# Popular Science Monthly/Volume 15/June 1879/Are Explosions in Coal Mines Preventable?

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* ARE EXPLOSIONS IN COAL MINES PREVENTABLE?
By FRANCIS R. CONDER, C. E.
THE heaviest tax that can be imposed upon a nation is one that is paid in human lives. From whatever point of view the subject may be regarded, this conclusion is irresistible. If we look at it according to purely economical considerations, we may obtain very remarkable results. It has been estimated that an actual money cost of £300 is incurred in raising a boy, cradled among the poorest classes, from birth to manhood. It does not require us to ascend very high in the social scale before we find that this estimate must be trebled. If we take what we may call the cost price of the human unit at any definite time, say at £500 on arriving at maturity, the producing power of the unit in question will bear some relation to that sum; the more costly and careful education producing, as a rule, the more valuable result, as to productive power. If the laborer who earns 14s. or 15s. a week adds £50 per annum to the wealth of the country, the physician, the scientific military or naval officer, the barrister, or the engineer, may look forward to the time when his yearly labor will be worth more than a hundred times that amount, even if appraised only by the price he is actually paid for his time. Taking any producing individual, whether valued at £50 or at £5,000 per annum, at any period of his career, no income tax to which he can be subjected can approach in its pressure the extravagant tax of death, For the payment of that tax at once annihilates the total earning power of which there was, until that moment, a fair mathematical expectation.
The tax upon human life which is caused by war is one as to which philosophers and philanthropists have long written, and as to which generation after generation has complacently declared its own advance on its barbarous ancestors; although generation after generation has too often seen increasing holocausts offered on the altar of battle, with continually less and less excuse—the word justification it is too often but a mockery to use. We have seen, not so very long ago, that peace has its death tax as well as war. And we wish to call attention to a tax of this nature which, as far back as statistics have been collected, appears to be paid in this country with a grim and appalling regularity.
Regularity, that is to say, when viewed in the light of statistical returns. From any other point of view the deaths of which we speak occur with the most frightful and unexpected caprice. There may be a period of months during which none of the calamities which quietly occur are brought under public notice. Then there may be a terrific telegram, and an announcement in the largest letters used by the daily press, "Frightful calamity at a coal mine—sixty lives lost!" Again, ​at another time, three or four minor calamities occur on the same day, at different spots; or within a few hours or days of one another. The public is, no doubt, deeply moved by these announcements. Free and charitable aid never fails to be forthcoming for the widowed and orphaned survivors of a colliery massacre. The question is ever newly raised, "Can nothing be done to prevent these terrible disasters?" Legislators try their hands at prevention. Men of science try their hands at prevention. It is pointed out authoritatively that much of the loss of life thus occurring is preventable loss. Robert Stephenson, when admittedly standing at the head of his profession, being himself a large colliery owner, and having for several years of his life had to descend a coal-pit at 4 a. m. daily, to visit all the workings of the mine, declared that there was hardly a colliery in England that might not be worked with perfect safety from explosions; and pointed out that the great means for insuring safety was to quadruple the shaft area in every colliery. And yet the slaughter goes on! In 1864 it was at its minimum. Only 857 lives destroyed in coal mines are reported for that year, being at the rate of a human life for every 110,000 tons of coal raised. In 1866 it attained its maximum, the lives lost amounting to 1,484, or one for every 68,000 tons of coal. From 1861 to 1875 inclusive, 15,908 lives were lost in raising 1,608,576,193 tons of coal, being very nearly a thousand deaths in each year. Roughly speaking, the life tax is at the rate of a life per 100,000 tons of coal.
The comparison of the number of men employed, of tons of coal raised, and of lives lost, year by year does not appear to throw much light on the subject. Such a comparison, indeed, shows a steady decline in the industrial and productive power of the colliers. But no relation is discernible between the out-put per man, taken as indicating either the number of hours worked on the average, or the industry exerted in these hours, and the death rate. From 1861 to 1866 occurred a steady increase in the productive power, not only of the collieries of Great Britain, but of the individual colliers. In 1861 the total yield of 86,039,211 tons of coal was produced by 282,473 men, being at the rate of 305 tons of coal per man. In 1866 the yield had risen to 315 tons per man, and in 1870 to 321 tons per man. From this year the productive power of the miners has decreased, although that of the collieries has continued to advance. In 1874 each miner only raised 249 tons of coal. In 1875, 133,306,486 tons of coal were raised by 525,843 men, being at the rate of 253 tons apiece. Thirty years previously, in 1845, the number of tons of coal raised in the year was 31,500,000. An increase to a fourfold amount, when the figures attained are so large, is probably without a parallel in productive industry. In 1840 about 700 collier vessels were employed in the London trade. Their average cargoes were 220 tons. In 1876 the fuel shipped to foreign countries amounted to 16,299,077 tons, and that sent coastwise to 11,015,178 tons.
​At the time when the details of the coastwise coal trade were discussed by the Institution of Civil Engineers, in the presence of Mr. Robert Stephenson, in 1855, so little was it anticipated that railway conveyance would compete with the sea-borne traffic in coal for long distances, that the possibility was not even suggested in the debate. The Great Northern Railway was then open to Doncaster, and the coals conveyed over the line were enough to make the gross weight passed over the up lines as 1·74 to 1, the cost of maintenance being as 1·98 to 1. Mr. Carr observed that more damage was done to the permanent way, as might be supposed, by the extreme loads of the coal trains than by ordinary goods and passenger trains, and said that "this would account for the deterioration increasing more rapidly than the tonnage." Mr. Stephenson stated that the wear and tear of the way was proportionate to the number of pairs of wheels that ran over it, and to the weight on those wheels; and declared on another occasion that he could not, as a man of honor, be a party to the carrying of his own Clay Cross coals on the London and Northwestern Railway, at the freight of one halfpenny per ton per mile, as such a rate was injurious to the railway company.
To return to the casualties of the coal mines. The most terrific form of destruction, that of explosion, is not the most fatal, numerically regarded. Taking an average of fifteen years, twenty per cent, of the fatal casualties were attributable to explosions, thirty-three per cent, to falls of coal and of roof, fifteen per cent, to shaft accidents, and the rest to miscellaneous causes. Thus of the tax of ten lives per million tons of coals, the fifth part, or two lives per million tons, may be regarded as deaths that are certainly preventable by the due enforcement of those provisions which the mining engineer decides to be proper. In the years 1867-'69 the mortality from explosions amounted to twenty-nine per cent, of the whole. The general average for those years shows a death rate of one life per 84,000 tons of coal; so that we may regard the effect of the precautionary measures taken by the Legislature as having effected a saving of about a third of the number of human lives that would otherwise have fallen victims to explosions.
The question not unnaturally arises, What is the real cause that leads the miner to affront a peril of this frightful magnitude? It is all very well to speak of recklessness of life, of objection to innovation, of ignorance of scientific principles, and the like, but those who are most familiar with the working classes will be the least disposed to admit that the true knot of the question can thus be cut. It requires no instruction in chemistry for the miner to be made acquainted with the fact that the vapor (if we must not use the word gas) that be sees burning brightly as it issues from the coals in his kitchen fire is apt to issue from the face of certain coal mines, and that it will take fire in the mine as readily as in the grate. He may not be, and probably is ​not, aware that this fire-damp is composed of about one third hydrogen and two thirds carbon. He may be ignorant that the proportions of admixture of fire-damp with ordinary air which are such as to cause explosion are, when the former is more than one fourth, and less than one sixteenth, of the quantity of the latter. But he knows that when he enters a fiery mine his life is in his hand, he may not know that the barometer indicates a more or less dangerous condition, as a rule, in every fiery mine. But he does know that any blow of his pick may open a "blower," or jet of fire-damp, in the mine; that if this jet meets a naked light it will take fire; and that unless the ventilation sweeping through the mine be such as to maintain a complete control over the issue of the fire-damp, which is always to a certain extent going on, the workings will be wrapped in a blast of flame, and none will be left alive to tell how it occurs. He knows, too, that the "Geordie," the invention of an old miner, whose name should be held in honor by the British workman as that of a family saint or household god, instead of setting the "fire-jack" alight, will indicate its presence by a harmless explosion within its own tube, and will then become extinguished. Or if the mine in which he works be one in which the "Davy" lamp is used, instead of the "Geordie," he knows that the little cage of wire gauze will become filled with flame if placed near a "blower" or held in the top of a working where there is too much gas to be safe, but that the flame will not pass through the meshes of the protecting shield. His is not the class of mind which can be brought to regard the safety-lamp as a talisman, giving protection to the miner who works with a naked light close by his fire-proof companion. It is more than probable that the increased safety from explosions to which we have referred may be mainly, if not altogether, due to the action of the Government inspectors in preventing the use of powder in fiery mines. Where blasting is allowed, the onus of responsibility is taken from the shoulders of the miner, and thrown on those of the superintendent. But, in the last two terrible casualties which have brought desolation to so many homes in the Black Country, there has been no question of blasting. A sudden outpour of fire-damp must, in each of these cases, have come in contact with a naked light. In cases where no miner has been left alive to tell the tale, there has often been found a mute but unimpeachable witness. A lamp has been found unlocked, a candle half burned, a box of matches half consumed. One or more of the miners, in spite of regulation, in spite of inspection, in spite of peril of his life, has had a naked light in his possession. What can have induced him to run the risk?
It is not surprising that the question should have proved utterly insoluble to those who have never been underground; nay, more, to those who have never worked underground. In the absence of that personal experience which throws a very strong ray of light on the obscurity of the question, it is easy to take a leaf out of the book of a ​certain group of teachers, and throw the whole blame on the "depravity of human nature." True, it is not conducive to delicacy of feeling or to accuracy of scientific perception to toil for hours together in the Cimmerian gloom of the coal mine. Very little idea can be formed, by forty-nine fiftieths of the population of this country, of the cost of human toil at which their houses are kept warm and bright. Especially when the coal is worked in thin beds is the toil of the miner all but intolerable. In some instances he actually lies full length on the floor of the working, clad in nothing but a scanty pair of drawers, working with his pick a little in advance of his head as he lies. Nor does he cast off the badge of toil when he returns to the light of day. The other day a colonel in the army, a man deeply interested in all mechanical and scientific improvement, who was staying in one of the great mining centers, happened to go to a public establishment in the town in order to take a Turkish bath. While he was waiting for his room, two miners came out, who had been enjoying that unusual luxury. "I say, Jack," said one of them, "Moll won't know me. She never saw my skin white." His wife had never seen him washed, except his face. This may be an extreme case; as in some of the Welsh districts the "tubbing" of the men on the Saturday night takes place before the doors of their houses. But we give the incident as it actually occurred.
But pass all this. Let us attribute to the miner as extravagant a perversity of nature as the most zealous missionary can insist upon—he is at all events something better than a beast. Even a beast has the instinct of self-preservation. In man it is, there can be no denial, usually the very keenest of his instincts. And whatever the miner may know, and of whatever he may be ignorant, from his first apprenticeship underground he has had held up to his imagination the fearful and ever-present peril of the fire-damp. Abuse him as we may—and for our own part we should be very sorry to speak of him in any terms but those of cordial respect—we have not got a single step on our journey toward the solution of the question, What makes him run a risk that he knows to be hazardous?
Reader, have you ever been underground—not for amusement or out of curiosity, but in the discharge of your duty? If so, have you ever been alone underground, in a solitary point of the workings? And, if so, have you ever, by any accident, found yourself left in total darkness. The writer has had this experience, and it is one that leads him to speak with somewhat more of human sympathy for the collier than might be natural for a literary man who is not also a workman.
The oppression of utter darkness on the human organization is terrible. And hardly less than the oppression of utter darkness is the irritation produced by inadequate light. When, as they begin to number seven times seven years, the gradual diminution in the focal length of the vision often suffers a rather rapid increase, persons who ​have had the disagreeable experience know that the first intimation that they must have recourse to spectacles is one of the most painful experiences of ordinary human life. At all times the want of sufficient light to see by is a hard trial. The more need there is of attentive vision, or the more the eye perceives the failing of its own power, the more intolerable is the hardship. Now, in mining the attention has to be kept vividly directed to the effect of every blow of the pick. There are many kinds of work which can be done with but little exertion of eyesight. Mining is not one of them. In a fair face of coal the operation of "getting," as it is called, may be a straightforward one; but this is far from being always the case. We have seen, too, that it is not always to the face of the coal that the chief care of the miner has to be directed. One third of the lives lost are due to falls, of face or of roof. With every blow of the miner's pick that danger has to be borne in mind. It is a danger increased tenfold by obscurity. The experience of our public works is enough to prove that, if the workings of our mines could be made as light as day, both shaft accidents and accidents from fall of roof would be enormously diminished in number. Does the reader know how the miner has to ascertain whether the roof is coming in upon him, or whether the "creep" from below is overpowering his hastily fixed props and polling boards? We can tell him from experience.
A piece of damp clay is, or should be, always at hand in a mine. Frequently it is to be met with in the workings. If not, some should always be brought down. In cases where there is no fear of explosion, and indeed in all cases fifty years ago, a bit of wet clay forms the usual miner's candlestick. In cases where luxury is studied, a bit of wood with a hole in it carries the "farthing dip." But even this fastidious candlestick, if it has to be set down on the ground, is made secure from a casual overset by a dab of wet clay. Now, if any undue cracking is heard in the timbers, or if a rattle from above gives warning that the roof is not altogether in a stable condition, what does the miner do? He smears a bit of wet clay into any crack that he observes in a prop, polling board, or junction of the timbering of the mine, and then quietly watches, to see whether the damp clay cracks. If not, it is probable that the timbering is sufficient for its work. If it does, the timbering has, in all haste, to be strengthened. Peril of life is on the one hand, anxiety to see as clearly as possible on the other. The miserable ray thrown by the miner's lamp seems only to mock his anxiety. Is there any wonder if he affronts the more distant peril in his desire to avoid the more threatening one? His nose, he may think, will give him timely warning of the neighborhood of "fire-jack." To guard against the more fatal danger of roof-fall he has only his eyes. Is there any wonder that he seeks for more light, even at the risk of a naked flame?
We do not, of course, for a moment intimate that it is only for the ​sake of looking to the safety of the roof that the miner has a naked light when he ought not to have one. But we think that there is little doubt that such is often the case. And we mention this only as one of those countless occasions, known only to those who have had subterranean experience, in which the desire for more light than that afforded by the ordinary safety-lamp may become uncontrollable. Our argument is, that some strong instinct of human nature must be at work in order to lead the miner to affront the known danger of explosion from the use of naked lights so frequently as we have but too much evidence that he is in the habit of doing. And we think that there is enough to account for this in the instinctive desire for light, and more especially in the maddening effect of obscurity when accuracy of vision is required.
If we have thus rightly judged, the first effect of the remark should be to remove a very heavy load of obloquy under which our colliers as a body have hitherto labored. More than that, the more any public writer has been acquainted with the chemistry of the coal mine, the louder has usually been his condemnation of the recklessness of the miner. No doubt, from the chemist's point of view, there is but too much reason for this. Avoid naked light and avoid blasting, and you avoid explosion. This logic is undeniable. But the chemistry of the mine is not the matter which most directly presses upon the miner. The mechanic, the physiologist, the optician, each has to be consulted. Grim fact shows that the chemical danger is, and always has been, affronted. The need of light explains why this has been the case. What, then, is the outcome of the whole inquiry?
It is this: The miner requires light. It is now half a century since science has done much to aid him in this respect. It was in or about the year 1815 that Sir Humphry Davy and George Stephenson entered on their honorable rivalry as to the safety-lamp. Foreign engineers have provided, in the lamps used in the deep Belgian mines, a sort of compound of the "Geordie" and the "Davy," under the name of the Mueseler lamp. MM. Liaute and Denoyel have invented an electric lamp, perfect as a scientific toy, but too cumbersome and liable to derangement for the rough usage of the miner. What is required is a lamp which shall at the same time give abundant light and afford perfect protection. It must not be cumbersome; it must not be heavy; it must not be costly. Miners have been known to dash in pieces the Upton and Roberts safety-lamp, merely from the irritation caused by its weight. If the miner can be provided with a lamp which, with the safety and the convenience of the "Davy," can give the light of eight or ten candles, can throw that light where it is wanted, and can do that at a moderate cost, the saving of life in our coal mines will be very great. For, by such an appliance, not only may the mortality caused by explosions be prevented, but that due to falls of roof, if not to other causes, may be most materially diminished.
​This points to the inquiry, What is the true source of light? From what materials, as matter of principle, and apart from any question of the state of the science of illumination at the moment, is artificial light more certainly to be obtained?
To that question the reply is simple. We know, as matter of chemistry, what kind of combustion produces the greatest amount of light, as we also know what produces the greatest amount of heat. The two are by no means identical. Light can not be produced without the liberation of heat. On the other hand, a very high degree of heat can be developed when, little or no light is produced. As matter of principle, this is the key to the question now to be reviewed.
We need not at the moment step aside to inquire into the future of the electric light. As to the cost at. which that elegant source of concentrated brilliancy may be maintained, we are in the way of having experimental proof. The first great trial in London, that of the Jablochkoff candles at Billingsgate Market, has proved a failure, as regards both the quantity and the quality of the light produced, as well as with reference to the cost of production, and has in consequence been abandoned. But, be the cost of producing an equal quantity of light by the new or the old fashioned process of combustion the greater, the former is out of the question as far as coal mines are concerned. A brilliant light at the bottom of the shaft would of course be a great desideratum. But no one who has studied the plan of the workings of a coal mine can fail to be aware that nothing will supersede the miner's lamp. Each man who works at the face must be provided with his own light; and no general illumination, were such possible, would make up for the want of this. In vast underground caverns, such as that of the Peak, in Derbyshire, or such as those of some of the Cheshire salt mines, a brilliant and concentrated light may, no doubt, be extremely effective. But in speaking of the working of collieries, whether in the "long wall" system or on any modification of the "pillar and stall," we must look to such a lamp as each miner can carry for himself.
In speaking of illumination, we are as yet without any unit of light. Our measurements in this respect are made pretty much by rule of thumb. The sperm candle, burning or supposed to burn at the rate of one hundred and twenty grammes per hour, is our nominal unit. In ascertaining the illuminative power of gas, two of these candles are used by way of measure. But there is no check as to the accuracy of their consumption. The use of a screen made diaphanous in one portion by a little grease enables the analyst to form a very accurate appreciation of the illuminative power of two lights. The screen is placed between the two, and moved backward or forward until the spot caused by the grease vanishes, which is the case when the intensity of the transmitted is exactly equal to that of the reflected light. By accurately measuring the distances, and applying the rule that the ​intensity of the radiant center is inversely proportionate to the square of the distance from the screen, a very reliable comparison is attainable. But the weak point is the variable and ill-defined character of the unit of comparison. In the French experiments this defect is to a great extent avoided by the use of a Carcel lamp, which not only is intended to consume a given quantity of oil per hour, but is further weighed at the commencement and at the close of each observation, so that a correction is made in case of any variation in the actual combustion. Still, the Carcel lamp is an arbitrary unit. It is equal to about 9·6 English standard sperm candles; but when we have said that, we have only compared one arbitrary unit with another. In the case of the unit of heat, although it has been arrived at in terms of capacity (as regards the water heated) and of Fahrenheit's thermometer, which is in itself an arbitrary scale, it so happens that the Joule equivalent is exactly equal to the quantity of heat that is liberated by the combustion (if chemically perfect) of half a grain of carbon. If we take the same unit for the measurement of light, it must further be specified that the combustion of the carbon must be so effected as to produce carbonic acid and not carbonic oxide, and that it must take place in atmospheric air, and not in pure oxygen, or any other medium. That being borne in mind, it is probable that the combustion of a definite quantity of carbon would prove a better measure of light than any that has yet been tried. It would, at all events, link the phenomena of luminiferous to those of calorific combustion, and afford a ready means of detecting waste of illuminative power.
Various analyses have been given of ordinary coal-gas. Indeed, not only does that gas vary according to the quality of the coal from which it is-produced, but it differs according to the process by which it is produced from coal of the same quality. Experts are divided, for example, as to the degrees of heat at which it is best to effect the distillation of coal-gas. But for our present inquiry it is enough to assume the composition of coal-gas as analyzed by Mr. Vernon Harcourt, who gives the proportions of fifty-eight per cent, of carbon and twenty-three per cent, of hydrogen. The details are given by Mr. D. K. Clark, in his invaluable work, the "Manual of Rules, Tables, and Data for Mechanical Engineers." Of this gas thirty cubic feet, at the temperature of 62° Fahr., weigh one pound. And the heating power of one pound of this gas (chemically speaking) is given by the same analyst at 22,684 British units of heat, of which sixty-three per cent. is due to the combustion of the hydrogen, and thirty-seven per cent, to that of the carbon. It thus follows that coal-gas is far more highly effective as a fuel than it is as a source of illumination. Other analyses give a yet higher proportion of hydrogen, the heat-giving element.
There is, however, a mineral fuel in which this distribution of the elements is very different. Petroleum is a natural fluid, consisting of hydrogen and carbon, which has been distilled in the great laboratory ​of nature, and which exists in large quantities in various parts of the world. It is, comparatively speaking, a very recent discovery. The first well was sunk in Pennsylvania in 1858. The first "flowing well," or bore hole from which the rock oil flows naturally, dates in 1861. From that date the annual production has increased with marvelous rapidity. In 1878 it was computed that several hundred million gallons were annually raised, although only about one-half per cent, of the 2,000 square miles of area in which the mineral oil is to be found was then worked. The oil is also known to exist in Virginia, in Ohio, in Kentucky, in California, in Canada, in South America, in China, in Japan, in Java, on the north coast of Africa, in Italy, France, Austria, Wallachia, Turkey, and Russia. There is every reason to suppose that an unfailing supply might be obtained by boring in the valley of the Jordan, in which rapid stream masses of bitumen are often found borne down to the salt waters of the Dead Sea. On the shores of the Caspian it is found in such abundance that it is used as fuel for steamers. At Cheeriley, about twenty-five miles to the west of Kertch, it is stated by Mr. Ross that there are five wells owned by an Englishman, two of which produce about one hundred and thirty-five barrels of petroleum daily. Bitumen and bituminous shales producing oil are to be found in every country of Europe, and there is good reason to suppose that the existing stores of the liquid mineral are no less ample than those of the solid beds of coal.
As to cost, the crude petroleum oil is sold at the mouth of the wells, in Pennsylvania, at from 10s. to 15s. per ton, or from 12d. to 34d. per gallon. The refined petroleum at New York is worth about 6d. per gallon, but half of this is the price of the casks or other vessels that contain it. If a large and steady demand were to set up, it would be easy to construct ships of which the hold should be composed of a series of air-tight compartments, in wrought iron, into which the oil might be turned directly by means of mains, like gas or water mains in our cities, and from which it might be pumped on its arrival in the Thames or in the Mersey. The cost of the delivery of this liquid fuel may thus be expected to be, hereafter, less per ton than that of coal. It only needs the first expense, that of sinking the shaft. It will then mine itself, raise itself, carry itself, and may be made to load itself on shipboard. As to the cost of the process of refinement, we are without adequate information. But, in the event of a brisk demand for the refined oil, there can be little doubt that the usual course of manufacturing industry would be followed, and that an economical method would be applied.
It is thus of interest to compare the respective properties of coal, coal-gas, and petroleum, both as regards their lighting and their heating capacities, as far as the present state of definite scientific information attainable will allow us to do so.
​Coal has now receded in England to the old minimum price of 4s. 6d. at the pit's mouth. Some of our northern railways are paying 6s. a ton for coal. The price of the best Wall's End coal delivered at private residences in London, at the end of January, 1879, was 29s. per ton. Thus, even in the three hundred miles which divide the metropolis from the pit's mouth, it will be seen that the price of coal is so regulated by local conditions, and distance from the collieries, that it is not easy to strike an average. We may therefore assume a price, equal to that of petroleum, of 10s. per ton, for the sake of comparison, and it will then be easy to apply the correction due to the price of coal in any particular spot. The undetermined charges for interest on capital, merchants' profits, and delivery to consumers, may also be roundly taken, for the sake of comparison, as equal for the different materials.
The cost of the manufacture and distribution of gas in London (exclusive of the cost of coal) is about twenty per cent. over the amount realized for the sale of the residual products of distillation, of course excluding the gas. 10,000 cubic feet of gas per ton is a high, though not the highest, production. The price of the residual products, as a rule, is so far regulated by the price of coal at the spot, that it is usually reckoned that the local price of gas in England is nearly independent of the local variation in the price of coal, sales balancing purchases. Thus, if we take 10,000 cubic feet of gas as costing the same as one ton of coal, we shall be within twenty or twenty-five per cent. of exactitude, as a general rule. We have, then, to compare the luminiferous and calorific value of a ton of coal, a ton of petroleum, and 10,000 feet of cubic gas, assuming the approximate price of each of these quantities to be equal.
For lighting purposes, indeed, coal is nowhere. It has been occasionally used for giving light on public works, such as railways, when it was necessary to carry them on by night. But the light of a "devil," or iron basket of live coals, is fitful and costly. As recently as 1815 the dangerous Bell Rock, at the entrance to the Firth of Tay, was lighted by a fire-basket, or "chauffer," of live coals. It is stated in the "Life of Robert Stevenson," the great lighthouse engineer, that the consumption of coal in this "chauffer" was four hundred tons per annum, while the light was never reliable when most required. In violent gales the coal never burned on the windward side of the fire; and the guardian actually laid hold of the bars of the "chauffer," on the windward, to steady himself while putting on more fuel. Thus, in the direction where, and at the time when, the light was most required, it was all but totally invisible. The gas requisite to maintain a light equal to one hundred Carcel burners, or nine hundred and sixty candles, for twelve hours, is producible from half a ton of coal, as distilled in the gas-works. This would yield a splendid light (if the locality were such as to allow of its introduction); while the consumption of twenty-two hundred weight per night of coal only made darkness visible.
​As to the calorific properties of coal, it is well known that the theoretic quantity of heat that should be chemically liberated by the consumption of a given quantity of that fuel is more than ten times as much as that which is ordinarily obtained, even by well-constructed steam-boilers. For a pound of coal to evaporate eight pounds of water may be taken as a very favorable average. In domestic consumption there is nothing approaching to this economy of heat. A considerable quantity of unburned carbon passes up the chimney in the form of smoke; and probably three fourths of the heat actually liberated by combustion is carried off in the same manner by the draught.
According to the experiments made by Mr. Vernon Harcourt, before referred to as quoted by Mr. D. K. Clark in his "Manual of Rules, Tables, and Data," a pound of gas, with a volume of thirty cubic feet, will evaporate thirty pounds of water from 212°, or 21·4 pounds from 62°. This gas is reckoned at 9,000 cubic feet to the ton of coal; so that the evaporation (of one pound of water by one cubic foot of gas) is effected by the quantity of the latter derived from almost exactly a quarter of a pound of coal. At the more ordinary allowance of 10,000 cubic feet per ton, ·224 pound of coal yields a foot of gas. It has to be borne in mind that only about thirty-six per cent, of the coal ordinarily used for gas is volatilized in the process of distillation. Of the coke, which is the chief residual product, from fifty-eight to ninety-three per cent, is carbon; sulphur and other impurities going to make up the rest of the bulk. There are produced on the average thirteen and one-half hundred weight of coke, and ten gallons of tar, from a ton of coals, besides the gas. The calorific and luminiferous values of these residual products are thus much greater than that of the gas itself. But a better use can be made of tar than to burn it; and we have considered the value of these products as absorbed by the cost of the process of making gas.
With these qualifications, the calorific effect of the gas produced from a pound of coal is about half that which would be produced by the burning of a pound of coal under a well-constructed boiler, where of course both coke and tar are consumed together with the gas. But in cases of domestic consumption the economy in the use of gas will be immense. There is no waste, no smoke. Instead of seventy-five per cent, of the heat going up the chimney, nearly all will be directly utilized. There is no loss of heat in lighting the fire; none in cooling when the work is done; no labor in the carriage of coal to the furnace; none in the removal of the ashes. Bearing: in mind all these sources of economy, the domestic use of gas for heating purposes is so advantageous that it is extraordinary that the introduction of so clean, cheap, and manageable a source of comfort should make such slow progress in England. In America the improvement is more rapid and more general.
​For luminiferous purposes we have seen that there is no comparison between the consumption of crude coal and that of coal-gas. Allowing the mean proportion of 10,000 cubic feet of gas to the ton of coal which we have before taken, the consumption of an ordinary gas-burner, whether an argand or a fish-tail, is about five cubic feet per hour, giving a light of from twelve to sixteen candles, according to the richness of the gas. If we take Mr. Vernon Harcourt's analysis, thirty cubic feet, or one pound of gas, contains 4,060 grains of carbon. Five cubic feet therefore contain 67·6 grains, which will be the hourly consumption of pure carbon in an ordinary gas-light.
Petroleum, however, contains from eighty-two to eighty-seven per cent. of carbon, and from eleven to fifteen per cent. of hydrogen. Averaging this at eighty-four per cent. of the former and thirteen of the latter, a pound of petroleum contains 6,080 grains of carbon and 910 grains of hydrogen. Its luminiferous power is thus almost exactly fifteen times that of coal-gas, taking equal weights. Its calorific power, supposing a perfect combustion, will be ten per cent. less than that according to Mr. Vernon Harcourt's estimate, and less than half that of the highest estimate given by Mr. Clark.
It is thus as clear as any deduction from chemical data can be, that while the economy in the use of coal-gas as a source of heat is so great as to render it worth while to keep up the distillation of this product, as now carried on, for calorific purposes alone, even exclusive of its use for a light, for the purposes of illumination petroleum offers an immense advantage over coal-gas, its illuminating powers being as much as fifteen-fold. And when we are speaking, not of an organized system of fixed lights, but of the convenience of a hand lamp, the price and the illuminative value of petroleum indicate it as the source of the economical light of the future. In fact, its light-giving power is ten per cent. more than that of either tallow or olive-oil, and four per cent. more than that of wax, weight for weight, notwithstanding the great difference in price.
The question of the miner's safety, then, resolves itself into the construction of a petroleum lamp, which shall have the safety of the "Geordie," while giving the light of one, or even of two or three fish-tail burners of gas, and which shall be so made as neither to empty nor to be extinguished if laid on the side.
It is desirable, in an inquiry of this nature, to avoid anything that assumes the appearance of advertisement, or of an attempt to introduce anything of a commercial bearing. For that reason less must be said than honestly and fairly might be said as to the principles on which such a lamp may be unquestionably constructed. Two or three patents exist, which would require due consideration. It is always, indeed, doubtful how far recent patents will stand the test of thorough investigation. The latest patents for electric lighting are now found, in many cases, to be reproductions of methods long since introduced and ​abandoned. Moreover, it may be hoped that if it were found that a great national benefit, such as a true miner's lamp would be, involved either a long delay before it could be offered to the collier, or serious compensation for an unexpectedly valuable patent right, no very exorbitant claim would be raised to avoid the saving of a human life per day.
The one simple principle on which a lamp, whether a safety-lamp or any other, may be made to yield the full light due to the perfect combustion of the carbon of its aliment, is one long known to the miner as applied to ventilation. A single shaft will not ventilate a mine. In the same way, if a lamp or a candle be surrounded by a glass shade only open at the top, it will not burn properly. The taller the glass chimney the redder and dimmer will be the flame, until it is actually extinguished by the product of its own combustion. This is usually avoided by a free admission of air below the chimney, which is not practicable in a safety-lamp. But if for one shaft two be substituted, or even if the single shaft be divided—the miners call it "bratticed"—into two vertical sections, a little heat will produce an upward current in the one, which will be fed by a descending current in the other. The lamp is only the mine in miniature.
Very brilliant results have already attended the introduction of a lamp constructed in accordance with this simple law, in the illumination of railway carriages. No mechanical man can doubt that a modification of the lamp now used in the royal saloon carriages might put in the hands of the miner a real life-preserver. It would be a lamp which, while impenetrable to fire-damp, or rather impenetrable from within as a source of explosion, would give him what he now wants—light in the darkness of the mine.
We have seen that, out of the half million of colliers, to whose perilous labors we owe the warmth and comfort of our homes, the speed and regularity of our traveling both by land and by sea, and the aliment of that mighty host of mechanical horses which now perform the bulk of the sheer hard labor required above-ground in the United Kingdom, a tax on human lives at the rate of at least ten lives per million tons of coal is exacted with much regularity. From a fourth to a half of these lives are sacrificed by preventable calamities. It is by satisfying the mute instinctive demand of the miner for light, in his painful and dangerous toil, that these casualties which are preventable can alone be certainly prevented. Is it necessary to say more in order to turn the attention of the collier and of the engineer, of the man of capital and of the man of science, of the economist and of the philanthropist, to the urgent question of providing the miner with a safe, convenient, and luminous lamp?
P. S. Since the above was in type, has appeared the announcement of a Royal Commission of Inquiry into Mining Explosions, to the attention of which the above remarks may be respectfully commended.—Fraser's Magazine.