The Story of a Piece of Coal - Part 4

Part 4

The honour of first accomplishing the task fell to Mr Hannay, of Glasgow, who succeeded in producing very small but comparatively soft diamonds, by heating lampblack under great pressure, in company with one or two other ingredients. The process was a costly one, and beyond being a great scientific feat, the discovery led to little result.

A young French chemist, M. Henri Moissau, has since come to the front, and the diamonds which he has produced have stood every test for the true diamond to which they could be subjected; above all, the density of the product is 3.5, _i.e._, that of the diamond, that of graphite reaching 2 only.

He recognised that in all diamonds which he had consumed--and he consumed some 150 worth in order to a.s.sure himself of the fact--there were always traces of iron in their composition. He saw that iron in fusion, like other metals, always dissolves a certain quant.i.ty of carbon. Might it not be that molten iron, cooling in the presence of carbon, deep in volcanic depths where there was little scope for the iron to expand in a.s.suming the solid form, would exert such tremendous pressure upon the particles of carbon which it absorbed, that these would a.s.sume the crystalline state?

He packed a cylinder of soft iron with the carbon of sugar, and placed the whole in a crucible filled with molten iron, which was raised to a temperature of 3000 by means of an electric furnace. The soft cylinder melted, and dissolved a large portion of the carbon. The crucible was thrown into water, and a ma.s.s of solid iron was formed. It was allowed further to cool in the open air, but the expansion which the iron would have undergone on cooling, was checked by the crucible which contained it. The result was a tremendous pressure, during which the carbon, which was still dissolved, was crystallised into minute diamonds.

These showed themselves as minute points which were easily separable from the ma.s.s by the action of acids. Thus the wonderful transformation from sugar to the diamond was accomplished.

It should be mentioned that iron, silver, and water, alone possess the peculiar property of expanding when pa.s.sing from the liquid to the solid state.

The diamonds so obtained were of both kinds. The particles of white diamond resembled in every respect the true brilliant. But there was also an appreciable quant.i.ty of the variety known as the "black diamond."

These diamonds seem to approximate more closely to carbon as we are most familiar with it. They are not considered as of such value as the transparent form, but they are still of considerable commercial value.

The _carbonado_, as this kind is called, possesses so great a degree of hardness that by means of it it is possible to bore through the hardest rocks. The diamond drill, used for boring purposes, is furnished around the outer edge of the cylinder of the "boring bit," as it is called, with perhaps a dozen black diamonds, together with another row of Brazilian diamonds on the inside. By the rotation of the boring tool the sharp edges of the diamonds cut their way through rocks of all degrees of hardness, leaving a core of the rock cut through, in the centre of the cylindrical drill. It is found that the durability of the natural edge of the diamond is far greater than that of the edge caused by _artificial_ cutting and tr.i.m.m.i.n.g. The cutting of a pane of gla.s.s by means of a ring set with an artificially-cut diamond, cannot therefore be done without injuring to a slight extent the edge of the stone.

The diamond is the hardest of all known substances, leaving a scratch on any substance across which it may be drawn. Yet it is one whose form can be changed, and whose hardness can be completely destroyed, by the simple process of combustion. It can be deprived of its high l.u.s.tre, and of its power of breaking up by refraction the light of the sun into the various tints of the solar spectrum, simply by heating it to a red heat, and then plunging it into a jar of oxygen gas. It immediately expands, changes into a ma.s.s, and burns away. The product left behind is a mixture of carbon and oxygen, in the proportions in which it is met with in carbonic-anhydride, or, carbonic acid gas deprived of its water. This is indeed a strange transformation, from the most valuable of all our precious stones to a compound which is the same in chemical const.i.tuents as the poisonous gas which we and all animals exhale. But there is this to be said. Probably in the far-away days when the diamond began to be formed, the tree or other vegetable product which was its far-removed ancestor abstracted carbonic acid gas from the atmosphere, just as do our plants in the present day. By this means it obtained the carbon wherewith to build up its tissues. Thus the combustion of the diamond into carbonic-anhydride now is, after all, only a return to the same compound out of which it was originally formed. How it was formed is a secret: probably the time occupied in the formation of the diamond may be counted by centuries, but the time of its re-transformation into a ma.s.s of matter is but the work of seconds!

There is another form of carbon which was formerly of much greater importance than it is now, and which, although not a natural product, is yet deserving of some notice here. Charcoal is the substance referred to.

In early days the word "coal," or, as it was also spelt, "cole," was applied to any substance which was used as fuel; hence we have a reference in the Bible to a "fire of coals," so translated when the meaning to be conveyed was probably not coal as we know it. Wood was formerly known as coal, whilst charred wood received the name of charred-coal, which was soon corrupted into charcoal. The charcoal-burners of years gone by were a far more flourishing community than they are now. When the old baronial halls and country-seats depended on them for the basis of their fuel, and the log was a more frequent occupant of the fire-grate than now, these occupiers of midforest were a people of some importance.

We must not overlook the fact that there is another form of charcoal, namely, animal charcoal or bone-black. This can be obtained by heating bones to redness in closed iron vessels. In the refining of raw sugar the discoloration of the syrup is brought about by filtering it through animal-charcoal; by this means the syrup is rendered colourless.

When properly prepared, charcoal exhibits very distinctly the rings of annual growth which may have characterised the wood from which it was formed. It is very light in consequence of its porous nature, and it is wonderfully indestructible.

But its greatest, because it is its most useful property, is undoubtedly the power which it has of absorbing great quant.i.ties of gas into itself.

It is in fact what may be termed an all-round purifier. It is a deodoriser, a disinfectant, and a decoloriser. It is an absorbent of bad odours, and partially removes the smell from tainted meat. It has been used when offensive manures have been spread over soils, with the same object in view, and its use for the purification of water is well known to all users of filters. Some idea of its power as a disinfectant may be gained by the fact that one volume of wood-charcoal will absorb no less than 90 volumes of ammonia, 35 volumes of carbonic anhydride, and 65 volumes of sulphurous anhydride.

Other forms of carbon which are well-known are (1), the residue left when coal has been subjected to a great heat in a closed retort, but from which all the bye-products of coal have been allowed to escape; (2) soot and lamp-black, the former of which is useful as a manure in consequence of ammonia being present in it, whilst the latter is a specially prepared soot, and is used in the manufacture of Indian ink and printers' ink.



It is somewhat strange to think that where once existed the solitudes of an ancient carboniferous forest now is the site of a busy underground town. For a town it really is. The various roads and pa.s.sages which are cut through the solid coal as excavation of a coal-mine proceeds, represent to a stranger all the intricacies of a well-planned town. Nor is the extent of these underground towns a thing to be despised. There is an old pit near Newcastle which contains not less than fifty miles of pa.s.sages. Other pits there are whose main thoroughfares in a direct line are not less than four or five miles in length, and this, it must be borne in mind, is the result of excavation wrought by human hands and human labour.

So great an extent of pa.s.sages necessarily requires some special means of keeping the air within it in a pure state, such as will render it fit for the workers to breathe. The further one would go from the main thoroughfare in such a mine, the less likely one would be to find air of sufficient purity for the purpose. It is as a consequence necessary to take some special steps to provide an efficient system of ventilation throughout the mine. This is effectually done by two shafts, called respectively the downcast and the upcast shaft. A shaft is in reality a very deep well, and may be circular, rectangular or oval in form. In order to keep out water which may be struck in pa.s.sing through the various strata, it is protected by plank or wood tubbing, or the shaft is bricked over, or sometimes even cast-iron segments are sunk. In many shafts which, owing to their great depth, pa.s.s through strata of every degree of looseness or viscosity, all three methods are utilised in turn.

In Westphalia, where coal is worked beneath strata of more recent geological age, narrow shafts have been, in many cases, sunk by means of boring apparatus, in preference to the usual process of excavation, and the practice has since been adopted in South Wales. In England the usual form of the pit is circular, but elliptical and rectangular pits are also in use. On the Continent polygonal-shaped shafts are not uncommon, all of them, of whatever shape, being constructed with a view to resist the great pressure exerted by the rock around.

[Ill.u.s.tration: FIG. 31.--Engine-House and Buildings at head of a Coal-Pit.]

If there be one of these shafts at one end of the mine, and another at a remote distance from it, a movement of the air will at once begin, and a rough kind of ventilation will ensue. This is, however, quite insufficient to provide the necessary quant.i.ty of air for inhalation by the army of workers in the coal-mine, for the current thus set up does not even provide sufficient force to remove the effete air and impurities which acc.u.mulate from hundreds of perspiring human bodies.

It is therefore necessary to introduce some artificial means, by which a strong and regular current shall pa.s.s down one shaft, through the mine in all its workings, and out at the other shaft. This is accomplished in various ways. It took many years before those interested in mines came thoroughly to understand how properly to secure ventilation, and in bygone days the system was so thoroughly bad that a tremendous amount of sickness prevailed amongst the miners, owing to the poisonous effects of breathing the same air over and over again, charged, as it was, with more or less of the gases given off by the coal itself. Now, those miners who do so great a part in furnishing the means of warming our houses in winter, have the best contrivances which can be devised to furnish them with an ever-flowing current of fresh air.

Amongst the various mechanical appliances which have been used to ensure ventilation may be mentioned pumps, fans, and pneumatic screws. There is, as we have said, a certain, though slight, movement of the air in the two columns which const.i.tute the upcast and the downcast shafts, but in order that a current may flow which shall be equal to the necessities of the miners, some means are necessary, by which this condition of almost equilibrium shall be considerably disturbed, and a current created which shall sweep all foul gases before it. One plan was to force fresh air into the downcast, which should in a sense push the foetid air away by the upcast. Another was to exhaust the upcast, and so draw the gases in the train of the exhausted air. In other cases the plan was adopted of providing a continual falling of water down the downcast shaft.

These various plans have almost all given way to that which is the most serviceable of all, namely, the plan of having an immense furnace constantly burning in a specially-constructed chamber at the bottom of the upcast. By this means the column of air above it becomes rarefied under the heat, and ascends, whilst the cooler air from the downcast rushes in and spreads itself in all directions whence the bad air has already been drawn. On the other hand, to so great a state of perfection have ventilating fans been brought, that one was recently erected which would be capable of changing the air of Westminster Hall thirty times in one hour.

Having procured a current of sufficient power, it will be at once understood that, if left to its own will, it would take the nearest path which might lie between its entrance and its exit, and, in this way, ventilating the street only, would leave all the many off-shoots from it undisturbed. It is consequently manipulated by means of barriers and tight-fitting doors, in such a way that the current is bound in turn to traverse every portion of the mine. A large number of boys, known as trappers, are employed in opening the doors to all comers, and in carefully closing the doors immediately after they have pa.s.sed, in order that the current may not circulate through pa.s.sages along which it is not intended that it should pa.s.s.

The greatest dangers which await the miners are those which result, in the form of terrible explosions, from the presence of inflammable gases in the mines. The great walls of coal which bound the pa.s.sages in mines are constantly exuding supplies of gas into the air. When a bank of coal is brought down by an artificial explosion, by dynamite, by lime cartridges, or by some other agency, large quant.i.ties of gas are sometimes disengaged, and not only is this highly detrimental to the health of the miners, if not carried away by proper ventilation, but it const.i.tutes a constant danger which may at any time cause an explosion when a naked light is brought into contact with it. Fire-damp may be sometimes heard issuing from fiery seams with a peculiar hissing sound.

If the volume be great, the gas forms what is called a _blower_, and this often happens in the neighbourhood of a fault. When coal is brought down in any large volume, the blowers which commence may be exhausted in a few moments. Others, however, have been known to last for years, this being the case at Wallsend, where the blower gave off 120 feet of gas per minute. In such cases the gas is usually conveyed in pipes to a place where it can be burned in safety.

In the early days of coal-mining the explosions caused by this gas soon received the serious attention of the scientific men of the age. In the _Philosophical Transactions of the Royal Society_ we find a record of a gas explosion in 1677. The amusing part of such records was that the explosions were ascribed by the miners to supernatural agencies. Little attention seemed to have been paid to the fact, which has since so thoroughly been established, that the explosions were caused by acc.u.mulations of gas, mixed in certain proportions with air. As a consequence, tallow candles with an exposed flame were freely used, especially in Britain. These were placed in niches in the workings, where they would give to the pitman the greatest amount of light. Previous to the introduction of the safety-lamp, workings were tested before the men entered them, by "trying the candle". Owing to the specific gravity of fire-damp (.555) being less than that of air, it always finds a lodgement at the roofs of the workings, so that, to test the condition of the air, it was necessary to steadily raise the candle to the roof at certain places in the pa.s.sages, and watch carefully the action of the flame. The presence of fire-damp would be shown by the flame a.s.suming a blue colour, and by its elongation; the presence of other gases could be detected by an experienced man by certain peculiarities in the tint of the flame.

This testing with the open flame has almost entirely ceased since the introduction of the perfected Davy lamp.

The use of candles for illumination soon gave place in most of the large collieries to the introduction of small oil-lamps. In the less fiery mines on the Continent, oil-lamps of the well-known Etruscan pattern are still in use, whilst small metal lamps, which can conveniently be attached to the cap of the worker, occasionally find favour in the shallower Scotch mines. These lamps are very useful in getting the coal from the thinner seams, where progress has to be made on the hands and feet. At the close of the last century, as workings began to be carried deeper, and coal was obtained from places more and more infested with fire-damp, it soon came to be realised that the old methods of illumination would have to be replaced by others of a safer nature.

It is noteworthy that mere red heat is insufficient in itself to ignite fire-damp, actual contact with flame being necessary for this purpose.

Bearing this in mind, Spedding, the discoverer of the fact, invented what is known as the "steel-mill" for illuminating purposes. In this a toothed wheel was made to play upon a piece of steel, the sparks thus caused being sufficient to give a moderate amount of illumination. It was found, however, that this method was not always trustworthy, and lamps were introduced by Humboldt in 1796, and by Clanny in 1806. In these lamps the air which fed the flame was isolated from the air of the mine by having to bubble through a liquid. Many miners were not, however, provided with these lamps, and the risks attending naked lights went on as merrily as ever.

In order to avoid explosions in mines which were known to give off large quant.i.ties of gas, "fiery" pits as they are called, Sir Humphrey Davy in 1815 invented his safety lamp, the principle of which can be stated in a few words.

If a piece of fine wire gauze be held over a gas-jet before it is lit, and the gas be then turned on, it can be lit above the gauze, but the flame will not pa.s.s downwards towards the source of the gas; at least, not until the gauze has become over-heated. The metallic gauze so rapidly conducts away the heat, that the temperature of the gas beneath the gauze is unable to arrive at the point of ignition. In the safety-lamp the little oil-lamp is placed in a circular funnel of fine gauze, which prevents the flame from pa.s.sing through it to any explosive gas that may be floating about outside, but at the same time allows the rays of light to pa.s.s through readily. Sir Humphrey Davy, in introducing his lamp, cautioned the miners against exposing it to a rapid current of air, which would operate in such a way as to force the flame through the gauze, and also against allowing the gauze to become red-hot. In order to minimise, as far as possible, the necessity of such caution the lamp has been considerably modified since first invented, the speed of the ventilating currents not now allowing of the use of the simple Davy lamp, but the principle is the same.

During the progress of Sir Humphrey Davy's experiments, he found that when fire-damp was diluted with 85 per cent. of air, and any less proportion, it simply ignited without explosion. With between 85 per cent. and 89 per cent. of air, fire-damp a.s.sumed its most explosive form, but afterwards decreased in explosiveness, until with 94-1/4 per cent. of air it again simply ignited without explosion. With between 11 and 12 per cent. of fire-damp the mixture was most dangerous. Pure fire-damp itself, therefore, is not dangerous, so that when a small quant.i.ty enters the gauze which surrounds the Davy lamp, it simply burns with its characteristic blue flame, but at the same time gives the miner due notice of the danger which he was running.

[Ill.u.s.tration: FIG. 32.--Gas Jet and Davy Lamp.]

With the complicated improvements which have since been made in the Davy lamp, a state of almost absolute safety can be guaranteed, but still from time to time explosions are reported. Of the cause of many we are absolutely ignorant, but occasionally a light is thrown upon their origin by a paragraph appearing in a daily paper. Two men are charged before the magistrates with being in the possession of keys used exclusively for unlocking their miners' safety-lamps. There is no defence. These men know that they carry their lives in their hands, yet will risk their own and those of hundreds of others, in order that they may be able to light their pipes by means of their safety-lamps. Sometimes in an unexpected moment there is a great dislodgement of coal, and a tremendous quant.i.ty of gas is set free, which may be sufficient to foul the pa.s.sages for some distance around. The introduction or exposure of a naked light for even so much as a second is sufficient to cause explosion of the ma.s.s; doors are blown down, props and tubbing are charred up, and the volume of smoke, rushing up by the nearest shaft and overthrowing the engine-house and other structures at the mouth, conveys its own sad message to those at the surface, of the dreadful catastrophe that has happened below.

Perhaps all that remains of some of the workers consists of charred and scorched bodies, scarcely recognisable as human beings. Others escape with scorched arms or legs, and singed hair, to tell the terrible tale to those who were more fortunately absent; to speak of their own sufferings when, after having escaped the worst effects of the explosion, they encountered the asphyxiating rush of the after-damp or choke-damp, which had been caused by the combustion of the fire-damp. "Choke-damp" in very truth it is, for it is composed of our old acquaintance carbonic acid gas (carbon dioxide), which is well known as a non-supporter of combustion and as an asphyxiator of animal life.

It seems a terrible thing that on occasions the workings and walls themselves of a coal-mine catch fire and burn incessantly. Yet such is the case. Years ago this happened in the case of an old colliery near Dudley, at the surface of which, by means of the heat and steam thus afforded, early potatoes for the London market, we are told, were grown; and it was no unusual thing to see the smoke emerging from cracks and crevices in the rocks in the vicinity of the town.

From fire on the one hand, we pa.s.s, on the other, to the danger which awaits miners from a sudden inrush of water. During the great coal strike of 1893, certain mines became unworkable in consequence of the quant.i.ty of water which flooded the mines, and which, continually pa.s.sing along the natural fractures in the earth's crust, is always ready to find a storage reservoir in the workings of a coal-mine. This is a difficulty which is always experienced in the sinking of shafts, and the shutting off of water engages the best efforts of mining engineers.

Added to these various dangers which exist in the coal-mine, we must not omit to notice those accidents that are continually being caused by the falling-in of roofs or of walls, from the falling of insecure timber, or of what are known as "coal-pipes" or "bell-moulds." Then, again, every man that enters the mine trusts his life to the cage by which he descends to his labour, and shaft accidents are not infrequent.

The following table shows the number of deaths from colliery accidents for a period of ten years, compiled by a Government inspector, and from this it will be seen that those resulting from falling roofs number considerably more than one-third of the whole.

------------------------------------------------------------------- | Causes of Death. | No. of | Proportion | | | Deaths. | per cent. | ------------------------------------------------------------------- | Deaths resulting from fire-damp | | | | explosions | 2019 | 20.36 | | | | | | Deaths resulting from falling | | | | roofs and coals | 3953 | 39.87 | | | | | | Deaths resulting from shaft | | | | accidents | 1710 | 17.24 | | | | | | Deaths resulting from miscellaneous | | | | causes and above ground | 2234 | 22.53 | | |------------|------------| | | 9916 | 100.00 | ------------------------------------------------------------------|

Every reader of the daily papers is familiar with the harrowing accounts which are there given of coal-mine explosions.

This kind of accident is one, which is, above all, a.s.sociated in the public mind with the dangers of the coal-pit. Yet the accidents arising from this cause number but 20 per cent. of those recorded, and granted there be proper inspection, and the use of naked lights be absolutely abolished, this low percentage might still be considerably reduced.

A terrific explosion occurred at Whitwick Colliery, Leicestershire, in 1893, when two lads were killed, whilst a third was rescued after a very narrow escape. The lads, it is stated, _were working with naked lights_, when a sudden fall of coal released a quant.i.ty of gas, and an immediate explosion was the natural result. Accidents had been so rare at this pit that it was regarded as particularly safe, and it was alleged that the use of naked lights was not uncommon.

This is an instance of that large number of accidents which are undoubtedly preventable.

An interesting commentary on the careless manner in which miners risk their lives was shown in the discoveries made after an explosion at a colliery near Wrexham in 1889. Near the scene of the explosion an unsecured safety lamp was found, and the general opinion at the time was that the disaster was caused by the inexcusable carelessness of one of the twenty victims. Besides this, when the clothing of the bodies recovered was searched, the contents, taken, it should be noted, with the pitmen into the mines, consisted of pipes, tobacco, matches, and even keys for unlocking the lamps. It is a strange reflection on the manner in which this mine had been examined previous to the men entering upon their work, that the under-looker, but half an hour previously, had reported the pit to be free from gas.

Another instance of the same foolhardiness on the part of the miners is contained in the report issued in regard to an explosion which occurred at Denny, in Stirlingshire, on April 26th, 1895. By this accident thirteen men lost their lives, and upon the bodies of eight of the number the following articles were found; upon Patrick Carr, tin matchbox half full of matches and a contrivance for opening lamps; John Comrie, split nail for opening lamps; Peter Conway, seven matches and split key for opening lamps; Patrick Dunton, split nail for opening lamps; John Herron, clay pipe and piece of tobacco; Henry M'Govern, tin matchbox half full of matches; Robert Mitch.e.l.l, clay pipe and piece of tobacco; John Nicol, wooden pipe, piece of tobacco, one match, and box half full of matches.

The report stated that the immediate cause of the disaster was the ignition of fire-damp by naked light, the conditions of temperature being such as to exclude the possibility of spontaneous combustion. Henry M'Govern had previously been convicted of having a pipe in the mine. With regard to the question of sufficient ventilation it continued:--"And we are therefore led, on a consideration of the whole evidence, to the conclusion that the accident cannot be attributed to the absence of ventilation, which the mine owners were bound under the Mines Regulation Act and the special rules to provide." The report concluded as follows:-- "On the whole matter we have to report that, in our opinion, the explosion at Quarter Pit on April 26th, 1895, resulting in the loss of thirteen lives, was caused by the ignition of an acc.u.mulation or an outburst of gas coming in contact with a naked light, 'other than an open safety-lamp,' which had been unlawfully kindled by one of the miners who were killed. In our opinion, the intensity of the explosion was aggravated, and its area extended, by the ignition of coal-dust."