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heard continually hissing out its way. The viewer, for our special wonder, lit the roof of the passage where we stood, and one long, soft, blue lambent flame played innocently over our heads, until it was "dowsed," or beaten out by bags and jackets. But when the compression of gas is very high, then oftentimes a "blower" will break forth with a sudden and perilous discharge. The "fouling" effects are extraordinary in the cases of the eruption of the high pressure gas. A few instances, scarcely known at all to the public, will excite interest.*
In Haswell colliery there are certain "drifts," through which, on one occasion, no less than 9,760 cubic feet of air per minute were passing to ventilate them. The sectional area of one drift was 37 square feet, and the velocity of the air-current was therefore 4.39 feet per second; safety-lamps were used in the "face," or front of the workings of the coal. While the hewer was at work in this drift, he heard a loud noise, and immediately retreated some distance, and heard a sound like that of falling water, occasioned by the rushing out of the gas at the face. The "deputy" ran to warn some men who were exposed to extinguish their lights, and, returning, he found the aircourse foul. By opening a door, and by other judicious steps, he cleared the mine in less than half an hour. Afterwards it was found that the mass of inflammable air produced by the eruption of this gas was at least 35,000 cubic feet, or about 1,300 cubic yards, a quantity sufficient to account for the heaviest mining explosion. It is estimated that the quantity of fire-damp alone was from 3,000 to 4,000 cubic feet.
In another instance, at Walker colliery, so powerful was the pent-up gas, that it forcibly displaced a block of coal, which, with the shattered coal around, weighed eleven tons; and it was found that this issue of gas had fouled the air to a distance of 41,681 cubic feet.
Some other sudden discharges of "bags" or "blowers" of gas might be mentioned; but the above are sufficiently illustrative. By careful examination of these instances and their results, we may arrive at some opinion as to the amounts of gas that have caused the heavy pit explosions in the North. A careful inquirer (Mr. T. J. Taylor) has thus conjectured that several such explosions have been caused by quantities of fire-damp
* At Wall's-End colliery is now witnessed by all an example, not of sudden eruption, but of continuous issue. A five-inch metal pipe is brought from the bottom of the pit to the surface of the ground, as a conduit of fire-damp: underground it reaches to an insulated portion of the coal strata of about five acres in extent. The quantity of gas drawn off from this portion was at first eleven hogsheads per minute, or 15,840 hogsheads of gas per diem! Now it only discharges about five and a half hogsheads per minute, night and day. The end of the pipe above ground was ignited, and it has from the first continued to stream forth flame night and day to the present hour. It is, in fact, a permanent gas-light supplied direct from an immense natural gasometer. We have often watched it flaming forth, with much interest.
Inadequacy of the Steam Jet against the Gases.
varying from 2,000 to 4,000 cubic feet; that is to say, by such quantities as we know by experience are discharged from a single working place, without warning, in the space of a minute or two, or even in less time. Here, then, we learn the subtle and enormously powerful enemy which miners have to contend against in the most fiery mines.* It is clear that superior and continual ventilation is required to remove and dilute the ordinary and extraordinary issues of fire-damp. But it is equally clear that we must not rely solely on ventilation; this must not be propounded as the panacea. For, if we consider the force of our enemy, we shall discover the weakness of our own forces. Our mines are ventilated by a power which, in favourable cases, is represented by a column of water of three to five inches in height, and perhaps, on an average, four inches. "Now," says Mr. T. J. Taylor, "let us suppose that a bag of gas possesses the proved compression of three atmospheres above the common atmosphere, then those three atmospheres are measured by 1,230 inches of water, being more than 300 times the power of the ventilating column. By what name shall we designate the mistaken confidence which thus puts into competition agents so hopelessly unequal?" And obviously no increase, such as may be reasonably expected, can be entirely successful; for, even if the ventilating powers could be augmented ten times beyond their present force, the ventilating agency would still be inefficient as compared with the cause of the explosion, in the proportion of one to thirty on the datum assumed, which, as regards the compression of the gas in some of its states, is doubtless far short of its maximuт.
Much of the amateur advice tendered to the managers of collieries by scientific chemists and others, proceeds upon ignorance of such facts as we have just stated. Folio pages have been written and printed to show the inadequacy of present means, and to prove the value of the steam jet. But now that accurate experiments and observations have been made, and are still in the course of being made, we discover the inadequacy of the steam jet, and the enormous force of the gases. Accom. plished mining engineers are as uneasy under such advice as
* The St. Hilda's pit, South Shields, may be mentioned as a remarkable and very fiery mine, easily visited by travellers. The depth of the shaft is about 850 feet. Extensive passages of old workings exist, which may measure seventy-five miles, amounting to upwards of 14,500,000 cubic feet. This mine was so full of gas, that no naked light was permitted even to approach the shaft. As a man, on December 31st, 1852, was carrying a shovel of burning coals upwards of twenty feet from it on the surface, the gas from the pit caught fire at the burning coals, and darted in a mass of flame into the shaft, forming a blazing area of upwards of ninety-eight feet. It blazed thus for hours, rushing into the atmosphere in flames sometimes forty feet high, and burning all within reach. Fortunately, atmospheric air had not descended into the workings, or there would have been formed one of the most tremendous explosive mixtures in the world. Had the flame descended the pit, and had an explosive mixture filled the fourteen millions of cubic feet, the explosion would have shaken part of South Shields like an earthquake.
accomplished Generals at the newspaper suggestions as to the mode of carrying on military operations.
We are, therefore, conducted by fair and necessary conclusions to the general or universal employment of the safetylamp in fiery mines. The form and value of this miner's friend is well known. In brief, it consists of a common oil-lamp, surrounded with a covered cylinder of very fine wire gauze, the apertures in which may be four hundred to the square inch, and from that to nine hundred, if desired. Since the fire-damp is not inflamed by heated wire, the thickness of the wire is not of importance, and it may be from one fortieth to one sixtieth of an inch in diameter. The wire-gauze cylinder must be carefully constructed with double joinings, and should not be more than two inches in diameter, since in large cylinders the combustion of the fire-damp renders the top too hot. A second top is always fixed above the first. A strong ring enables the miner to carry it in his hand. This is the simple lamp of Sir Humphrey Davy, which has probably brought him more general fame than any of his brilliant chemical discoveries.
The proportion of fire-damp necessary to render the air explosive has been already stated. In an explosive air the pitman observes the safety oil-lamp to increase in flame, and sometimes a brilliant combustion will take place within the lamp; but the flame will not pass through the minute apertures of the wire gauze. At first, Davy tried lamps with apertures four hundred to the square inch of gauze; and then the flame of the wick at first was lost amidst the flame with which the whole cylinder was filled, which was feeble, but green. The apertures may be increased to nine hundred in the square inch, thus diminishing the size to a very minute orifice; but the larger the apertures the greater the heat, and the more brilliant the flame. When the coal gas was from one to four or five, the flame of the wick never appeared; and always, as the quantity of inflammable air diminished, the flame became limited to the wick, and was gradually extinguished. These and other similar fundamental principles were stated by Davy, and led to his invention, and to its adoption in fiery mines. He, however, did not describe its state under extreme danger; then the upper part of the lamp becomes quite red, a continued rushing noise and crackling of the gauze is heard, and the smoke and the smell emitted from the lamp show the active combustion going on within its cylinder of immunity. In this condition the sudden, sharp movement of the lamp, or its exposure to a current of air, would expose the mine to extreme danger; so that, in the event of indiscretion in the midst of such warnings, it was not intended to pronounce the lamp perfectly safe. With such visible and audible admonitions of peril, every pitman is expected to retire from the scene. Davy himself admonished
his friends in the North of these perils as being possible. It may be well to quote his words to the colliery manager who received his first lamps, and who declared to the writer of this article, as well as to Committees, that Davy "warned him there would be no danger, except in exposing the lamp to a strong current, by which the explosion might be passed through the cylinder."
A very long and animated controversy has existed between two parties on the question of the safety of the Davy lamp. The Committee of the Commons of 1852, often alluded to above, seemed to have obtained evidence disproving its safety. Experiments were made at the Polytechnic Institution, in which the flame was made to pass through the apertures of the Davy. On the other hand it is objected, that in these experiments the flame was made to pass by means of a pencil of gas forced upon the gauze; and that the gas employed was street gas, which the experimenter confesses is far more easily exploded than firedamp. This is obviously unfair and unnatural. Such experiments only prove that Davy's warning, as above quoted, was well founded. But they by no means disprove the safety of the Davy lamp in all ordinary cases. The Committee of 1854 approve of Davy lamps, and recommend their general adoption.
In such a question as this, we should naturally ask the opinions of those men who have tested the Davy lamp, by the employment of it in mines for a long course of years. The late Mr. Buddle, the most eminent of all the Northern mining engineers, has expressed before Committees, and to ourselves personally, his entire confidence in the Davy under all circumstances which the miner will commonly meet with in mines,-if used with discretion and care. The same is the opinion of Mr. Nicholas Wood, who is at present the most experienced and eminent viewer in the North. And the same is very generally the opinion of the whole body of Northern and experienced viewers. Neither have we ever found, amongst the numerous working miners with whom we have conversed, any well grounded opinion to the contrary. We prefer such evidence and opinions as these to that of a minority not distinguished by mining experience and long practice, though they may be worthily distinguished for a desire to benefit the miners, and to secure their safety. We commend their philanthropy, but we doubt their practical knowledge.
The safety of the common Davy, if not proved to strict demonstration, yet may be very fairly presumed from the fact, that in thirty-eight years of actual trial, there has been no well authenticated instance of an explosion having been caused by a lamp of this kind. Moreover, in the three coal-producing countries of the Continent, not a doubt is entertained of the safety of the Davy; and there the exclusion of exposed flame
from fire-damp mines has passed into a law. There, too, the common Davy lamp (with the exception of an improved form by Mueseler, of which eight thousand are in use) is in universal employment. Such facts ought to confirm the confidence of the working miner in his old friend, once, perhaps, doubted, now of tried and proved fidelity. But it should be strongly impressed on all miners, that the Davy lamp is no less a monitor than a friend.
We must admit that the common Davy is liable to some disadvantages; and they are chiefly these:-Owing to the permeability of the gauze, the light is acted upon too forcibly and too easily by currents of air. Nor is the light imparted equal to that of a candle; and, although the work may be done by the light of the Davy, it is the common complaint of the working pitmen, that they cannot see by it. This leads to a neglect of the Davy where danger does not appear imminent. Frequent attempts have been made to remove these objections by the construction of safety-lamps in variously modified forms, in all of which, however, the main principle of the Davy is retained. Some of these modifications are dangerous in their construction, others give even less light than the Davy, and many very little more, while all of them are necessarily heavier than the Davy, and more expensive. The ordinary Davy may be had at about 78. 6d.; the "improved" lamps cost considerably more.
Of the numerous proposed modifications and improvements, the best are the lamp of Clanny, and the Mueseler and Eloin lamps; the two latter being of Belgian origin, while the former is the production of the well known Dr. Clanny, of Sunderland,— to whom, as well as to Davy, much of the merit of proposing, if not of actually inventing, the safety-lamp is due.* These three lamps are glass lamps; for each of them has a short thick cylinder of glass surrounding the flame, and forming, with the cylinder of wire gauze, the case, and thus separating the flame within the lamp from the explosive atmosphere without. The glass, if subjected to a good annealing, may be made of great strength, and should be of the first quality. In such lamps the flame cannot be acted upon by sudden currents of air, as may be the case with the Davy; and this is very important. Many object to the liability of the glass to fracture; but Mr. Mackworth states that, at a coal mine near Liége, he found four hundred Mueseler lamps in constant use; and although the breakage of glass was from one to four weekly, yet a piece was
*The reader, when in London, can readily inspect forms of Davy lamps in the Museum of Practical Geology, Jermyn Street. There are preserved the first two lamps that Davy himself constructed. They are interesting, but appear small and poor when placed by the side of the more recent lamps. A new lamp by Dr. Glover and Mr. Cail has received high commendation from several practical men.-See "Journal of Art," December 9th, 1853.