. Perhaps it might be an improvement to use safety lamps instead of naked lights, hanging them in great numbers along the walls, so as to secure the complete. quiet combustion of the gas. But it must be confessed that, even under circumstances of the greatest danger, the naked lights have done very well, and no accident, so far as we are aware, has ever resulted from their use in this way.

Propositions have been made to explode the accumulated gas in workings before the workmen are allowed to enter it. In a rude way, this has frequently been done in fiery mines; and to remove all personal danger, it is now suggested that the explosion be effected by means of a battery. But this whole system of allowing the fire-damp to accumulate while the workmen are absent, and then firing it off all at once, strikes us as much inferior to the simple expedient of burning it gradually, as above de scribed.

FIRES IN MINES, AND THE MEANS OF EXTINGUISHING THEM.

In spite of all precautions in the way of proper ventilation and the careful use of safety lamps, fires will sometimes occur, as many mining communities have had terrible opportunities of knowing. The methods employed for extinguishing them are therefore worthy of notice. On this subject I cannot do better than quote the excellent essay of Mr. R. P. Rothwell, of Wilkesbarre, Pennsylvania, which appeared last summer in the New York Engineering and Mining Journal:

Taking account of the nature of the mineral, we are not surprised that fires should be much more frequent and dangerous in coal than in ore mines; they are, however, by no means confined to coal or lignite deposits, but may and do occur in all kinds of underground workings where timber is used. In the great majority of cases fires originate. below as above ground, through carelessness or imprudence. A miner will tean his lighted candle or lamp in such a position that it can ignite a prop or other piece of tim ber. Such appears to have been the case in the recent disastrous fire in the Crown Point, Kentuck, and Yellow Jacket mines. The careless or imprudent hanging of a grate or fire-pot near the coal at the foot of our downcast shafts or slopes (where it is placed in winter to prevent the pumps and rods from being covered with ice) has been the cause of fires in several of our anthracite mines. Ignorance of, or inattention to, the proper manner of constructing ventilating furnaces has also been a frequent cause of fires in coal mines, but probably the most fruitful cause of these disasters is the igni tion of fire-damp, or carbureted hydrogen in coal mines; the ignition first produces explosion, and in mines yielding an inflammable coal it frequently ignites the fine particles blown about in a burning atmosphere, and these communicate the fire to the solid coal of the pillars; or the gas may continue to burn at some "blower” till it has ignited the coal in which the fissure or vent occurs. These so-called "accidents" are generally due to carelessness in the use of "open" lights, or in the opening of safety lamps in places where the gas exists in quantity. The practice of blasting in coal mines, which produces large quantities of the dangerous gas, has also caused a great number of deplorable explosions and fires; and the question of substituting some other agent, such as water, wedges, &c., for powder in mines of this kind, is now receiving much attention among European mining engineers. "Fiery" mines, such as those in the Richmond (Virginia) bituminous basin, would be greatly benefited by the successful substitution of a safer agent for the powder now used, where rock or hard coal has to be mined. In our anthracite mines the hardness of the coal would render the use of pow der more necessary, while the smaller quantity of fire-damp found in it would, at the same time, make the substitution of a safer agent less desirable. The exercise of greater vigilance in the inspection and use of safety lamps would, doubtless, greatly diminish the number of explosions and fires in coal mines.

Many bituminous coals, and bituminous shales which are found among the coal beds. are, under certain circumstances, subject to "spontaneous combustion." This always occurs where the coal or shale is crushed in a confined space with an exceedingly feeble ventilation; indeed, spontaneous heating of the coal, accompanied as it is by an abun dant production of carbonic-acid gas, was generally attributed to the decomposition of iron pyrites (sulphuret of iron) under the influence of the moisture in the air, and a circulation of air so languid as not to dissipate the heat generated, while sufficient to

supply the oxygen necessary to support combustion. It has, however, been observed that the coals producing the greatest quantity of pyrites are not always the most subject 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 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 attaining 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 effectually 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 immediately 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 minewaste; 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 or 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 impracticable. 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 commene ing with those on the "outside" of the fire, or the side from which the air proceeds ta 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 tire goes, we prevent the danger of explosion by mixing carbonic acid with the air contained 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