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In driving main levels, and in opening the works of such fields, the utmost precaution should be used. In working back or robbing pillars, or when great falls of roof have taken place, too much care cannot be taken. Where gas is met with, no one who knows anything of it will hesitate what to do. He will remove it out of the mine as quickly as he can. When this is done, the Davy or any other lamp should be employed by the workmen, as a precaution against any stoppage in the ventilation, by falls of roof or derangement of air courses, or by the sudden liberation of gas from the roof or other part of a mine.

Lamps are frequently used in the opening of seams of coal, in driving fast places, and when pillars are being robbed or worked back, whilst naked lights are in common use over the greater part of the mine. This dangerous admixture should be openly condemned. The most experienced miner, or the best scientific man, will not be able to guard against the sudden coming of so invisible, intangible, and subtle an enemy as fire damp; nay, in many cases will not be able able to detect its presence by any of his · senses, unless a light is present. Persons who do not understand the nature and properties of fire damp, often talk about the reckless conduct of poor ignorant miners, as if the latter rushed wilfully into it, just as a lot of boys would jump into a pool of water for mere mischief. The smell of gas used for the purpose of artificial illumination, gives an unmistakable evidence of its presence by its smell. Yet how many accidents are there by people who assume to be far better educated than the working colliers, taking a lighted candle to see where it escapes! Fire damp, on the other hand, may exist in a most explosive state which cannot be detected by the sense of smell, even by the most experienced miners, who have long worked in fiery mines. Scarcely anything shows more clearly the indefinite

ideas the men have of this gas than the names they call it by sulphur, wild fire, fire damp, &o. To say nothing about working colliers, speaking for myself, I should be sorry to trust any experienced underlooker or officer's mere senses as to the presence of fire damp. I certainly once did so, and very narrowly escaped being badly burnt for my credulity.

It has been stated that every collier ought to be able to examine his own place before he commences his work. I wish they were so. So far as my knowledge extends, it will be long before they will possess such an amount of knowledge as to gas. Another circumstance, which proves how ignorant really practical men were of the nature of the enemy they had to deal with, was the fearful mode of trying a place for gas with a naked candle, and as the flame tapered up cut it off with their hands. This, it is to be hoped, is not now in use. Although doubtless some men were very clever in escaping being burnt in their investigation, their skill must be considered as that of thoroughly reckless men; just as reckless as if they were in a building full of casks containing a black powder, as well as some of the same kind of powder lying loos3, with a train of it reaching all the way to the door, and they wanted to find out its nature. To do this suppose they fired the train with a match and trusted to stamping the flame out with their feet, so as to prevent its communicating with the heap. This may seem a mad way of testing the presence of gunpowder, but it is rot a whit more insane than trying a fiery coal mine for fire damp with a naked candle. To my mind, ignorance of the origin and properties of fire damp is the chief cause of the explosions of fire damp in mines. This want of knowledge of the subtle enemy they have to deal with is, I fear, alike com. mon to both officers and men. The proverb that “knowledge is power" is nowhere more applicable than when applied to fire dazap in a coal mine, for

no intelligent officer who knows much of that gas will be long in removing it as soon as it is generated, and also be constantly prepared for its appearance in the mine when it is known to exist, or even where there is a probability of its existence. The mixed use of Davy lamps and candles in a mine where fire damp is known to be in any part of the workings or waste, is, to say the least of it, both reckless and dangerous,

A securely locked Davy lamp, with a shield, is a safe instrument in the hands of a careful man, who knows the principles on which it is constructed. By this I mean that it is invaluable for an intelligent fireman to examine the workings with, before the men are sent into them, and for workmen to use it as a precaution in a well ventilated mine against accidents in the ventilation; but it should never be used as a substitute for ventilation, and in places so full of gas as to have the gauze full of flame. There is no excuse in the world for working with lamps full of flame for any length of time, and if it is persisted in, accidents sooner or later are sure to occur. Often when in a dead place lamps are filled with flame, there being too much fire damp present to make the air explosive, the admittance of a current of air will suddenly dilute the gas to the point of greatest explosion, namely, one of fire damp and seven of air, and a series of explosions will take place in the lamp. It is then said to be very sharp gas, and some practical men think that the mixture contains other gases than fire damp and air, but all investigations up to this time have failed to detect such gases, and I therefore still think that the sharpness arises from its being at the mixture of greatest explosion.

It is very difficult to pass flame through good standard gauze, even the flame of coal gas containing a considerable amount of olefiant gas, as my experiments now exhibited clearly show; but still flame will pass through gauze saturated with oil and covered with cannel coal dust.

In cleaning lamps which have had coal dust burnt into a cinder on them, it is very difficult to get it off, and in doing so the gauze is sometimes damaged. Accidents occur frequently from damaged gauze, and too great care cannot be bestowed in examining the gauze before the lamp is used.

Before proceeding to the consideration of mining lamps, it will be well to say something on the nature of flame, as all the safety belonging to them depends on their power to prevent flame passing from the inside of the lamp to the outside. Flame, according to Sir Humphrey Davy, “is gaseous matter heated so highly as to become luminous, and that to a degree of temperature beyond the white heat of solid bodies, as shewn by the circumstance that air not luminous will communicate this degree of heat. This is proved by the simple experiment of holding a fine wire of platinum about th of an inch from the exterior of the middle of the flame of a spirit lamp, and concealing the flame by an opaque body, the wire will become white hot in a space where there is no visible light. When an attempt is made to pass flame through a fine mesh of wire gauze, at the common temperature, the gauze cools each portion of the elastic matter that passes through it, so as to reduce its temperature below that degree at which it is luminous, and the diminution of temperature must be proportional to the smallness of the mesh and the mass of the metal. The power of a metallic or other tissue, to prevent explosion, will depend upon the heat required to produce the combustion, as compared with that acquired by the tissue; and the flame of the most inflammable substances, and of those that produce most heat on combustion, will pass through a metallic tissue that will interrupt the flame of less inflammable substances, or those that produce little heat or combustion. Or the tissue being the same, and impermeable to all flames at common temperatures, the flames of the most combustible substances, and of those that produce most heat, will most readily pass through it when heated, and each will pass through it at a different degree of temperature. In short, all the circunstances which apply to the effect of cooling mixtures upon flame, will apply to cooling perforated surfaces."* The same author also states that when rapid currents of explosive mixtures are made to act on wire gauze, it is of course much more rapidly heated; and therefore the same mesh which arrests the mixtures of explosive mixtures at rest, will suffer them to pass when in rapid motion; but by increasing the cooling surface, by diminishing the size or increasing the depth of the aperture, all flames, however rapid their motion, may be arrested." Sir H. Davy, in one of his latest papers, says “I have had lamps made of thick twilled gauze of wires of oth of an inch 16 to the warp and 30 to the weft, which being rivetted to the screw caunot be displaced; from its flexibility it cannot be broken, and from its strength it cannot be crushed, except by a very strong blow. Since the discovery of Sir Humphrey Davy in 1816, when he produced a light enclosed in a cylinder of wire gauze 8 inches high, and not more than 2 inches in diameter, the wire being when twilled not less than oth of an inch in thickness, and 30 in the warp, and 16 to 18 in the weft; and when plain not less than both of an inch in diameter, and from 28 to 30 both warp and woof, -little has been done in the way of improving it. In common use throughout the United Kingdom, the lamp is pretty much the same as when it came out of the hands of the inventor. For simplicity, utility, and cheapness, the lamp will in the opinion of most

• Miscellaneous papers and researches on flame and the safety lamp, p. 73.

1 lbid, p. 78.

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