"The climate of the southern part of America appears particularly favourable to the production of peat. In the Falkland Islands almost every kind of plant, even the coarse grass which covers the whole surface of the land, becomes converted into this substance: scarcely any situation checks its growth; some of the beds are as much as twelve feet thick, and the lower part becomes so solid when dry that it will hardly burn. Although every plant lends its aid, yet in most parts the Astelia is the most efficient.

"It is rather a singular circumstance, as being so very different from what occurs in Europe, that I nowhere saw moss forming by its decay any portion of the peat in South America. With respect to the northern limit at which the climate allows of that peculiar kind of slow decomposition which is necessary for its production, I believe that in Chiloe (lat. 41 deg. to 42 deg.), although there is much swampy ground, no well characterised peat occurs; but in the Chonos Islands, three degrees farther southward, we have seen that it is abundant. On the eastern coast in La Plata (lat. 35 deg.) I was told by a Spanish resident, who had visited Ireland, that he had often sought for this substance, but had never been able to find any. He showed me, as the nearest approach to it which he had discovered, a black peaty soil, so penetrated with roots as to allow of an extremely slow and imperfect combustion."

The next stage in the making of coal is one in which the change has proceeded a long way from the starting-point. Lignite is the name which has been applied to a form of impure coal, which sometimes goes under the name of "brown coal." It is not a true coal, and is a very long way from that final stage to which it must attain ere it takes rank with the most valuable of earth's products. From the very commencement, an action has being going on which has caused the amount of the gaseous constituents to become less and less, and which has consequently caused the carbon remaining behind to occupy an increasingly large proportion of the whole mass. So, when we arrive at the lignite stage, we find that a considerable quantity of volatile matter has already been parted with, and that the carbon, which in ordinary living wood is about 50 per cent. of the whole, has already increased to about 67 per cent. In most lignites there is, as a rule, a comparatively large proportion of sulphur, and in such cases it is rendered useless as a domestic fuel. It has been used as a fuel in various processes of manufacture, and the lignite of the well-known Bovey Tracey beds has been utilised in this way at the neighbouring potteries. As compared with true coal, it is distinguished by the abundance of smoke which it produces and the choking sulphurous fumes which also accompany its combustion, but it is largely used in Germany as a useful source of paraffin and illuminating oils. In Silesia, Saxony, and in the district about Bonn, large quantities of lignite are mined, and used as fuel. Large stores of lignite are known to exist in the Weald of the south-east of England, and although the mining operations which were carried on at one time at Heathfield, Bexhill, and other places, were failures so far as the actual discovery of true coal was concerned, yet there can be no doubt as to the future value of the lignite in these parts, when England's supplies of coal approach exhaustion, and attention is turned to other directions for the future source of her gas and paraffin oils.

Beside the Bovey Tracey lignitic beds to which we have above referred, other tertiary clays are found to contain this early promise of coal. The eocene beds of Brighton are an important instance of a tertiary lignite, the seam of surturbrand, as it is locally called, being a somewhat extensive deposit.

We have now closely approached to true coal, and the next step which we shall take will be to consider the varieties in which the black mineral itself is found. The principal of these varieties are as follows, against each being placed the average proportion of pure carbon which it contains:—

Splint or Hard Coal, 83 per cent.; Cannel, Candle or Parrott Coal, 84 per cent.; Cherry or Soft Coal, 85 per cent.; Common Bituminous, or Caking Coal, 88 per cent.; Anthracite, Blind Coal, Culm, Glance, or Stone Coal, from South Wales, 93 per cent.

As far as the gas-making properties of the first three are concerned, the relative proportions of carbon and volatile products are much the same. Everybody knows a piece of cannel coal when it is seen, how it appears almost to have been once in a molten condition, and how it breaks with a conchoidal fracture, as opposed to the cleavage of bituminous coal into thin layers; and, most apparent and most noticeable of all, how it does not soil the hands after the manner of ordinary coal. It is at times so dense and compact that it has been fashioned into ornaments, and is capable of receiving a polish like jet. From the large percentage of volatile products which it contains, it is greatly used in gasworks.

Caking coal and the varieties of coal which exist between it and anthracite, are familiar to every householder; the more it approaches the composition of the latter the more difficult it is to get it to burn, but when at last fairly alight it gives out great heat, and what is more important, a less quantity of volatile constituents in the shape of gas, smoke, ammonia, ash and sulphurous acid. For this reason it has been proposed to compel consumers to adopt anthracite as the domestic coal by Act of Parliament. Certainly by this means the amount of impurities in the air might be appreciably lessened, but as it would involve the reconstruction of some millions of fire-places, and an increase in price in consequence of the general demand for it, it is not likely that a government would be so rash as to attempt to pass such a measure; even if passed, it would probably soon become as dead and obsolete and impotent as those many laws with which our ancestors attempted, first to arrest, and then to curb the growth in the use of coal of any sort. Anthracite is not a "homely" coal. If we use it alone it will not give us that bright and cheerful blaze which English-speaking people like to obtain from their fires.

It is a significant fact, and one which proves that the various kinds of coal which are found are nothing but stages begotten by different degrees of disentanglement of the contained gases, that where, as in some parts, a mass of basalt has come into contact with ordinary bituminous coal, the coal has assumed the character of anthracite, whilst the change has in some instances gone so far as to convert the anthracite into graphite. The basalt, which is one of the igneous rocks, has been erupted into the coal-seam in a state of fusion, and the heat contained in it has been sufficient to cause the disentanglement of the gases, the extraction of which from the coal brings about the condition of anthracite and graphite.

The mention of graphite brings us to the next stage. Graphite, plumbago, or, as it is more commonly called, black-lead, which, we may say in passing, has nothing of lead about it at all, is best known in the shape of that very useful and cosmopolitan article, the black-lead pencil. This is even purer carbon than anthracite, not more than 5 per cent. of ash and other impurities being present. It is well-known by its grey metallic lustre; the chemist uses it mixed with fire-clay to make his crucibles; the engineer uses it, finely powdered, to lubricate his machinery; the house-keeper uses it to "black-lead" her stoves to prevent them from rusting. An imperfect graphite is found inside some of the hottest retorts from which gas is distilled, and this is used as the negative element in zinc and carbon electricity-making cells, whilst its use as the electrodes or carbons of the arc-lamp is becoming more and more widely adopted, as installations of electric light become more general.

One great source of true graphite for many years was the famous mine at Borrowdale, in Cumberland, but this is now almost exhausted. The vein lay between strata of slate, and was from eight to nine feet thick. As much as L100,000 is said to have been realised from it in one year. Extensive supplies of graphite are found in rocks of the Laurentian age in Canada. In this formation nothing which can undoubtedly be classed as organic has yet been discovered. Life at this early period must have found its home in low and humble forms, and if the eozooen of Dawson, which has been thought to represent the earliest type of life, turns out after all not to be organic, but only a deceptive appearance assumed by certain of the strata, we at least know that it must have been in similarly humble forms that life, if it existed at all, did then exist. We can scarcely, therefore, expect that the vegetable world had made any great advance in complexity of organism at this time, otherwise the supplies of graphite or plumbago which are found in the formation, would be attributed to dense forest growths, acted upon, after death, in a similar manner to that which awaited the vegetation which, ages after, went to form beds of coal. At present we know of no source of carbon except through the intervention and the chemical action of plants. Like iron, carbon is seldom found on the earth except in combination. If there were no growth of vegetation at this far-away period to give rise to these deposits of graphite, we are compelled to ask ourselves whether, perchance, there did not then exist conditions of which we are not now cognisant on the earth, and which allowed graphite to be formed without assistance from the vegetable kingdom. At present, however, science is in the dark as to any other process of its formation, and we are left to assume that the vegetable growth of the time was enormous in quantity, although there is nothing to show the kind of vegetation, whether humble mosses or tall forest trees, which went to constitute the masses of graphite. Geologists will agree that this is no small assumption to make, since, if true, it may show that there was an abundance of vegetation at a time when animal life was hidden in one or more very obscure forms, one only of which has so far been detected, and whose very identity is strongly doubted by nearly all competent judges. At the same time there may have been an abundance of both animal and vegetable life at the time. We must not forget that it is a well-ascertained fact that in later ages, the minute seed-spores of forest trees were in such abundance as to form important seams of coal in the true carboniferous era, the trees which gave birth to them being now classed amongst the humble cryptogams, the ferns, and club-mosses, &c. The graphite of Laurentian age may not improbably have been caused by deposits of minute portions of similar lowly specimens of vegetable life, and if the eozooen the "dawn-animalcule," does represent the animal life of the time, life whose types were too minute to leave undoubted traces of their existence, both animal life and vegetable life may be looked upon as existing side by side in extremely humble forms, neither as yet having taken an undoubted step forward in advance of the other in respect to complexity of organism.



There is but one more form of carbon with which we have to deal in running through the series. We have seen that coal is not the summum bonum of the series. Other transformations take place after the stage of coal is reached, which, by the continued disentanglement of gases, finally bring about the plumbago stage.

What the action is which transforms plumbago or some other form of carbon into the condition of a diamond cannot be stated. Diamond is the purest form of carbon found in nature. It is a beautiful object, alike from the results of its powers of refraction, as also from the form into which its carbon has been crystallised. How Nature, in her wonderful laboratory, has precipitated the diamond, with its wonderful powers of spectrum analysis, we cannot say with certainty. Certain chemists have, at a great expense, produced crystals which, in every respect, stand the tests of true diamonds; but the process of their production at a great expense has in no way diminished the value of the natural product.

The process by which artificial diamonds have been produced is so interesting, and the subject may prove to be of so great importance, that a few remarks upon the process may not be unacceptable.

The experiments of the great French chemist, Dumas, and others, satisfactorily proved the fact, which has ever since been considered thoroughly established, that the diamond is nothing but carbon crystallised in nearly a pure state, and many chemists have since been engaged in the hitherto futile endeavour to turn ordinary carbon into the true diamond.

Despretz at one time considered that he had discovered the process, which consisted in his case of submitting a piece of charcoal to the action of an electric battery, having in his mind the similar process of electrolysis, by which water is divided up into the two gases, hydrogen and oxygen. He obtained a microscopic deposit on the poles of the battery, which he pronounced to be diamond dust, but which, a long time after, was proved to be nothing but graphite in a crystallised state. This was, however, certainly a step in the right direction.

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 L150 worth in order to assure 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 quantity 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 assuming the solid form, would exert such tremendous pressure upon the particles of carbon which it absorbed, that these would assume 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 deg. 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 mass 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 mass 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 passing 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 quantity 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 trimming. The cutting of a pane of glass 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 lustre, 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 coky mass, 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 constituents 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 mass of coky 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 quantities 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) coke, 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.



CHAPTER IV.

THE COAL-MINE AND ITS DANGERS.

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 passages 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 passages. 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 passages 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 passing 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, pass 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.



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 quantity 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 accumulate from hundreds of perspiring human bodies.

It is therefore necessary to introduce some artificial means, by which a strong and regular current shall pass 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 constitute 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 principal 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 passed, in order that the current may not circulate through passages along which it is not intended that it should pass.

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 passages 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 quantities 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 constitutes 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 accumulations 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 passages, and watch carefully the action of the flame. The presence of fire-damp would be shown by the flame assuming 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 quantities 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 pass 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 passing through it to any explosive gas that may be floating about outside, but at the same time allows the rays of light to pass 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 assumed 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 quantity 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.



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 quantity of gas is set free, which may be sufficient to foul the passages 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 mass; 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 principally 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 pass, 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 quantity of water which flooded the mines, and which, continually passing 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, associated 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 quantity 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 Mitchell, 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 accumulation 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."

We have mentioned that accidents have frequently occurred from the falling of "coal-pipes," or, as they are also called, "bell-moulds." We must explain what is meant by this term. They are simply what appear to be solid trunks of trees metamorphosed into coal. If we go into a tropical forest we find that the woody fibre of dead trees almost invariably decays faster than the bark. The result is that what may appear to be a sound tree is nothing but an empty cylinder of bark. This appears to have been the case with many of the trees in coal-mines, where they are seen to pierce the strata, and around which the miners are excavating the coal. As the coaly mass collected around the trunk when the coal was being formed, the interior was undergoing a process of decomposition, while the bark assumed the form of coal. The hollow interior then became filled with the shale or sandstone which forms the roof of the coal, and its sole support when the coal is removed from around it, is the thin rind of carbonised bark. When this falls to pieces, or loses its cohesion, the sandstone trunk falls of its own weight, often causing the death of the man that works beneath it. Sir Charles Lyell mentions that in a colliery near Newcastle, no less than thirty sigillaria trees were standing in their natural position in an area of fifty yards square, the interior in each case being sandstone, which was surrounded by a bark of friable coal.



The last great danger to which we have here to make reference, is the explosive action of a quantity of coal-dust in a dry condition. It is only now commencing to be fully recognised that this is really a most dangerous explosive. As we have seen, large quantities of coal are formed almost exclusively of lepidodendron spores, and such coal is productive of a great quantity of dust. Explosions which are always more or less attributable to the effects of coal-dust are generally considered, in the official statistics, to have been caused by fire-damp. The Act regulating mines in Great Britain is scarcely up to date in this respect. There is a regulation which provides for the watering of all dry and dusty places within twenty yards from the spot where a shot is fired, but the enforcement of this regulation in each and every pit necessarily devolves on the managers, many of whom in the absence of an inspector leave the requirement a dead letter. Every improvement which results in the better ventilation of a coal-mine tends to leave the dust in a more dangerous condition. The air, as it descends the shaft and permeates the workings, becomes more and more heated, and licks up every particle of moisture it can touch. Thorough ventilation results in more greatly freeing a mine of the dangerous fire-damp, but the remedy brings about another disease, viz., the drying-up of all moisture. The dust is thus left in a dangerously inflammable condition, acting like a train of gunpowder, to be started, it may be, by the slightest breath of an explosion. There is apparently little doubt that the presence of coal-dust in a dry state in a mine appreciably increases the liability of explosion in that mine.

So far as Great Britain is concerned, a Royal Commission was appointed by Lord Rosebery's Government to inquire into and investigate the facts referring to coal-dust. Generally speaking, the conclusion arrived at was that fine coal-dust was inflammable under certain conditions. There was considerable difference of opinion as to what these conditions were. Some were of opinion that coal-dust and air alone were of an explosive nature, whilst others thought that alone they were not, but that the addition of a small quantity of fire-damp rendered the mixture explosive. An important conclusion was come to, that, with the combustion of coal-dust alone, there was little or no concussion, and that the flame was not of an explosive character.

Coal-dust was, however, admittedly dangerous, especially if in a dry condition. The effects of an explosion of gas might be considerably extended by its presence, and there seems every reason to believe that, with a suitable admixture of air and a very small proportion of gas, it forms a dangerous explosive. Legislation in the direction of the report of the Commission is urgently needed.

We have seen elsewhere what it is in the dust which makes it dangerous, how that, for the most part, it consists of the dust-like spores of the lepidodendron tree, fine and impalpable as the spores on the backs of some of our living ferns, and the fact that this consists of a large proportion of resin makes it the easily inflammable substance it is. Nothing but an incessant watering of the workings in such cases will render the dust innocuous. The dust is extremely fine, and is easily carried into every nook and crevice, and when, as at Bridgend in 1892, it explodes, it is driven up and out of the shaft, enveloping everything temporarily in dust and darkness.

In some of the pits in South Wales a system of fine sprays of water is in use, by which the water is ejected from pin-holes pricked in a series of pipes which are carried through the workings. A fine mist is thus caused where necessary, which is carried forward by the force of the ventilating current.

A thorough system of inspection in coal-mines throughout the world is undoubtedly urgently called for, in order to ensure the proper carrying out of the various regulations framed for their safety. It is extremely unfortunate that so many of the accidents which happen are preventable, if only men of knowledge and of scientific attainments filled the responsible positions of the overlookers.



CHAPTER V.

EARLY HISTORY—ITS USE AND ITS ABUSE.

The extensive use of coal throughout the civilised world for purposes of heating and illumination, and for the carrying on of manufactures and industries, may be regarded as a well-marked characteristic of the age in which we live.

Coal must have been in centuries past a familiar object to many generations. People must have long been living in close proximity to its outcrops at the sides of the mountains and at the surface of the land, yet without being acquainted with its practical value, and it seems strange that so little use was made of it until about three centuries ago, and that its use did not spread earlier and more quickly throughout civilised countries.

A mineral fuel is mentioned by Theophrastus about 300 B.C., from which it is inferred that thus early it was dug from some of the more shallow depths. The Britons before the time of the Roman invasion are credited with some slight knowledge of its industrial value. Prehistoric excavations have been found in Monmouthshire, and at Stanley, in Derbyshire, and the flint axes there actually found imbedded in the layer of coal are reasonably held to indicate its excavation by neolithic or palaeolithic (stone-age) workmen.

The fact that coal cinders have been found on old Roman walls in conjunction with Roman tools and implements, goes to prove that its use, at least for heating purposes, was known in England prior to the Saxon invasion, whilst some polygonal chambers in the six-foot seam near the river Douglas, in Lancashire, are supposed also to be Roman.

The Chinese were early acquainted with the existence of coal, and knew of its industrial value to the extent of using it for the baking of porcelain.

The fact of its extensive existence in Great Britain, and the valuable uses to which it might be put, did not, however, meet with much notice until the ninth century, when, owing to the decrease of the forest-area, and consequently of the supply of wood-charcoal therefrom, it began to attract attention as affording an excellent substitute for charcoal.

The coal-miner was, however, still a creation of the future, and even as peat is collected in Ireland at the present day for fuel, without the laborious process of mining for it, so those people living in coal-bearing districts found their needs satisfied by the quantity of coal, small as it was, which appeared ready to hand on the sides of the carboniferous mountains. Till then, and for a long time afterwards, the principal source of fuel consisted of vast forests, amidst which the charcoal-burners, or "colliers" as they were even then called, lived out their lonely existence in preparing charcoal and hewing wood, for the fires of the baronial halls and stately castles then swarming throughout the land. As the forests became used up, recourse was had more and more to coal, and in 1239 the first charter dealing with and recognising the importance of the supplies was granted to the freemen of Newcastle, according them permission to dig for coals in the Castle fields. About the same time a coal-pit at Preston, Haddingtonshire, was granted to the monks of Newbattle.

Specimens of Newcastle coal were sent to London, but the city was loth to adopt its use, objecting to the innovation as one prejudicial to the health of its citizens. By the end of the 16th century, two ships only were found sufficient to satisfy the demand for stone-coal in London. This slow progress may, perhaps, have been partially owing to the difficulties which were placed in the way of its universal use. Great opposition was experienced by those who imported it into the metropolis, and the increasing amount which was used by brewers and others about the year 1300, caused serious complaints to be made, the effect of which was to induce Parliament to obtain a proclamation from the King prohibiting its use, and empowering the justices to inflict a fine on those who persisted in burning it. The nuisance which coal has since proved itself, in the pollution of the atmosphere and in the denuding of wide tracts of country of all vegetation, was even thus early recognised, and had the efforts which were then made to stamp out its use, proved successful, those who live now in the great cities might never have become acquainted with that species of black winter fog which at times hangs like a pall over them, and transforms the brightness of day into a darkness little removed from that of night. At the same time, we must bear in mind that it is universally acknowledged that England owes her prosperity, and her pre-eminence in commerce, in great part, to her happy possession of wide and valuable coal-fields, and many authorities have not hesitated to say, that, in their opinion, the length of time during which England will continue to hold her prominent position as an industrial nation is limited by the time during which her coal will last.

The attempt to prohibit the burning of coal was not, however, very successful, for in the reign of Edward III. a license was again granted to the freemen of Newcastle to dig for coals. Newcastle was thus the first town to become famous as the home of the coal-miner, and the fame which it early acquired, it has held unceasingly ever since.

Other attempts at prohibition of the article were made at various times subsequently, amongst them being one which was made in Elizabeth's reign. It was supposed that the health of the country squires, who came to town to attend the session of Parliament, suffered considerably during their sojourn in London, and, to remedy this serious state of affairs, the use of stone-coal during the time Parliament was sitting was once more prohibited.

Coal was, however, by this time beginning to be recognised as a most valuable and useful article of fuel, and had taken a position in the industrial life of the country from which it was difficult to remove it. Rather than attempt to have arrested the growing use of coal, Parliament would have been better employed had it framed laws compelling the manufacturers and other large burners to consume their own smoke, and instead of aiming at total prohibition, have encouraged an intelligent and more economical use of it.

In spite of all prohibition its use rapidly spread, and it was soon applied to the smelting of iron and to other purposes. Iron had been largely produced in the south of England from strata of the Wealden formation, during the existence of the great forest which at one time extended for miles throughout Surrey and Sussex. The discovery of coal, however, and the opening up of many mines in the north, gave an important impetus to the smelting of iron in those counties, and as the forests of the Weald became exhausted, the iron trade gradually declined. Furnace after furnace became extinguished, until in 1809 that at Ashburnham, which had lingered on for some years, was compelled to bow to the inevitable fate which had overtaken the rest of the iron blast-furnaces.

In referring to this subject, Sir James Picton says:—"Ironstone of excellent quality is found in various parts of the county, and was very early made use of. Even before the advent of the Romans, the Forest of Dean in the west, and the Forest of Anderida, in Sussex, in the east, were the two principal sources from which the metal was derived, and all through the mediaeval ages the manufacture was continued. After the discovery of the art of smelting and casting iron in the sixteenth century, the manufacture in Sussex received a great impulse from the abundance of wood for fuel, and from that time down to the middle of the last century it continued to flourish. One of the largest furnaces was at Lamberhurst, on the borders of Kent, where the noble balustrade surrounding St Paul's Cathedral was cast at a cost of about L11,000. It is stated by the historian Holinshed that the first cast-iron ordnance was manufactured at Buxted. Two specialities in the iron trade belonged to Sussex, the manufacture of chimney-backs, and cast-iron plates for grave-stones. At the time when wood constituted the fuel the backs of fire-places were frequently ornamented with neat designs. Specimens, both of the chimney-backs and of the monuments, are occasionally met with. These articles were exported from Rye. The iron manufacture, of course, met with considerable discouragement on the discovery of smelting with pit-coal, and the rapid progress of iron works in Staffordshire and the North, but it lingered on until the great forest was cut down and the fuel exhausted."

In his interesting work, "Sylvia," published in 1661, Evelyn, in speaking of the noxious vapours poured out into the air by the increasing number of coal fires, writes, "This is that pernicious smoke which sullies all her glory, superinducing a sooty crust or furr upon all that it lights, spoiling movables, tarnishing the plate, gildings and furniture, and corroding the very iron bars and hardest stones with those piercing and acrimonious spirits which accompany its sulphur, and executing more in one year than the pure air of the country could effect in some hundreds." The evils here mentioned are those which have grown and have become intensified a hundred-fold during the two centuries and a half which have since elapsed. When the many efforts which were made to limit its use in the years prior to 1600 are remembered; at which time, we are informed, two ships only were engaged in bringing coal to London, it at once appears how paltry are the efforts made now to moderate these same baneful influences on our atmosphere, at a time when the annual consumption of coal in the United Kingdom has reached the enormous total of 190 millions of tons. The various smoke-abatement associations which have started into existence during the last few years are doing a little, although very little, towards directing popular attention to the subject; but there is an enormous task before them, that of awakening every individual to an appreciation of the personal interest which he has in their success, and to realise how much might at once be done if each were to do his share, minute though it might be, towards mitigating the evils of the present mode of coal-consumption. Probably very few householders ever realise what important factories their chimneys constitute, in bringing about air pollution, and the more they do away with the use of bituminous coal for fuel, the nearer we shall be to the time when yellow fog will be a thing of the past.

A large proportion of smoke consists of particles of pure unconsumed carbon, and this is accompanied in its passage up our chimneys by sulphurous acid, begotten by the sulphur which is contained in the coal to the amount of about eight pounds in every thousand; by sulphuretted hydrogen, by hydro-carbons, and by vapours of various kinds of oils, small quantities of ammonia, and other bodies not by any means contributing to a healthy condition of the atmosphere. A good deal of the heavier carbon is deposited along the walls of chimneys in the form of soot, together with a small percentage of sulphate of ammonia; this is as a consequence very generally used for manure. The remainder is poured out into the atmosphere, there to undergo fresh changes, and to become a fruitful cause of those thick black fogs with which town-dwellers are so familiar. Sulphuretted hydrogen (H_{2}S) is a gas well known to students of chemistry as a most powerful reagent, its most characteristic external property being the extremely offensive odour which it possesses, and which bears a strong resemblance to that of rotten eggs or decomposing fish. It tarnishes silver work and picture frames very rapidly. On combustion it changes to sulphurous acid (SO_{2}), and this in turn has the power of taking up from the air another atom of oxygen, forming sulphuric acid (SO_{3} + water), or, as we more familiarly know it, oil of vitriol.

Yet the smoke itself, including as it does all the many impurities which exist in coal, is not only evil in itself, but is evil in its influences. Dr Siemens has said:—"It has been shown that the fine dust resulting from the imperfect combustion of coal was mainly instrumental in the formation of fog; each particle of solid matter attracting to itself aqueous vapour. These globules of fog were rendered particularly tenacious and disagreeable by the presence of tar vapour, another result of imperfect combustion of raw fuel, which might be turned to better account at the dyeworks. The hurtful influence of smoke upon public health, the great personal discomfort to which it gave rise, and the vast expense it indirectly caused through the destruction of our monuments, pictures, furniture, and apparel, were now being recognised."

The most effectual remedy would result from a general recognition of the fact that wherever smoke was produced, fuel was being consumed wastefully, and that all our calorific effects, from the largest furnace to the domestic fire, could be realised as completely, and more economically, without allowing any of the fuel employed to reach the atmosphere unburnt. This most desirable result might be effected by the use of gas for all heating purposes, with or without the additional use of coke or anthracite. The success of the so-called smoke-consuming stoves is greatly open to question, whilst some of them have been reported upon by those appointed to inspect them as actually accentuating the incomplete combustion, the abolition of which they were invented to bring about.

The smoke nuisance is one which cuts at the very basis of our business life. The cloud which, under certain atmospheric conditions, rests like a pall over our great cities, will not even permit at times of a single ray of sunshine permeating it. No one knows whence it rises, nor at what hour to expect it. It is like a giant spectre which, having lain dormant since the carboniferous age, has been raised into life and being at the call of restless humanity; it is now punishing us for our prodigal use of the wealth it left us, by clasping us in its deadly arms, cutting off our brilliant sunshine, and necessitating the use in the daytime of artificial light; inducing all kinds of bronchial and throat affections, corroding telegraph and telephone wires, and weathering away the masonry of public buildings.

The immense value to us of the coal-deposits which lie buried in such profusion in the earth beneath us, can only be appreciated when we consider the many uses to which coal has been put. We must remember, as we watch the ever-extending railway ramifying the country in every direction, that the first railway and the first locomotive ever built, were those which were brought into being in 1814 by George Stephenson, for the purpose of the carriage of coals from the Killingworth Colliery. To the importance of coal in our manufactures, therefore, we owe the subsequent development of steam locomotive power as the means of the introduction of passenger traffic, and by the use of coal we are enabled to travel from one end of the country to the other in a space of time inconceivably small as compared with that occupied on the same journey in the old coaching days. The increased rapidity with which our vessels cross the wide ocean we owe to the use of coal; our mines are carried to greater depths owing to the power our pumping-engines obtain from coal in clearing the mines of water and in ensuring ventilation; the enormous development of the iron trade only became possible with the increased blast power obtained from the consumption of coal, and the very hulls and engines of our steamships are made of this iron; our railroads and engines are mostly of iron, and when we think of the extensive use of iron utensils in every walk in life, we see how important becomes the power we possess of obtaining the necessary fuel to feed the smelting furnaces. Evaporation by the sun was at one time the sole means of obtaining salt from seawater; now coal is used to boil the salt pans and to purify the brine from the salt-mines in the triassic strata of Cheshire. The extent to which gas is used for illuminating purposes reminds us of another important product obtained from coal. Paraffin oil and petroleum we obtain from coal, whilst candles, oils, dyes, lubricants, and many other useful articles go to attest the importance of the underground stores of that mineral which has well and deservedly been termed the "black diamond."



CHAPTER VI.

HOW GAS IS MADE—ILLUMINATING OILS AND BYE-PRODUCTS.

Accustomed as we are at the present day to see street after street of well-lighted thoroughfares, brilliantly illuminated by gas-lamps maintained by public authority, we can scarcely appreciate the fact that the use of gas is, comparatively speaking, of but recent growth, and that, like the use of coal itself, it has not yet existed a century in public favour. Valuable as coal is in very many different ways, perhaps next in value to its actual use as fuel, ranks the use of the immediate product of its distillation—viz., gas; and although gas is in some respects waning before the march of the electric light in our day, yet, even as gas at no time has altogether superseded old-fashioned oil, so we need not anticipate a time when gas in turn will be likely to be superseded by the electric light, there being many uses to which the one may be put, to which the latter would be altogether inapplicable; for, in the words of Dr Siemens, assuming the cost of electric light to be practically the same as gas, the preference for one or other would in each application be decided upon grounds of relative convenience, but gas-lighting would hold its own as the poor man's friend. Gas is an institution of the utmost value to the artisan; it requires hardly any attention, is supplied upon regulated terms, and gives, with what should be a cheerful light, a genial warmth, which often saves the lighting of a fire.

The revolution which gas has made in the appearance of the streets, where formerly the only illumination was that provided by each householder, who, according to his means, hung out a more or less efficient lantern, and consequently a more or less smoky one, cannot fail also to have brought about a revolution in the social aspects of the streets, and therefore is worthy to be ranked as a social reforming agent; and some slight knowledge of the process of its manufacture, such as it is here proposed to give, should be in the possession of every educated individual. Yet the subjects which must be dealt with in this chapter are so numerous and of such general interest, that we shall be unable to enter more than superficially into any one part of the whole, but shall strive to give a clear and comprehensive view, which shall satisfy the inquirer who is not a specialist.

The credit of the first attempt at utilising the gaseous product of coal for illumination appears to be due to Murdock, an engineer at Redruth, who, in 1792, introduced it into his house and offices, and who, ten years afterwards, as the result of numerous experiments which he made with a view to its utilisation, made a public display at Birmingham on the occasion of the Peace of Amiens, in 1802.

More than a century before, however, the gas obtained from coal had been experimented upon by a Dr Clayton, who, about 1690, conceived the idea of heating coal until its gaseous constituents were forced out of it. He described how he obtained steam first of all, then a black oil, and finally a "spirit," as our ancestors were wont to term the gas. This, to his surprise, ignited on a light being applied to it, and he considerably amused his friends with the wonders of this inflammatory spirit. For a century afterwards it remained in its early condition, a chemical wonder, a thing to be amused with; but it required the true genius and energy of Murdock to show the great things of which it was capable.

London received its first instalment of gas in 1807, and during the next few years its use became more and more extended, houses and streets rapidly receiving supplies in quick succession. It was not, however, till about the year 1820 that its use throughout the country became at all general, St James' Park being gas-lit in the succeeding year. This is not yet eighty years ago, and amongst the many wonderful things which have sprung up during the present century, perhaps we may place in the foremost rank for actual utility, the gas extracted from coal, conveyed as it is through miles upon miles of underground pipes into the very homes of the people, and constituting now almost as much a necessity of a comfortable existence as water itself.

The use of gas thus rapidly extended for illuminating purposes, and to a very great extent superseded the old-fashioned means of illumination.



The gas companies which sprang up were not slow to notice that, seeing the gas was supplied by meter, it was to their pecuniary advantage "to give merely the prescribed illuminating power, and to discourage the invention of economical burners, in order that the consumption might reach a maximum. The application of gas for heating purposes had not been encouraged, and was still made difficult in consequence of the objectionable practice of reducing the pressure in the mains during daytime to the lowest possible point consistent with prevention of atmospheric indraught."

The introduction of an important rival into the field in the shape of the electric light has now given a powerful impetus to the invention and introduction of effective gas-lamps, and amongst inventors of recent years no name is, perhaps, in this respect so well known as the name of Sugg. As long as gas retained almost the monopoly, there was no incentive to the gas companies to produce an effective light cheaply; but now that the question of the relative cheapness of gas and electricity is being actively discussed, the gas companies, true to the instinct of self-preservation, seem determined to show what can be done when gas is consumed in a scientific manner.

In order to understand how best a burner should be constructed in order that the gas that is burnt should give the greatest possible amount of illumination, let us consider for a moment the composition of the gas flame. It consists of three parts, (1) an interior dark space, in which the elements of the gas are in an unconsumed state; (2) an inner ring around the former, whence the greatest amount of light is obtained, and in which are numerous particles of carbon at a white heat, each awaiting a supply of oxygen in order to bring about combustion; and (3) an outer ring of blue flame in which complete combustion has taken place, and from which the largest amount of heat is evolved.

The second of these portions of the flame corresponds with the "reducing" flame of the blow-pipe, since this part, if turned upon an oxide, will reduce it, i.e., abstract its oxygen from it. This part also corresponds with the jet of the Bunsen burner, when the holes are closed by which otherwise air would mingle with the gas, or with the flame from a gas-stove when the gas ignites beneath the proper igniting-jets, and which gives consequently a white or yellow flame.

The third portion, on the other hand, corresponds with the "oxidising" flame of the blow-pipe, since it gives up oxygen to bodies that are thirsting for it. This also corresponds with the ordinary blue flame of the Bunsen burner, and with the blue flame of gas-stoves where heat, and not light, is required, the blue flame in both cases being caused by the admixture of air with the gas.

Thus, in order that gas may give the best illumination, we must increase the yellow or white space of carbon particles at a white heat, and a burner that will do this, and at the same time hold the balance so that unconsumed particles of carbon shall not escape in the way of smoke, will give the most successful illuminating results. With this end in view the addition of albo-carbon to a bulb in the gas-pipe has proved very successful, and the incandescent gas-jet is constructed on exactly the same chemical principle. The invention of burners which brought about this desirable end has doubtless not been without effect in acting as a powerful obstacle to the widespread introduction of the electric light.

Without entering into details of the manufacture of gas, it will be as well just to glance at the principal parts of the apparatus used.

The gasometer, as it has erroneously been called, is a familiar object to most people, not only to sight but unfortunately also to the organs of smell. It is in reality of course only the gas-holder, in which the final product of distillation of the coal is stored, and from which the gas immediately passes into the distributing mains.

The first, and perhaps, most important portion of the apparatus used in gas-making is the series of retorts into which the coal is placed, and from which, by the application of heat, the various volatile products distil over. These retorts are huge cast-iron vessels, encased in strong brick-work, usually five in a group, and beneath which a large furnace is kept going until the process is complete. Each retort has an iron exit pipe affixed to it, through which the gases generated by the furnace are carried off. The exit pipes all empty themselves into what is known as the hydraulic main, a long horizontal cylinder, and in this the gas begins to deposit a portion of its impurities. The immediate products of distillation are, after steam and air, gas, tar, ammoniacal liquor, sulphur in various forms, and coke, the last being left behind in the retort. In the hydraulic main some of the tar and ammoniacal liquor already begin to be deposited. The gas passes on to the condenser, which consists of a number of U-shaped pipes. Here the impurities are still further condensed out, and are collected in the tar-pit whilst the gas proceeds, still further lightened of its impurities. It may be mentioned that the temperature of the gas in the condenser is reduced to about 60 deg. F., but below this some of the most valuable of the illuminants of coal-gas would commence to be deposited in liquid form, and care has to be taken to prevent a greater lowering of temperature. A mechanical contrivance known as the exhauster is next used, by which the gas is, amongst other things, helped forward in its onward movement through the apparatus. The gas then passes to the washers or scrubbers, a series of tall towers, from which water is allowed to fall as a fine spray, and by means of which large quantities of ammonia, sulphuretted hydrogen, carbonic acid and oxide, and cyanogen compounds, are removed. In the scrubber the water used in keeping the coke, with which it is filled, damp, absorbs these compounds, and the union of the ammonia with certain of them takes place, resulting in the formation of carbonate of ammonia (smelling salts), sulphide and sulphocyanide of ammonia.



Hitherto the purification of the gas has been brought about by mechanical means, but the gas now enters the "purifier," in which it undergoes a further cleansing, but this time by chemical means.



The agent used is either lime or hydrated oxide of iron, and by their means the gas is robbed of its carbonic acid and the greater part of its sulphur compounds. The process is then considered complete, and the gas passes on into the water chamber over which the gas-holder is reared, and in which it rises through the water, forcing the huge cylinder upward according to the pressure it exerts.

The gas-holder is poised between a number of upright pillars by a series of chains and pulleys, which allow of its easy ascent or descent according as the supply is greater or less than that drawn from it by the gas mains.



When we see the process which is necessary in order to obtain pure gas, we begin to appreciate to what an extent the atmosphere is fouled when many of the products of distillation, which, as far as the production of gas is concerned, may be called impurities, are allowed to escape free without let or hindrance. In these days of strict sanitary inspection it seems strange that the air in the neighbourhood of gas-works is still allowed to become contaminated by the escape of impure compounds from the various portions of the gas-making apparatus. Go where one may, the presence of these compounds is at once apparent to the nostrils within a none too limited area around them, and yet their deleterious effects can be almost reduced to a minimum by the use of proper purifying agents, and by a scientific oversight of the whole apparatus. It certainly behoves all sanitary authorities to look well after any gas-works situated within their districts.

Now let us see what these first five products of distillation actually are.

Firstly, house-gas. Everybody knows what house-gas is. It cannot, however, be stated to be any one gas in particular, since it is a mechanical mixture of at least three different gases, and often contains small quantities of others.

A very large proportion consists of what is known as marsh-gas, or light carburetted hydrogen. This occurs occluded or locked up in the pores of the coal, and often oozes out into the galleries of coal-mines, where it is known as firedamp (German _dampf_, vapour). It is disengaged wherever vegetable matter has fallen and has become decayed. If it were thence collected, together with an admixture of ten times its volume of air, a miniature coal-mine explosion could be produced by the introduction of a match into the mixture. Alone, however, it burns with a feebly luminous flame, although to its presence our house-gas owes a great portion of its heating power. Marsh-gas is the first of the series of hydro-carbons known chemically as the _paraffins_, and is an extremely light substance, being little more than half the weight of an equal bulk of air. It is composed of four atoms of hydrogen to one of carbon (CH_{4}).

Marsh-gas, together with hydrogen and the monoxide of carbon, the last of which burns with the dull blue flame often seen at the surface of fires, particularly coke and charcoal fires, form about 87 per cent. of the whole volume of house-gas, and are none of them anything but poor illuminants.

The illuminating power of house-gas depends on the presence therein of olefiant gas (ethylene), or, as it is sometimes termed, heavy carburetted hydrogen. This is the first of the series of hydro-carbons known as the olefines, and is composed of two atoms of carbon to every four atoms of hydrogen (C{2}H{4}). Others of the olefines are present in minute quantities. These assist in increasing the illuminosity, which is sometimes greatly enhanced, too, by the presence of a small quantity of benzene vapour. These illuminants, however, constitute but about 6 per cent. of the whole.

Added to these, there are four other usual constituents which in no way increase the value of gas, but which rather detract from it. They are consequently as far as possible removed as impurities in the process of gas-making. These are nitrogen, carbonic acid gas, and the destructive sulphur compounds, sulphuretted hydrogen and carbon bisulphide vapour. It is to the last two to which are to be attributed the injurious effects which the burning of gas has upon pictures, books, and also the tarnishing which metal fittings suffer where gas is burnt, since they give rise to the formation of oil of vitriol (sulphuric acid), which is being incessantly poured into the air. Of course the amount so given off is little as compared with that which escapes from a coal fire, but, fortunately for the inmates of the room, in this case the greater quantity goes up the chimney; this, however, is but a method of postponing the evil day, until the atmosphere becomes so laden with impurities that what proceeds at first up the chimney will finally again make its way back through the doors and windows. A recent official report tells us that, in the town, of St Helen's alone, sufficient sulphur escapes annually into the atmosphere to finally produce 110,580 tons of sulphuric acid, and a computation has been made that every square mile of land in London is deluged annually with 180 tons of the same vegetation-denuding acid. It is a matter for wonder that any green thing continues to exist in such places at all.

The chief constituents of coal-gas are, therefore, briefly as follows:—

/ (1) Hydrogen, (2) Marsh-gas (carburetted hydrogen or fire-damp), (3) Carbon monoxide, (4) Olefiant gas (ethylene, or heavy carburetted hydrogen), with other olefines, / (5) Nitrogen, (6) Carbonic acid gas, (7) Sulphuretted hydrogen, (8) Carbon bisulphide (vapour),

the last four being regarded as impurities, which are removed as far as possible in the manufacture.

In the process of distillation of the coal, we have seen that various other important substances are brought into existence. The final residue of coke, which is impregnated with the sulphur which has not been volatilised in the form of sulphurous gases, we need scarcely more than mention here. But the gas-tar and the ammoniacal liquor are two important products which demand something more than our casual attention. At one time regarded by gas engineers as unfortunately necessary nuisances in the manufacture of gas, they have both become so valuable on account of materials which can be obtained from them, that they enable gas itself to be sold now at less than half its original price. The waste of former generations is being utilised in this, and an instance is recorded in which tar, which was known to have been lying useless at the bottom of a canal for years, has been purchased by a gas engineer for distilling purposes. It has been estimated that about 590,000 tons of coal-tar are distilled annually.

Tar in its primitive condition has been used, as every one is aware, for painting or tarring a variety of objects, such as barges and palings, in fact, as a kind of protection to the object covered from the ravages of insects or worms, or to prevent corrosion when applied to metal piers. But it is worthy of a better purpose, and is capable of yielding far more useful and interesting substances than even the most imaginative individual could have dreamed of fifty years ago.

In the process of distillation, the tar, after standing in tanks for some time, in order that any ammoniacal liquor which may be present may rise to the surface and be drawn off, is pumped into large stills, where a moderate amount of heat is applied to it. The result is that some of the more volatile products pass over and are collected in a receiver. These first products are known as first light oils, or crude coal-naphtha, and to this naphtha all the numerous natural naphthas which have been discovered in various portions of the world, and to which have been applied numerous local names, bear a very close resemblance. Such an one, for instance, was that small but famous spring at Biddings, in Derbyshire, from which the late Mr Young—Paraffin Young—obtained his well-known paraffin oil, which gave the initial impetus to what has since developed into a trade of immense proportions in every quarter of the globe.

After a time the crude coal-naphtha ceases to flow over, and the heat is increased. The result is that a fresh series of products, known as medium oils, passes over, and these oils are again collected and kept separate from the previous series. These in turn cease to flow, when, by a further increase of heat, what are known as the heavy oils finally pass over, and when the last of these, green grease, as it is called, distils over, pitch alone is left in the still. Pitch is used to a large extent in the preparation of artificial asphalte, and also of a fuel known as "briquettes."

The products thus obtained at the various stages of the process are themselves subjected to further distillation, and by the exercise of great care, requiring the most delicate and accurate treatment, a large variety of oils is obtained, and these are retailed under many and various fanciful names.

One of the most important and best known products of the fractional distillation of crude coal-naphtha is that known as benzene, or benzole, (C{6}H{6}). This, in its unrefined condition, is a light spirit which distils over at a point somewhat below the boiling point of water, but a delicate process of rectification is necessary to produce the pure spirit. Other products of the same light oils are toluene and xylene.

Benzene of a certain quality is of course a very familiar and useful household supplement. It is sometimes known and sold as benzene collas, and is used for removing grease from clothing, cleaning kid gloves, &c. If pure it is in reality a most dangerous spirit, being very inflammable; it is also extremely volatile, so much so that, if an uncorked bottle be left in a warm room where there is a fire or other light near, its vapour will probably ignite. Should the vapour become mixed with air before ignition, it becomes a most dangerous explosive, and it will thus be seen how necessary it is to handle the article in household use in a most cautious manner. Being highly volatile, a considerable degree of cold is experienced if a drop be placed on the hand and allowed to evaporate.

Benzene, which is only a compound of carbon and hydrogen, was first discovered by Faraday in 1825; it is now obtained in large quantities from coal-tar, not so much for use as benzene; is for its conversion, in the first place, by the action of nitric acid, into nitro-benzole, a liquid having an odour like the oil of bitter almonds, and which is much used by perfumers under the name of essence de mirbane; and, in the second place, for the production from this nitro-benzole of the far-famed aniline. After the distillation of benzene from the crude coal-naphtha is completed, the chief impurities in the residue are charred and deposited by the action of strong sulphuric acid. By further distillation a lighter oil is given off, often known as artificial turpentine oil, which is used as a solvent for varnishes and lackers. This is very familiar to the costermonger fraternity as the oil which is burned in the flaring lamps which illuminate the New Cut or the Elephant and Castle on Saturday and other market nights.

By distillation of the heavy oils, carbolic acid and commercial anthracene are produced, and by a treatment of the residue, a white and crystalline substance known as naphthalin (C{10}H{8}) is finally obtained.

Thus, by the continued operation of the chemical process known as fractional distillation of the immediate products of coal-tar, these various series of useful oils are prepared.

The treatment is much the same which has resulted in the production of paraffin oil, to which we have previously referred, and an account of the production of coal-oils would be very far from satisfactory, which made no mention of the production of similar commodities by the direct distillation of shale. Oil-shales, or bituminous shales, exist in all parts of the world, and may be regarded as mineral matter largely impregnated by the products of decaying vegetation. They therefore greatly resemble some coals, and really only differ therefrom in degree, in the quantity of vegetable matter which they contain. Into the subject of the various native petroleums which have been found—for these rock-oils are better known as petroleums—in South America, in Burmah (Rangoon Oil), at Baku, and the shores of the Caspian, or in the United States of America, we need not enter, except to note that in all probability the action of heat on underground bituminous strata of enormous extent has been the cause of their production, just as on a smaller scale the action of artificial heat has forced the reluctant shale to give up its own burden of mineral oil. However, previous to 1847, although native mineral oil had been for some years a recognised article of commerce, the causes which gave rise to the oil-wells, and the source, probably a deep-seated one, of the supply of oil, does not appear to have been well known, or at least was not enquired after. But in that year Mr Young, a chemist at Manchester, discovered that by distilling some petroleum, which he obtained from a spring at Riddings in Derbyshire, he was able to procure a light oil, which he used for burning in lamps, whilst the heavier product which he also obtained proved a most useful lubricant for machinery. This naturally distilled oil was soon found to be similar to that oil which was noticed dripping from the roof of a coal-mine. Judging that the coal, being under the influence of heat, was the cause of the production of the oil, Mr Young tested this conclusion by distilling the coal itself. Success attended his endeavour thus to procure the oil, and indelibly Young stamped his name upon the roll of famous men, whose industrial inventions have done so much towards the accomplishment of the marvellous progress of the present century. From the distillation he obtained the well-known Young's Paraffin Oil, and the astonishing developments of the process which have taken place since he obtained his patent in 1850, for the manufacture of oils and solid paraffin, must have been a source of great satisfaction to him before his death, which occurred in 1883.

Cannel coal, Boghead or Bathgate coal, and bituminous shales of various qualities, have all been requisitioned for the production of oils, and from these various sources the crude naphthas, which bear a variety of names according to some peculiarity in their origin, or place of occurrence, are obtained. Boghead coal, also known as "Torebanehill mineral," gives Boghead naphtha, while the crude naphtha obtained from shales is often quoted as shale-oil. In chemical composition these naphthas are closely related to one another, and by fractional distillation of them similar series of products are obtained as those we have already seen as obtained from the crude coal-naphtha of coal-tar.

In the direct distillation of cannel-coal for the production of paraffin, it is necessary that the perpendicular tubes or retorts into which the coal is placed be heated only to a certain temperature, which is considerably lower than that applied when the object is the production of coal-gas. By this means nearly all the volatile matters pass over in the form of condensible vapours, and the crude oils are at once formed, from whence are obtained at different temperatures various volatile ethers, benzene, and artificial turpentine oil or petroleum spirit. After these, the well-known safety-burning paraffin oil follows, but it is essential that the previous three volatile products be completely cleared first, since, mixed with air, they form highly dangerous explosives. To the fact that the operation is carried on in the manufactories with great care and accuracy can only be attributed the comparative rareness of explosions of the oil used in households.

After paraffin, the heavy lubricating oils are next given off, still increasing the temperature, and, the residue being in turn subjected to a very low temperature, the white solid substance known as paraffin, so much used for making candles, is the result. By a different treatment of the same residue is produced that wonderful salve for tender skins, cuts, and burns, known popularly as vaseline. Probably no such widely-advertised remedial substance has so deserved its success as this universally-used waste product of petroleum.

We have noticed the fact that in order to procure safety-burning oils, it is absolutely necessary that the more volatile portions be completely distilled over first. By Act of Parliament a test is applied to all oils which are intended for purposes of illumination, and the test used consists of what is known as the flashing-point. Many of the more volatile ethers, which are highly inflammable, are given off even at ordinary temperatures, and the application of a light to the oil will cause the volatile portion to "flash," as it is called. A safety-burning oil, according to the Act, must not flash under 100 deg. Fahrenheit open test, and all those portions which flash at a less temperature must be volatilised off before the residue can be deemed a safe oil. It seems probable that the flashing-point will sooner or later be raised.

One instance may be cited to show how necessary it is that the native mineral oils which have been discovered should have this effectual test applied to them.

When the oil-wells were first discovered in America, the oil was obtained simply by a process of boring, and the fountain of oil which was bored into at times was so prolific, that it rushed out with a force which carried all obstacles before it, and defied all control. In one instance a column of oil shot into the air to a height of forty feet, and defied all attempts to keep it under. In order to prevent further accident, all lights in the immediate neighbourhood were extinguished, the nearest remaining being at a distance of four hundred feet. But in this crude naphtha there was, as usual, a quantity of volatile spirit which was being given off even at the temperature of the surrounding atmosphere. This soon became ignited, and with an explosion the column of oil was suddenly converted into a roaring column of fire. The owner of the property was thrown a distance of twenty feet by the explosion, and soon afterwards died from the burns which he had received from it. Such an accident could not now, however, happen. The tapping, stopping, and regulating of gushing wells can now be more effectually dealt with, and in the process of refining; the most inflammable portions are separated, with a result that, as no oil is used in the country which flashes under 100 deg. F. open test, and as our normal temperature is considerably less than this, there is little to be feared in the way of explosion if the Act be complied with.

When the results of Mr Young's labours became publicly known, a number of companies were started with the object of working on the lines laid down in his patent, and these not only in Great Britain but also in the United States, whither quantities of cannel coal were shipped from England and other parts to feed the retorts. In 1860, according to the statistics furnished, some seventy factories were established in the United States alone with the object of extracting oil from coal and other mineral sources, such as bituminous shale, etc. When Young's patent finally expired, a still greater impetus was given to its production, and the manufacture would probably have continued to develop were it not that attention had, two years previously, been forcibly turned to those discoveries of great stores of natural oil in existence beneath a comparatively thin crust of earth, and which, when bored into, spouted out to tremendous heights.

The discovery of these oil-fountains checked for a time the development of the industry, but with the great production there has apparently been a greatly increased demand for it, and the British industry once again appears to thrive, until even bituminous shales have been brought under requisition for their contribution to the national wealth.

Were it not for the nuisance and difficulty experienced in the proper cleaning and trimming of lamps, there seems no other reason why mineral oil should not in turn have superseded the use of gas, even as gas had, years before, superseded the expensive animal and vegetable oils which had formerly been in use.

Although this great development in the use of mineral oils has taken place only within the last thirty years, it must not be thought that their use is altogether of modern invention. That they were not altogether unknown in the fifth century before Christ is a matter of certainty, and at the time when the Persian Empire was at the zenith of its glory, the fires in the temples of the fire-worshippers were undoubtedly kept fed by the natural petroleum which the districts around afforded. It is thought by some that the legend which speaks of the fire which came down from heaven, and which lit the altars of the Zoroastrians, may have had its origin in the discovery of a hitherto unknown petroleum spring. More recently, the remarks of Marco Polo in his account of his travels in A.D. 1260 and following years, are particularly interesting as showing that, even then, the use of mineral oil for various purposes was not altogether unknown. He says that on the north of Armenia the Greater is "Zorzania, in the confines of which a fountain is found, from which a liquor like oil flows, and though unprofitable for the seasoning of meat, yet is very fit for the supplying of lamps, and to anoint other things; and this natural oil flows constantly, and that in plenty enough to lade camels."

From this we can infer that the nature of the oil was entirely unknown, for it was a "liquor like oil," and was also, strange to say, "unprofitable for the seasoning of meat"! In another place in Armenia, Marco Polo states that there was a fountain "whence rises oil in such abundance that a hundred ships might be at once loaded with it. It is not good for eating, but very fit for fuel, for anointing the camels in maladies of the skin, and for other purposes; for which reason people come from a great distance for it, and nothing else is burned in all this country."

The remedial effects of the oil, when used as an ointment, were thus early recognised, and the far-famed vaseline of the present day may be regarded as the lineal descendent, so to speak, of the crude medicinal agent to which Marco Polo refers.