ON SAFETY LAMPS
FOR LIGHTING COAL MINES,
By NICHOLAS WOOD, Esq.,
PRESIDENT OF THE INSTITUTE.
In the year 1813 a society was instituted, of which the late Sir Ralph Milbanke, Bart., was president, for preventing accidents in coal mines; and in 1814 the society published its first report, which practically consisted of a letter from the late Mr. Buddle, on the various modes employed in the ventilation of collieries, illustrated by plans and sections. I need scarcely say that a copy of this letter must be in the possession of every member of the society; as besides, containing a description of the then methods of ventilation, most valuable suggestions were made by that able and sound practical mining engineer, on ventilation generally, and likewise on what was required to complete the system.
At that period the only light used in coal mines was the candle, which was described as being made of ox or sheep tallow, with a cotton wick, forty-five candles to the pound, ox tallow being considered the best.
And, when the air in the mine became mixed with inflammable gas, or carburetted hydrogen gas, the mode of ascertaining its existence, and the degree of inflammability was described by Mr. Buddle as follows.
“In the first place the candle, called by the colliers the ‘low,’ is trimmed - that is, the liquid fat is wiped off - the wick snuffed short, and carefully cleansed of red cinders, so that the flame may burn as purely as possible.
“The candle being thus prepared, is holden between the fingers and thumb of the one hand, and the palm of the other hand is placed between the eye of the observer and the flame, so that nothing but the spire of the flame can be seen, as it gradually towers over the upper margin of the hand. The observation is generally commenced near the floor of the mine, and the light and hand are gently raised upwards till the true state of the circulating current is ascertained.
”The first indication of the presence of inflammable air is a slight tinge of blue, a blueish grey colour, shooting up from the top of the spire of the candle, and terminating in a fine extended point. This spire increases in size, and receives a deeper tinge of blue, as it rises through an increased proportion of inflammable gas, till it reaches the firing point. But the experienced collier knows accurately enough all the gradations of ‘shew’ (as it is called) upon the candle, and it is very rarely fired upon excepting in cases of sudden discharge of inflammable gas.”
Mr. Buddle then goes on further to state, “that the shew upon the top of the candle varies very much according to the length of run, or distance which the current of air has passed through,” and that “the same size of spire which would indicate danger in a current which had passed only one mile might be perfectly harmless in a current that had run five or six miles.” That “the air course for a short distance beyond, a small discharge of fire-damp may be highly inflammable; but by passing a few yards further it becomes so diluted as to be perfectly harmless.” And “that long experience and attentive observation are consequently necessary to obtain a thorough practical knowledge of the art.”
Such was, in 1814, the general mode of lighting coal mines, and the above graphic, and correct description of the mode of ascertaining the presence, and of dealing with the existence of inflammable gas, exhibits the delicate, ticklish, and extremely dangerous method of encountering such an insidious enemy.
When, from cases of extreme discharge of gas, or in pillar working, the current of air brought to bear upon the enemy was not sufficient to dilute the gas, so as to reduce it below the inflammable point, then the steel mill was resorted to.
The steel mill was an instrument well known in the profession, and consisted of a wheel of steel of about 6 inches in diameter turned rapidly round by a wheel and pinion, a dexterous practitioner, then, by applying a piece of flint to the periphery of the wheel a continuous succession of sparks was elicited, and this produced certainly, at best, a precarious, rather uncertain, but certainly a sufficient light to enable the workman to perform some descriptions of work, and at least to travel pretty well through the workings.
This light, however, required one operator with the mill to produce a light for one workman, and hence, as may be supposed, in cases where the mine could not be cleared of gas to such an extent as that candles could with safety be used, the expense was such that the coal could not be worked at all. And hence, very little pillar working in mines discharging inflammable gas could be practised. Looking at the immense extent of the mines in this district which was thus rendered incapable of being worked, an extent which was daily, and constantly increasing, in the ratio of the quantity of whole coal excavated in those mines which contained gas, it need scarcely be stated that a powerful and accumulating incentive existed to obtain some mode of lighting mines, to enable such a valuable property to be recovered, and brought into profitable and useful productiveness. Added to this, also, was the prevailing opinion, that the occurrence of frequent accidents, notwithstanding all the “experence and thoroughly practical knowledge,” alluded to by Mr. Buddle, of the persons in charge of the mines, required some mode of lighting mines, liable to be suddenly rendered inflammable, which would not in such cases explode the gas.
Some rather severe accidents which occurred about the year 1814, directed public attention, and still more that of the scientific world more strongly to the subject. Dr. Clanny, to whom the mining interest owes a debt of gratitude, was the first to produce a lamp by which a light could be used in an inflammable mixture of gas with impunity. The insulation of the flame by this lamp was by means of water, and though the first lamp which was produced, it was too complicated and cumbrous for general use.
In the autumn of the year 1815, however, circumstances occurred which accomplished the object required, and which has been productive of consequences in coal mining of the utmost importance to humanity and to the mining and commercial interests of the country generally. At the same time, and in distant localities, the late Mr. George Stephenson and the late Sir Humphrey Davy, both produced lamps which insulated lights in inflammable mixtures of fire-damp without exploding the gas externally.
It is not my wish, neither indeed is it necessary to arouse the then much debated question, as to which of those gentlemen the mining interests are indebted for the first discovery of this invention. Enquiries then made, and subsequent investigations have, in my mind, satisfactorily established, that both those gentlemen were original discoverers; and that it was one of those, not indeed only cases in science where two persons in distant localities, without communication with each other, stumbled upon, or made the same discovery at the same time, and, as in this case, arrived at the same results by very different processes of reasoning and deduction.
Having been privy to the whole process by which my lamented friend Mr. Stephenson arrived at his discovery, it may not be out of place, neither is it, I trust, an inappropriate opportunity, to give a short detail of the circumstances by which that gentleman arrived at such a valuable discovery.
Mr. Stephenson had observed, that when the fire-damp was accidentally exploded in narrow drifts or passages, a tangible and considerable time elapsed between the instant of explosion at one end and the arrival of the inflamed gas at the other – that in fact the explosion passed along the drift or passage at a defined velocity – and, reasoning upon this fact, he supposed that such velocity would be dependent upon the area of the drift and that it was possible to arrest the flame; and he thought if motion could be impaired to the current of air in such a drift in a contrary direction and of a greater velocity than that at which the explosion passed, the explosion could be arrested or prevented from passing along the drift. He had also observed, that when blowers of gas were ignited, and lighted candles were placed to windward of such blowers, the flame of the blowers was extinguished by the burnt air of the candles.
He then conceived, as he himself stated at the time, “that if a lamp could be made to contain the burnt air above the flame, and to permit the fire-damp to come in below in a small quantity, to be burnt as it came in, the burnt air would prevent the passing of explosion upwards; and the velocity of the current from below would also prevent it passing downwards.”
A lamp was accordingly made of tin, with a hole in the bottom, for the admission of air to the interior of the lamp, and a top perforated with holes. There was also a slide in the bottom to diminish the size of the hole at pleasure. This lamp was tried in inflammable mixtures, and the area of the hole was diminished until the aperture did not pass the flame. It was, however, found, that when so diminished, the least quantity of gas in the air put out the lamp. To remedy this, three tubes were used, when it was found that a greater aggregate quantity of air could be admitted into the lamp without passing the flame; and, subsequently, a lamp with plates perforated with small holes, for the admission of air, was used, which it was found did not pass the flame. At this period of the investigation the reason why the flame did not pass through the apertures was not known. Although it was clear from the number of holes, that the theory of the velocity of the air passing through such perforations into the lamp did not act in preventing the flame from passing outwards. All this time the burnt air passed through perforations in the top of the lamp.
Mr. Stephenson had now arrived at the discovery that apertures of a certain area did not pass the flame of fire-damp, and had thus discovered the true principles of a safety-lamp. Sir H. Davy at about the same time communicated to the Rev. W. Hodgson, of Newcastle, that he had “discovered that explosive mixtures of mine damp will not pass through small apertures or tubes, and that if a lamp or lanthorn be made airtight on the sides, and furnished with apertures to admit the air, it will not communicate flame to the outward atmosphere,” and he subsequently found that “iron wire gauze, composed of wires from one-fortieth to one-sixtieth of an inch in diameter, and containing twenty-eight wires, or 784 apertures to the inch, was safe under all circumstances.”
The process by which Sir H. Davy arrived at the above conclusion is given by himself in a small work “On the Safety-Lamp for Coal Mines with some Researches on Flame,” which, explaining the principles on which the safe insulation of the light is accomplished, is interesting. Sir H. Davy states – “I found that it (the fire-damp) required to be mixed with large quantities of atmospheric air to produce explosion; even when mixed with three or nearly four times its bulk of air, it burnt quietly and extinguished a taper. When mixed with between five and six times its volume of air it exploded feebly; it exploded with more energy when mixed with seven or eight times its volume of air; and mixtures of fire-damp and air retained their explosive powers when the proportions were one of gas to fourteen of air; when the air was in larger quantity the flame of a taper was merely enlarged in the mixture, an effect which was still perceived in thirty parts of air to one of gas.”
“I found fire-damp much less combustible than other inflammable gases. It was not exploded or fired by red-hot charcoal, or red hot iron; it required iron to be white hot, and itself in brilliant combustion for its inflammation. The heat produced by it in combustion was likewise much less that that of most other inflammable gases.”
“On mixing one part of carbonic acid or fixed air with seven parts of an explosive mixture of fire-damp, or one part of azote with six parts, their powers of exploding were destroyed.”
“In exploding a mixture in a glass tube of one-fourth of an inch in diameter and a foot long, more than a second was required before the flame reached from one end to the other, and that metallic tubes prevented explosion better than gas tubes.”
”In reasoning upon the various phenomena,” says Sir Humphrey, “it occurred to me - as a considerable heat was required for the inflammation of the fire-damp, and as it produced in burning comparatively a small degree of heat, that the effect of carbonic acid and azote, and of the surfaces of the small tubes in preventing its explosion, depended upon their cooling powers, upon their lowering the temperature of the exploding mixture so much that it was no longer sufficient for its continuous inflammation.”
”This idea, which was confirmed by various obvious considerations, led to an immediate result - the possibility of constructing a lamp, in which the cooling powers of the azote or carbonic acid, formed by combustion, or the cooling powers of the apertures through which the air entered or made its exit-should prevent the communication of explosion.”
It is curious to observe the minute difference of circumstances under which those gentlemen arrived at the same result. Mr. Stephenson had observed that candles placed to windward of a blower extinguished the flame by the azotic air produced by the combustion of the candles. Sir H. Davy found, by applying azotic and carbonic acid gas to fire-damp in a state of inflammability, they extinguished the flame; and hence, both conceived the notion that the burnt air of the flame within, would, in its passage out of the lamp, as one of the causes, prevent the explosion from passing outwards. Then comes the difference. Mr. Stephenson thought that by admitting small quantities of air through the bottom, the velocity of the current would prevent the passage of the flame outwards, (and this, be it observed, was a fact which Sir H. Davy also discovered, for he had found that in a glass tube, 12 inches long, it required a second before the flame passed from one end to the other); and hence, his lamp was fed first by one hole with a slide, next with three tubes, and ultimately by small perforated holes. Sir H. Davy, on the other hand, finding that the fire-damp required a very high temperature for its explosion, conceived the idea of applying radiating surfaces, through which the flame would have to pass from the interior of the lamp, and by these to reduce its temperature below that which was required for its continuous inflammation.
Ultimately, iron wire gauze was used by Sir H. Davy, as possessing the greatest radiating or cooling surface, and Mr. Stephenson used small perforated holes for the admission of the air into his lamp, these small holes acting as radiating surfaces to reduce the temperature of the flame, as well as in accordance with the principles on which his lamp was originally constructed.
As previously stated, Sir H. Davy found that iron wire gauze of 1-40th to 1-60th of an inch diameter, with 28 wires, or 784 apertures to the square inch, was perfectly safe; and up to this time the lamp bearing his name has been so constructed.
Mr. Stephenson’s lamp has been much improved, and the lamp which is now in use, comprises a glass cylinder covered by a cylinder of wire gauze, and instead of the air passing through a perforated plate it passes through the meshes of the wire gauze. This lamp differs from the Davy lamp, inasmuch as in the latter the air has access through the entire meshes of the wire gauze on all sides, consequently, when immersed in an inflammable mixture, the whole cylinder becomes filled with flame, and if it is continued in such mixture, the wire becomes red hot. Whereas in the Stephenson lamp, the air being only admitted through a few meshes of the gauze within the glass cylinder, the latter preventing the entry of any air or gas from the sides, consequently, a very small portion of gas is permitted to enter, and therefore, the interior of the lamp never being filled with flame no injury can arise to the wires of the gauze. The small quantity of air or gas entering is, however, productive of another result, viz:- When mixed with gas, there not being a sufficiency of atmospheric air for the combustion of the oil, and not a sufficiency of inflammable gas to support the requisite temperature for its inflammation, the light is extinguished. In the Davy lamp there is a sufficient body of gas to keep up the requisite temperature, and when the lamp is kept in an inflammable mixture, the gas continues burning entirely independent of the combustion of the oil, the wire becomes red hot, radiating the heat sufficient to keep the temperature of the wires below that required for the passage of the flame through the meshes, but still sufficiently high to support the combustion of the gas. There is, however, no acceleration or accumulation of intensity of heat, the wires keep at a dull red heat, if kept in a still atmosphere, and the lamp continues to burn with safety as regards the transmission of the flame through the meshes of the wire gauze.
These are the principles of the two lamps, and I have been a little more minute in the, explanation of them, as most of the modern lamps are modifications of one, or the other, or of both; either admitting the air within the lamp unrestrictedly through the meshes of the gauze, allowing continuous inflammation to go on within the lamp, and relying for protection from the radiating property of the gauze as in Sir H. Davy’s lamp; or restricting or diminishing the quantity of air admitted into the lamp, as in the Stephenson lamp, and allowing it to go out when immersed in an inflammable mixture, when the atmosphere does not contain sufficient oxygen to support the combustion of the oil.
There has, however, recently been a new element brought into operation, which has an important bearing on the construction and safety of these lamps, viz., that of producing a better or more powerful light than the Davy lamp, and which has led to the rejection of the use of wire gauze as an insulating medium, or the cover of wire gauze over the glass cylinder on the sides of the lamps, and to the employment of glass cylinders alone, to insulate the flame on the sides, the air in all these cases being admitted within and passing out of the interior of the lamp through wire gauze. The principle of insulation for the passage and exit of the air, is therefore, the same as in the Davy lamp, viz., the radiation of the gauze; but then we have only the cylinder of glass as a protection between the flame of the lamp and the external air. The most extensively used lamp of this description is the Clanny lamp - the construction of this lamp being that of a glass cylinder for the purpose of light, and a wire gauze top.
The Museler lamp is a lamp most extensively used in Belgium, and does not differ much from that of Clanny, having a glass cylinder, for the light, and a gauze top; but in this lamp there is a copper chimney to carry off the smoke from the wick of the burner, and to force the air entering through the wire gauze downwards between the copper chimney and the glass cylinder upon the flame of the burner, the air being admitted through the gauze at the top.
The Boty, lamp is another modification of this principle, having a glass cylinder with a wire gauze top; but in this the air is admitted through a ring of perforated copper at the bottom of the lamp. In other respects it does not much differ from the Museler lamp.
The Eloin lamp has also a glass cylinder; the air is admitted through wire gauze near the bottom of the lamp, and is thrown against the burner by a thin copper cap. No other air enters the lamp than that at the bottom through the gauze, consequently it is easily extinguished. Instead of having a cylinder of gauze for the top, this lamp has a copper or brass top, so that the only entry for air is at the bottom, the exit for the vitiated air being at the top through wire gauze. This lamp has not been much used. It has an argand burner, or flat wick.
There are a variety of lamps constructed on this principle, viz., that of obtaining increased light by the use of glass cylinders, all of course of larger diameter than the wire gauze cylinder of the Davy.
Dr. Glover’s lamp has a double cylinder of glass, the air being admitted from the top between the two cylinders, and passing downwards enters within the inner cylinder at the bottom of the lamp, through wire gauze, or apertures, and so passes to the burner. The two cylinders are for protection in case of accidents, and the air being passed between the cylinders operates in keeping them cool The top of the lamp is wire gauze.
It was my intention to have given drawings of the different lamps; their construction is, however, well known to the profession, and the requisite plates would have extended this paper beyond the limits which I had prescribed to myself in this communication.
I shall now proceed to examine how far the Davy and other lamps can be depended on in practice for safety in lighting mines abounding in inflammable gas.
It is well known to the profession that the safety of the Davy-lamp has been questioned very generally, and more particularly by persons having no experience in its use. Dr. Priara, in 1833, made some experiments to prove its insecurity, but these experiments were made with coal gas, which, being essentially different in its inflammability from the fire-damp in mines, could not be considered conclusive; and though the object was to prove the superiority of Upton and Roberts’ lamp, yet even comparatively the experiments were of little value, as the only result found with regard to Upton and Roberts’ lamp was, that when immersed in the inflammable mixture it went out.
The South Shields Committee came to the conclusion “that the Davy-lamp was absolutely unsafe;” “that the Davy-lamp has been found, by experiment and in practice, to explode the external gas by the passage of the flame through the gauze,” and that “no doubt can remain that it has been the cause of some of the hitherto unaccountable accidents which have occurred.”
Mr. Darlington, in his evidence before the Committee in 1852, says:- “I can state from my own practical knowledge of the Davy-lamp, and from the opinions of miners who have for years worked with the Davy-lamp, that it is not a safe instrument in an explosive mixture under a strong current;” and again, “ I have, in a mine, passed the explosive mixture, but not with a cool clean lamp; it has been at a red heat;” and in answer to the question, “Is it not the fact that dust will fly off in sparks or scintillas, and that one spark would create an explosion ?” Mr. Darlington says, “There are very numerous instances of accidents taking place that we could attribute to nothing else.”
The Committee of 1852 state their “concurrence. in the opinion expressed directly or indirectly by the committees of 1835 and 1849, and also with that so strongly expressed by the South Shields Committee, that where a proper degree of ventilation does not exist in a mine, the Davy-lamp, or any modification of it, must be considered rather as a lure to danger than as a perfect security.”
Having had considerable experience during the last 40 years in the use of both Davy’s and Stephenson’s lamps, and having had no well authenticated cases of the lamp passing the flame, and having also, at and since the introduction of the safety-lamps, made experiments with gas from blowers in the mines, I had certainly arrived at a different conclusion. Considering, however, that the subject was of vital importance to the mining interests generally, and to the miners more particularly, who venture their lives daily in immense numbers, on the safety of those lamps, I thought it proper to institute a set of experiments, by which the lamps could be subjected to a more severe test than I had ever yet done.
For this purpose a blower was selected in the Killingworth Pit, which had been discharging gas for the last 16 years, a gasometer was prepared 2 feet 6 inches in diameter, and 3 feet in height, shown at a b c d, Fig. 1, in which the gas was mixed with atmospheric air in certain proportions required, this was placed within a tub e f g h in the usual manner, and water was run into the tub for discharging the gas out of the gasometer into the following apparatus - a box 2 feet 9 inches square, and 1 foot 4 inches in depth, i k l m, was placed near the gasometer, with an upright spindle n, in which an arm o was fastened, as shown in the drawing; on the end of this arm the lamp p was fastened, and the spindle was turned round by a handle H on the outside of the box.
The box was filled with gas from the gasometer, by pouring in water into the tub e f g h, and forcing the gas through the pipe A, and the gasometer was again filled by letting off the water, the gas being obtained from the blower B, by the pipe C, and the atmospheric air by the pipe A.
The experiments were conducted as follows :-
The lamp was placed within the box, as shown in the drawing, and the box was filled with fire-damp from the gasometer, the lamp was then allowed to remain stationary until the flame became elongated, and in those lamps where the supply of gas to the interior of the lamp was such as to keep up a state of combustion, the lamp was allowed to remain at rest until the wire gauze became red hot; it was then turned round, gradually at first, lest the motion should put it out, then accelerated, to increase the intensity of the flame, and so increase the intensity until the wires were in a state of white heat, and until the lamp passed the flame.
Killingworth Colliery, May 23, 1853.
EXPERIMENTS with the Davy Lamp to ascertain if the flame may be passed in an explosive mixture of fire-damp and at what velocity.
Davy Lamp, 1st Experiment.- Velocity attained was 9¼ feet per second, without passing the flame.
Ditto, 2nd Experiment.- 3 revolutions in 3 seconds, which is equal to a velocity of 7⅓ feet per second, without passing the flame.
Ditto, 3rd Experiment. - 38 revolutions in 36 seconds, which gives a velocity of 7⅔ feet per second without passing the flame.
Ditto, 4th, Experiment. - 9 revolutions in 6 seconds, which gives a velocity of 11 feet per second, and did pass the flame.
Ditto, 5th Experiment. - 15 revolutions in 8 seconds, giving a velocity of nearly 14 feet per second, and did not pass the flame.
It is to be remarked that in the experiments, with the exception of No. 4, the lamp was put in motion when first full of explosive mixture, and in a comparative cool state, but in the case of No. 4, the lamp was at a state of red heat, before being put in motion at a high velocity.
Killingworth Colliery, June 6, 1853.
EXPERIMENTS with various Safety Lamps to ascertain if the flame may be passed in an explosive mixture of fire-damp, and at what velocity.
The experiments were made in the box 2 feet 9 inches long, 2 feet 9 inches broad, and 1 foot 4 inches deep, having plate glass windows on one side for observation. In the box was fitted an axle with arms, at the ends of which were uprights about the length of a lamp, having rings and screws attached for fixing the lamp. On the under side of the box was placed a handle for turning the axle, working with two wheels, the smaller of which made four revolutions in the time the larger wheel made one. The top of the box was a lid loosely fitted, so that an explosion should not injure the apparatus.
Diameter of circle the lamp travelled, 28 inches - 88 inches each revolution of area. The gas was collected from the blower, mixed with air in the gasometer, and by water pressure forced into the box. In each experiment the lamp, after the gauze being gradually heated to a red heat, was then put in motion.
The following results were obtained:-
No. 1. - Davy Lamp, after making 160 revolutions in 116½ seconds, and attaining a velocity of 10 feet a second, did not pass the flame. This lamp was again tried, and still did not pass the flame, having made 200 revolutions in 114 seconds, which gives an average velocity of 13⅔ feet a second.
No. 2. - Davy Lamp was then tried, and the flame passed in two experiments, the lamp having been moved on the first experiment at a velocity of 15 feet a second, making 60 revolutions in 29 seconds; and in the second experiment, at a velocity of 19 feet a second, making 26 revolutions in 10 seconds.
No. 3. - Jack Lamp, being a common Davy, with an outside glass cylinder halfway up the lamp, leaving about 3 inches of the wire gauze exposed. In the experiment the flame passed, but the velocity was not ascertained.
No. 4. - Stepkenson Lamp, without a glass, passed the flame whilst moving at a velocity of 14.6 feet a second, 28 revolutions having been made in 14½ seconds.
No. 5. - Clanny Lamp, copper gauze, passed the flame at a velocity of 12½ feet a second (12 revolutions in 7 seconds).
No. 6. - Clanny Lamp, with bent iron wire gauze and cracked glass, was twice experimented with, and at the velocity of 16 and 15 feet a second respectively, did not pass the flame, but in each case the lamp fell off the arms, and was extinguished - 96 revolutions in 44 seconds in the first case, and 20 revolutions in 10 seconds in the last. The same lamp in its damaged state was again tried and moved at a velocity of 12 feet per second (68 revolutions in 29 seconds), but without the flame being passed, the lamp having become extinguished.
Killingworth Colliery, June 29, 1853.
RESUMED EXPERIMENTS with various Safety-Lamps to ascertain if the flame may be passed in an explosive mixture of fire-damp, and at what velocity.
No. 1. - Davy Lamp (1st Experiment).- In this instance the lamp, after arriving at a dull red heat, was put in motion at a velocity of 15 feet a second without passing the flame, having made 248 revolutions in 61 seconds, the temperature in the box during the experiment varying from 69° to 94° Fahrenheit.
No. 2. - Davy Lamp (2nd Experiment.) - The lamp, after being heated to a similar state, as in the last experiment, was moved at a velocity of 13 feet a second, having made 52 revolutions in 29 seconds, and the flame passed. Temperature in box varied from 69° to 82°.
A Davy Lamp was afterwards heated to a red heat, and whilst being moved at a considerable velocity, very fine coal dust was thrown upon it by means of a pair of bellows, the nosle of which was inserted in the side of the box. On this being done, the dust produced small and luminous explosions within the gauze, which would lead an observer to imagine that the flame had actually passed through the gauze, but it did not. Oil was then poured upon the gauze, together with coal dust, so as to put the lamp in a condition as nearly as might be approximating to that it would be in, in the bands of a careless workman. It was then put into quick motion, and continued for some time without the flame being passed.
No. 3. – Clanny’s Lamp (1st Experiment) was tested in the same manner as the Davy Lamp in the first and second experiments, and the flame passed on attaining high velocity, and the glass cracked. The same lamp in its damaged state was again tried and moved at a velocity of 17 feet per second (68 revolutions in 29 seconds), but without the flame being passed, the lamp having become extinguished.
No. 4. - Boty Lamp (used in Belgium, being authorized by the Government Inspectors).- This lamp, after making 12 revolutions in 6 seconds, which is equal to a velocity of nearly 15 feet per second, passed the flame and cracked the glass. Temperature of the box during the experiment varied from 70° to 88° Fahrenheit.
No. 5. - Eloin Lamp, with a gauze, but without the glass. In this experiment, which was conducted in a manner similar to the others, the time and revolutions were not ascertained, but the flame passed when the lamp was moving at a considerable velocity.
No. 6. - Lamp, similar to Eloin Lamp, without a glass, was also tried, and the flame passed, but the velocity was not ascertained.
Hall’s Lamp, with a double wire gauze top, tested in the same manner, did not pass the flame, the velocity in this case having been 13 feet per second.
Cail and Glover’s Lamp was also tested, and the flame did not pass, but the inner glass cracked.
The mode of conducting the experiments was a most severe test, such as could scarcely occur in practice, in the first place, the gas being inclosed in a box, when rapid velocity was imparted to the lamp, it would be subjected to an increased pressure of the air from its confinement within the box on the front of the lamp, the centrifugal force imparted to the air by the circular motion of the lamp would also produce additional pressure to force the air through the meshes of the gauze. It can scarcely, therefore, be supposed that the same velocity imparted to a lamp moved with the hand or carried in the mine, would have the same effect in passing the flame. Not having been able, by any velocity which I could impart to a lamp in a rectilinear direction to pass the flame through the meshes, it was necessary that some such severe test as adopted should be used.
It appeared also, that, as stated by Sir H. Davy, the flame would not pass through the meshes at a dull red heat, and that it was necessary, before the flame passed, that the wires of the gauze should be heated to a white heat, this I had never been able to produce in the previous experiments, and it could only be done by an apparatus similar to that used by which an accelerated motion could be produced, to raise the temperature to the highest possible degree of heat. In performing each experiment the motion was at first very slow, and then gradually accelerated; otherwise, the lamp went out; when, however, a white heat was produced, any increase of velocity only added to the intensity of the heat, and had no tendency to put out the flame.
On examining the experiments, it will be seen, that on the 23rd May, none of the experiments passed the flame through the meshes of the gauze, although the velocity with which the lamp was moved was 14 feet per second in the 5th experiment, but, as was afterwards ascertained, the experiment was not continued sufficiently long to produce the requisite temperature of the gauze, though it had traversed 110 feet, at the rate of 9½ miles an hour, and the heat was much beyond what could be produced by any current of air in a mine. In experiment No. 1, June 6th, although the experiment was continued for 116½ seconds in one case, and 114 seconds in another, the distance traversed being respectively 1173 and 1466 feet, and the average velocities 10 and 13 feet per second, the last experiment showed that a velocity of 13 per second, kept up for 114 seconds, or while traversing nearly 500 yards, at the rate of about 9 miles an hour, did not cause the flame to pass through the meshes, and that it was only when a velocity of 15 feet per second, and 19 feet per second, and when the wires were heated to a white heat, that the flame passed. It was always found that, however long the lamp was immersed in the fire-damp, so long as it was kept standing, or not subjected to a current, that the heat never exceeded that of a dull red heat, a degree of heat much below that at which the flame passed the meshes.
With the Stephenson lamp complete, or with the glass, there was no tendency to pass the flame, the wires, from the diminished quantity of air introduced, could not by any possibility be heated beyond that of dull redness, so fir, therefore, as passing the flame while in a perfect state, this lamp may be said to be a perfectly safe lamp; the glass protects the lamp from the effects of any current of air, or of motion, and the wire cannot be heated beyond that which the inflammable air, in a state of still combustion, can impart to it, and which, as before stated, does not pass the flame. It is only when the glass is broken, and when the lamp becomes, in fact, a Davy-lamp, that motion of the air through the gauze can be attended with danger, and in this state the No. 2 experiment of June 6th was made. In this experiment the flame passed when the velocity was about 14½ feet per second, nearly about the same result of the Davy-lamp.
The Jack-lamp is a Davy-lamp, with a glass cylinder around the gauze opposite the flame of the lamp, or about half the height of the gauze. The cylinder of gauze of the Davy-lamp being about 6 inches in length, the glass cylinder was about 3 inches, leaving 3 inches of wire cylinder above the glass unprotected. This lamp, as shown by No. 3, passes the flame when subjected to motion which produced a white heat to the gauze.
Clanny’s lamp having a cylinder of wire gauze of about 5 inches in length above the glass, also passed the flame when subjected to a white heat; and it is necessary to observe that a wire gauze of copper passed the flame much more readily than gauze of iron wire, viz., at a velocity of 12½ feet per second when the space traversed was only 88 yards.
The Boty or Belgian lamp, having also a cylinder of wire gauze above the glass, passed the flame at a velocity of 15 feet per second, and when subjected to a white heat. The length of the cylinder of wire gauze of this lamp is less than that of the Davy-lamp; but the diameter of the cylinder is larger, and, therefore, containing as large a quantity of gas within the cylinder, the same result as with the Davy took place.
The Eloin lamp another Belgian lamp, is differently constructed, having a brass top with a wire gauze cap, but having about two inches of glass, and admitting the air at the bottom; while perfect, it went out with the slightest motion when immersed in the fire-damp. I took off the glass, and substituted wire gauze, and though the cylinder of gauze was only two inches in length, and about two inches in diameter, it contained within that space sufficient gas, when put into rapid motion, as to produce a white heat, and so pass the flame through the gauze. And I tried another lamp, No. 6 experiment, June 29th, with a cylinder of gauze 2½ inches in height, and about 1¾ inches diameter, which also passed the flame under the same circumstances.
During the prosecution of those experiments, it was objected to them that the test was such as could not occur in practice, and that the more correct way of testing the safety of the lamps, would be by subjecting them to rectilinear motion, as more consonant with what was likely to occur in practice, whether the lamp was subjected to a current of air, to a fall from a height - gas being forced upon it by falls of stone, or by blowers - or by persons running away with the lamp in an explosive mixture of gas. No doubt this is correct; but as before explained, I had never been able, under such circumstances, to cause the flame to pass through the gauze. Mr. Thomas John Taylor, however, instituted a set of experiments with similar lamps at the blower of gas at Wallsend; and as these experiments are very valuable as contrasted with mine, I have the permission of that gentleman to embody them in this paper.
VARIOUS SAFETY LAMPS, TRIED AT WALLSEND COLLIERY,
JUNE 28th, 1853.
Present - Mr. Thomas J. Taylor; Mr. George Clark; Mr. Thomas Irvine, Engineer of Colliery; the Master Wasteman, and others.
The gas made use of is direct from the mine, being conveyed in a 4-inch pipe from a barred-up space of about 50 acres at the depth of 140 fathoms, and thence up the C. Pit shaft. It was received, by means of a small pipe and stop-cock, into a horizontal wooden box 12 feet long, and 18 inches square inside, with windows at each end, and two windows on the top.
A double groove was made at 3 inches from the bottom of the box, with a sliding platform which moved in it, and on which the lamps were firmly fixed by wedge pieces.
A horizontal wheel was placed outside at each end of the box, the two wheels being connected by a cord which passed round the periphery of both; one cord being outside and the other inside the box. The inside cord was attached to each end of the moveable platform. A check string was also attached, which allowed a movement in either direction of 11 feet, and prevented the lamps from coming into contact with the ends of the box.
An upright shaft with a handle was attached to one of the wheels, by turning which various rates of velocity might be communicated at pleasure to the moveable platform, and the lamp upon it, in the interior.
The indications of foulness were at once apparent from the effect on the lamps.
The box was kept cool by admitting fresh air in the intervals of, and sometimes during the experiments, the ends being moveable.
The temperature of the external air was 64°.
The temperature of the gas was 65½°.
‘The time was measured by a watch with a large second hand pointer, capable of determining
accurately a quarter of a second.
Experiment 1st. - With the Common Davy Lamp.- The lamp, immersed in an inflammable atmosphere, and filled with flame, was moved backwards and forwards, always completing the distance of 11 feet within the second. Taking into account the slightly diminished velocity at the commencement and termination of the movement, and the greater velocity in the middle of it, the lamp moved at rates of from 10 to 12 feet per second during the experiment.
The rapid movement increased the brightness of the gas combustion in the interior of the lamp, but had no other effect, until, by a still greater increase of speed, the flame was extinguished.
2nd. - Repeated the same experiment, after re-lighting the lamp and preparing a new inflammable atmosphere in the box.
The results were as in experiment 1st.
3rd. - Repeated the same experiment with the same results.
4th. - Allowed the Davy-lamp to remain in the inflammable atmosphere until the gauze was above a red heat; and then moved it as before with a velocity of 10 to 12 feet per second. The lamp in motion presented a column of light, brighter than in experiments 1, 2, and 3; and, by increasing the velocity, was extinguished.
5th. - Jerked the Davy-lamp backwards and forwards in the inflammable atmosphere with great velocity, while the gauze was above red heat. At each reversal of the jerk, a flash took place in the interior of the lamp, but no other effect followed, until the lamp was extinguished by the violence of the motion.
In all these experiments the entire lamp was filled with ignited gas, but the flame of the wick continued visible. There can be no question as to the clear character of the experiments.
6th.- Stephenson’s Lamp was extinguished at a much lower velocity than that to which the Davy admitted of being subjected.
7th. - Museler’s Lamp, with a copper chimney inside, was extinguished as in No. 6.
8th. - Clanny’s Lamp (1st experiment). - Moved backwards and forwards without passing any explosion: but was extinguished before being submitted to as high a velocity as that of the Davy experiments.
9th. - Clanny’s Lamp (2nd trial). - Went out after being moved backwards and forwards several times, though kept full of flame for some time without the glass becoming so heated as might have been expected. Velocity of movement much less than that of the Davy.
10th. - Glover’s Lamp went out at 3rd movement (less velocity than the Davy).
11th. - Glover’s Lamp (2nd trial). - Results as in 10th experiment.
12th. - Eloin Lamp (a German lamp), Thornton & Co. - Went out on moving a few times, with much less velocity than the Davy.
13th. - Eloin Lamp (2nd trial). - Went out as soon as it filled.
14th. - Upton and Roberts’ Lamp. - Went out at once in inflammable atmosphere.
THOMAS JOHN TAYLOR.
These experiments prove that whatever motion could be imparted to the lamps moved in a rectilinear direction, had not the effect of producing such a degree of heat as to allow of the passage of the flame through the meshes of the gauze.
The practical results of the whole of these experiments on the different safety-lamps appear to be as follows:
1.- With the Davy-lamp, or with lamps, the insulation of the flame in the inside of the lamp being accomplished by single wire gauze alone, and when the length of the cylinder of gauze is from two to six inches, the diameter about two inches, these lamps are perfectly safe, placed in a still atmosphere of fire-damp. That while so placed the wire becomes of a dull red heat, but such heat does not increase in intensity; and so long as the wires remain in that state of heat, the lamp kept still, and so long as the gauze remains perfect, it will not pass the flame. But it is clear that, in practice, such lamps should not be allowed to remain in such an atmosphere; but on the wires becoming red hot, the lamp should be immediately and carefully withdrawn.
2. - It also results from these experiments, that currents up to ten feet per second of inflammable air, or moving the lamp through an atmosphere of inflammable air at that velocity, has not the effect of increasing the intensity of the heat of the wires so that the flame will pass the meshes; but as we have seen, by these experiments, that an increased velocity, under certain circumstances, does raise the intensity of the flame within the lamp so as to heat the wires to a white heat, and so pass the flame; it follows that it is desirable in practice that the lamp should be properly shielded from the effect of such a current of air, or from the effect of rapid motion; and that, likewise, when the lamp is found to become red hot it should be withdrawn from the gas or current of inflammable air as speedily and as carefully as possible.
3. - And with respect to shields for such lamps and in such cases as the above, it has been shown that a shield three inches in depth encircling the gauze, leaving two or three inches of the cylinder of gauze exposed, is no preventative of the passage of the flame throng the meshes of the gauze, when the velocity of the current of air, or the velocity with which the lamp is moved, is beyond ten feet per second, or such as to raise the heat of the wires from a dull red to a white heat. Either such lamp must not be subjected, as in 2, to such currents or such motion, or the shields should be such as to cover or protect the lamp to such an extent that such currents do not increase the intensity of the flame of gas within the lamp, so as to make the wires o£ a white heat, and so pass the flame. It may be observed, that the shield ordinarily used is only a protection to the flame of the wick of the lamp from the effect of a current of air, or the motion of the lamp; it is not, however, until the whole of the interior of the lamp becomes filled with flame, when the flame leaves the wick, and when it consists of a combustion of the gases, and not the flame of the wick or combustion of the oil, that the danger commences, and that a current acting on such combustion raises the heat of the wires; and then, as shown by the experiments, the ordinary shield of the lamp is of no use in. preventing the increase of intensity of heat produced by a current, or motion of the lamp.
4. - Stephenson’s lamp, and such lamps where the gauze is entirely shielded or covered by glass, allowing only such a quantity of air to pass into the interior of the lamp as is sufficient for the combustion of the wick or oil of the lamp, but not such a quantity of air as will keep up the combustion of the gas within the lamp, are perfectly safe lamps, so long as the shield or cover of the gauze remains perfect. As such lamps are never subjected to a greater heat in the interior of the lamp than that given to them by the flame of the wick, or by the elongated flame produced by the admission of the inflammable air, previous to the air being in an explosive state, the intensity of the heat cannot be raised by any current which can pass through the diminished number of apertures into the interior of the lamp so as to make it unsafe. The principle of such lamps being, that the quantity of air admitted is only sufficient for the combustion of the wick or oil, and not sufficient to keep up the combustion of the gases when the air becomes in an explosive state. When, therefore, the air of the mine becomes explosive, the combustion leaves the wick, and it would then produce a combustion of the gases; and as, in the Davy-lamp, the effect of a current of air acting upon such combustion increases the intensity of the flame, and raises the heat of the wires from a red to a white heat, and so allows the flame to pass. The Stephenson lamp, on the contrary, will not keep up a combustion of the gases, the flame within the lamp being extinguished for the want of a sufficient quantity of air to support such a combustion of the gases.
5. - It has been urged against the Davy-lamp, and those lamps of single gauze insulation without shields, that the dust of the mine, or their being in a dirty, state, renders them unsafe. The experiment No. 2, June 29th, shows that it is difficult to pass the flame through the meshes by throwing coal dust upon the gauze when the wires are red hot, or by spilling oil upon it in that state; but it need scarcely be added, that lamps should not be permitted to be subjected to any such tests when red hot, they should, as stated in 2, be immediately removed and the lamps should be subjected to the requisite examination to ensure their always being in a clean and perfect state.
6. - It has also been objected to the Davy-lamp, or lamps insulated with wire gauze, that they do not afford the requisite degree of illuminating power to allow the workmen to pursue their avocations, and, consequently, insulation by glass or talc has been resorted to. Without adverting here to the degree of safety of such insulating substances, the experiments on such lamps show that if the air is admitted freely into the interior of such lamps by the use of wire gauze tops (such as in the Clanny lamp and the Museler lamp), and where, consequently, the quantity of air admitted into the interior of the lamp is such as to support the combustion of the gases; such lamps, when subjected to currents or motion under the circumstances shown in the experiments, pass the flame. It becomes, therefore, apparent that such lamps present twofold danger, viz., the risk of breakage of the glass, and the danger arising from the intensity of the combustion of the gases within the lamp when subjected to a current of inflammable air, or motion; and it would appear that the remedy for the latter would be to so construct the lamp that such a combustion of the gases cannot exist in the interior of the lamp to produce such an effect. This can easily be done by diminishing the quantity of air admitted into the interior of the lamp, and which, indeed, is done in some of the lamps.
7. - With reference to the use of the glass or talc as insulating substances, the fact of the employment of such numbers of lamps as those, of Clanny and the Museler lamp every day, without any or so few accidents from the cracking or breaking of the glass, would prove that such an insulating substance as glass properly annealed, and the lamp properly constructed, is a safe lamp. The Clanny lamp, in these experiments, when the wire was in a state of nearly white heat had water thrown upon the glass by a jet thrown into the box, the water had the effect of cracking the glass, but the flame did not pass. The glass of these lamps are, however, liable to crack from the expansion when subjected to great heat, where proper care has not been taken to allow of the free expansion of the glass in the construction of the lamp; but this is easily remedied.
8. - Lamps have been produced, such as Dr. Glover’s, with two cylinders of glass, the air being admitted into the interior of the lamp by passing between the cylinders, for the purpose of keeping the glasses cool - and some lamps with water between the glasses. No doubt double glasses add to the security, but if such lamps have an unprotected wire gauze top, the effect of the heat of the combustion of the gases is much beyond the cooling effect of any air passing between the glasses, and the intensity of such heat, besides adding to the risk by the flame passing the gauze, also tends to heat and crack the glass. These lamps do not necessarily require wire gauze tops, as brass or copper tops, such as are used in the Eloin lamp, may be adopted. Double wire gauze tops such as T. Y. Hall’s and Dr. Fife’s lamps, have been used, counteracting to a certain degree, the effect of interior combustion, as the outer cylinder of gauze, not being subjected to the direct action of the flame, remains free from injury.
9.- It would appear, as a summary of all these results, that if the Davy-lamp is used, or lamps, the insulation of which is accomplished by cylinders of wire gauze alone, proper precautions should be enforced for their careful removal when the internal combustion of the gases take place, or when the wires of the gauze become red hot, as the margin of danger is between the wires being at a red and becoming of a white heat. Or that shields of glass or other materials should be used in such lamps, to so diminish the quantity of air or gas admitted into the interior .of the lamp, that active combustion of the gases cannot exist, so as to raise the heat of the wires from a red to a white heat:- taking care of course, that the lamp is supplied with the requisite quantity of air, when the atmosphere of the mine is at, or just below, the inflammable point, to support the combustion of the wick or oil. With such a lamp, when the mine becomes explosive, the gas will explode in the lamp, combustion of the gases will commence, and the flame will leave the wick; but as there is not a sufficient quantity of air admitted to keep up a continuous combustion of the gases, the flame will be extinguished, and, consequently, the wires can never become of a white heat or the lamp become dangerous.
And, that in all lamps where glass is used as the insulating medium, the admission of air into the interior of such lamps should be so diminished as that active combustion o£ the gases cannot take place within the lamp; and, more particularly, that tops of single wire gauze unprotected, and therefore liable, in explosive mixtures of gas, to the objections heretofore stated, should be avoided.
From: The North of England Institute of Mining and Mechanical Engineers Transactions, Vol. I (1852-3), p. 301-322