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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/12762-0.txt b/12762-0.txt new file mode 100644 index 0000000..adc9933 --- /dev/null +++ b/12762-0.txt @@ -0,0 +1,4392 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 12762 *** + +THE STORY OF +A PIECE OF COAL + +WHAT IT IS, WHENCE IT COMES, +AND WHITHER IT GOES + +BY +EDWARD A. MARTIN, F.G.S. + +1896 + + + + + +PREFACE. + + +The knowledge of the marvels which a piece of coal possesses within +itself, and which in obedience to processes of man's invention it is +always willing to exhibit to an observant enquirer, is not so widespread, +perhaps, as it should be, and the aim of this little book, this record of +one page of geological history, has been to bring together the principal +facts and wonders connected with it into the focus of a few pages, where, +side by side, would be found the record of its vegetable and mineral +history, its discovery and early use, its bearings on the great +fog-problem, its useful illuminating gas and oils, the question of the +possible exhaustion of British supplies, and other important and +interesting bearings of coal or its products. + +In the whole realm of natural history, in the widest sense of the term, +there is nothing which could be cited which has so benefited, so +interested, I might almost say, so excited mankind, as have the wonderful +discoveries of the various products distilled from gas-tar, itself a +distillate of coal. + +Coal touches the interests of the botanist, the geologist, and the +physicist; the chemist, the sanitarian, and the merchant. + +In the little work now before the reader I have endeavoured to recount, +without going into unnecessary detail, the wonderful story of a piece of +coal. + +E.A.M. + +THORNTON HEATH, + +_February_, 1896. + + + + +CONTENTS. + + + I. THE ORIGIN OF COAL AND THE PLANTS OF WHICH IT IS COMPOSED + + II. A GENERAL VIEW OF THE COAL-BEARING STRATA + + III. VARIOUS FORMS OF COAL AND CARBON + + IV. THE COAL-MINE AND ITS DANGERS + + V. EARLY HISTORY--ITS USE AND ITS ABUSE + + VI. HOW GAS IS MADE--ILLUMINATING OILS AND BYE-PRODUCTS + + VII. THE COAL SUPPLIES OF THE WORLD + +VIII. THE COAL-TAR COLOURS + +CHART SHEWING THE PRODUCTS OF COAL + +GENERAL INDEX + + + +LIST OF ILLUSTRATIONS. + +FIG. 1. _Stigmaria_ + " 2. _Annularia radiata_ + " 3. _Rhacopteris inaequilatera_ + " 4. Frond of _Pecopteris_ + " 5. _Pecopteris Serlii_ + " 6. _Sphenopteris affinis_ + " 7. _Catamites Suckowii_ + " 8. _Calamocladus grandis_ + " 9. _Asterophyllites foliosa_ + " 10. _Spenophyllum cuneifolium_ + " 11. Cast of _Lepidodendron_ + " 12. _Lepidodendron longifolium_ + " 13. _Lepidodendron aculeatum_ + " 14. _Lepidostrobus_ + " 15. _Lycopodites_ + " 16. _Stigmaria ficoides_ + " 17. Section of _Stigmaria_ + " 18. Sigillarian trunks in sandstone + " 19. _Productus_ + " 20. _Encrinite_ + " 21. Encrinital limestone + " 22. Various _encrinites_ + " 23. _Cyathophyllum_ + " 24. _Archegosaurus minor_ + " 25. _Psammodus porosus_ + " 26. _Orthoceras_ + " 27. _Fenestella retepora_ + " 28. _Goniatites_ + " 29. _Aviculopecten papyraceus_ + " 30. Fragment of _Lepidodendron_ + " 31. Engine-house at head of a Coal-Pit + " 32. Gas Jet and Davy Lamp + " 33. Part of a Sigillarian trunk + " 34. Inside a Gas-holder + " 35. Filling Retorts by Machinery + " 36. "Condensers" + " 37. "Washers" + " 38. "Purifiers" + + + + +CHAPTER I. + +THE ORIGIN OF COAL AND THE PLANTS OF +WHICH IT IS COMPOSED. + + +From the homely scuttle of coal at the side of the hearth to the +gorgeously verdant vegetation of a forest of mammoth trees, might have +appeared a somewhat far cry in the eyes of those who lived some fifty +years ago. But there are few now who do not know what was the origin of +the coal which they use so freely, and which in obedience to their demand +has been brought up more than a thousand feet from the bowels of the +earth; and, although familiarity has in a sense bred contempt for that +which a few shillings will always purchase, in all probability a stray +thought does occasionally cross one's mind, giving birth to feelings of a +more or less thankful nature that such a store of heat and light was long +ago laid up in this earth of ours for our use, when as yet man was not +destined to put in an appearance for many, many ages to come. We can +scarcely imagine the industrial condition of our country in the absence +of so fortunate a supply of coal; and the many good things which are +obtained from it, and the uses to which, as we shall see, it can be put, +do indeed demand recognition. + +Were our present forests uprooted and overthrown, to be covered by +sedimentary deposits such as those which cover our coal-seams, the amount +of coal which would be thereby formed for use in some future age, would +amount to a thickness of perhaps two or three inches at most, and yet, in +one coal-field alone, that of Westphalia, the 117 most important seams, +if placed one above the other in immediate succession, would amount to no +less than 294 feet of coal. From this it is possible to form a faint idea +of the enormous growths of vegetation required to form some of our +representative coal beds. But the coal is not found in one continuous +bed. These numerous seams of coal are interspersed between many thousands +of feet of sedimentary deposits, the whole of which form the +"coal-measures." Now, each of these seams represents the growth of a +forest, and to explain the whole series it is necessary to suppose that +between each deposit the land became overwhelmed by the waters of the sea +or lake, and after a long subaqueous period, was again raised into dry +land, ready to become the birth-place of another forest, which would +again beget, under similarly repeated conditions, another seam of coal. +Of the conditions necessary to bring these changes about we will speak +later on, but this instance is sufficient to show how inadequate the +quantity of fuel would be, were we dependent entirely on our own existing +forest growths. + +However, we will leave for the present the fascinating pursuit of +theorising as to the how and wherefore of these vast beds of coal, +relegating the geological part of the study of the carboniferous system +to a future chapter, where will be found some more detailed account of +the position of the coal-seams in the strata which contain them. At +present the actual details of the coal itself will demand our attention. + +Coal is the mineral which has resulted, after the lapse of thousands of +thousands of years, from the accumulations of vegetable material, caused +by the steady yearly shedding of leaves, fronds and spores, from forests +which existed in an early age; these accumulated where the trees grew +that bore them, and formed in the first place, perhaps, beds of peat; the +beds have since been subjected to an ever-increasing pressure of +accumulating strata above them, compressing the sheddings of a whole +forest into a thickness in some cases of a few inches of coal, and have +been acted upon by the internal heat of the earth, which has caused them +to part, to a varying degree, with some of their component gases. If we +reason from analogy, we are compelled to admit that the origin of coal is +due to the accumulation of vegetation, of which more scattered, but more +distinct, representative specimens occur in the shales and clays above +and below the coal-seams. But we are also able to examine the texture +itself of the various coals by submitting extremely thin slices to a +strong light under the microscope, and are thus enabled to decide whether +the particular coal we are examining is formed of conifers, horse-tails, +club-mosses, or ferns, or whether it consists simply of the accumulated +sheddings of all, or perhaps, as in some instances, of innumerable +spores. + +In this way the structure of coal can be accurately determined. Were we +artificially to prepare a mass of vegetable substance, and covering it up +entirely, subject it to great pressure, so that but little of the +volatile gases which would be formed could escape, we might in the course +of time produce something approaching coal, but whether we obtained +lignite, jet, common bituminous coal, or anthracite, would depend upon +the possibilities of escape for the gases contained in the mass. + +Everybody has doubtless noticed that, when a stagnant pool which contains +a good deal of decaying vegetation is stirred, bubbles of gas rise to the +surface from the mud below. This gas is known as marsh-gas, or light +carburetted hydrogen, and gives rise to the _ignis fatuus_ which hovers +about marshy land, and which is said to lure the weary traveller to his +doom. The vegetable mud is here undergoing rapid decomposition, as there +is nothing to stay its progress, and no superposed load of strata +confining its resulting products within itself. The gases therefore +escape, and the breaking-up of the tissues of the vegetation goes on +rapidly. + +The chemical changes which have taken place in the beds of vegetation of +the carboniferous epoch, and which have transformed it into coal, are +even now but imperfectly understood. All we know is that, under certain +circumstances, one kind of coal is formed, whilst under other conditions, +other kinds have resulted; whilst in some cases the processes have +resulted in the preparation of large quantities of mineral oils, such as +naphtha and petroleum. Oils are also artificially produced from the +so-called waste-products of the gas-works, but in some parts of the world +the process of their manufacture has gone on naturally, and a yearly +increasing quantity is being utilised. In England oil has been pumped up +from the carboniferous strata of Coalbrook Dale, whilst in Sussex it has +been found in smaller quantities, where, in all probability, it has had +its origin in the lignitic beds of the Wealden strata. Immense quantities +are used for fuel by the Russian steamers on the Caspian Sea, the Baku +petroleum wells being a most valuable possession. In Sicily, Persia, and, +far more important, in the United States, mineral oils are found in great +quantity. + +In all probability coniferous trees, similar to the living firs, pines, +larches, &c., gave rise for the most part to the mineral oils. The class +of living _coniferae_ is well known for the various oils which it +furnishes naturally, and for others which its representatives yield on +being subjected to distillation. The gradually increasing amount of heat +which we meet the deeper we go beneath the surface, has been the cause of +a slow and continuous distillation, whilst the oil so distilled has found +its way to the surface in the shape of mineral-oil springs, or has +accumulated in troughs in the strata, ready for use, to be drawn up when +a well has been sunk into it. + +The plants which have gone to make up the coal are not at once apparent +to the naked eye. We have to search among the shales and clays and +sandstones which enclose the coal-seams, and in these we find petrified +specimens which enable us to build up in our mind pictures of the +vegetable creation which formed the jungles and forests of these +immensely remote ages, and which, densely packed together on the old +forest floor of those days, is now apparent to us as coal. + +[Illustration: Fig. 2.--_Annularia radiata._ Carboniferous sandstone.] + +A very large proportion of the plants which have been found in the +coal-bearing strata consists of numerous species of ferns, the number of +actual species which have been preserved for us in our English coal, +being double the number now existing in Europe. The greater part of these +do not seem to have been very much larger than our own living ferns, and, +indeed, many of them bear a close resemblance to some of our own living +species. The impressions they have left on the shales of the +coal-measures are most striking, and point to a time when the sandy clay +which imbedded them was borne by water in a very tranquil manner, to be +deposited where the ferns had grown, enveloping them gradually, and +consolidating them into their mass of future shale. In one species known +as the _neuropteris_, the nerves of the leaves are as clear and as +apparent as in a newly-grown fern, the name being derived from two Greek +words meaning "nerve-fern." It is interesting to consider the history of +such a leaf, throughout the ages that have elapsed since it was part of a +living fern. First it grew up as a new frond, then gradually unfolded +itself, and developed into the perfect fern. Then it became cut off by +the rising waters, and buried beneath an accumulation of sediment, and +while momentous changes have gone on in connection with the surface of +the earth, it has lain dormant in its hiding-place exactly as we see it, +until now excavated, with its contemporaneous vegetation, to form fuel +for our winter fires. + +[Illustration: FIG. 3.--_Rhacopteris inaequilatera._ Carboniferous +limestone.] + +Although many of the ferns greatly resembled existing species, yet there +were others in these ancient days utterly unlike anything indigenous to +England now. There were undoubted tree-ferns, similar to those which +thrive now so luxuriously in the tropics, and which throw out their +graceful crowns of ferns at the head of a naked stem, whilst on the bark +are the marks at different levels of the points of attachment of former +leaves. These have left in their places cicatrices or scars, showing the +places from which they formerly grew. Amongst the tree-ferns found are +_megaphyton_, _paloeopteris_, and _caulopteris_, all of which have these +marks upon them, thus proving that at one time even tree-ferns had a +habitat in England. + +[Illustration: Fig. 4.--Frond of _Pecopteris._ Coal-shale.] + +One form of tree-fern is known by the name of _Psaronius_, and this was +peculiar in the possession of masses of aerial roots grouped round the +stem. Some of the smaller species exhibit forms of leaves which are +utterly unknown in the nomenclature of living ferns. Most have had names +assigned to them in accordance with certain characteristics which they +possess. This was the more possible since the fossilised impressions had +been retained in so distinct a manner. Here before us is a specimen in a +shale of _pecopteris_, as it is called, (_pekos_, a comb). The leaf in +some species is not altogether unlike the well-known living fern +_osmunda_. The position of the pinnules on both sides of the central +stalk are seen in the fossil to be shaped something like a comb, or a +saw, whilst up the centre of each pinnule the vein is as prominent and +noticeable as if the fern were but yesterday waving gracefully in the +air, and but to-day imbedded in its shaly bed. + +[Illustration: FIG. 5.--_Pecopteris Serlii_. Coal-shale.] + +_Sphenopteris_, or "wedge-fern," is the name applied to another +coal-fern; _glossopteris_, or "tongue-leaf"; _cyclopteris_, or +"round-leaf"; _odonlopteris,_ or "tooth-leaf," and many others, show +their chief characteristics in the names which they individually bear. +_Alethopteris_ appears to have been the common brake of the coal-period, +and in some respects resembles _pecopteris_. + +[Illustration: Fig. 6.--_Sphenopteris Affinis._ Coal-shale.] + +In some species of ferns so exact are the representations which they have +impressed on the shale which contains them, that not only are the veins +and nerves distinctly visible, but even the fructification still remains +in the shape of the marks left by the so-called seeds on the backs of the +leaves. Something more than a passing look at the coal specimens in a +good museum will well repay the time so spent. + +What are known as septarian nodules, or snake-stones, are, at certain +places, common in the carboniferous strata. They are composed of layers +of ironstone and sandstone which have segregated around some central +object, such as a fern-leaf or a shell. When the leaf of a fern has been +found to be the central object, it has been noticed that the leaf can +sometimes be separated from the stone in the form of a carbonaceous film. + +Experiments were made many years ago by M. Goppert to illustrate the +process of fossilisation of ferns. Having placed some living ferns in a +mass of clay and dried them, he exposed them to a red heat, and obtained +thereby striking resemblances to fossil plants. According to the degree +of heat to which they were subjected, the plants were found to be either +brown, a shining black, or entirely lost. In the last mentioned case, +only the impression remained, but the carbonaceous matter had gone to +stain the surrounding clay black, thus indicating that the dark colour of +the coal-shales is due to the carbon derived from the plants which they +included. + +Another very prominent member of the vegetation of the coal period, was +that order of plants known as the _Calamites_. The generic distinctions +between fossil and living ferns were so slight in many cases as to be +almost indistinguishable. This resemblance between the ancient and the +modern is not found so apparent in other plants. The Calamites of the +coal-measures bore indeed a very striking resemblance, and were closely +related, to our modern horse-tails, as the _equiseta_ are popularly +called; but in some respects they differed considerably. + +Most people are acquainted with the horse-tail (_equisetum fluviatile)_ +of our marshes and ditches. It is a somewhat graceful plant, and stands +erect with a jointed stem. The foliage is arranged in whorls around the +joints, and, unlike its fossil representatives, its joints are protected +by striated sheaths. The stem of the largest living species rarely +exceeds half-an-inch in diameter, whilst that of the calamite attained a +thickness of five inches. But the great point which is noticeable in the +fossil calamites and _equisetites_ is that they grew to a far greater +height than any similar plant now living, sometimes being as much as +eight feet high. In the nature of their stems, too, they exhibited a more +highly organised arrangement than their living representatives, having, +according to Dr Williamson, a "fistular pith, an exogenous woody stem, +and a thick smooth bark." The bark having almost al ways disappeared has +left the fluted stem known to us as the calamite. The foliage consisted +of whorls of long narrow leaves, which differed only from the fern +_asterophyllites_ in the fact that they were single-nerved. Sir William +Dawson assigns the calamites to four sub-types: _calamite_ proper, +_calamopitus, calamodendron_, and _eucalamodendron_. + +[Image: FIG. 7.--Root of _Catamites Suckowii_. Coal-shale.] + +[Image: FIG 8.--_Calamocladus grandis_. Carboniferous sandstone.] + +Having used the word "exogenous," it might be as well to pay a little +attention, in passing, to the nomenclature and broad classification of +the various kinds of plants. We shall then doubtless find it far easier +thoroughly to understand the position in the scale of organisation to +which the coal plants are referable. + +[Illustration: FIG. 9.--_Asterophyllites foliosa_. Coal-measures.] + +The plants which are lowest in organisation are known as _Cellular_. They +are almost entirely composed of numerous cells built up one above the +other, and possess none of the higher forms of tissue and organisation +which are met with elsewhere. This division includes the lichens, +sea-weeds, confervae (green aquatic scum), fungi (mushrooms, dry-rot), +&c. + +The division of _Vascular_ plants includes the far larger proportion of +vegetation, both living and fossil, and these plants are built up of +vessels and tissues of various shapes and character. + +All plants are divided into (1) Cryptogams, or Flowerless, such as +mosses, ferns, equisetums, and (2) Phanerogams, or Flowering. Flowering +plants are again divided into those with naked seeds, as the conifers and +cycads (gymnosperms), and those whose seeds are enclosed in vessels, or +ovaries (angiosperms). + +Angiosperms are again divided into the monocotyledons, as the palms, and +dicotyledons, which include most European trees. + +Thus:-- + +------------------------------------------------------------------- +| (M.A. Brongniart). | |(Lindley). | +|CELLULAR | | | +| _Cryptogams_ (Flowerless) |Fungi, seaweeds, |Thallogens | +| | lichens | | +| | | | +|VASCULAR | | | +| _Cryptogams_ (Flowerless) |Ferns, equisetums, |Acrogens | +| | mosses, lycopodiums| | +| _Phanerogams_ (Flowering) | | | +| Gymnosperms (having |Conifers and |Gymnogens | +| naked seeds) | cycads | | +| Two or more Cotyledons | | | +| Angiosperms (having | | | +| enclosed seeds) | | | +| Monocotyledons |Palms, lilies, |Endogens | +| | grasses | | +| Dicotyledons |Most European |Exogens | +| | trees and shrubs | | +------------------------------------------------------------------- + +Adolphe Brongniart termed the coal era the "Age of Acrogens," because, as +we shall see, of the great predominance in those times of vascular +cryptogamic plants, known in Dr Lindley's nomenclature as "Acrogens." + +[Illustration: FIG. 10.--_Spenophyllum cuneifolium._ Coal-shale.] + +Two of these families have already been dealt with, viz., the ferns +(_felices_), and the equisetums, (_calamites_ and _equisetites_), and we +now have to pass on to another family. This is that which includes the +fossil representatives of the Lycopodiums, or Club-mosses, and which goes +to make up in some coals as much as two-thirds of the whole mass. +Everyone is more or less familiar with some of the living Lycopodiums, +those delicate little fern-like mosses which are to be found in many a +home. They are but lowly members of our British flora, and it may seem +somewhat astounding at first sight that their remote ancestors occupied +so important a position in the forests of the ancient period of which we +are speaking. Some two hundred living species are known, most of them +being confined to tropical climates. They are as a rule, low creeping +plants, although some few stand erect. There is room for astonishment +when we consider the fact that the fossil representatives of the family, +known as _Lepidodendra_, attained a height of no less than fifty feet, +and, there is good ground for believing, in many cases, a far greater +magnitude. They consist of long straight stems, or trunks which branch +considerably near the top. These stems are covered with scars or scales, +which have been caused by the separation of the petioles or leaf-stalks, +and this gives rise to the name which the genus bears. The scars are +arranged in a spiral manner the whole of the way up the stem, and the +stems often remain perfectly upright in the coal-mines, and reach into +the strata which have accumulated above the coal-seam. + +[Illustration: FIG. 11.--Cast of _lepidodendron_ in sandstone.] + +Count Sternberg remarked that we are unacquainted with any existing +species of plant, which like the _Lepidodendron_, preserves at all ages, +and throughout the whole extent of the trunk, the scars formed by the +attachment of the petioles, or leaf-stalks, or the markings of the leaves +themselves. The yucca, dracaena, and palm, entirely shed their scales +when they are dried up, and there only remain circles, or rings, arranged +round the trunk in different directions. The flabelliform palms preserve +their scales at the inferior extremity of the trunk only, but lose them +as they increase in age; and the stem is entirely bare, from the middle +to the superior extremity. In the ancient _Lepidodendron_, on the other +hand, the more ancient the scale of the leaf-stalk, the more apparent it +still remains. Portions of stems have been discovered which contain +leaf-scars far larger than those referred to above, and we deduce from +these fragments the fact that those individuals which have been found +whole, are not by any means the largest of those which went to form so +large a proportion of the ancient coal-forests. The _lepidodendra_ bore +linear one-nerved leaves, and the stems always branched dichotomously and +possessed a central pith. Specimens variously named _knorria, +lepidophloios, halonia_, and _ulodendron_ are all referable to this +family. + +[Illustration: FIG. 12.--_Lepidodendron longifolium._ Coal-shale.] + +[Illustration: FIG. 13.--_Lepidodendron aculeatum_ in sandstone.] + +In some strata, as for instance that of the Shropshire coalfield, +quantities of elongated cylindrical bodies known as _lepidostrobi_ have +been found, which, it was early conjectured, were the fruit of the giant +club-mosses about which we have just been speaking. Their appearance can +be called to mind by imagining the cylindrical fruit of the maize or +Indian corn to be reduced to some three or four inches in length. The +sporangia or cases which contained the microscopic spores or seeds were +arranged around a central axis in a somewhat similar manner to that in +which maize is found. These bodies have since been found actually +situated at the end of branches of _lepidodendron_, thus placing their +true nature beyond a doubt. The fossil seeds (spores) do not appear to +have exceeded in volume those of recent club-mosses, and this although +the actual trees themselves grew to a size very many times greater than +the living species. This minuteness of the seed-germs goes to explain the +reason why, as Sir Charles Lyell remarked, the same species of +_lepidodendra_ are so widely distributed in the coal measures of Europe +and America, their spores being capable of an easy transportation by the +wind. + +[Illustration: FIG. 14.--_Lepidostrobus._ Coal-shale.] + +One striking feature in connection with the fruit of the _lepidodendron_ +and other ancient representatives of the club-moss tribe, is that the +bituminous coals in many, if not in most, instances, are made up almost +entirely of their spores and spore-cases. Under a microscope, a piece of +such coal is seen to be thronged with the minute rounded bodies of the +spores interlacing one another and forming almost the whole mass, whilst +larger than these, and often indeed enclosing them, are flattened +bag-like bodies which are none other than the compressed sporangia which +contained the former. + +[Illustration: FIG. 15.--_Lycopodites_. Coal sandstone.] + +Now, the little Scottish or Alpine club-moss which is so familiar, +produces its own little cones, each with its series of outside scales or +leaves; these are attached to the bags or spore-cases, which are crowded +with spores. Although in miniature, yet it produces its fruit in just the +same way, at the terminations of its little branches, and the spores, the +actual germs of life, when examined microscopically, are scarcely +distinguishable from those which are contained in certain bituminous +coals. And, although ancient club-mosses have been found in a fossilised +condition at least forty-nine feet high, the spores are no larger than +those of our miniature club-mosses of the present day. + +The spores are more or less composed of pure bitumen, and the bituminous +nature of the coal depends largely on the presence or absence of these +microscopic bodies in it. The spores of the living club-mosses contain so +much resinous matter that they are now largely used in the making of +fireworks, and upon the presence of this altered resinous matter in coal +depends its capability of providing a good blazing coal. + +At first sight it seems almost impossible that such a minute cause should +result in the formation of huge masses of coal, such an inconceivable +number of spores being necessary to make even the smallest fragment of +coal. But if we look at the cloud of spores that can be shaken from a +single spike of a club-moss, then imagine this to be repeated a thousand +times from each branch of a fairly tall tree, and then finally picture a +whole forest of such trees shedding in due season their copious showers +of spores to earth, we shall perhaps be less amazed than we were at first +thought, at the stupendous result wrought out by so minute an object. + +Another well-known form of carboniferous vegetation is that known as the +_Sigillaria_, and, connected with this form is one, which was long +familiar under the name of _Stigmaria_, but which has since been +satisfactorily proved to have formed the branching root of the +sigillaria. The older geologists were in the habit of placing these +plants among the tree-ferns, principally on account of the cicatrices +which were left at the junctions of the leaf-stalks with the stem, after +the former had fallen off. No foliage had, however, been met with which +was actually attached to the plants, and hence, when it was discovered +that some of them had long attenuated leaves not at all like those +possessed by ferns, geologists were compelled to abandon this +classification of them, and even now no satisfactory reference to +existing orders of them has been made, owing to their anomalous +structure. The stems are fluted from base to stem, although this is not +so apparent near the base, whilst the raised prominences which now form +the cicatrices, are arranged at regular distances within the vertical +grooves. + +When they have remained standing for some length of time, and the strata +have been allowed quietly to accumulate around the trunks, they have +escaped compression. They were evidently, to a great extent, hollow like +a reed, so that in those trees which still remain vertical, the interior +has become filled up by a coat of sandstone, whilst the bark has become +transformed into an envelope of an inch, or half an inch of coal. But +many are found lying in the strata in a horizontal plane. These have been +cast down and covered up by an ever-increasing load of strata, so that +the weight has, in the course of time, compressed the tree into simply +the thickness of the double bark, that is, of the two opposite sides of +the envelope which covered it when living. + +_Sigillarae_ grew to a very great height without branching, some +specimens having measured from 60 to 70 feet long. In accordance with +their outside markings, certain types are known as _syringodendron_, +_favularia_, and _clathraria_. _Diploxylon_ is a term applied to an +interior stem referable to this family. + +[Illustration: FIG. 16.--_Stigmaria ficoides_. Coal-shale.] + +But the most interesting point about the _sigillariae_ is the root. This +was for a long time regarded as an entirely distinct individual, and the +older geologists explained it in their writings as a species of succulent +aquatic plant, giving it the name of _stigmaria_. They realized the fact +that it was almost universally found in those beds which occur +immediately beneath the coal seams, but for a long time it did not strike +them that it might possibly be the root of a tree. In an old edition of +Lyell's "Elements of Geology," utterly unlike existing editions in +quality, quantity, or comprehensiveness, after describing it as an +extinct species of water-plant, the author hazarded the conjecture that +it might ultimately be found to have a connection with some other +well-known plant or tree. It was noticed that above the coal, in the +roof, stigmariae were absent, and that the stems of trees which occurred +there, had become flattened by the weight of the overlying strata. The +stigmariae on the other hand, abounded in the _underclay_, as it is +called, and were not in any way compressed but retained what appeared to +be their natural shape and position. Hence to explain their appearance, +it was thought that they were water-plants, ramifying the mud in every +direction, and finally becoming overwhelmed and covered by the mud +itself. On botanical grounds, Brongniart and Lyell conjectured that they +formed the roots of other trees, and this became the more apparent as it +came to be acknowledged that the underclays were really ancient soils. +All doubt was, however, finally dispelled by the discovery by Mr Binney, +of a sigillaria and a stigmaria in actual connection with each other, in +the Lancashire coal-field. + +Stigmariae have since been found in the Cape Breton coal-field, attached +to Lepidodendra, about which we have already spoken, and a similar +discovery has since been made in the British coal-fields. This, +therefore, would seem to shew the affinity of the sigillaria to the +lepidodendron, and through it to the living lycopods, or +club-mosses. + +Some few species of stigmarian roots had been discovered, and various +specific names had been given to them before their actual nature was made +out. What for some time were thought to be long cylindrical leaves, have +now been found to be simply rootlets, and in specimens where these have +been removed, the surface of the stigmaria has been noticed to be covered +with large numbers of protuberant tubercles, which have formed the bases +of the rootlets. There appears to have also been some special kind of +arrangement in their growth, since, unlike the roots of most living +plants, the tubercles to which these rootlets were attached, were +arranged spirally around the main root. Each of these tubercles was +pitted in the centre, and into these the almost pointed ends of the +rootlets fitted, as by a ball and socket joint. + +[Illustration: FIG. 17--_Section of stigmaria_.] + +"A single trunk of _sigillaria_ in an erect forest presents an epitome of +a coal-seam. Its roots represent the _stigmaria_ underclay; its bark the +compact coal; its woody axis, the mineral charcoal; its fallen leaves and +fruits, with remains of herbaceous plants growing in its shade, mixed +with a little earthy matter, the layers of coarse coal. The condition of +the durable outer bark of erect trees, concurs with the chemical theory +of coal, in showing the especial suitableness of this kind of tissue for +the production of the purer compact coals."--(Dawson, "Structures in +Coal.") + +There is yet one other family of plants which must be mentioned, and +which forms a very important portion of the constituent _flora_ of the +coal period. This is the great family of the _coniferae_, which although +differing in many respects from the highly organised dicotyledons of the +present day, yet resembled them in some respects, especially in the +formation of an annual ring of woody growth. + +The conifers are those trees which, as the name would imply, bear their +fruit in the form of cones, such as the fir, larch, cedar, and others. +The order is one which is familiar to all, not only on account of the +cones they bear, and their sheddings, which in the autumn strew the +ground with a soft carpet of long needle-like leaves, but also because of +the gum-like secretion of resin which is contained in their tissues. Only +a few species have been found in the coal-beds, and these, on examination +under the microscope, have been discovered to be closely related to the +araucarian division of pines, rather than to any of our common firs. The +living species of this tree is a native of Norfolk Island, in the +Pacific, and here it attains a height of 200 feet, with a girth of 30 +feet. From the peculiar arrangement of the ducts in the elongated +cellular tissue of the tree, as seen under the microscope, the fossil +conifers, which exhibit this structure, have been placed in the same +division. + +The familiar fossil known to geologists as _Sternbergia_ has now been +shown to be the cast of the central pith of these conifers, amongst which +may be mentioned _cordaites, araucarites_, and _dadoxylon._. The central +cores had become replaced with inorganic matter after the pith had shrunk +and left the space empty. This shrinkage of the pith is a process which +takes place in many plants even when living, and instances will at once +occur, in which the stems of various species of shrubs when broken open +exhibit the remains of the shrunken pith, in the shape of thin discs +across the interval cavity. + +We might reasonably expect that where we find the remains of fossil +coniferous trees, we should also meet with the cones or fruit which they +bear. And such is the case. In some coal-districts fossil fruits, named +_cardiocarpum_ and _trigonocarpum_, have been found in great quantities, +and these have now been decided by botanists to be the fruits of certain +conifers, allied, not to those which bear hard cones, but to those which +bear solitary fleshy fruits. Sir Charles Lyell referred them to a Chinese +genus of the yew tribe called _salisburia_. Dawson states that they are +very similar to both _taxus_ and _salisburia._. They are abundant in some +coal-measures, and are contained, not only in the coal itself, but also +in the sandstones and shales. The under-clays appear to be devoid of +them, and this is, of course, exactly what might have been expected, +since the seeds would remain upon the soil until covered up by vegetable +matter, but would never form part of the clay soil itself. + +In connection with the varieties which have been distinguished in the +families of the conifers, calamites, and sigillariae, Sir William Dawson +makes the following observations: "I believe that there was a +considerably wide range of organisation in _cordaitinae_ as well as in +_calamites_ and _sigillariae_, and that it will eventually be found that +there were three lines of connection between the higher cryptogams +(flowerless) and the phaenogams (flowering), one leading from the +lycopodes by the _sigillariae_, another leading by the _cordaites_, and +the third leading from the _equisetums_ by the _calamites_. Still further +back the characters, afterwards separated in the club-mosses, +mare's-tails, and ferns, were united in the _rhizocarps_, or, as some +prefer to call them, the heterosporous _filicinae_." + +In concluding this chapter dealing with the various kinds of plants which +have been discovered as contributing to the formation of +coal-measures, it would be as well to say a word or two concerning the +climate which must have been necessary to permit of the growth of such an +abundance of vegetation. It is at once admitted by all botanists that a +moist, humid, and warm atmosphere was necessary to account for the +existence of such an abundance of ferns. The gorgeous waving +tree-ferns which were doubtless an important feature of the landscape, +would have required a moist heat such as does not now exist in this +country, although not necessarily a tropical heat. The magnificent giant +lycopodiums cast into the shade all our living members of that class, the +largest of which perhaps are those that flourish in New Zealand. In New +Zealand, too, are found many species of ferns, both those which are +arborescent and those which are of more humble stature. Add to these the +numerous conifers which are there found, and we shall find that a forest +in that country may represent to a certain extent the appearance +presented by a forest of carboniferous vegetation. The ferns, lycopods, +and pines, however, which appear there, it is but fair to add, are mixed +with other types allied to more recent forms of vegetation. + +There are many reasons for believing that the amount of carbonic acid gas +then existing in the atmosphere was larger than the quantity which we now +find, and Professor Tyndall has shown that the effect of this would be to +prevent radiation of heat from the earth. The resulting forms of +vegetation would be such as would be comparable with those which are now +reared in the green-house or conservatory in these latitudes. The gas +would, in fact, act as a glass roof, extending over the whole world. + + + + +CHAPTER II. + +A GENERAL VIEW OF THE COAL-BEARING STRATA. + + +In considering the source whence coal is derived, we must be careful to +remember that coal itself is but a minor portion of the whole formation +in which it occurs. The presence of coal has indeed given the name to the +formation, the word "carboniferous" meaning "coal-bearing," but in taking +a comprehensive view of the position which it occupies in the bowels of +the earth, it will be necessary to take into consideration the strata in +which it is found, and the conditions, so far as are known, under which +these were deposited. + +Geologically speaking, the Carboniferous formation occurs near the close +of that group of systems which have been classed as "palaeozoic," younger +in point of age than the well known Devonian and Old Red Sandstone +strata, but older by far than the Oolites, the Wealden, or the Cretaceous +strata. + +In South Wales the coal-bearing strata have been estimated at between +11,000 and 12,000 feet, yet amongst this enormous thickness of strata, +the whole of the various coal-seams, if taken together, probably does not +amount to more than 120 feet. This great disproportion between the total +thickness and the thickness of coal itself shows itself in every +coal-field that has been worked, and when a single seam of coal is +discovered attaining a thickness of 9 or 10 feet, it is so unusual a +thing in Great Britain as to cause it to be known as the "nine" or +"ten-foot seam," as the case may be. Although abroad many seams are found +which are of greater thicknesses, yet similarly the other portions of the +formation are proportionately greater. + +It is not possible therefore to realise completely the significance of +the coal-beds themselves unless there is also a knowledge of the +remaining constituents of the whole formation. The strata found in the +various coal-fields differ considerably amongst themselves in character. +There are, however, certain well-defined characteristics which find +representation in most of the principal coal-fields, whether British or +European. Professor Hull classifies these carboniferous beds as +follows:-- + + UPPER CARBONIFEROUS. + _Upper coal-measures._ + Reddish and purple sandstones, red and grey clays and shales, + thin bands of coal, ironstone and limestone, with _spirorbis_ + and fish. + + _Middle coal-measures._ + Yellow and gray sandstones, blue and black clays and shales, + bands of coal and ironstone, fossil plants, bivalves + and fish, occasional marine bands. + + MIDDLE CARBONIFEROUS. + _Gannister beds_ or _Lower coal-measures._ + _Millstone grit._ Flagstone series in Ireland. + _Yoredale beds._ Upper shale series of Ireland. + + LOWER CARBONIFEROUS. + _Mountain limestone_. + _Limestone shale_. + +Each of the three principal divisions has its representative in Scotland, +Belgium, and Ireland, but, unfortunately for the last-named country, the +whole of the upper coal-measures are there absent. It is from these +measures that almost all our commercial coals are obtained. + +This list of beds might be further curtailed for all practical purposes +of the geologist, and the three great divisions of the system would thus +stand:-- + + Upper Carboniferous, or Coal-measures proper. + + Millstone grit. + + Lower Carboniferous, or Mountain limestone. + +In short, the formation consists of masses of sandstone, shale, limestone +and coal, these also enclosing clays and ironstones, and, in the +limestone, marbles and veins of the ores of lead, zinc, and antimony, and +occasionally silver. + +[Illustration: FIG. 18.--Sigillarian trunks in current-bedded sandstone. +St Etienne.] + +As the most apparent of the rocks of the system are sandstone, shale, +limestone, and coal, it will be necessary to consider how these were +deposited in the waters of the carboniferous ages, and this we can best +do by considering the laws under which strata of a similar nature are now +being deposited as sedimentary beds. + +A great proportion consists of sandstone. Now sandstone is the result of +sand which has been deposited in large quantities, having become +indurated or hardened by various processes brought to bear upon it. It is +necessary, therefore, first to ascertain whence came the sand, and +whether there are any peculiarities in its method of deposition which +will explain its stratification. It will be noticed at once that it bears +a considerable amount of evidence of what is called "current-bedding," +that is to say, that the strata, instead of being regularly deposited, +exhibit series of wedge-shaped masses, which are constantly thinning out. + +Sand and quartz are of the same chemical composition, and in all +probability the sand of which every sandstone in existence is composed, +appeared on this earth in its first solid form in the shape of quartz. +Now quartz is a comparatively heavy mineral, so also, therefore, will +sand be. It is also very hard, and in these two respects it differs +entirely from another product of sedimentary deposition, namely, mud or +clay, with which we shall have presently to deal when coming to the +shales. Since quartz is a hard mineral it necessarily follows that it +will suffer, without being greatly affected, a far greater amount of +wearing and knocking about when being transported by the agency of +currents and rivers, than will a softer substance, such as clay. An equal +amount of this wearing action upon clay will reduce it to a fine +impalpable silt. The grains of sand, however, will still remain of an +appreciable average size, and where both sand and clay are being +transported to the sea in one and the same stream, the clay will be +transported to long distances, whilst the sand, being heavier, bulk for +bulk, and also consisting of grains larger in size than grains of clay, +will be rapidly deposited, and form beds of sand. Of course, if the +current be a violent one, the sand is transported, not by being held in +suspension, but rather by being pushed along the bed of the river; such +an action will then tend to cause the sand to become powdered into still +finer sand. + +When a river enters the sea it soon loses its individuality; it becomes +merged in the body of the ocean, where it loses its current, and where +therefore it has no power to keep in suspension the sediment which it had +brought down from the higher lands. When this is the case, the sand borne +in suspension is the first to be deposited, and this accumulates in banks +near the entrance of the river into the sea. We will suppose, for +illustration, that a small river has become charged with a supply of +sand. As it gradually approaches the sea, and the current loses its +force, the sand is the more sluggishly carried along, until finally it +falls to the bottom, and forms a layer of sand there. This layer +increases in thickness until it causes the depth of water above it to +become comparatively shallow. On the shallowing process taking place, the +current will still have a certain, though slighter, hold on the sand in +suspension, and will transport it yet a little further seaward, when it +will be thrown down, at the edge of the bank or layer already formed, +thus tending to extend the bank, and to shallow a wider space of +river-bed. + +As a result of this action, strata would be formed, shewing +stratification diagonally as well as horizontally, represented in section +as a number of banks which had seemingly been thrown down one above the +other, ending in thin wedge-shaped terminations where the particular +supply of sediment to which each owed its formation had failed. + +The masses of sandstone which are found in the carboniferous formation, +exhibit in a large degree these wedge-shaped strata, and we have +therefore a clue at once, both as to their propinquity to sea and land, +and also as to the manner in which they were formed. + +[Illustration: FIG. 19.--_Productus_. Coal-measures.] + +There is one thing more, too, about them. Just as, in the case we were +considering, we could observe that the wedge-shaped strata always pointed +away from the source of the material which formed them, so we can +similarly judge that in the carboniferous strata the same deduction holds +good, that the diagonally-pointing strata were formed in the same way, +and that their thinning out was simply owing to temporary failure of +sediment, made good, however, by a further deposition of strata when the +next supply was borne down. + +It is scarcely likely, however, that sand in a pure state was always +carried down by the currents to the sea. Sometimes there would be some +silt mixed with it. Just as in many parts large masses of almost pure +sandstone have been formed, so in other places shales, or, as they are +popularly known by miners, "bind," have been formed. Shales are formed +from the clays which have been carried down by the rivers in the shape of +silt, but which have since become hardened, and now split up easily into +thin parallel layers. The reader has no doubt often handled a piece of +hard clay when fresh from the quarry, and has remembered how that, when +he has been breaking it up, in order, perhaps, to excavate a +partially-hidden fossil, it has readily split up in thin flakes or layers +of shaly substance. This exhibits, on a small scale, the chief +peculiarity of the coal shales. + +The formation of shales will now demand our attention. When a river is +carrying down with it a quantity of mud or clay, it is transported as a +fine, dusty silt, and when present in quantities, gives the muddy tint to +the water which is so noticeable. We can very well see how that silt will +be carried down in greater quantities than sand, since nearly all rivers +in some part of their course will travel through a clayey district, and +finely-divided clay, being of a very light nature, will be carried +forward whenever a river passes over such a district. And a very slight +current being sufficient to carry it in a state of suspension, it follows +that it will have little opportunity of falling to the bottom, until, by +some means or other, the current, which is the means of its conveyance, +becomes stopped or hindered considerably in its flow. + +When the river enters a large body of water, such as the ocean or a lake, +in losing its individuality, it loses also the velocity of its current, +and the silt tends to sink down to the bottom. But being less heavy than +the sand, about which we have previously spoken, it does not sink all at +once, but partly with the impetus it has gained, and partly on account of +the very slight velocity which the current still retains, even after +having entered the sea, it will be carried out some distance, and will +the more gradually sink to the bottom. The deeper the water in which it +falls the greater the possibility of its drifting farther still, since in +sinking, it would fall, not vertically, but rather as the drops of rain +in a shower when being driven before a gale of wind. Thus we should +notice that clays and shales would exhibit a regularity and uniformity of +deposition over a wide area. Currents and tides in the sea or lake would +tend still further to retard deposition, whilst any stoppages in the +supply of silt which took place would give the former layer time to +consolidate and harden, and this would assist in giving it that bedded +structure which is so noticeable in the shales, and which causes it to +split up into fine laminae. This uniformity of structure in the shales +over wide areas is a well ascertained characteristic of the coal-shales, +and we may therefore regard the method of their deposition as given here +with a degree of certainty. + +There is a class of deposit found among the coal-beds, which is known as +the "underclay," and this is the most regular of all as to the position +in which it is found. The underclays are found beneath every bed of coal. +"Warrant," "spavin," and "gannister" are local names which are sometimes +applied to it, the last being a term used when the clay contains such a +large proportion of silicious matter as to become almost like a hard +flinty rock. Sometimes, however, it is a soft clay, at others it is mixed +with sand, but whatever the composition of the underclays may be, they +always agree in being unstratified. They also agree in this respect that +the peculiar fossils known as _stigmariae_ abound in them, and in some +cases to such an extent that the clay is one thickly-matted mass of the +filamentous rootlets of these fossils. We have seen how these gradually +came to be recognised as the roots of trees which grew in this age, and +whose remains have subsequently become metamorphosed into coal, and it is +but one step farther to come to the conclusion that these underclays are +the ancient soils in which the plants grew. + +No sketch of the various beds which go to form the coal-measures would be +complete which did not take into account the enormous beds of mountain +limestone which form the basis of the whole system, and which in thinner +bands are intercalated amongst the upper portion of the system, or the +true coal-measures. + +Now, limestones are not formed in the same way in which we have seen that +sandstones and shales are formed. The last two mentioned owe their origin +to their deposition as sediment in seas, estuaries or lakes, but the +masses of limestone which are found in the various geological formations +owe their origin to causes other than that of sedimentary deposition. + +In carboniferous times there lived numberless creatures which we know +nowadays as _encrinites_. These, when growing, were fixed to the bed of +the ocean, and extended upward in the shape of pliant stems composed of +limestone joints or plates; the stem of each encrinite then expanded at +the top in the shape of a gorgeous and graceful starfish, possessed of +numberless and lengthy arms. These encrinites grew in such profusion that +after death, when the plates of which their stems consisted, became +loosened and scattered over the bed of the sea, they accumulated and +formed solid beds of limestone. Besides the encrinites, there were of +course other creatures which were able to create the hard parts of their +structures by withdrawing lime from the sea, such as _foraminifera_, +shell-fish, and especially corals, so that all these assisted after death +in the accumulation of beds of limestone where they had grown and lived. + +[Illustration: FIG. 20.--Encrinite.] + +[Illustration: FIG. 21.--Encrinital limestone.] + +There is one peculiarity in connection with the habitats of the +encrinites and corals which goes some distance in supplying us with a +useful clue as to the conditions under which this portion of the +carboniferous formation was formed. These creatures find it a difficult +matter, as a rule, to live and secrete their calcareous skeleton in any +water but that which is clear, and free from muddy or sandy sediment. +They are therefore not found, generally speaking, where the other +deposits which we have considered, are forming, and, as these are always +found near the coasts, it follows that the habitats of the creatures +referred to must be far out at sea where no muddy sediments, borne by +rivers, can reach them. We can therefore safely come to the conclusion +that the large masses of encrinital limestone, which attain such an +enormous thickness in some places, especially in Ireland, have been +formed far away from the land of the period; we can at the same time draw +the conclusion that if we find the encrinites broken and snapped asunder, +and the limestone deposits becoming impure through being mingled with a +proportion of clayey or sandy deposits, that we are approaching a +coast-line where perhaps a river opened out, and where it destroyed the +growth of encrinites, mixing with their dead remains the sedimentary +dêbris of the land. + +[Illustration: FIG. 22.--Encrinites: various. Mountain limestone.] + +We have lightly glanced at the circumstances attending the deposition of +each of the principal rocks which form the beds amongst which coal is +found, and have now to deal with the formation of the coal itself. We +have already considered the various kinds of plants and trees which have +been discovered as contributing their remains to the formation of coal, +and have now to attempt an explanation of how it came to be formed in so +regular a manner over so wide an area. + +Each of the British coal-fields is fairly extensive. The Yorkshire and +Derbyshire coal-fields, together with the Lancashire coal-field, with +which they were at one time in geological connection, give us an area of +nearly 1000 square miles, and other British coal-fields show at least +some hundreds of square miles. And yet, spread over them, we find a +series of beds of coal which in many cases extend throughout the whole +area with apparent regularity. If we take it, as there seems every reason +to believe was the case, that almost all these coal-fields were not only +being formed at the same time, but were in most instances in continuation +with one another, this regularity of deposition of comparatively narrow +beds of coal, appears all the more remarkable. + +The question at once suggests itself, Which of two things is probable? +Are we to believe that all this vegetable matter was brought down by some +mighty river and deposited in its delta, or that the coal-plants grew +just where we now find the coal? + +Formerly it was supposed that coal was formed out of dead leaves and +trees, the refuse of the vegetation of the land, which had been carried +down by rivers into the sea and deposited at their mouths, in the same +way that sand and mud, as we have seen, are swept down and deposited. If +this were so, the extent of the deposits would require a river with an +enormous embouchure, and we should be scarcely warranted in believing +that such peaceful conditions would there prevail as to allow of the +layers of coal to be laid down with so little disturbance and with such +regularity over these wide areas. But the great objection to this theory +is, that not only do the remains still retain their perfection of +structure, but they are comparatively _pure,--i.e.,_ unmixed with +sedimentary depositions of clay or sand. Now, rivers would not bring down +the dead vegetation alone; their usual burden of sediment would also be +deposited at their mouths, and thus dead plants, sand, and clay would be +mixed up together in one black shaly or sandy mass, a mixture which would +be useless for purposes of combustion. The only theory which explained +all the recognised phenomena of the coal-measures was that the plants +forming the coal actually grew where the coal was formed, and where, +indeed, we now find it. When the plants and trees died, their remains +fell to the ground of the forest, and these soon turned to a black, +pasty, vegetable mass, the layer thus formed being regularly increased +year by year by the continual accumulation of fresh carbonaceous matter. +By this means a bed would be formed with regularity over a wide area; the +coal would be almost free from an admixture of sandy or clayey sediment, +and probably the rate of formation would be no more rapid in one part of +the forest than another. Thus there would be everywhere uniformity of +thickness. The warm and humid atmosphere, which it is probable then +existed, would not only have tended towards the production of an abnormal +vegetation, but would have assisted in the decaying and disintegrating +processes which went on amongst the shed leaves and trees. + +When at last it was announced as a patent fact that every bed of coal +possessed its underclay, and that trees had been discovered actually +standing upon their own roots in the clay, there was no room at all for +doubt that the correct theory had been hit upon--viz., that coal is now +found just where the trees composing it had grown in the past. + +But we have more than one coal-seam to account for. We have to explain +the existence of several layers of coal which have been formed over one +another on the same spot at successive periods, divided by other periods +when shale and sandstones only have been formed. + +A careful estimate of the Lancashire coal-field has been made by +Professor Hull for the Geological Survey. Of the 7000 feet of +carboniferous strata here found, spread out over an area of 217 square +miles, there are on the average eighteen seams of coal. + +This is only an instance of what is to be found elsewhere. Eighteen +coal-seams! what does this mean? It means that, during carboniferous +times, on no less than eighteen occasions, separate and distinct forests +have grown on this self-same spot, and that between each of these +occasions changes have taken place which have brought it beneath the +waters of the ocean, where the sandstones and shales have been formed +which divide the coal-seams from each other. We are met here by a +wonderful demonstration of the instability of the surface of the earth, +and we have to do our best to show how the changes of level have been +brought about, which have allowed of this game of geological see-saw to +take place between sea and land. Changes of level! Many a hard geological +nut has only been overcome by the application of the principle of changes +of level in the surface of the earth, and in this we shall find a sure +explanation of the phenomena of the coal-measures. + +Great changes of the level of the land are undoubtedly taking place even +now on the earth's surface, and in assuming that similar changes took +place in carboniferous times, we shall not be assuming the former +existence of an agent with which we are now unfamiliar. And when we +consider the thicknesses of sandstone and shale which intervene beneath +the coal-seams, we can realise to a certain extent the vast lapses of +years which must have taken place between the existence of each forest; +so that although now an individual passing up a coal-mine shaft may +rapidly pass through the remains of one forest after another, the rise of +the strata above each forest-bed then was tremendously slow, and the +period between the growth of each forest must represent the passing away +of countless ages. Perhaps it would not be too much to say that the +strata between some of the coal-seams would represent a period not less +than that between the formation of the few tertiary coals with which we +are acquainted, and a time which is still to us in the far-away future. + +The actual seams of coal themselves will not yield much information, from +which it will be possible to judge of the contour of the landmasses at +this ancient period. Of one thing we are sure, namely, that at the time +each seam was formed, the spot where it accumulated was dry land. If, +therefore, the seams which appear one above the other coincide fairly +well as to their superficial extent, we can conclude that each time the +land was raised above the sea and the forest again grew, the contour of +the land was very similar. This conclusion will be very useful to go +upon, since whatever decision may be come to as an explanation of one +successive land-period and sea-period on the same spot, will be +applicable to the eighteen or more periods necessary for the completion +of some of the coal-fields. + +We will therefore look at one of the sandstone masses which occur between +the coal-seams, and learn what lessons these have to teach us. In +considering the formation of strata of sand in the seas around our +river-mouths, it was seen that, owing to the greater weight of the +particles of the sand over those of clay, the former the more readily +sank to the bottom, and formed banks not very far away from the land. It +was seen, too, that each successive deposition of sand formed a +wedge-shaped layer, with the point of the wedge pointing away from the +source of origin of the sediment, and therefore of the current which +conveyed the sediment. Therefore, if in the coal-measure sandstones the +layers were found with their wedges all pointing in one direction, we +should be able to judge that the currents were all from one direction, +and that, therefore, they were formed by a single river. But this is just +what we do not find, for instead of it the direction of the wedge-shaped +strata varies in almost every layer, and the current-bedding has been +brought about by currents travelling in every direction. Such diverse +current-bedding could only result from the fact that the spot where the +sand was laid down was subject to currents from every direction, and the +inference is that it was well within the sphere of influence of numerous +streams and rivers, which flowed from every direction. The only condition +of things which would explain this is that the sandstone was originally +formed in a closed sea or large lake, into which numerous rivers flowing +from every direction poured their contents. + +Now, in the sandstones, the remains of numerous plants have been found, +but they do not present the perfect appearance that they do when found in +the shales; in fact they appear to have suffered a certain amount of +damage through having drifted some distance. This, together with the fact +that sandstones are not formed far out at sea, justify the safe +conclusion that the land could not have been far off. Wherever the +current-bedding shows itself in this manner we may be sure we are +examining a spot from which the land in every direction could not have +been at a very great distance, and also that, since the heavy materials +of which sandstone is composed could only be transported by being +impelled along by currents at the bed of the sea, and that in deep water +such currents could not exist, therefore we may safely decide that the +sea into which the rivers fell was a comparatively shallow one. + +Although the present coal-fields of England are divided from one another +by patches of other beds, it is probable that some of them were formerly +connected with others, and a very wide sheet of coal on each occasion was +laid down. The question arises as to what was the extent of the inland +sea or lake, and did it include the area covered by the coal basins of +Scotland and Ireland, of France and Belgium? And if these, why not those +of America and other parts? The deposition of the coal, according to the +theory here advanced, may as well have been brought about in a series of +large inland seas and lakes, as by one large comprehensive sea, and +probably the former is the more satisfactory explanation of the two. But +the astonishing part of it is that the changes in the level of the land +must have been taking place simultaneously over these large areas, +although, of course, while one quarter may have been depressed beneath +the sea, another may have been raised above it. + +In connection with the question of the contour of the land during the +existence of the large lakes or inland seas, Professor Hull has prepared, +in his series of maps illustrative of the Palaeo-Geography of the British +Islands, a map showing on incontestible grounds the existence during the +coal-ages of a great central barrier or ridge of high land stretching +across from Anglesea, south of Flint, Staffordshire, and Shropshire +coal-fields, to the eastern coast of Norfolk. He regards the British +coal-measures as having been laid down in two, or at most three, areas of +deposition--one south of this ridge, the remainder to the north of it. In +regard to the extent of the former deposits of coal in Ireland, there is +every probability that the sister island was just as favourably treated +in this respect as Great Britain. Most unfortunately, Ireland has since +suffered extreme denudation, notably from the great convulsions of nature +at the close of the very period of their deposition, as well as in more +recent times, resulting in the removal of nearly all the valuable upper +carboniferous beds, and leaving only the few unimportant +coal-beds to which reference has been made. + +[Illustration: FIG. 23.--_Cyathophyllum_. Coral in encrinital limestone.] + +We are unable to believe in the continuity of our coal-beds with those of +America, for the great source of sediment in those times was a continent +situated on the site of the Atlantic Ocean, and it is owing to this +extensive continent that the forms of _flora_ found in the coal-beds in +each country bear so close a resemblance to one another, and also that +the encrinital limestone which was formed in the purer depths of the +ocean on the east, became mixed with silt, and formed masses of shaly +impure limestone in the south-western parts of Ireland. + +It must be noted that, although we may attribute to upheaval from beneath +the fact that the bed of the sea became temporarily raised at each period +into dry land, the deposits of sand or shale would at the same time be +tending to shallow the bed, and this alone would assist the process of +upheaval by bringing the land at least very near to the surface of the +water. + +Each upheaval, however, could have been but a temporary arrest of the +great movement of crust subsidence which was going on throughout the coal +period, so that, at its close, when the last coal forest grew upon the +surface of the land, there had disappeared, in the case of South Wales, a +thickness of 11,000 feet of material. + +Of the many remarkable things in connection with coal-beds, not the least +is the state of purity in which coal is found. On the floor of each +forest there would be many a streamlet or even small river which would +wend its way to meet the not very distant sea, and it is surprising at +first that so little sediment found its way into the coal itself. But +this was cleverly explained by Sir Charles Lyell, who noticed, on one of +his visits to America, that the water of the Mississippi, around the rank +growths of cypress which form the "cypress swamps" at the mouths of that +river, was highly charged with sediment, but that, having passed through +the close undergrowth of the swamps, it issued in almost a pure state, +the sediment which it bore having been filtered out of it and +precipitated. This very satisfactorily explained how in some places +carbonaceous matter might be deposited in a perfectly pure state, whilst +in others, where sandstone or shale was actually forming, it might be +impregnated by coaly matter in such a way as to cause it to be stained +black. In times of flood sediment would be brought in, even where pure +coal had been forming, and then we should have a thin "parting" of +sandstone or shale, which was formed when the flood was at its height. Or +a slight sinking of the land might occur, in which case also the +formation of coal would temporarily cease, and a parting of foreign +matter would be formed, which, on further upheaval taking place, would +again give way to another forest growth. Some of the thicker beds have +been found presenting this aspect, such as the South Staffordshire +ten-yard coal, which in some parts splits up into a dozen or so smaller +beds, with partings of sediment between them. + +In the face of the stupendous movements which must have happened in order +to bring about the successive growth of forests one above another on the +same spot, the question at once arises as to how these movements of the +solid earth came about, and what was the cause which operated in such a +manner. We can only judge that, in some way or other, heat, or the +withdrawal of heat, has been the prime motive power. We can perceive, +from what is now going on in some parts of the earth, how great an +influence it has had in shaping the land, for volcanoes owe their +activity to the hidden heat in the earth's interior, and afford us an +idea of the power of which heat is capable in the matter of building up +and destroying continents. No less certain is it that heat is the prime +factor in those more gradual vertical movements of the land to which we +have referred elsewhere, but in regard to the exact manner in which it +acts we are very much in the dark. Everybody knows that, in the majority +of instances, material substances of all kinds expand under the influence +of heat, and contract when the source of heat is withdrawn. If we can +imagine movements in the quantity of heat contained in the solid crust, +the explanation is easy, for if a certain tract of land receive an +accession of heat beneath it, it is certain that the principal effect +will be an elevation of the land, consequent on the expansion of its +materials, with a subsequent depression when the heat beneath the tract +in question becomes gradually lessened. Should the heat be retained for a +long period, the strata would be so uplifted as to form an anticlinal, or +saddle-back, and then, should subsequent denudation take place, more +ancient strata would be brought to view. It was thus in the instance of +the tract bounded by the North and South Downs, which were formerly +entirely covered by chalk, and in the instance of the uprising of the +carboniferous limestone between the coal-fields of Lancashire, +Staffordshire, and Derbyshire. + +How the heat-waves act, and the laws, if any, which they obey in their +subterranean movements, we are unable to judge. From the properties which +heat possesses we know that its presence or absence produces marked +differences in the positions of the strata of the earth, and from +observations made in connection with the closing of some volcanoes, and +the opening up of fresh earth-vents, we have gone a long way towards +establishing the probability that there are even now slow and ponderous +movements taking place in the heat stored in the earth's crust, whose +effects are appreciably communicated to the outside of the thin rind of +solid earth upon which we live. + +Owing to the great igneous and volcanic activity at the close of the +deposition of the carboniferous system of strata, the coal-measures +exhibit what are known as _faults_ in abundance. The mountain limestone, +where it outcrops at the surface, is observed to be much jointed, so much +so that the work of quarrying the limestone is greatly assisted by the +jointed structure of the rock. Faults differ from joints in that, whilst +the strata in the latter are still in relative position on each side of +the joint, they have in the former slipped out of place. In such a case +the continuation of a stratum on the opposite side of a fault will be +found to be depressed, perhaps a thousand feet or more. It will be seen +at once how that, in sinking a new shaft into a coal-seam, the +possibility of an unknown fault has to be brought into consideration, +since the position of the seam may prove to have been depressed to such +an extent as to cause it to be beyond workable depth. Many seams, on the +other hand, which would have remained altogether out of reach of mining +operations, have been brought within workable depth by a series of +_step-faults_, this being a term applied to a series of parallel faults, +in none of which the amount of down-throw is great. + +The amount of the down-throw, or the slipping-down of the beds, is +measured, vertically, from the point of disappearance of a layer to an +imaginary continuation of the same layer from where it again appears +beyond the fault. The plane of a fault is usually more or less inclined, +the amount of the inclination being known as the _hade_ of the fault, and +it is a remarkable characteristic of faults that, as a general rule, they +hade to the down-throw. This will be more clearly understood when it is +explained that, by its action, a seam of coal, which is subject to +numerous faults, can never be pierced more than once by one and the same +boring. In mountainous districts, however, there are occasions when the +hade is to the up-throw, and this kind of fault is known as an _inverted +fault_. + +Lines of faults extend sometimes for hundreds of miles. The great Pennine +Fault of England is 130 miles long, and others extend for much greater +distances. The surfaces on both sides of a fault are often smooth and +highly polished by the movement which has taken place in the strata. They +then show the phenomenon known as _slicken-sides_. Many faults have +become filled with crystalline minerals in the form of veins of ore, +deposited by infiltrating waters percolating through the natural +fissures. + +In considering the formation and structure of the better-known +coal-bearing beds of the carboniferous age, we must not lose sight of the +fact that important beds of coal also occur in strata of much more recent +date. There are important coal-beds in India of Permian age. There are +coal-beds of Liassic age in South Hungary and in Texas, and of Jurassic +age in Virginia, as well as at Brora in Sutherlandshire; there are coals +of Cretaceous age in Moravia, and valuable Miocene Tertiary coals in +Hungary and the Austrian Alps. + +Again, older than the true carboniferous age, are the Silurian +anthracites of Co. Cavan, and certain Norwegian coals, whilst in New +South Wales we are confronted with an assemblage of coal-bearing strata +which extend apparently from the Devonian into Mesozoic times. + +Still, the age we have considered more closely has an unrivalled right to +the title, coal appearing there not merely as an occasional bed, but as a +marked characteristic of the formation. + +The types of animal life which are found in this formation are varied, +and although naturally enough they do not excel in number, there are yet +sufficient varieties to show probabilities of the existence of many with +which we are unfamiliar. The highest forms yet found, show an advance as +compared with those from earlier formations, and exhibit amphibian +characteristics intermediate between the two great classes of fishes and +reptiles. Numerous specimens proper to the extinct order of +_labyrinthodontia_ have been arranged into at least a score of genera, +these having been drawn from the coal-measures of Newcastle, Edinburgh, +Kilkenny, Saärbruck, Bavaria, Pennsylvania, and elsewhere. The +_Archegosaurus,_ which we have figured, and the _Anthracosaurus,_ are +forms which appear to have existed in great numbers in the swamps and +lakes of the age. The fish of the period belong almost entirely to the +ancient orders of the ganoids and placoids. Of the ganoids, the great +_megalichthys Hibberti_ ranges throughout the whole of the system. +Wonderful accumulations of fish remains are found at the base of the +system, in the bone-bed of the Bristol coal-field, as well as in a +similar bed at Armagh. Many fishes were armed with powerful conical +teeth, but the majority, like the existing Port Jackson shark, were +possessed of massive palates, suited in some cases for crushing, and in +others for cutting. + +[Illustration: FIG. 24.--_Archegosaurus minor_. Coal-measures.] + +[Illustration: FIG. 25.--_Psammodus porosus_. Crushing palate of a fish.] + +[Illustration: FIG. 26.--_Orthoceras_. Mountain limestone.] + +In the mountain limestone we see, of course, the predominance of marine +types, encrinital remains forming the greater proportion of the mass. +There are occasional plant remains which bear evidence of having drifted +for some distance from the shore. But next to the _encrinites_, the +corals are the most important and persistent. Corals of most beautiful +forms and capable of giving polished marble-like sections, are in +abundance. _Polyzoa_ are well represented, of which the lace-coral +(_fenestella_) and screw-coral (_archimedopora_) are instances. +_Cephalopoda_ are represented by the _orthoceras_, sometimes five or six +feet long, and _goniatites_, the forerunner of the familiar _ammonite_. +Many species of brachiopods and lammellibranchs are met with. _Lingula_, +most persistent throughout all geological time, is abundant in the +coal-shales, but not in the limestones. _Aviculopecten_ is there abundant +also. In the mountain limestone the last of the trilobites (_Phillipsia_) +is found. + +[Illustration: FIG. 27.--_Fenestella retipora_. Mountain limestone.] + +[Illustration: FIG. 28.--_Goniatites_. Mountain limestone.] + +We have evidence of the existence in the forests of a variety of +_centipede_, specimens having been found in the erect stump of a hollow +tree, although the fossil is an extremely rare one. The same may be said +of the only two species of land-snail which have been found connected +with the coal forests, viz., _pupa vetusta_ and _zonites priscus_, both +discovered in the cliffs of Nova Scotia. These are sufficient to +demonstrate that the fauna of the period had already reached a high stage +of development. In the estuaries of the day, masses of a species of +freshwater mussel (_anthracosia_) were in existence, and these have left +their remains in the shape of extensive beds of shells. They are familiar +to the miner as _mussel-binds_, and are as noticeable a feature of this +long ago period, as are the aggregations of mussels on every coast at +the present day. + +[Illustration: FIG. 29.--_Aviculopecten papyraceus_. Coal-shale.] + + + + +CHAPTER III. + +VARIOUS FORMS OF COAL AND CARBON. + + +In considering the various forms and combinations into which coal enters, +it is necessary that we should obtain a clear conception of what the +substance called "carbon" is, and its nature and properties generally, +since this it is which forms such a large percentage of all kinds of +coal, and which indeed forms the actual basis of it. In the shape of +coke, of course, we have a fairly pure form of carbon, and this being +produced, as we shall see presently, by the driving off of the volatile +or vaporous constituents of coal, we are able to perceive by the residue +how great a proportion of coal consists of carbon. In fact, the two have +almost an identical meaning in the popular mind, and the fact that the +great masses of strata, in which are contained our principal and most +valuable seams of coal, are termed "carboniferous," from the Latin +_carbo_, coal, and _fero_, I bear, tends to perpetuate the existence of +the idea. + +There is always a certain, though slight, quantity of carbon in the air, +and this remains fairly constant in the open country. Small though it may +be in proportion to the quantity of pure air in which it is found, it is +yet sufficient to provide the carbon which is necessary to the growth of +vegetable life. Just as some of the animals known popularly as the +_zoophytes_, which are attached during life to rocks beneath the sea, are +fed by means of currents of water which bring their food to them, so the +leaves, which inhale carbon-food during the day through their +under-surfaces, are provided with it by means of the currents of air +which are always circulating around them; and while the fuel is being +taken in beneath, the heat and light are being received from above, and +the sun supplies the motive power to digestion. + +It is assumed that it is, within the knowledge of all that, for the +origin of the various seams and beds of coaly combinations which exist in +the earth's crust, we must look to the vegetable world. If, however, we +could go so far back in the world's history as the period when our +incandescent orb had only just severed connection with a +gradually-diminishing sun, we should probably find the carbon there, but +locked up in the bonds of chemical affinities with other elements, and +existing therewith in a gaseous condition. But, as the solidifying +process went on, and as the vegetable world afterwards made its +appearance, the carbon became, so to speak, wrenched from its +combinations, and being absorbed by trees and plants, finally became +deposited amongst the ruins of a former vegetable world, and is now +presented to us in the form of coal. + +We are able to trace the gradual changes through which the pasty mass of +decaying vegetation passed, in consequence of the fact that we have this +material locked up in various stages of carbonisation, in the strata +beneath our feet. These we propose to deal with individually, in as +unscientific and untechnical a manner as possible. + +First of all, when a mass of vegetable matter commences to decay, it soon +loses its colour. There is no more noticeable proof of this, than that +when vitality is withdrawn from the leaves of autumn, they at once +commence to assume a rusty or an ashen colour. Let the leaves but fall to +the ground, and be exposed to the early frosts of October, the damp mists +and rains of November, and the rapid change of colour is at once +apparent. Trodden under foot, they soon assume a dirty blackish hue, and +even when removed they leave a carbonaceous trace of themselves behind +them, where they had rested. Another proof of the rapid acquisition of +their coaly hue is noticeable in the spring of the year. When the trees +have burst forth and the buds are rapidly opening, the cases in which the +buds of such trees as the horse-chestnut have been enclosed will be found +cast off, and strewing the path beneath. Moistened by the rains and the +damp night-mists, and trodden under foot, these cases assume a jet black +hue, and are to all appearance like coal in the very first stages of +formation. + +But of course coal is not made up wholly and only of leaves. The branches +of trees, twigs of all sizes, and sometimes whole trunks of trees are +found, the last often remaining in their upright position, and piercing +the strata which have been formed above them. At other times they lie +horizontally on the bed of coal, having been thrown down previously to +the formation of the shale or sandstone, which now rests upon them. They +are often petrified into solid sandstone themselves, whilst leaving a +rind of coal where formerly was the bark. Although the trunk of a tree +looks so very different to the leaves which it bears upon its branches, +it is only naturally to be supposed that, as they are both built up after +the same manner from the juices of the earth and the nourishment in the +atmosphere, they would have a similar chemical composition. One very +palpable proof of the carbonaceous character of tree-trunks suggests +itself. Take in your hand a few dead twigs or sticks from which the +leaves have long since dropped; pull away the dead parts of the ivy which +has been creeping over the summer-house; or clasp a gnarled old monster +of the forest in your arms, and you will quickly find your hand covered +with a black smut, which is nothing but the result of the first stage +which the living plant has made, in its progress towards its condition as +dead coal. But an easy, though rough, chemical proof of the constituents +of wood, can be made by placing a few pieces of wood in a medium-sized +test-tube, and holding it over a flame. In a short time a certain +quantity of steam will be driven off, next the gaseous constituents of +wood, and finally nothing will be left but a few pieces of black brittle +charcoal. The process is of course the same in a fire-grate, only that +here more complete combustion of the wood takes place, owing to its being +intimately exposed to the action of the flames. If we adopt the same +experiment with some pieces of coal, the action is similar, only that in +this case the quantity of gases given off is not so great, coal +containing a greater proportion of carbon than wood, owing to the fact +that, during its long burial in the bowels of the earth, it has been +acted upon in such a way as to lose a great part of its volatile +constituents. + +From processes, therefore, which are to be seen going on around us, it is +easily possible to satisfy ourselves that vegetation will in the long run +undergo such changes as will result in the formation of coal. + +There are certain parts in most countries, and particularly in Ireland, +where masses of vegetation have undergone a still further stage in +metamorphism, namely, in the well-known and famous peat-bogs. Ireland is +_par excellence_ the land of bogs, some three millions of acres being +said to be covered by them, and they yield an almost inexhaustible supply +of peat. One of the peat-bogs near the Shannon is between two and three +miles in breadth and no less than fifty in length, whilst its depth +varies from 13 feet to as much as 47 feet. Peat-bogs have in no way +ceased to be formed, for at their surfaces the peat-moss grows afresh +every year; and rushes, horse-tails, and reeds of all descriptions grow +and thrive each year upon the ruins of their ancestors. The formation of +such accumulations of decaying vegetation would only be possible where +the physical conditions of the country allowed of an abundant rainfall, +and depressions in the surface of the land to retain the moisture. Where +extensive deforesting operations have taken place, peat-bogs have often +been formed, and many of those in existence in Europe undoubtedly owe +their formation to that destruction of forests which went on under the +sway of the Romans. Natural drainage would soon be obstructed by fallen +trees, and the formation of marsh-land would follow; then with the growth +of marsh-plants and their successive annual decay, a peaty mass would +collect, which would quickly grow in thickness without let or hindrance. + +In considering the existence of inland peat-bogs, we must not lose sight +of the fact that there are subterranean forest-beds on various parts of +our coasts, which also rest upon their own beds of peaty matter, and very +possibly, when in the future they are covered up by marine deposits, they +will have fairly started on their way towards becoming coal. + +Peat-bogs do not wholly consist of peat, and nothing else. The trunks of +such trees as the oak, yew, and fir, are often found mingled with the +remains of mosses and reeds, and these often assume a decidedly coaly +aspect. From the famous Bog of Allen in Ireland, pieces of oak, generally +known as "bog-oak," which have been buried for generations in peat, have +been excavated. These are as black as any coal can well be, and are +sufficiently hard to allow of their being used in the manufacture of +brooches and other ornamental objects. Another use to which peat of some +kinds has been put is in the manufacture of yarn, the result being a +material which is said to resemble brown worsted. On digging a ditch to +drain a part of a bog in Maine, U.S., in which peat to a depth of twenty +feet had accumulated, a substance similar to cannel coal itself was +found. As we shall see presently, cannel coal is one of the earliest +stages of true coal, and the discovery proved that under certain +conditions as to heat and pressure, which in this case happened to be +present, the materials which form peat may also be metamorphosed into +true coal. + +Darwin, in his well-known "Voyage in the _Beagle_" gives a peculiarly +interesting description of the condition of the peat-beds in the Chonos +Archipelago, off the Chilian coast, and of their mode of formation. "In +these islands," he says, "cryptogamic plants find a most congenial +climate, and within the forest the number of species and great abundance +of mosses, lichens, and small ferns, is quite extraordinary. In Tierra +del Fuego every level piece of land is invariably covered by a thick bed +of peat. In the Chonos Archipelago where the nature of the climate more +closely approaches that of Tierra del Fuego, every patch of level ground +is covered by two species of plants (_Astelia pumila_ and _Donatia +megellanica_), which by their joint decay compose a thick bed of elastic +peat. + +"In Tierra del Fuego, above the region of wood-land, the former of these +eminently sociable plants is the chief agent in the production of peat. +Fresh leaves are always succeeding one to the other round the central +tap-root; the lower ones soon decay, and in tracing a root downwards in +the peat, the leaves, yet holding their places, can be observed passing +through every stage of decomposition, till the whole becomes blended in +one confused mass. The Astelia is assisted by a few other plants,--here +and there a small creeping Myrtus (_M. nummularia_), with a woody stem +like our cranberry and with a sweet berry,--an Empetrum (_E. rubrum_), +like our heath,--a rush (_Juncus grandiflorus_), are nearly the only ones +that grow on the swampy surface. These plants, though possessing a very +close general resemblance to the English species of the same genera, are +different. In the more level parts of the country the surface of the peat +is broken up into little pools of water, which stand at different +heights, and appear as if artificially excavated. Small streams of water, +flowing underground, complete the disorganisation of the vegetable +matter, and consolidate the whole. + +"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° +to 42°), 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°) 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 £100,000 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 _eozoön_ 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 _eozoön_ 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. + +[Illustration: FIG 30.--_Lepidodendron_. Portion of Sandstone stem after +removal of bark of a giant club-moss] + +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 £150 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° 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. + +[Illustration: FIG. 31.--Engine-House and Buildings at head of a +Coal-Pit.] + +If there be one of these shafts at one end of the mine, and another at a +remote distance from it, a movement of the air will at once begin, and a +rough kind of ventilation will ensue. This is, however, quite +insufficient to provide the necessary 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. + +[Illustration: FIG. 32.--Gas Jet and Davy Lamp.] + +With the complicated improvements which have since been made in the Davy +lamp, a state of almost absolute safety can be guaranteed, but still from +time to time explosions are reported. Of the cause of many we are +absolutely ignorant, but occasionally a light is thrown upon their origin +by a paragraph appearing in a daily paper. Two men are charged before the +magistrates with being in the possession of keys used exclusively for +unlocking their miners' safety-lamps. There is no defence. These men know +that they carry their lives in their hands, yet will risk their own and +those of hundreds of others, in order that they may be able to light +their pipes by means of their safety-lamps. Sometimes in an unexpected +moment there is a great dislodgement of coal, and a tremendous 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. + +[Illustration: Fig. 33--Part of a trunk of _Sigillaria_, showing the thin +outer carbonised bark, with leaf-scars, and the seal-like impressions +where the bark is removed.] + +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 £11,000. 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. + +[Illustration: FIG. 34.--Inside a Gas-Holder.] + +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° 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. + +[Illustration: FIG. 35.--Filling Retorts by Machinery.] + +[Illustration: FIG. 36.--CONDENSERS.] + +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. + +[Illustration: FIG. 37.] + +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. + +[Illustration: FIG. 38.] + +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° 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° 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. + +The term asphalt has been applied to so many and various mixtures, that +one scarcely associates it with natural mineral pitch which is found in +some parts of the world. From time immemorial this compact, bituminous, +resinous mineral has been discovered in masses on the shores of the Dead +Sea, which has in consequence received the well-known title of Lake +Asphaltites. Like the naphthas and petroleums which have been noticed, +this has had its origin in the decomposition of vegetable matter, and +appears to be thrown up in a liquid form by the volcanic energies which, +are still believed to be active in the centre of the lake, and which may +be existent beneath a stratum, or bed, of oil-producing bitumen. + +In connection with the formation of this substance, the remarks of Sir +Charles Lyell, the great geologist, may well be quoted, as showing the +transformation of vegetable matter into petroleum, and afterwards into +solid-looking asphalt. At Trinidad is a lake of bitumen which is a mile +and a half in circumference. "The Orinoco has for ages been rolling down +great quantities of woody and vegetable bodies into the surrounding sea, +where, by the influence of currents and eddies, they may be arrested, and +accumulated in particular places. The frequent occurrence of earthquakes +and other indications of volcanic action in those parts, lend countenance +to the opinion that these vegetable substances may have undergone, by the +agency of subterranean fire, those transformations or chemical changes +which produce petroleum; and this may, by the same causes, be forced up +to the surface, where, by exposure to the air, it becomes inspissated, +and forms those different varieties of earth-pitch or asphaltum so +abundant in the island." + +It is interesting to note also that it was obtained, at an ancient +period, from the oil-fountains of Is, and that it was put to considerable +use in the embalming of the bodies of the Egyptians. It appears, too, to +have been employed in the construction of the walls of Babylon, and thus +from very early times these wonderful products and results of decayed +vegetation have been brought into use for the service of man. + +Aniline has been previously referred (p. 135) to as having been prepared +from nitro-benzole, or _essence de mirbane_, and its preparation, by +treating this substance with iron-filings and acetic acid, was one of the +early triumphs of the chemists who undertook the search after the unknown +contained in gas-tar. It had previously been obtained from oils distilled +from bones. The importance of the substance lies in the fact that, by the +action of various chemical reagents, a series of colouring matters of +very great richness are formed, and these are the well-known _aniline +dyes_. + +As early as 1836, it was discovered that aniline, when heated with +chloride of lime, acquired a beautiful blue tint. This discovery led to +no immediate practical result, and it was not until twenty-one years +after that a further discovery was made, which may indeed be said to have +achieved a world-wide reputation. It was found that, by adding bichromate +of potash to a solution of aniline and sulphuric acid, a powder was +obtained from which the dye was afterwards extracted, which is known as +_mauve_. Since that time dyes in all shades and colours have been +obtained from the same source. _Magenta_ was the next dye to make its +appearance, and in the fickle history of fashion, probably no colours +have had such extraordinary runs of popularity as those of mauve and +magenta. Every conceivable colour was obtained in due course from the +same source, and chemists began to suspect that, in the course of time, +the colouring matter of dyer's madder, which was known as _alizarin_, +would also be obtained therefrom. Hitherto this had been obtained from +the root of the madder-plant, but by dint of careful and well-reasoned +research, it was obtained by Dr Groebe, from a solid crystalline coal-tar +product, known as _anthracene_, (C_{12}H_{14}). This artificial alizarin +yields colours which are purer than those of natural madder, and being +derived from what was originally regarded as a waste product, its cost of +production is considerably cheaper. + +We have endeavoured thus far to deal with (1) gas, and (2) tar, the two +principal products in the distillation of coal. We have yet to say a few +words concerning the useful ammoniacal liquor, and the final residue in +the retorts, _i.e._, coke. + +The ammoniacal liquor which has been passing over during distillation of +the coal, and which has been collecting in the hydraulic main and in +other parts of the gas-making apparatus, is set aside to be treated to a +variety of chemical reactions, in order to wrench from it its useful +constituents. Amongst these, of course, _ammonia_ stands in the first +rank, the others being comparatively unimportant. In order to obtain +this, the liquor is first of all neutralised by being treated with a +quantity of acid, which converts the principal constituent of the liquor, +viz., carbonate of ammonia (smelling salts), into either sulphate of +ammonia, or chloride of ammonia, familiarly known as sal-ammoniac, +according as sulphuric acid or hydrochloric acid is the acid used. Thus +carbonate of ammonia with sulphuric acid will give sulphate of ammonia, +but carbonate of ammonia with hydrochloric acid will give sal-ammoniac +(chloride of ammonia). By a further treatment of these with lime, or, as +it is chemically known, oxide of calcium, ammonia is set free, whilst +chloride of lime (the well-known disinfectant), or sulphate of lime +(gypsum, or "plaster of Paris" ), is the result. + +Thus: + +Sulphate of ammonia + lime = plaster of Paris + ammonia. + +or, + +Sal-ammoniac + lime = chloride of lime + ammonia. + +Ammonia itself is a most powerful gas, and acts rapidly upon the eyes. It +has a stimulating effect upon the nerves. It is not a chemical element, +being composed of three parts of hydrogen by weight to one of nitrogen, +both of which elements alone are very harmless, and, the latter indeed, +very necessary to human life. Ammonia is fatal to life, producing great +irritation of the lungs. + +It has also been called "hartshorn," being obtained by destructive +distillation of horn and bone. The name "ammonia" is said to have been +derived from the fact that it was first obtained by the Arabs near the +temple of Jupiter Ammon, in Lybia, North Africa, from the excrement of +camels, in the form of sal-ammoniac. There are always traces of it in the +atmosphere, especially in the vicinity of large towns and manufactories +where large quantities of coal are burned. + +Coke, if properly prepared, should consist of pure carbon. Good coal +should yield as much as 80 per cent. of coke, but owing to the +unsatisfactory manner of its production, this proportion is seldom +yielded, whilst the coke which is familiar to householders, being the +residue left in the retorts after gas-making, usually contains so large a +proportion of sulphur as to make its combustion almost offensive. No +doubt the result of its unsatisfactory preparation has been that it has +failed to make its way into households as it should have done, but there +is also another objection to its use, namely, the fact that, owing to the +quantity of oxygen required in its combustion, it gives rise to feelings +of suffocation where insufficient ventilation of the room is provided. + +Large quantities of coke are, however, consumed in the feeding of furnace +fires, and in the heating of boilers of locomotives, as well as in +metallurgical operations; and in order to supply the demand, large +quantities of coal are "coked," a process by which the volatile products +are completely combusted, pure coke remaining behind. This process is +therefore the direct opposite to that of "distillation," by which the +volatile products are carefully collected and re-distilled. + +The sulphurous impurities which are always present in the coal, and which +are, to a certain extent, retained in coke made at the gas-works, +themselves have a value, which in these utilitarian days is not long +likely to escape the attention of capitalists. In coal, bands of bright +shining iron pyrites are constantly seen, even in the homely scuttle, and +when coal is washed, as it is in some places, the removal of the pyrites +increases the value of the coal, whilst it has a value of its own. + +The conversion of the sulphur which escapes from our chimneys into +sulphuretted hydrogen, and then into sulphuric acid, or oil of vitriol, +has already been referred to, and we can only hope that in these days +when every available source of wealth is being looked up, and when there +threatens to remain nothing which shall in the future be known as +"waste," that the atmosphere will be spared being longer the receptacle +for the unowned and execrated brimstone of millions of fires and +furnaces. + + + + +CHAPTER VII. + +THE COAL SUPPLIES OF THE WORLD. + + +As compared with some of the American coal-fields, those of Britain are +but small, both in extent and thickness. They can be regarded as falling +naturally into three principal areas. + + The northern coal-field, including those of Fife, Stirling, and Ayr + in Scotland; Cumberland, Newcastle, and Durham in England; Tyrone + in Ireland. + + The middle coal-field, all geologically in union, including those of + Yorkshire, Derbyshire, Shropshire, Staffordshire, Flint, and + Denbigh. + + The southern coal-field, including South Wales, Forest of Dean, + Bristol, Dover, with an offshoot at Leinster, &c., and Millstreet, + Cork. + +Thus it will be seen that while England and Scotland are, in comparison +with their extent of surface, bountifully supplied with coal-areas, in +the sister island of Ireland coal-producing areas are almost absent. The +isolated beds in Cork and Tipperary, in Tyrone and Antrim, are but the +remnants left of what were formerly beds of coal extending the whole +breadth and length of Ireland. Such beds as there remain undoubtedly +belong to the base of the coal-measures, and observations all go to show +that the surface suffered such extreme denudation subsequent to the +growth of the coal-forests, that the wealth which once lay there, has +been swept away from the surface which formerly boasted of it. + +On the continent of Europe the coal-fields, though not occupying so large +a proportion of the surface of the country as in England, are very far +from being slight or to be disregarded. The extent of forest-lands still +remaining in Germany and Austria are sufficing for the immediate needs of +the districts where some of the best seams occur. It is only where there +is a dearth of handy fuel, ready to be had, perhaps, by the simple +felling of a few trees, that man commences to dig into the earth for his +fuel. But although on the continent not yet occupying so prominent a +position in public estimation as do coal-fields in Great Britain, those +of the former have one conspicuous characteristic, viz., the great +thickness of some of the individual seams. + +In the coal-field of Midlothian the seams of coal vary from 2 feet to 5 +feet in thickness. One of them is known as the "great seam," and in spite +of its name attains a thickness only of from 8 to 10 feet thick. There +are altogether about thirty seams of coal. When, however, we pass to the +continent, we find many instances, such as that of the coal-field of +Central France, in which the seams attain vast thicknesses, many of them +actually reaching 40 and 60 feet, and sometimes even 80 feet. One of the +seams in the district of St. Etienne varies from 30 to 70 feet thick, +whilst the fifteen to eighteen workable seams give a thickness of 112 +feet, although the total area of the field is not great. Again, in the +remarkable basin of the Saône-et-Loire, although there are but ten beds +of coal, two of them run from 30 to 60 feet each, whilst at Creusot the +main seam actually runs locally to a thickness varying between 40 and 130 +feet. + +The Belgian coal-field stretches in the form of a narrow strip from 7 to +9 miles wide by about 100 miles long, and is divided into three principal +basins. In that stretching from Liége to Verviers there are eighty-three +seams of coal, none of which are less than 3 feet thick. In the basin of +the Sambre, stretching from Namur to Charleroi, there are seventy-three +seams which are workable, whilst in that between Mons and Thulin there +are no less than one hundred and fifty-seven seams. The measures here are +so folded in zigzag fashion, that in boring in the neighbourhood of Mons +to a depth of 350 yards vertical, a single seam was passed through no +less than six times. + +Germany, on the west side of the Rhine, is exceptionally fortunate in the +possession of the famous Pfalz-Saarbrücken coal-field, measuring about 60 +miles long by 20 miles wide, and covering about 175 square miles. Much of +the coal which lies deep in these coal-measures will always remain +unattainable, owing to the enormous thickness of the strata, but a +careful computation made of the coal which can be worked, gives an +estimate of no less than 2750 millions of tons. There is a grand total of +two hundred and forty-four seams, although about half of them are +unworkable. + +Beside other smaller coal-producing areas in Germany, the coal-fields of +Silesia in the southeastern corner of Prussia are a possession unrivalled +both on account of their extent and thickness. It is stated that there +exist 333 feet of coal, all the seams of which exceed 2-1/2 feet, and +that in the aggregate there is here, within a workable depth, the +scarcely conceivable quantity of 50,000 million tons of coal. + +The coal-field of Upper Silesia, occupying an area about 20 miles long by +15 miles broad, is estimated to contain some 10,000 feet of strata, with +333 feet of good coal. This is about three times the thickness contained +in the South Wales coal-field, in a similar thickness of coal-measures. +There are single seams up to 60 feet thick, but much of the coal is +covered by more recent rocks of New Red and Cretaceous age. In Lower +Silesia there are numerous seams 3-1/2 feet to 5 feet thick, but owing to +their liability to change in character even in the same seam, their value +is inferior to the coals of Upper Silesia. + +When British supplies are at length exhausted, we may anticipate that +some of the earliest coals to be imported, should coal then be needed, +will reach Britain from the upper waters of the Oder. + +The coal-field of Westphalia has lately come into prominence in +connection with the search which has been made for coal in Kent and +Surrey, the strata which are mined at Dortmund being thought to be +continuous from the Bristol coal-field. Borings have been made through +the chalk of the district north of the Westphalian coal-field, and these +have shown the existence of further coal-measures. The coal-field extends +between Essen and Dortmund a distance of 30 miles east and west, and +exhibits a series of about one hundred and thirty seams, with an +aggregate of 300 feet of coal. + +It is estimated that this coal-field alone contains no less than 39,200 +millions of tons of coal. + +Russia possesses supplies of coal whose influence has scarcely yet been +felt, owing to the sparseness of the population and the abundance of +forest. Carboniferous rocks abut against the flanks of the Ural +Mountains, along the sides of which they extend for a length of about a +thousand miles, with inter-stratifications of coal. Their actual contents +have not yet been gauged, but there is every reason to believe that those +coal-beds which have been seen are but samples of many others which will, +when properly worked, satisfy the needs of a much larger population than +the country now possesses. + +Like the lower coals of Scotland, the Russian coals are found in the +carboniferous limestone. This may also be said of the coal-fields in the +governments of Tula and Kaluga, and of those important coal-bearing +strata near the river Donetz, stretching to the northern corner of the +Sea of Azov. In the last-named, the seams are spread over an area of +11,000 square miles, in which there are forty-four workable seams +containing 114 feet of coal. The thickest of known Russian coals occur at +Lithwinsk, where three seams are worked, each measuring 30 feet to 40 +feet thick. + +An extension of the Upper Silesian coal-field appears in Russian Poland. +This is of upper Carboniferous age, and contains an aggregate of 60 feet +of coal. + +At Ostrau, in Upper Silesia (Austria), there is a remarkable coal-field. +Of its 370 seams there are no less than 117 workable ones, and these +contain 350 feet of coal. The coals here are very full of gas, which even +percolates to the cellars of houses in the town. A bore hole which was +sunk in 1852 to a depth of 150 feet, gave off a stream of gas, which +ignited, and burnt for many years with a flame some feet long. + +The Zwickau coal-field in Saxony is one of the most important in Europe. +It contains a remarkable seam of coal, known as Russokohle or soot-coal, +running at times 25 feet thick. It was separated by Geinitz and others +into four zones, according to their vegetable contents, viz.:-- + +1. Zone of Ferns. + +2. Zone of Annularia and Calamites. + +3. Zone of Sigillaria. + +4. Zone of Sagenaria (in Silesia), equivalent to the culm-measures of + Devonshire. + +Coals belonging to other than true Carboniferous age are found in Europe +at Steyerdorf on the Danube, where there are a few seams of good coal in +strata of Liassic age, and in Hungary and Styria, where there are +tertiary coals which approach closely to those of true Carboniferous age +in composition and quality. + +In Spain there are a few small scattered basins. Coal is found overlying +the carboniferous limestone of the Cantabrian chain, the seams being from +5 feet to 8 feet thick. In the Satero valley, near Sotillo, is a single +seam measuring from 60 feet to 100 feet thick. Coal of Neocomian age +appears at Montalban. + +When we look outside the continent of Europe, we may well be astonished +at the bountiful manner in which nature has laid out beds of coal upon +these ancient surfaces of our globe. + +Professor Rogers estimated that, in the United States of America, the +coal-fields occupy an area of no less than 196,850 square miles. + +Here, again, it is extremely probable that the coal-fields which remain, +in spite of their gigantic existing areas, are but the remnants of one +tremendous area of deposit, bounded only on the east by the Atlantic, and +on the west by a line running from the great lakes to the frontiers of +Mexico. The whole area has been subjected to forces which have produced +foldings and flexures in the Carboniferous strata after deposition. These +undulations are greatest near the Alleghanies, and between these +mountains and the Atlantic, whilst the flexures gradually dying out +westward, cause the strata there to remain fairly horizontal. In the +troughs of the foldings thus formed the coal-measures rest, those +portions which had been thrown up as anticlines having suffered loss by +denudation. Where the foldings are greatest there the coal has been +naturally most altered; bituminous and caking-coals are characteristic of +the broad flat areas west of the mountains, whilst, where the contortions +are greatest, the coal becomes a pure anthracite. + +It must not be thought that in this huge area the coal is all uniformly +good. It varies greatly in quality, and in some districts it occurs in +such thin seams as to be worthless, except as fuel for consumption by the +actual coal-getters. There are, too, areas of many square miles in +extent, where there are now no coals at all, the formation having been +denuded right down to the palaeozoic back-bone of the country. + +Amongst the actual coal-fields, that of Pennsylvania stands +pre-eminent. The anthracite here is in inexhaustible quantity, its output +exceeding that of the ordinary bituminous coal. The great field of which +this is a portion, extends in an unbroken length for 875 miles N.E. and +S.W., and includes the basins of Ohio, Maryland, Virginia, Kentucky, and +Tennessee. The workable seams of anthracite about Pottsville measure in +the aggregate from 70 to 207 feet. Some of the lower seams individually +attain an exceptional thickness, that at Lehigh Summit mine containing a +seam, or rather a bed, of 30 feet of good coal. + +A remarkable seam of coal has given the town of Pittsburg its name. This +is 8 feet thick at its outcrop near the town, and although its thickness +varies considerably, Professor Rogers estimates that the sheet of coal +measures superficially about 14,000 square miles. What a forest there +must have existed to produce so widespread a bed! Even as it is, it has +at a former epoch suffered great denudation, if certain detached basins +should be considered as indicating its former extent. + +The principal seam in the anthracite district of central Pennsylvania, +which extends for about 650 miles along the left bank of the Susquehanna, +is known as the "Mammoth" vein, and is 29-1/2 feet thick at Wilkesbarre, +whilst at other places it attains to, and even exceeds, 60 feet. + +On the west of the chain of mountains the foldings become gentler, and +the coal assumes an almost horizontal position. In passing through Ohio +we find a saddle-back ridge or anticline of more ancient strata than the +coal, and in consequence of this, we have a physical boundary placed upon +the coal-fields on each side. + +Passing across this older ridge of denuded Silurian and other rocks, we +reach the famous Illinois and Indiana coal-field, whose +coal-measures lie in a broad trough, bounded on the west by the uprising +of the carboniferous limestone of the upper Mississippi. This limestone +formation appears here for the first time, having been absent on the +eastern side of the Ohio anticline. The area of the coal-field is +estimated at 51,000 square miles. + +In connection with the coal-fields of the United States, it is +interesting to notice that a wide area in Texas, estimated at 3000 square +miles, produces a large amount of coal annually from strata of the +Liassic age. Another important area of production in eastern Virginia +contains coal referable to the Jurassic age, and is similar in fossil +contents to the Jurassic of Whitby and Brora. The main seam in eastern +Virginia boasts a thickness of from 30 to 40 feet of good coal. + +Very serviceable lignites of Cretaceous age are found on the Pacific +slope, to which age those of Vancouver's Island and Saskatchewan River +are referable. + +Other coal-fields of less importance are found between Lakes Huron and +Erie, where the measures cover an area of 5000 square miles, and also in +Rhode Island. + +In British North America we find extensive deposits of valuable +coal-measures. Large developments occur in New Brunswick and Nova Scotia. +At South Joggins there is a thickness of 14,750 feet of strata, in which +are found seventy-six coal-seams of 45 feet in total thickness. At Picton +there are six seams with a total of 80 feet of coal. In the lower +carboniferous group is found the peculiar asphaltic coal of the Albert +mine in New Brunswick. Extensive deposits of lignite are met with both in +the Dominion and in the United States, whilst true coal-measures flank +both sides of the Rocky Mountains. Coal-seams are often encountered in +the Arctic archipelago. + +The principal areas of deposit in South America are in Brazil, Uruguay, +and Peru. The largest is the Candiota coal-field, in Brazil, where +sections in the valley of the Candiota River show five good seams with a +total of 65 feet of coal. It is, however, worked but little, the +principal workings being at San Jeronimo on the Jacahahay River. + +In Peru the true carboniferous coal-seams are found on the higher ground +of the Andes, whilst coal of secondary age is found in considerable +quantities on the rise towards the mountains. At Porton, east of +Truxillo, the same metamorphism which has changed the ridge of sandstone +to a hard quartzite has also changed the ordinary bituminous coal into an +anthracite, which is here vertical in position. The coals of Peru usually +rise to more than 10,000 feet above the sea, and they are practically +inaccessible. + +Cretaceous coals have been found at Lota in Chili, and at Sandy Point, +Straits of Magellan. + +Turning to Asia, we find that coal has been worked from time to time at +Heraclea in Asia Minor. Lignites are met with at Smyrna and Lebanon. + +The coal-fields of Hindoostan are small but numerous, being found in all +parts of the peninsula. There is an important coal-field at Raniganj, +near the Hooghly, 140 miles north of Calcutta. It has an area of 500 +square miles. In the Raniganj district there are occasional seams 20 feet +to 80 feet in thickness, but the coals are of somewhat inferior quality. + +The best quality amongst Indian coals has come from a small coal-field of +about 11 square miles in extent, situated at Kurhurbali on the East +Indian Railway. Other coal-fields are found at Jherria and on the Sone +River, in Bengal, and at Mopani on the Nerbudda. Much is expected in +future from the large coal-field of the Wardha and Chanda districts, in +the Central Provinces, the coal of which may eventually prove to be of +Permian age. + +The coal-deposits of China are undoubtedly of tremendous extent, although +from want of exploration it is difficult to form any satisfactory +estimate of them. Near Pekin there are beds of coal 95 feet thick, which +afford ample provision for the needs of the city. In the mountainous +districts of western China the area over which carboniferous strata are +exposed has been estimated at 100,000 square miles. The coal-measures +extend westward to the Mongolian frontier, where coal-seams 30 feet thick +are known to lie in horizontal plane for 200 miles. Most of the Chinese +coal-deposits are rendered of small value, either owing to the +mountainous nature of the valleys in which they outcrop, or to their +inaccessibility from the sea. Japan is not lacking in good supplies of +coal. A colliery is worked by the government on the island of Takasima, +near Nagasaki, for the supply of coals for the use of the navy. + +The British possession of Labuan, off the island of Borneo, is rich in a +coal of tertiary age, remarkable for the quantity of fossil resin which, +it contains. Coal is also found in Sumatra, and in the Malayan +Archipelago. + +In Cape Colony and Natal the coal-bearing Karoo beds are probably of New +Red age. The coal is reported to be excellent in quantity. + +In Abyssinia lignites are frequently met with in the high lands of the +interior. + +Coal is very extensively developed throughout Australasia. In New South +Wales, coal-measures occur in large detached portions between 29° and 35° +S. latitude. The Newcastle district, at the mouth of the Hunter river, is +the chief seat of the coal trade, and the seams are here found up to 30 +feet thick. Coal-bearing strata are found at Bowen River, in Queensland, +covering an area of 24,000 square miles, whilst important mines of +Cretaceous age are worked at Ipswich, near Brisbane. In New Zealand +quantities of lignite, described as a hydrous coal, are found and +utilised; also an anhydrous coal which may prove to be either of +Cretaceous or Jurassic age. + +We have thus briefly sketched the supplies of coal, so far as they are +known, which are to be found in various countries. But England has of +late years been concerned as to the possible failure of her home supplies +in the not very distant future, and the effects which such failure would +be likely to produce on the commercial prosperity of the country. + +Great Britain has long been the centre of the universe in the supply of +the world's coal, and as a matter of fact, has been for many years +raising considerably more than one half of the total amount of coal +raised throughout the whole world. There is, as we have seen, an +abundance of coal elsewhere, which will, in the course of time, compete +with her when properly worked, but Britain seems to have early taken the +lead in the production of coal, and to have become the great universal +coal distributor. Those who have misgivings as to what will happen when +her coal is exhausted, receive little comfort from the fact that in North +America, in Prussia, in China and elsewhere, there are tremendous +supplies of coal as yet untouched, although a certain sense of relief is +experienced when that fact becomes generally known. + +If by the time of exhaustion of the home mines Britain is still dependent +upon coal for fuel, which, in this age of electricity, scarcely seems +probable, her trade and commerce will feel with tremendous effect the +blow which her prestige will experience when the first vessel, laden with +foreign coal, weighs anchor in a British harbour. In the great coal +lock-out of 1893, when, for the greater part of sixteen weeks scarcely a +ton of coal reached the surface in some of her principal coal-fields, it +was rumoured, falsely as it appeared, that a collier from America had +indeed reached those shores, and the importance which attached to the +supposed event was shown by the anxious references to it in the public +press, where the truth or otherwise of the alarm was actively discussed. +Should such a thing at any time actually come to pass, it will indeed be +a retribution to those who have for years been squandering their +inheritance in many a wasteful manner of coal-consumption. + +Thirty years ago, when so much small coal was wasted and wantonly +consumed in order to dispose of it in the easiest manner possible at the +pitmouths, and when only the best and largest coal was deemed to be of +any value, louder and louder did scientific men speak in protest against +this great and increasing prodigality. Wild estimates were set on foot +showing how that, sooner or later, there would be in Britain no native +supply of coal at all, and finally a Royal Commission was appointed in +1866, to collect evidence and report upon the probable time during which +the supplies of Great Britain would last. + +This Commission reported in 1871, and the outcome of it was that a period +of twelve hundred and seventy-three years was assigned as the period +during which the coal would last, at the then-existing rate of +consumption. The quantity of workable coal within a depth of 4000 feet +was estimated to be 90,207 millions of tons, or, including that at +greater depths, 146,480 millions of tons. Since that date, however, there +has been a steady annual increase in the amount of coal consumed, and +subsequent estimates go to show that the supplies cannot last for more +than 250 years, or, taking into consideration a possible decrease in +consumption, 350 years. Most of the coal-mines will, indeed, have been +worked out in less than a hundred years hence, and then, perhaps, the +competition brought about by the demand for, and the scarcity of, coal +from the remaining mines, will have resulted in the dreaded importation +of coal from abroad. + +In referring to the outcome of the Royal Commission of 1866, although the +Commissioners fixed so comparatively short a period as the probable +duration of the coal supplies, it is but fair that it should be stated +that other estimates have been made which have materially differed from +their estimate. Whereas one estimate more than doubled that of the Royal +Commission, that of Sir William Armstrong in 1863 gave it as 212 years, +and Professor Jevons, speaking in 1875 concerning Armstrong's estimate, +observed that the annual increase in the amount used, which was allowed +for in the estimate, had so greatly itself increased, that the 212 years +must be considerably reduced. + +One can scarcely thoroughly appreciate the enormous quantity of coal that +is brought to the surface annually, and the only wonder is that there are +any supplies left at all. The Great Pyramid which is said by Herodotus to +have been twenty years in building, and which took 100,000 men to build, +contains 3,394,307 cubic yards of stone. The coal raised in 1892 would +make a pyramid which would contain 181,500,000 cubic yards, at the low +estimate that one ton could be squeezed into one cubic yard. + +The increase in the quantity of coal which has been raised in succeeding +years can well be seen from the following facts. + +In 1820 there were raised in Great Britain about 20 millions of tons. By +1855 this amount had increased to 64-1/2 millions. In 1865 this again had +increased to 98 millions, whilst twenty years after, viz., in 1885, this +had increased to no less than 159 millions, such were the giant strides +which the increase in consumption made. + +In the return for 1892, this amount had farther increased to 181-1/2 +millions of tons, an advance in eight years of a quantity more than equal +to the total raised in 1820, and in 1894 the total reached +199-1/2 millions; this was produced by 795,240 persons, employed in and +about the mines. + + + + +CHAPTER VIII. + +THE COAL-TAR COLOURS. + + +In a former chapter some slight reference has been made to those +bye-products of coal-tar which have proved so valuable in the production +of the aniline dyes. It is thought that the subject is of so interesting +a nature as to deserve more notice than it was possible to bestow upon it +in that place. With abstruse chemical formulae and complex chemical +equations it is proposed to have as little as possible to do, but even +the most unscientific treatment of the subject must occasionally +necessitate a scientific method of elucidation. + +The dyeing industry has been radically changed during the last half +century by the introduction of what are known as the _artificial_ dyes, +whilst the _natural_ colouring matters which had previously been the sole +basis of the industry, and which had been obtained by very simple +chemical methods from some of the constituents of the animal kingdom, or +which were found in a natural state in the vegetable kingdom, have very +largely given place to those which have been obtained from coal-tar, a +product of the mineralised vegetation of the carboniferous age. + +The development and discovery of the aniline colouring matters were not, +of course, possible until after the extensive adoption of +house-gas for illuminating purposes, and even then it was many years +before the waste products from the gas-works came to have an appreciable +value of their own. This, however, came with the increased utilitarianism +of the commerce of the present century, but although aniline was first +discovered in 1826 by Unverdorben, in the materials produced by the dry +distillation of indigo (Portuguese, _anil_, indigo), it was not until +thirty years afterwards, namely, in 1856, that the discovery of the +method of manufacture of the first aniline dye, mauveine, was announced, +the discovery being due to the persistent efforts of Perkin, to whom, +together with other chemists working in the same field, is due the great +advance which has been made in the chemical knowledge of the carbon, +hydrogen, and oxygen compounds. Scientists appeared to work along two +planes; there were those who discovered certain chemical compounds in the +resulting products of reactions in the treatment of _existing_ +vegetation, and there were those who, studying the wonderful constituents +in coal-tar, the product of a _past_ age, immediately set to work to find +therein those compounds which their contemporaries had already +discovered. Generally, too, with signal success. + +The discovery of benzene in 1825 by Faraday was followed in the course of +a few years by its discovery in coal-tar by Hofmann. Toluene, which was +discovered in 1837 by Pelletier, was recognised in the fractional +distillation of crude naphtha by Mansfield in 1848. Although the method +of production of mauveine on a large scale was not accomplished until +1856, yet it had been noticed in 1834, the actual year of its recognition +as a constituent of coal-tar, that, when brought into contact with +chloride of lime, it gave brilliant colours, but it required a +considerable cheapening of the process of aniline manufacture before the +dyes commenced to enter into competition with the old natural dyes. + +The isolation of aniline from coal-tar is expensive, in consequence of +the small quantities in which it is there found, but it was discovered by +Mitscherlich that by acting upon benzene, one of the early distillates of +coal-tar, for the production of nitro-benzole, a compound was produced +from which aniline could be obtained in large quantities. There were thus +two methods of obtaining aniline from tar, the experimental and the +practical. + +In producing nitrobenzole (nitrobenzene), chemically represented as +(C_{6}H_{5}NO_{2}), the nitric acid used as the reagent with benzene, is +mixed with a quantity of sulphuric acid, with the object of absorbing +water which is formed during the reaction, as this would tend to dilute +the efficiency of the nitric acid. The proportions are 100 parts of +purified benzene, with a mixture of 115 parts of concentrated nitric acid +(HNO_{3}) and 160 parts of concentrated sulphuric acid. The mixture is +gradually introduced into the large cast-iron cylinder into which the +benzene has been poured. The outside of the cylinder is supplied with an +arrangement by which fine jets of water can be made to play upon it in +the early stages of the reaction which follows, and at the end of from +eight to ten hours the contents are allowed to run off into a storage +reservoir. Here they arrange themselves into two layers, the top of which +consists of the nitrobenzene which has been produced, together with some +benzene which is still unacted upon. The mixture is then freed from the +latter by treatment with a current of steam. Nitrobenzene presents itself +as a yellowish oily liquid, with a peculiar taste as of bitter almonds. +It was formerly in great demand by perfumers, but its poisonous +properties render it a dangerous substance to deal with. In practice a +given quantity of benzene will yield about 150 per cent of nitrobenzene. +Stated chemically, the reaction is shown by the following equation:-- + +C_{6}H_{6} + HNO_{3} = C_{6}H_{5}NO_{2}, + H_{2}O +(Benzene) (Nitric acid) (Nitrobenzene) (Water). + +The water which is thus formed in the process, by the freeing of one of +the atoms of hydrogen in the benzene, is absorbed by the sulphuric acid +present, although the latter takes no actual part in the reaction. + +From the nitrobenzene thus obtained, the aniline which is now used so +extensively is prepared. The component atoms of a molecule of aniline are +shown in the formula C_{6}H_{5}NH_{2}. It is also known as phenylamine or +amido-benzole, or commercially as aniline oil. There are various methods +of reducing nitrobenzene for aniline, the object being to replace the +oxygen of the former by an equivalent number of atoms of hydrogen. The +process generally used is that known as Béchamp's, with slight +modifications. Equal volumes of nitrobenzene and acetic acid, together +with a quantity of iron-filings rather in excess of the weight of the +nitrobenzene, are placed in a capacious retort. A brisk effervescence +ensues, and to moderate the increase of temperature which is caused by +the reaction, it is found necessary to cool the retort. Instead of acetic +acid hydrochloric acid has been a good deal used, with, it is said, +certain advantageous results. From 60 to 65 per cent. of aniline on the +quantity of nitrobenzene used, is yielded by Béchamp's process. + +Stated in a few words, the above is the process adopted on all hands for +the production of commercial aniline, or aniline oil. The details of the +distillation and rectification of the oil are, however, as varied as they +can well be, no two manufacturers adopting the same process. Many of the +aniline dyes depend entirely for their superiority, on the quality of the +oil used, and for this reason it is subject to one or more processes of +rectification. This is performed by distilling, the distillates at the +various temperatures being separately collected. + +When pure, aniline is a colourless oily liquid, but on exposure rapidly +turns brown. It has strong refracting powers and an agreeable aromatic +smell. It is very poisonous when taken internally; its sulphate is, +however, sometimes used medicinally. It is by the action upon aniline of +certain oxidising agents, that the various colouring matters so well +known as aniline dyes are obtained. + +Commercial aniline oil is not, as we have seen, the purest form of +rectified aniline. The aniline oils of commerce are very variable in +character, the principal constituents being pure aniline, para- and +meta-toluidine, xylidines, and cumidines. They are best known to the +colour manufacturer in four qualities-- + +(_a_) Aniline oil for blue and black. + +(_b_) Aniline oil for magenta. + +(_c_) Aniline oil for safranine. + +(_d_) _Liquid toluidine. + +From the first of these, which is almost pure aniline, aniline black is +derived, and a number of organic compounds which are further used for the +production of dyes. The hydrochloride of aniline is important and is +known commercially as "aniline salt." + +The distillation and rectification of aniline oil is practised on a +similar principle to the fractional distillation which we have noticed as +being used for the distillation of the naphthas. First, light aniline +oils pass over, followed by others, and finally by the heavy oils, or +"aniline-tailings." It is a matter of great necessity to those engaged in +colour manufacture to apply that quality oil which is best for the +production of the colour required. This is not always an easy matter, and +there is great divergence of opinion and in practice on these points. + +The so-called aniline colours are not all derived from aniline, such +colouring matters being in some cases derived from other coal-tar +products, such as benzene and toluene, phenol, naphthalene, and +anthracene, and it is remarkable that although the earlier dyes were +produced from the lighter and more easily distilled products of +coal-tar, yet now some of the heaviest and most stubborn of the +distillates are brought under requisition for colouring matters, those +which not many years ago were regarded as fit only to be used as +lubricants or to be regarded as waste. + +It is scarcely necessary or advisable in a work of this kind to pursue +the many chemical reactions, which, from the various acids and bases, +result ultimately in the many shades and gradations of colour which are +to be seen in dress and other fabrics. Many of them, beautiful in the +extreme, are the outcome of much careful and well-planned study, and to +print here the complicated chemical formulae which show the great changes +taking place in compounds of complex molecules, or to mention even the +names of these many-syllabled compounds, would be to destroy the purpose +of this little book. The Rosanilines, the Indulines, and Safranines; the +Oxazines, the Thionines: the Phenol and Azo dyes are all substances which +are of greater interest to the chemical students and to the colour +manufacturer than to the ordinary reader. Many of the names of the bases +of various dyes are unknown outside the chemical dyeworks, although each +and all have complicated; reactions of their own. In the reds are +rosanilines, toluidine xylidine, &c.; in the blues--phenyl-rosanilines, +diphenylamine, toluidine, aldehyde, &c.; violets--rosaniline, mauve, +phenyl, ethyl, methyl, &c.; greens--iodine, aniline, leucaniline, +chrysotoluidine, aldehyde, toluidine, methyl-anilinine, &c.; yellows and +orange--leucaniline, phenylamine, &c.; browns--chrysotoluidine, &c.; +blacks--aniline, toluidine, &c. + +To take the rosanilines as an instance of the rest. + +Aniline red, magenta, azaleine, rubine, solferino, fuchsine, chryaline, +roseine, erythrobenzine, and others, are colouring matters in this group +which are salts of rosaniline, and which are all recognised in commerce. + +The base rosaniline is known chemically by the formula C_{20}H_{l9}N_{3}, +and is prepared by heating a mixture of magenta aniline, toluidine, and +pseudotoluidine, with arsenic acid and other oxidising agents. It is +important that water should be used in such quantities as to prevent the +solution of arsenic acid from depositing crystals on cooling. Unless +carefully crystallised rosaniline will contain a slight proportion of the +arseniate, and when articles of clothing are dyed with the salt, it is +likely to produce an inflammatory condition of skin, when worn. Some +years ago there was a great outcry against hose and other articles dyed +with aniline dyes, owing to the bad effects which were produced, and this +has no doubt proved very prejudicial to aniline dyes as a whole. + +Again, the base known as mauve, or mauveine, has a composition shown by +the formula C_{27}H_{24}N_{4}. It is produced from the sulphate of +aniline by mixing it with a cold saturated solution of bichromate of +potash, and allowing the mixture to stand for ten or twelve hours. A +blue-black precipitate is then formed, which, after undergoing a process +of purification, is dissolved in alcohol and evaporated to dryness. A +metallic-looking powder is then obtained, which constitutes this +all-important base. Mauve forms with acids a series of well-defined salts +and is capable of expelling ammonia from its combinations. Mauve was the +first aniline dye which was produced on a large scale, this being +accomplished by Perkin in 1856. + +The substance known as carbolic acid is so useful a product of a piece of +coal that a description of the method of its production must necessarily +have a place here. It is one of the most powerful antiseptic agents with +which we are acquainted, and has strong anaesthetic qualities. Some +useful dyes are also obtained from it. It is obtained in quantities from +coal-tar, that portion of the distillate known as the light oils being +its immediate source. The tar oil is mixed with a solution of caustic +soda, and the mixture is violently agitated. This results in the caustic +soda dissolving out the carbolic acid, whilst the undissolved oils +collect upon the surface, allowing the alkaline solution to be drawn from +beneath. The soda in the solution is then neutralised by the addition of +a suitable quantity of sulphuric acid, and the salt so formed sinks while +the carbolic acid rises to the surface. + +Purification of the product is afterwards carried out by a process of +fractional distillation. There are various other methods of preparing +carbolic acid. + +Carbolic acid is known chemically as C_{6}H_{5}(HO). When pure it appears +as colourless needle-like crystals, and is exceedingly poisonous. It has +been used with marked success in staying the course of disease, such as +cholera and cattle plague. It is of a very volatile nature, and its +efficacy lies in its power of destroying germs as they float in the +atmosphere. Modern science tells us that all diseases have their origin +in certain germs which are everywhere present and which seek only a +suitable _nidus_ in which to propagate and flourish. Unlike mere +deodorisers which simply remove noxious gases or odours; unlike +disinfectants which prevent the spread of infection, carbolic acid +strikes at the very root and origin of disease by oxidising and consuming +the germs which breed it. So powerful is it that one part in five +thousand parts of flour paste, blood, &c., will for months prevent +fermentation and putrefaction, whilst a little of its vapour in the +atmosphere will preserve meat, as well as prevent it from becoming +fly-blown. Although it has, in certain impure states, a slightly +disagreeable odour, this is never such as to be in any way harmful, +whilst on the other hand it is said to act as a tonic to those connected +with its preparation and use. + +The new artificial colouring matters which are continually being brought +into the market, testify to the fact that, even with the many beautiful +tints and hues which have been discovered, finality and perfection have +not yet been reached. A good deal of popular prejudice has arisen against +certain aniline dyes on account of their inferiority to many of the old +dye-stuffs in respect to their fastness, but in recent years the +manufacture of many which were under this disadvantage of looseness of +dye, has entirely ceased, whilst others have been introduced which are +quite as fast, and sometimes even faster than the natural dyes. + +It is convenient to express the constituents of coal-tar, and the +distillates of those constituents, in the form of a genealogical chart, +and thus, by way of conclusion, summarise the results which we have +noticed. + + COAL. + | + .----------+-----------+----+-------------------+--------+----. + | | | | | | + Water House-gas Coal-tar Ammoniacal Coke | + | liquor | + .---------+-------+---------+---------. | Sulphur + | | | | | | (sulphurreted + First Second Heavy Anthracene Pitch | hydrogen: + light light oils (green | sulphurous + oils oils (creosote oils) | acid: oil + | (crude oils) | | of vitriol) + .----+----. naphtha) | Anthracene | + | | | | | | +Ammoniacal Benzene | | Alizarin or | + liquor toluene,| | dyer's madder | + &c. | | | + | | | + | | Sulphuric acid=Carbonate of=Hydrochloric + | | | ammonia acid + | | | (smelling + | | | salts) + | | | + | | Lime=Sulphate of Lime=Chloride of + | | | ammonia | ammonia (sal + | | | | ammoniac) + | | | | + | | .----+----. .----+----. + | | | | | | + | | Ammonia Sulphate Ammonia Chloride + | | of lime of lime. + | | (Plaster of Paris) + | | + | .--+-----+----------. + | | | | + | Crude Carbolic Naphthalin + | Creosote acid + | + .--------------+---+--+-------+--------+-----------. + | | | | | + Benzene=Nitric Acid Toluene Nylene Artificial Burning + | turpentine oils + Nitrobenzene= } Iron filings oil (solvent + (Essence de | } and acetic acid naphtha) + mirbane) | + | + Aniline=Various reagents + | + Aniline dyes + + + + + + +INDEX. + +A. + +Accidents, causes of mining +"Age of _Acrogens_" +_Alethopteris_ +Alizarin +American coal-fields +Ammoniacal liquor +Aniline +Aniline dyes +Aniline oil, commercial +Aniline salt +Aniline "tailings" +Anthracene +Anthracite +Artificial turpentine oil +Asphalt +Australian coals +_Aviculopecten_ + +B. + +Béchamp's process +Benzene +Bind +Bitumen in Trinidad +"Blower" a +Boghead coal +Bog-oak +Boring diamonds +Borrowdale graphite mine +Bovey Tracey lignite +British coal-fields +British North-American coal-measures +Briquettes + +C. + +_Calamites_, extinct horsetails +Carbolic acid +Carboniferous formation, the +_Cardiocarpum_, fossil fruit +Carelessness of miners +Causes of earth-movements +Changes of level +Charcoal as a disinfectant +Chemistry of a gas-flame +Chinese coals +Clanny's safety-lamp +Clayton's experiments with gas +Clay, regularity in deposition of +Club-mosses, great height of fossil +Coal-dust, danger from +Coal formed in large lakes or closed seas +Coal formation, geological position of +Coal formed by escape of gases +Coal-mine, the +Coal not the result of drifted vegetation +Coal-period, climate of +"Coal-pipes" +Coal-plants, classification of +Coal-seam, each, a forest growth +Coals of non-carboniferous age +Coal, vegetable origin of +Coke +"Cole" +"Condensers" +Cones of _Lepidodendra_ +Conifers in coal-measures +Current-bedding in sandstone + +D. + +Davy-lamp +Dangers of benzene +Darwin on the Chonos Archipelago +Diamonds, how made artificially +Disintegration of vegetable substances +Disproportion in relative thickness of coal and coal-measures + +E. + +Early use of coal +Effects of an explosion +Encrinital limestone +_Equiseta_ +"Essence de mirbane" +European coal-fields +Evelyn on the use of coal +Experiments illustrating fossilisation + +F. + +Filling retorts by machinery +Firedamp +Fire, mines on +First light oils +First record of an explosion +Flashing-point of oil +Flooding of pits +Fog and smoke +_Foraminifera_ +Fossil ferns +Fructification on fossil-ferns +Furnace, ventilating + +G. + +Gas, coal +Gasholder, the +Gas, house, constituents of +_Glossopteris_ +Graphite +"Green Grease" + +H. + +Hannay, of Glasgow +Heavy oils +Humboldt's safety-lamp +Hydraulic Main + +I. + +Impurities in house-gas +Indian coals +Insertion of rootlets of _stigmaria_ +Insufficiency of modern forest growths +Ireland denuded of coal-beds +Iron, supplies of + +L. + +_Lepidodendra_ +_Lepidostrobi_ +Lignite +London lit by gas + +M. + +Mammoth trees +Marco Polo +Marsh gas +Medium oils +Metamorphism of coal by igneous agency +Methods of ventilation +Mountain limestone +Murdock's use of gas +Mussel beds + +N. + +Napthalin +_Neuropteris_ +Newcastle, charters to +Nitro-benzole + +O. + +Objections to use of coal +Oils from coal and lignite +Oil-wells of America +Olefiant gas +_Orthoceras_ + +P. + +Paraffins +Peat +_Pecopteris_ +Pennsylvanian anthracite +Persian fire-worshippers +Pitch +Plumbago +_Polyzoa_ +Prejudice against aniline dyes +Prohibitions of the use of coal +Proportions of explosive mixtures +_Psaronius_ +"Purifiers" +Pyrites in coal + +Q. + +Quantity of coal raised in Great Britain + +R. + +Reptiles of the coal-era +Resemblance of American and British coal-_flora_ +Retorts +Roman use of coal +Rosanilines, the +Royal Commission of 1866 + +S. + +Sandstone, how formed +Shales +_Sigillaria_ +South American coals +Spores of _lepidodrendron_ +Spores, resinous matter in +Spores, inflammability of +Steel-mill +_Sternbergia_ +_Stigmaria_ +Subsidence throughout coal-era +Surturbrand at Brighton +Sussex iron-works + +T. + +Tar +Testing pits by the candle +Texas coal +Toluene, discovery of +Torbanehill mineral +Trappers + +U. + +Underclays +Uses to which coal is put + +V. + +Vaseline +Vegetation of the coal age +Ventilation of coal-pits + +W. + +"Washers" +Waste of fuel +Wealden lignite +Westphalian coal-field + +Y. + +Young's Paraffin Oil + +Z. + +Zoroastrians + + + + + +End of Project Gutenberg's The Story of a Piece of Coal, by Edward A. 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Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..596e8ac --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #12762 (https://www.gutenberg.org/ebooks/12762) diff --git a/old/12762-8.txt b/old/12762-8.txt new file mode 100644 index 0000000..b876d96 --- /dev/null +++ b/old/12762-8.txt @@ -0,0 +1,4781 @@ +Project Gutenberg's The Story of a Piece of Coal, by Edward A. Martin + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Story of a Piece of Coal + What It Is, Whence It Comes, and Whither It Goes + +Author: Edward A. Martin + +Release Date: June 28, 2004 [EBook #12762] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE STORY OF A PIECE OF COAL *** + + + + +Produced by Miranda van de Heijning, Luiz Antonio de Souza and PG +Distributed Proofreaders + + + + + +THE STORY OF +A PIECE OF COAL + +WHAT IT IS, WHENCE IT COMES, +AND WHITHER IT GOES + +BY +EDWARD A. MARTIN, F.G.S. + +1896 + + + + + +PREFACE. + + +The knowledge of the marvels which a piece of coal possesses within +itself, and which in obedience to processes of man's invention it is +always willing to exhibit to an observant enquirer, is not so widespread, +perhaps, as it should be, and the aim of this little book, this record of +one page of geological history, has been to bring together the principal +facts and wonders connected with it into the focus of a few pages, where, +side by side, would be found the record of its vegetable and mineral +history, its discovery and early use, its bearings on the great +fog-problem, its useful illuminating gas and oils, the question of the +possible exhaustion of British supplies, and other important and +interesting bearings of coal or its products. + +In the whole realm of natural history, in the widest sense of the term, +there is nothing which could be cited which has so benefited, so +interested, I might almost say, so excited mankind, as have the wonderful +discoveries of the various products distilled from gas-tar, itself a +distillate of coal. + +Coal touches the interests of the botanist, the geologist, and the +physicist; the chemist, the sanitarian, and the merchant. + +In the little work now before the reader I have endeavoured to recount, +without going into unnecessary detail, the wonderful story of a piece of +coal. + +E.A.M. + +THORNTON HEATH, + +_February_, 1896. + + + + +CONTENTS. + + + I. THE ORIGIN OF COAL AND THE PLANTS OF WHICH IT IS COMPOSED + + II. A GENERAL VIEW OF THE COAL-BEARING STRATA + + III. VARIOUS FORMS OF COAL AND CARBON + + IV. THE COAL-MINE AND ITS DANGERS + + V. EARLY HISTORY--ITS USE AND ITS ABUSE + + VI. HOW GAS IS MADE--ILLUMINATING OILS AND BYE-PRODUCTS + + VII. THE COAL SUPPLIES OF THE WORLD + +VIII. THE COAL-TAR COLOURS + +CHART SHEWING THE PRODUCTS OF COAL + +GENERAL INDEX + + + +LIST OF ILLUSTRATIONS. + +FIG. 1. _Stigmaria_ + " 2. _Annularia radiata_ + " 3. _Rhacopteris inaequilatera_ + " 4. Frond of _Pecopteris_ + " 5. _Pecopteris Serlii_ + " 6. _Sphenopteris affinis_ + " 7. _Catamites Suckowii_ + " 8. _Calamocladus grandis_ + " 9. _Asterophyllites foliosa_ + " 10. _Spenophyllum cuneifolium_ + " 11. Cast of _Lepidodendron_ + " 12. _Lepidodendron longifolium_ + " 13. _Lepidodendron aculeatum_ + " 14. _Lepidostrobus_ + " 15. _Lycopodites_ + " 16. _Stigmaria ficoides_ + " 17. Section of _Stigmaria_ + " 18. Sigillarian trunks in sandstone + " 19. _Productus_ + " 20. _Encrinite_ + " 21. Encrinital limestone + " 22. Various _encrinites_ + " 23. _Cyathophyllum_ + " 24. _Archegosaurus minor_ + " 25. _Psammodus porosus_ + " 26. _Orthoceras_ + " 27. _Fenestella retepora_ + " 28. _Goniatites_ + " 29. _Aviculopecten papyraceus_ + " 30. Fragment of _Lepidodendron_ + " 31. Engine-house at head of a Coal-Pit + " 32. Gas Jet and Davy Lamp + " 33. Part of a Sigillarian trunk + " 34. Inside a Gas-holder + " 35. Filling Retorts by Machinery + " 36. "Condensers" + " 37. "Washers" + " 38. "Purifiers" + + + + +CHAPTER I. + +THE ORIGIN OF COAL AND THE PLANTS OF +WHICH IT IS COMPOSED. + + +From the homely scuttle of coal at the side of the hearth to the +gorgeously verdant vegetation of a forest of mammoth trees, might have +appeared a somewhat far cry in the eyes of those who lived some fifty +years ago. But there are few now who do not know what was the origin of +the coal which they use so freely, and which in obedience to their demand +has been brought up more than a thousand feet from the bowels of the +earth; and, although familiarity has in a sense bred contempt for that +which a few shillings will always purchase, in all probability a stray +thought does occasionally cross one's mind, giving birth to feelings of a +more or less thankful nature that such a store of heat and light was long +ago laid up in this earth of ours for our use, when as yet man was not +destined to put in an appearance for many, many ages to come. We can +scarcely imagine the industrial condition of our country in the absence +of so fortunate a supply of coal; and the many good things which are +obtained from it, and the uses to which, as we shall see, it can be put, +do indeed demand recognition. + +Were our present forests uprooted and overthrown, to be covered by +sedimentary deposits such as those which cover our coal-seams, the amount +of coal which would be thereby formed for use in some future age, would +amount to a thickness of perhaps two or three inches at most, and yet, in +one coal-field alone, that of Westphalia, the 117 most important seams, +if placed one above the other in immediate succession, would amount to no +less than 294 feet of coal. From this it is possible to form a faint idea +of the enormous growths of vegetation required to form some of our +representative coal beds. But the coal is not found in one continuous +bed. These numerous seams of coal are interspersed between many thousands +of feet of sedimentary deposits, the whole of which form the +"coal-measures." Now, each of these seams represents the growth of a +forest, and to explain the whole series it is necessary to suppose that +between each deposit the land became overwhelmed by the waters of the sea +or lake, and after a long subaqueous period, was again raised into dry +land, ready to become the birth-place of another forest, which would +again beget, under similarly repeated conditions, another seam of coal. +Of the conditions necessary to bring these changes about we will speak +later on, but this instance is sufficient to show how inadequate the +quantity of fuel would be, were we dependent entirely on our own existing +forest growths. + +However, we will leave for the present the fascinating pursuit of +theorising as to the how and wherefore of these vast beds of coal, +relegating the geological part of the study of the carboniferous system +to a future chapter, where will be found some more detailed account of +the position of the coal-seams in the strata which contain them. At +present the actual details of the coal itself will demand our attention. + +Coal is the mineral which has resulted, after the lapse of thousands of +thousands of years, from the accumulations of vegetable material, caused +by the steady yearly shedding of leaves, fronds and spores, from forests +which existed in an early age; these accumulated where the trees grew +that bore them, and formed in the first place, perhaps, beds of peat; the +beds have since been subjected to an ever-increasing pressure of +accumulating strata above them, compressing the sheddings of a whole +forest into a thickness in some cases of a few inches of coal, and have +been acted upon by the internal heat of the earth, which has caused them +to part, to a varying degree, with some of their component gases. If we +reason from analogy, we are compelled to admit that the origin of coal is +due to the accumulation of vegetation, of which more scattered, but more +distinct, representative specimens occur in the shales and clays above +and below the coal-seams. But we are also able to examine the texture +itself of the various coals by submitting extremely thin slices to a +strong light under the microscope, and are thus enabled to decide whether +the particular coal we are examining is formed of conifers, horse-tails, +club-mosses, or ferns, or whether it consists simply of the accumulated +sheddings of all, or perhaps, as in some instances, of innumerable +spores. + +In this way the structure of coal can be accurately determined. Were we +artificially to prepare a mass of vegetable substance, and covering it up +entirely, subject it to great pressure, so that but little of the +volatile gases which would be formed could escape, we might in the course +of time produce something approaching coal, but whether we obtained +lignite, jet, common bituminous coal, or anthracite, would depend upon +the possibilities of escape for the gases contained in the mass. + +Everybody has doubtless noticed that, when a stagnant pool which contains +a good deal of decaying vegetation is stirred, bubbles of gas rise to the +surface from the mud below. This gas is known as marsh-gas, or light +carburetted hydrogen, and gives rise to the _ignis fatuus_ which hovers +about marshy land, and which is said to lure the weary traveller to his +doom. The vegetable mud is here undergoing rapid decomposition, as there +is nothing to stay its progress, and no superposed load of strata +confining its resulting products within itself. The gases therefore +escape, and the breaking-up of the tissues of the vegetation goes on +rapidly. + +The chemical changes which have taken place in the beds of vegetation of +the carboniferous epoch, and which have transformed it into coal, are +even now but imperfectly understood. All we know is that, under certain +circumstances, one kind of coal is formed, whilst under other conditions, +other kinds have resulted; whilst in some cases the processes have +resulted in the preparation of large quantities of mineral oils, such as +naphtha and petroleum. Oils are also artificially produced from the +so-called waste-products of the gas-works, but in some parts of the world +the process of their manufacture has gone on naturally, and a yearly +increasing quantity is being utilised. In England oil has been pumped up +from the carboniferous strata of Coalbrook Dale, whilst in Sussex it has +been found in smaller quantities, where, in all probability, it has had +its origin in the lignitic beds of the Wealden strata. Immense quantities +are used for fuel by the Russian steamers on the Caspian Sea, the Baku +petroleum wells being a most valuable possession. In Sicily, Persia, and, +far more important, in the United States, mineral oils are found in great +quantity. + +In all probability coniferous trees, similar to the living firs, pines, +larches, &c., gave rise for the most part to the mineral oils. The class +of living _coniferae_ is well known for the various oils which it +furnishes naturally, and for others which its representatives yield on +being subjected to distillation. The gradually increasing amount of heat +which we meet the deeper we go beneath the surface, has been the cause of +a slow and continuous distillation, whilst the oil so distilled has found +its way to the surface in the shape of mineral-oil springs, or has +accumulated in troughs in the strata, ready for use, to be drawn up when +a well has been sunk into it. + +The plants which have gone to make up the coal are not at once apparent +to the naked eye. We have to search among the shales and clays and +sandstones which enclose the coal-seams, and in these we find petrified +specimens which enable us to build up in our mind pictures of the +vegetable creation which formed the jungles and forests of these +immensely remote ages, and which, densely packed together on the old +forest floor of those days, is now apparent to us as coal. + +[Illustration: Fig. 2.--_Annularia radiata._ Carboniferous sandstone.] + +A very large proportion of the plants which have been found in the +coal-bearing strata consists of numerous species of ferns, the number of +actual species which have been preserved for us in our English coal, +being double the number now existing in Europe. The greater part of these +do not seem to have been very much larger than our own living ferns, and, +indeed, many of them bear a close resemblance to some of our own living +species. The impressions they have left on the shales of the +coal-measures are most striking, and point to a time when the sandy clay +which imbedded them was borne by water in a very tranquil manner, to be +deposited where the ferns had grown, enveloping them gradually, and +consolidating them into their mass of future shale. In one species known +as the _neuropteris_, the nerves of the leaves are as clear and as +apparent as in a newly-grown fern, the name being derived from two Greek +words meaning "nerve-fern." It is interesting to consider the history of +such a leaf, throughout the ages that have elapsed since it was part of a +living fern. First it grew up as a new frond, then gradually unfolded +itself, and developed into the perfect fern. Then it became cut off by +the rising waters, and buried beneath an accumulation of sediment, and +while momentous changes have gone on in connection with the surface of +the earth, it has lain dormant in its hiding-place exactly as we see it, +until now excavated, with its contemporaneous vegetation, to form fuel +for our winter fires. + +[Illustration: FIG. 3.--_Rhacopteris inaequilatera._ Carboniferous +limestone.] + +Although many of the ferns greatly resembled existing species, yet there +were others in these ancient days utterly unlike anything indigenous to +England now. There were undoubted tree-ferns, similar to those which +thrive now so luxuriously in the tropics, and which throw out their +graceful crowns of ferns at the head of a naked stem, whilst on the bark +are the marks at different levels of the points of attachment of former +leaves. These have left in their places cicatrices or scars, showing the +places from which they formerly grew. Amongst the tree-ferns found are +_megaphyton_, _paloeopteris_, and _caulopteris_, all of which have these +marks upon them, thus proving that at one time even tree-ferns had a +habitat in England. + +[Illustration: Fig. 4.--Frond of _Pecopteris._ Coal-shale.] + +One form of tree-fern is known by the name of _Psaronius_, and this was +peculiar in the possession of masses of aerial roots grouped round the +stem. Some of the smaller species exhibit forms of leaves which are +utterly unknown in the nomenclature of living ferns. Most have had names +assigned to them in accordance with certain characteristics which they +possess. This was the more possible since the fossilised impressions had +been retained in so distinct a manner. Here before us is a specimen in a +shale of _pecopteris_, as it is called, (_pekos_, a comb). The leaf in +some species is not altogether unlike the well-known living fern +_osmunda_. The position of the pinnules on both sides of the central +stalk are seen in the fossil to be shaped something like a comb, or a +saw, whilst up the centre of each pinnule the vein is as prominent and +noticeable as if the fern were but yesterday waving gracefully in the +air, and but to-day imbedded in its shaly bed. + +[Illustration: FIG. 5.--_Pecopteris Serlii_. Coal-shale.] + +_Sphenopteris_, or "wedge-fern," is the name applied to another +coal-fern; _glossopteris_, or "tongue-leaf"; _cyclopteris_, or +"round-leaf"; _odonlopteris,_ or "tooth-leaf," and many others, show +their chief characteristics in the names which they individually bear. +_Alethopteris_ appears to have been the common brake of the coal-period, +and in some respects resembles _pecopteris_. + +[Illustration: Fig. 6.--_Sphenopteris Affinis._ Coal-shale.] + +In some species of ferns so exact are the representations which they have +impressed on the shale which contains them, that not only are the veins +and nerves distinctly visible, but even the fructification still remains +in the shape of the marks left by the so-called seeds on the backs of the +leaves. Something more than a passing look at the coal specimens in a +good museum will well repay the time so spent. + +What are known as septarian nodules, or snake-stones, are, at certain +places, common in the carboniferous strata. They are composed of layers +of ironstone and sandstone which have segregated around some central +object, such as a fern-leaf or a shell. When the leaf of a fern has been +found to be the central object, it has been noticed that the leaf can +sometimes be separated from the stone in the form of a carbonaceous film. + +Experiments were made many years ago by M. Goppert to illustrate the +process of fossilisation of ferns. Having placed some living ferns in a +mass of clay and dried them, he exposed them to a red heat, and obtained +thereby striking resemblances to fossil plants. According to the degree +of heat to which they were subjected, the plants were found to be either +brown, a shining black, or entirely lost. In the last mentioned case, +only the impression remained, but the carbonaceous matter had gone to +stain the surrounding clay black, thus indicating that the dark colour of +the coal-shales is due to the carbon derived from the plants which they +included. + +Another very prominent member of the vegetation of the coal period, was +that order of plants known as the _Calamites_. The generic distinctions +between fossil and living ferns were so slight in many cases as to be +almost indistinguishable. This resemblance between the ancient and the +modern is not found so apparent in other plants. The Calamites of the +coal-measures bore indeed a very striking resemblance, and were closely +related, to our modern horse-tails, as the _equiseta_ are popularly +called; but in some respects they differed considerably. + +Most people are acquainted with the horse-tail (_equisetum fluviatile)_ +of our marshes and ditches. It is a somewhat graceful plant, and stands +erect with a jointed stem. The foliage is arranged in whorls around the +joints, and, unlike its fossil representatives, its joints are protected +by striated sheaths. The stem of the largest living species rarely +exceeds half-an-inch in diameter, whilst that of the calamite attained a +thickness of five inches. But the great point which is noticeable in the +fossil calamites and _equisetites_ is that they grew to a far greater +height than any similar plant now living, sometimes being as much as +eight feet high. In the nature of their stems, too, they exhibited a more +highly organised arrangement than their living representatives, having, +according to Dr Williamson, a "fistular pith, an exogenous woody stem, +and a thick smooth bark." The bark having almost al ways disappeared has +left the fluted stem known to us as the calamite. The foliage consisted +of whorls of long narrow leaves, which differed only from the fern +_asterophyllites_ in the fact that they were single-nerved. Sir William +Dawson assigns the calamites to four sub-types: _calamite_ proper, +_calamopitus, calamodendron_, and _eucalamodendron_. + +[Image: FIG. 7.--Root of _Catamites Suckowii_. Coal-shale.] + +[Image: FIG 8.--_Calamocladus grandis_. Carboniferous sandstone.] + +Having used the word "exogenous," it might be as well to pay a little +attention, in passing, to the nomenclature and broad classification of +the various kinds of plants. We shall then doubtless find it far easier +thoroughly to understand the position in the scale of organisation to +which the coal plants are referable. + +[Illustration: FIG. 9.--_Asterophyllites foliosa_. Coal-measures.] + +The plants which are lowest in organisation are known as _Cellular_. They +are almost entirely composed of numerous cells built up one above the +other, and possess none of the higher forms of tissue and organisation +which are met with elsewhere. This division includes the lichens, +sea-weeds, confervae (green aquatic scum), fungi (mushrooms, dry-rot), +&c. + +The division of _Vascular_ plants includes the far larger proportion of +vegetation, both living and fossil, and these plants are built up of +vessels and tissues of various shapes and character. + +All plants are divided into (1) Cryptogams, or Flowerless, such as +mosses, ferns, equisetums, and (2) Phanerogams, or Flowering. Flowering +plants are again divided into those with naked seeds, as the conifers and +cycads (gymnosperms), and those whose seeds are enclosed in vessels, or +ovaries (angiosperms). + +Angiosperms are again divided into the monocotyledons, as the palms, and +dicotyledons, which include most European trees. + +Thus:-- + +------------------------------------------------------------------- +| (M.A. Brongniart). | |(Lindley). | +|CELLULAR | | | +| _Cryptogams_ (Flowerless) |Fungi, seaweeds, |Thallogens | +| | lichens | | +| | | | +|VASCULAR | | | +| _Cryptogams_ (Flowerless) |Ferns, equisetums, |Acrogens | +| | mosses, lycopodiums| | +| _Phanerogams_ (Flowering) | | | +| Gymnosperms (having |Conifers and |Gymnogens | +| naked seeds) | cycads | | +| Two or more Cotyledons | | | +| Angiosperms (having | | | +| enclosed seeds) | | | +| Monocotyledons |Palms, lilies, |Endogens | +| | grasses | | +| Dicotyledons |Most European |Exogens | +| | trees and shrubs | | +------------------------------------------------------------------- + +Adolphe Brongniart termed the coal era the "Age of Acrogens," because, as +we shall see, of the great predominance in those times of vascular +cryptogamic plants, known in Dr Lindley's nomenclature as "Acrogens." + +[Illustration: FIG. 10.--_Spenophyllum cuneifolium._ Coal-shale.] + +Two of these families have already been dealt with, viz., the ferns +(_felices_), and the equisetums, (_calamites_ and _equisetites_), and we +now have to pass on to another family. This is that which includes the +fossil representatives of the Lycopodiums, or Club-mosses, and which goes +to make up in some coals as much as two-thirds of the whole mass. +Everyone is more or less familiar with some of the living Lycopodiums, +those delicate little fern-like mosses which are to be found in many a +home. They are but lowly members of our British flora, and it may seem +somewhat astounding at first sight that their remote ancestors occupied +so important a position in the forests of the ancient period of which we +are speaking. Some two hundred living species are known, most of them +being confined to tropical climates. They are as a rule, low creeping +plants, although some few stand erect. There is room for astonishment +when we consider the fact that the fossil representatives of the family, +known as _Lepidodendra_, attained a height of no less than fifty feet, +and, there is good ground for believing, in many cases, a far greater +magnitude. They consist of long straight stems, or trunks which branch +considerably near the top. These stems are covered with scars or scales, +which have been caused by the separation of the petioles or leaf-stalks, +and this gives rise to the name which the genus bears. The scars are +arranged in a spiral manner the whole of the way up the stem, and the +stems often remain perfectly upright in the coal-mines, and reach into +the strata which have accumulated above the coal-seam. + +[Illustration: FIG. 11.--Cast of _lepidodendron_ in sandstone.] + +Count Sternberg remarked that we are unacquainted with any existing +species of plant, which like the _Lepidodendron_, preserves at all ages, +and throughout the whole extent of the trunk, the scars formed by the +attachment of the petioles, or leaf-stalks, or the markings of the leaves +themselves. The yucca, dracaena, and palm, entirely shed their scales +when they are dried up, and there only remain circles, or rings, arranged +round the trunk in different directions. The flabelliform palms preserve +their scales at the inferior extremity of the trunk only, but lose them +as they increase in age; and the stem is entirely bare, from the middle +to the superior extremity. In the ancient _Lepidodendron_, on the other +hand, the more ancient the scale of the leaf-stalk, the more apparent it +still remains. Portions of stems have been discovered which contain +leaf-scars far larger than those referred to above, and we deduce from +these fragments the fact that those individuals which have been found +whole, are not by any means the largest of those which went to form so +large a proportion of the ancient coal-forests. The _lepidodendra_ bore +linear one-nerved leaves, and the stems always branched dichotomously and +possessed a central pith. Specimens variously named _knorria, +lepidophloios, halonia_, and _ulodendron_ are all referable to this +family. + +[Illustration: FIG. 12.--_Lepidodendron longifolium._ Coal-shale.] + +[Illustration: FIG. 13.--_Lepidodendron aculeatum_ in sandstone.] + +In some strata, as for instance that of the Shropshire coalfield, +quantities of elongated cylindrical bodies known as _lepidostrobi_ have +been found, which, it was early conjectured, were the fruit of the giant +club-mosses about which we have just been speaking. Their appearance can +be called to mind by imagining the cylindrical fruit of the maize or +Indian corn to be reduced to some three or four inches in length. The +sporangia or cases which contained the microscopic spores or seeds were +arranged around a central axis in a somewhat similar manner to that in +which maize is found. These bodies have since been found actually +situated at the end of branches of _lepidodendron_, thus placing their +true nature beyond a doubt. The fossil seeds (spores) do not appear to +have exceeded in volume those of recent club-mosses, and this although +the actual trees themselves grew to a size very many times greater than +the living species. This minuteness of the seed-germs goes to explain the +reason why, as Sir Charles Lyell remarked, the same species of +_lepidodendra_ are so widely distributed in the coal measures of Europe +and America, their spores being capable of an easy transportation by the +wind. + +[Illustration: FIG. 14.--_Lepidostrobus._ Coal-shale.] + +One striking feature in connection with the fruit of the _lepidodendron_ +and other ancient representatives of the club-moss tribe, is that the +bituminous coals in many, if not in most, instances, are made up almost +entirely of their spores and spore-cases. Under a microscope, a piece of +such coal is seen to be thronged with the minute rounded bodies of the +spores interlacing one another and forming almost the whole mass, whilst +larger than these, and often indeed enclosing them, are flattened +bag-like bodies which are none other than the compressed sporangia which +contained the former. + +[Illustration: FIG. 15.--_Lycopodites_. Coal sandstone.] + +Now, the little Scottish or Alpine club-moss which is so familiar, +produces its own little cones, each with its series of outside scales or +leaves; these are attached to the bags or spore-cases, which are crowded +with spores. Although in miniature, yet it produces its fruit in just the +same way, at the terminations of its little branches, and the spores, the +actual germs of life, when examined microscopically, are scarcely +distinguishable from those which are contained in certain bituminous +coals. And, although ancient club-mosses have been found in a fossilised +condition at least forty-nine feet high, the spores are no larger than +those of our miniature club-mosses of the present day. + +The spores are more or less composed of pure bitumen, and the bituminous +nature of the coal depends largely on the presence or absence of these +microscopic bodies in it. The spores of the living club-mosses contain so +much resinous matter that they are now largely used in the making of +fireworks, and upon the presence of this altered resinous matter in coal +depends its capability of providing a good blazing coal. + +At first sight it seems almost impossible that such a minute cause should +result in the formation of huge masses of coal, such an inconceivable +number of spores being necessary to make even the smallest fragment of +coal. But if we look at the cloud of spores that can be shaken from a +single spike of a club-moss, then imagine this to be repeated a thousand +times from each branch of a fairly tall tree, and then finally picture a +whole forest of such trees shedding in due season their copious showers +of spores to earth, we shall perhaps be less amazed than we were at first +thought, at the stupendous result wrought out by so minute an object. + +Another well-known form of carboniferous vegetation is that known as the +_Sigillaria_, and, connected with this form is one, which was long +familiar under the name of _Stigmaria_, but which has since been +satisfactorily proved to have formed the branching root of the +sigillaria. The older geologists were in the habit of placing these +plants among the tree-ferns, principally on account of the cicatrices +which were left at the junctions of the leaf-stalks with the stem, after +the former had fallen off. No foliage had, however, been met with which +was actually attached to the plants, and hence, when it was discovered +that some of them had long attenuated leaves not at all like those +possessed by ferns, geologists were compelled to abandon this +classification of them, and even now no satisfactory reference to +existing orders of them has been made, owing to their anomalous +structure. The stems are fluted from base to stem, although this is not +so apparent near the base, whilst the raised prominences which now form +the cicatrices, are arranged at regular distances within the vertical +grooves. + +When they have remained standing for some length of time, and the strata +have been allowed quietly to accumulate around the trunks, they have +escaped compression. They were evidently, to a great extent, hollow like +a reed, so that in those trees which still remain vertical, the interior +has become filled up by a coat of sandstone, whilst the bark has become +transformed into an envelope of an inch, or half an inch of coal. But +many are found lying in the strata in a horizontal plane. These have been +cast down and covered up by an ever-increasing load of strata, so that +the weight has, in the course of time, compressed the tree into simply +the thickness of the double bark, that is, of the two opposite sides of +the envelope which covered it when living. + +_Sigillarae_ grew to a very great height without branching, some +specimens having measured from 60 to 70 feet long. In accordance with +their outside markings, certain types are known as _syringodendron_, +_favularia_, and _clathraria_. _Diploxylon_ is a term applied to an +interior stem referable to this family. + +[Illustration: FIG. 16.--_Stigmaria ficoides_. Coal-shale.] + +But the most interesting point about the _sigillariae_ is the root. This +was for a long time regarded as an entirely distinct individual, and the +older geologists explained it in their writings as a species of succulent +aquatic plant, giving it the name of _stigmaria_. They realized the fact +that it was almost universally found in those beds which occur +immediately beneath the coal seams, but for a long time it did not strike +them that it might possibly be the root of a tree. In an old edition of +Lyell's "Elements of Geology," utterly unlike existing editions in +quality, quantity, or comprehensiveness, after describing it as an +extinct species of water-plant, the author hazarded the conjecture that +it might ultimately be found to have a connection with some other +well-known plant or tree. It was noticed that above the coal, in the +roof, stigmariae were absent, and that the stems of trees which occurred +there, had become flattened by the weight of the overlying strata. The +stigmariae on the other hand, abounded in the _underclay_, as it is +called, and were not in any way compressed but retained what appeared to +be their natural shape and position. Hence to explain their appearance, +it was thought that they were water-plants, ramifying the mud in every +direction, and finally becoming overwhelmed and covered by the mud +itself. On botanical grounds, Brongniart and Lyell conjectured that they +formed the roots of other trees, and this became the more apparent as it +came to be acknowledged that the underclays were really ancient soils. +All doubt was, however, finally dispelled by the discovery by Mr Binney, +of a sigillaria and a stigmaria in actual connection with each other, in +the Lancashire coal-field. + +Stigmariae have since been found in the Cape Breton coal-field, attached +to Lepidodendra, about which we have already spoken, and a similar +discovery has since been made in the British coal-fields. This, +therefore, would seem to shew the affinity of the sigillaria to the +lepidodendron, and through it to the living lycopods, or +club-mosses. + +Some few species of stigmarian roots had been discovered, and various +specific names had been given to them before their actual nature was made +out. What for some time were thought to be long cylindrical leaves, have +now been found to be simply rootlets, and in specimens where these have +been removed, the surface of the stigmaria has been noticed to be covered +with large numbers of protuberant tubercles, which have formed the bases +of the rootlets. There appears to have also been some special kind of +arrangement in their growth, since, unlike the roots of most living +plants, the tubercles to which these rootlets were attached, were +arranged spirally around the main root. Each of these tubercles was +pitted in the centre, and into these the almost pointed ends of the +rootlets fitted, as by a ball and socket joint. + +[Illustration: FIG. 17--_Section of stigmaria_.] + +"A single trunk of _sigillaria_ in an erect forest presents an epitome of +a coal-seam. Its roots represent the _stigmaria_ underclay; its bark the +compact coal; its woody axis, the mineral charcoal; its fallen leaves and +fruits, with remains of herbaceous plants growing in its shade, mixed +with a little earthy matter, the layers of coarse coal. The condition of +the durable outer bark of erect trees, concurs with the chemical theory +of coal, in showing the especial suitableness of this kind of tissue for +the production of the purer compact coals."--(Dawson, "Structures in +Coal.") + +There is yet one other family of plants which must be mentioned, and +which forms a very important portion of the constituent _flora_ of the +coal period. This is the great family of the _coniferae_, which although +differing in many respects from the highly organised dicotyledons of the +present day, yet resembled them in some respects, especially in the +formation of an annual ring of woody growth. + +The conifers are those trees which, as the name would imply, bear their +fruit in the form of cones, such as the fir, larch, cedar, and others. +The order is one which is familiar to all, not only on account of the +cones they bear, and their sheddings, which in the autumn strew the +ground with a soft carpet of long needle-like leaves, but also because of +the gum-like secretion of resin which is contained in their tissues. Only +a few species have been found in the coal-beds, and these, on examination +under the microscope, have been discovered to be closely related to the +araucarian division of pines, rather than to any of our common firs. The +living species of this tree is a native of Norfolk Island, in the +Pacific, and here it attains a height of 200 feet, with a girth of 30 +feet. From the peculiar arrangement of the ducts in the elongated +cellular tissue of the tree, as seen under the microscope, the fossil +conifers, which exhibit this structure, have been placed in the same +division. + +The familiar fossil known to geologists as _Sternbergia_ has now been +shown to be the cast of the central pith of these conifers, amongst which +may be mentioned _cordaites, araucarites_, and _dadoxylon._. The central +cores had become replaced with inorganic matter after the pith had shrunk +and left the space empty. This shrinkage of the pith is a process which +takes place in many plants even when living, and instances will at once +occur, in which the stems of various species of shrubs when broken open +exhibit the remains of the shrunken pith, in the shape of thin discs +across the interval cavity. + +We might reasonably expect that where we find the remains of fossil +coniferous trees, we should also meet with the cones or fruit which they +bear. And such is the case. In some coal-districts fossil fruits, named +_cardiocarpum_ and _trigonocarpum_, have been found in great quantities, +and these have now been decided by botanists to be the fruits of certain +conifers, allied, not to those which bear hard cones, but to those which +bear solitary fleshy fruits. Sir Charles Lyell referred them to a Chinese +genus of the yew tribe called _salisburia_. Dawson states that they are +very similar to both _taxus_ and _salisburia._. They are abundant in some +coal-measures, and are contained, not only in the coal itself, but also +in the sandstones and shales. The under-clays appear to be devoid of +them, and this is, of course, exactly what might have been expected, +since the seeds would remain upon the soil until covered up by vegetable +matter, but would never form part of the clay soil itself. + +In connection with the varieties which have been distinguished in the +families of the conifers, calamites, and sigillariae, Sir William Dawson +makes the following observations: "I believe that there was a +considerably wide range of organisation in _cordaitinae_ as well as in +_calamites_ and _sigillariae_, and that it will eventually be found that +there were three lines of connection between the higher cryptogams +(flowerless) and the phaenogams (flowering), one leading from the +lycopodes by the _sigillariae_, another leading by the _cordaites_, and +the third leading from the _equisetums_ by the _calamites_. Still further +back the characters, afterwards separated in the club-mosses, +mare's-tails, and ferns, were united in the _rhizocarps_, or, as some +prefer to call them, the heterosporous _filicinae_." + +In concluding this chapter dealing with the various kinds of plants which +have been discovered as contributing to the formation of +coal-measures, it would be as well to say a word or two concerning the +climate which must have been necessary to permit of the growth of such an +abundance of vegetation. It is at once admitted by all botanists that a +moist, humid, and warm atmosphere was necessary to account for the +existence of such an abundance of ferns. The gorgeous waving +tree-ferns which were doubtless an important feature of the landscape, +would have required a moist heat such as does not now exist in this +country, although not necessarily a tropical heat. The magnificent giant +lycopodiums cast into the shade all our living members of that class, the +largest of which perhaps are those that flourish in New Zealand. In New +Zealand, too, are found many species of ferns, both those which are +arborescent and those which are of more humble stature. Add to these the +numerous conifers which are there found, and we shall find that a forest +in that country may represent to a certain extent the appearance +presented by a forest of carboniferous vegetation. The ferns, lycopods, +and pines, however, which appear there, it is but fair to add, are mixed +with other types allied to more recent forms of vegetation. + +There are many reasons for believing that the amount of carbonic acid gas +then existing in the atmosphere was larger than the quantity which we now +find, and Professor Tyndall has shown that the effect of this would be to +prevent radiation of heat from the earth. The resulting forms of +vegetation would be such as would be comparable with those which are now +reared in the green-house or conservatory in these latitudes. The gas +would, in fact, act as a glass roof, extending over the whole world. + + + + +CHAPTER II. + +A GENERAL VIEW OF THE COAL-BEARING STRATA. + + +In considering the source whence coal is derived, we must be careful to +remember that coal itself is but a minor portion of the whole formation +in which it occurs. The presence of coal has indeed given the name to the +formation, the word "carboniferous" meaning "coal-bearing," but in taking +a comprehensive view of the position which it occupies in the bowels of +the earth, it will be necessary to take into consideration the strata in +which it is found, and the conditions, so far as are known, under which +these were deposited. + +Geologically speaking, the Carboniferous formation occurs near the close +of that group of systems which have been classed as "palaeozoic," younger +in point of age than the well known Devonian and Old Red Sandstone +strata, but older by far than the Oolites, the Wealden, or the Cretaceous +strata. + +In South Wales the coal-bearing strata have been estimated at between +11,000 and 12,000 feet, yet amongst this enormous thickness of strata, +the whole of the various coal-seams, if taken together, probably does not +amount to more than 120 feet. This great disproportion between the total +thickness and the thickness of coal itself shows itself in every +coal-field that has been worked, and when a single seam of coal is +discovered attaining a thickness of 9 or 10 feet, it is so unusual a +thing in Great Britain as to cause it to be known as the "nine" or +"ten-foot seam," as the case may be. Although abroad many seams are found +which are of greater thicknesses, yet similarly the other portions of the +formation are proportionately greater. + +It is not possible therefore to realise completely the significance of +the coal-beds themselves unless there is also a knowledge of the +remaining constituents of the whole formation. The strata found in the +various coal-fields differ considerably amongst themselves in character. +There are, however, certain well-defined characteristics which find +representation in most of the principal coal-fields, whether British or +European. Professor Hull classifies these carboniferous beds as +follows:-- + + UPPER CARBONIFEROUS. + _Upper coal-measures._ + Reddish and purple sandstones, red and grey clays and shales, + thin bands of coal, ironstone and limestone, with _spirorbis_ + and fish. + + _Middle coal-measures._ + Yellow and gray sandstones, blue and black clays and shales, + bands of coal and ironstone, fossil plants, bivalves + and fish, occasional marine bands. + + MIDDLE CARBONIFEROUS. + _Gannister beds_ or _Lower coal-measures._ + _Millstone grit._ Flagstone series in Ireland. + _Yoredale beds._ Upper shale series of Ireland. + + LOWER CARBONIFEROUS. + _Mountain limestone_. + _Limestone shale_. + +Each of the three principal divisions has its representative in Scotland, +Belgium, and Ireland, but, unfortunately for the last-named country, the +whole of the upper coal-measures are there absent. It is from these +measures that almost all our commercial coals are obtained. + +This list of beds might be further curtailed for all practical purposes +of the geologist, and the three great divisions of the system would thus +stand:-- + + Upper Carboniferous, or Coal-measures proper. + + Millstone grit. + + Lower Carboniferous, or Mountain limestone. + +In short, the formation consists of masses of sandstone, shale, limestone +and coal, these also enclosing clays and ironstones, and, in the +limestone, marbles and veins of the ores of lead, zinc, and antimony, and +occasionally silver. + +[Illustration: FIG. 18.--Sigillarian trunks in current-bedded sandstone. +St Etienne.] + +As the most apparent of the rocks of the system are sandstone, shale, +limestone, and coal, it will be necessary to consider how these were +deposited in the waters of the carboniferous ages, and this we can best +do by considering the laws under which strata of a similar nature are now +being deposited as sedimentary beds. + +A great proportion consists of sandstone. Now sandstone is the result of +sand which has been deposited in large quantities, having become +indurated or hardened by various processes brought to bear upon it. It is +necessary, therefore, first to ascertain whence came the sand, and +whether there are any peculiarities in its method of deposition which +will explain its stratification. It will be noticed at once that it bears +a considerable amount of evidence of what is called "current-bedding," +that is to say, that the strata, instead of being regularly deposited, +exhibit series of wedge-shaped masses, which are constantly thinning out. + +Sand and quartz are of the same chemical composition, and in all +probability the sand of which every sandstone in existence is composed, +appeared on this earth in its first solid form in the shape of quartz. +Now quartz is a comparatively heavy mineral, so also, therefore, will +sand be. It is also very hard, and in these two respects it differs +entirely from another product of sedimentary deposition, namely, mud or +clay, with which we shall have presently to deal when coming to the +shales. Since quartz is a hard mineral it necessarily follows that it +will suffer, without being greatly affected, a far greater amount of +wearing and knocking about when being transported by the agency of +currents and rivers, than will a softer substance, such as clay. An equal +amount of this wearing action upon clay will reduce it to a fine +impalpable silt. The grains of sand, however, will still remain of an +appreciable average size, and where both sand and clay are being +transported to the sea in one and the same stream, the clay will be +transported to long distances, whilst the sand, being heavier, bulk for +bulk, and also consisting of grains larger in size than grains of clay, +will be rapidly deposited, and form beds of sand. Of course, if the +current be a violent one, the sand is transported, not by being held in +suspension, but rather by being pushed along the bed of the river; such +an action will then tend to cause the sand to become powdered into still +finer sand. + +When a river enters the sea it soon loses its individuality; it becomes +merged in the body of the ocean, where it loses its current, and where +therefore it has no power to keep in suspension the sediment which it had +brought down from the higher lands. When this is the case, the sand borne +in suspension is the first to be deposited, and this accumulates in banks +near the entrance of the river into the sea. We will suppose, for +illustration, that a small river has become charged with a supply of +sand. As it gradually approaches the sea, and the current loses its +force, the sand is the more sluggishly carried along, until finally it +falls to the bottom, and forms a layer of sand there. This layer +increases in thickness until it causes the depth of water above it to +become comparatively shallow. On the shallowing process taking place, the +current will still have a certain, though slighter, hold on the sand in +suspension, and will transport it yet a little further seaward, when it +will be thrown down, at the edge of the bank or layer already formed, +thus tending to extend the bank, and to shallow a wider space of +river-bed. + +As a result of this action, strata would be formed, shewing +stratification diagonally as well as horizontally, represented in section +as a number of banks which had seemingly been thrown down one above the +other, ending in thin wedge-shaped terminations where the particular +supply of sediment to which each owed its formation had failed. + +The masses of sandstone which are found in the carboniferous formation, +exhibit in a large degree these wedge-shaped strata, and we have +therefore a clue at once, both as to their propinquity to sea and land, +and also as to the manner in which they were formed. + +[Illustration: FIG. 19.--_Productus_. Coal-measures.] + +There is one thing more, too, about them. Just as, in the case we were +considering, we could observe that the wedge-shaped strata always pointed +away from the source of the material which formed them, so we can +similarly judge that in the carboniferous strata the same deduction holds +good, that the diagonally-pointing strata were formed in the same way, +and that their thinning out was simply owing to temporary failure of +sediment, made good, however, by a further deposition of strata when the +next supply was borne down. + +It is scarcely likely, however, that sand in a pure state was always +carried down by the currents to the sea. Sometimes there would be some +silt mixed with it. Just as in many parts large masses of almost pure +sandstone have been formed, so in other places shales, or, as they are +popularly known by miners, "bind," have been formed. Shales are formed +from the clays which have been carried down by the rivers in the shape of +silt, but which have since become hardened, and now split up easily into +thin parallel layers. The reader has no doubt often handled a piece of +hard clay when fresh from the quarry, and has remembered how that, when +he has been breaking it up, in order, perhaps, to excavate a +partially-hidden fossil, it has readily split up in thin flakes or layers +of shaly substance. This exhibits, on a small scale, the chief +peculiarity of the coal shales. + +The formation of shales will now demand our attention. When a river is +carrying down with it a quantity of mud or clay, it is transported as a +fine, dusty silt, and when present in quantities, gives the muddy tint to +the water which is so noticeable. We can very well see how that silt will +be carried down in greater quantities than sand, since nearly all rivers +in some part of their course will travel through a clayey district, and +finely-divided clay, being of a very light nature, will be carried +forward whenever a river passes over such a district. And a very slight +current being sufficient to carry it in a state of suspension, it follows +that it will have little opportunity of falling to the bottom, until, by +some means or other, the current, which is the means of its conveyance, +becomes stopped or hindered considerably in its flow. + +When the river enters a large body of water, such as the ocean or a lake, +in losing its individuality, it loses also the velocity of its current, +and the silt tends to sink down to the bottom. But being less heavy than +the sand, about which we have previously spoken, it does not sink all at +once, but partly with the impetus it has gained, and partly on account of +the very slight velocity which the current still retains, even after +having entered the sea, it will be carried out some distance, and will +the more gradually sink to the bottom. The deeper the water in which it +falls the greater the possibility of its drifting farther still, since in +sinking, it would fall, not vertically, but rather as the drops of rain +in a shower when being driven before a gale of wind. Thus we should +notice that clays and shales would exhibit a regularity and uniformity of +deposition over a wide area. Currents and tides in the sea or lake would +tend still further to retard deposition, whilst any stoppages in the +supply of silt which took place would give the former layer time to +consolidate and harden, and this would assist in giving it that bedded +structure which is so noticeable in the shales, and which causes it to +split up into fine laminae. This uniformity of structure in the shales +over wide areas is a well ascertained characteristic of the coal-shales, +and we may therefore regard the method of their deposition as given here +with a degree of certainty. + +There is a class of deposit found among the coal-beds, which is known as +the "underclay," and this is the most regular of all as to the position +in which it is found. The underclays are found beneath every bed of coal. +"Warrant," "spavin," and "gannister" are local names which are sometimes +applied to it, the last being a term used when the clay contains such a +large proportion of silicious matter as to become almost like a hard +flinty rock. Sometimes, however, it is a soft clay, at others it is mixed +with sand, but whatever the composition of the underclays may be, they +always agree in being unstratified. They also agree in this respect that +the peculiar fossils known as _stigmariae_ abound in them, and in some +cases to such an extent that the clay is one thickly-matted mass of the +filamentous rootlets of these fossils. We have seen how these gradually +came to be recognised as the roots of trees which grew in this age, and +whose remains have subsequently become metamorphosed into coal, and it is +but one step farther to come to the conclusion that these underclays are +the ancient soils in which the plants grew. + +No sketch of the various beds which go to form the coal-measures would be +complete which did not take into account the enormous beds of mountain +limestone which form the basis of the whole system, and which in thinner +bands are intercalated amongst the upper portion of the system, or the +true coal-measures. + +Now, limestones are not formed in the same way in which we have seen that +sandstones and shales are formed. The last two mentioned owe their origin +to their deposition as sediment in seas, estuaries or lakes, but the +masses of limestone which are found in the various geological formations +owe their origin to causes other than that of sedimentary deposition. + +In carboniferous times there lived numberless creatures which we know +nowadays as _encrinites_. These, when growing, were fixed to the bed of +the ocean, and extended upward in the shape of pliant stems composed of +limestone joints or plates; the stem of each encrinite then expanded at +the top in the shape of a gorgeous and graceful starfish, possessed of +numberless and lengthy arms. These encrinites grew in such profusion that +after death, when the plates of which their stems consisted, became +loosened and scattered over the bed of the sea, they accumulated and +formed solid beds of limestone. Besides the encrinites, there were of +course other creatures which were able to create the hard parts of their +structures by withdrawing lime from the sea, such as _foraminifera_, +shell-fish, and especially corals, so that all these assisted after death +in the accumulation of beds of limestone where they had grown and lived. + +[Illustration: FIG. 20.--Encrinite.] + +[Illustration: FIG. 21.--Encrinital limestone.] + +There is one peculiarity in connection with the habitats of the +encrinites and corals which goes some distance in supplying us with a +useful clue as to the conditions under which this portion of the +carboniferous formation was formed. These creatures find it a difficult +matter, as a rule, to live and secrete their calcareous skeleton in any +water but that which is clear, and free from muddy or sandy sediment. +They are therefore not found, generally speaking, where the other +deposits which we have considered, are forming, and, as these are always +found near the coasts, it follows that the habitats of the creatures +referred to must be far out at sea where no muddy sediments, borne by +rivers, can reach them. We can therefore safely come to the conclusion +that the large masses of encrinital limestone, which attain such an +enormous thickness in some places, especially in Ireland, have been +formed far away from the land of the period; we can at the same time draw +the conclusion that if we find the encrinites broken and snapped asunder, +and the limestone deposits becoming impure through being mingled with a +proportion of clayey or sandy deposits, that we are approaching a +coast-line where perhaps a river opened out, and where it destroyed the +growth of encrinites, mixing with their dead remains the sedimentary +dêbris of the land. + +[Illustration: FIG. 22.--Encrinites: various. Mountain limestone.] + +We have lightly glanced at the circumstances attending the deposition of +each of the principal rocks which form the beds amongst which coal is +found, and have now to deal with the formation of the coal itself. We +have already considered the various kinds of plants and trees which have +been discovered as contributing their remains to the formation of coal, +and have now to attempt an explanation of how it came to be formed in so +regular a manner over so wide an area. + +Each of the British coal-fields is fairly extensive. The Yorkshire and +Derbyshire coal-fields, together with the Lancashire coal-field, with +which they were at one time in geological connection, give us an area of +nearly 1000 square miles, and other British coal-fields show at least +some hundreds of square miles. And yet, spread over them, we find a +series of beds of coal which in many cases extend throughout the whole +area with apparent regularity. If we take it, as there seems every reason +to believe was the case, that almost all these coal-fields were not only +being formed at the same time, but were in most instances in continuation +with one another, this regularity of deposition of comparatively narrow +beds of coal, appears all the more remarkable. + +The question at once suggests itself, Which of two things is probable? +Are we to believe that all this vegetable matter was brought down by some +mighty river and deposited in its delta, or that the coal-plants grew +just where we now find the coal? + +Formerly it was supposed that coal was formed out of dead leaves and +trees, the refuse of the vegetation of the land, which had been carried +down by rivers into the sea and deposited at their mouths, in the same +way that sand and mud, as we have seen, are swept down and deposited. If +this were so, the extent of the deposits would require a river with an +enormous embouchure, and we should be scarcely warranted in believing +that such peaceful conditions would there prevail as to allow of the +layers of coal to be laid down with so little disturbance and with such +regularity over these wide areas. But the great objection to this theory +is, that not only do the remains still retain their perfection of +structure, but they are comparatively _pure,--i.e.,_ unmixed with +sedimentary depositions of clay or sand. Now, rivers would not bring down +the dead vegetation alone; their usual burden of sediment would also be +deposited at their mouths, and thus dead plants, sand, and clay would be +mixed up together in one black shaly or sandy mass, a mixture which would +be useless for purposes of combustion. The only theory which explained +all the recognised phenomena of the coal-measures was that the plants +forming the coal actually grew where the coal was formed, and where, +indeed, we now find it. When the plants and trees died, their remains +fell to the ground of the forest, and these soon turned to a black, +pasty, vegetable mass, the layer thus formed being regularly increased +year by year by the continual accumulation of fresh carbonaceous matter. +By this means a bed would be formed with regularity over a wide area; the +coal would be almost free from an admixture of sandy or clayey sediment, +and probably the rate of formation would be no more rapid in one part of +the forest than another. Thus there would be everywhere uniformity of +thickness. The warm and humid atmosphere, which it is probable then +existed, would not only have tended towards the production of an abnormal +vegetation, but would have assisted in the decaying and disintegrating +processes which went on amongst the shed leaves and trees. + +When at last it was announced as a patent fact that every bed of coal +possessed its underclay, and that trees had been discovered actually +standing upon their own roots in the clay, there was no room at all for +doubt that the correct theory had been hit upon--viz., that coal is now +found just where the trees composing it had grown in the past. + +But we have more than one coal-seam to account for. We have to explain +the existence of several layers of coal which have been formed over one +another on the same spot at successive periods, divided by other periods +when shale and sandstones only have been formed. + +A careful estimate of the Lancashire coal-field has been made by +Professor Hull for the Geological Survey. Of the 7000 feet of +carboniferous strata here found, spread out over an area of 217 square +miles, there are on the average eighteen seams of coal. + +This is only an instance of what is to be found elsewhere. Eighteen +coal-seams! what does this mean? It means that, during carboniferous +times, on no less than eighteen occasions, separate and distinct forests +have grown on this self-same spot, and that between each of these +occasions changes have taken place which have brought it beneath the +waters of the ocean, where the sandstones and shales have been formed +which divide the coal-seams from each other. We are met here by a +wonderful demonstration of the instability of the surface of the earth, +and we have to do our best to show how the changes of level have been +brought about, which have allowed of this game of geological see-saw to +take place between sea and land. Changes of level! Many a hard geological +nut has only been overcome by the application of the principle of changes +of level in the surface of the earth, and in this we shall find a sure +explanation of the phenomena of the coal-measures. + +Great changes of the level of the land are undoubtedly taking place even +now on the earth's surface, and in assuming that similar changes took +place in carboniferous times, we shall not be assuming the former +existence of an agent with which we are now unfamiliar. And when we +consider the thicknesses of sandstone and shale which intervene beneath +the coal-seams, we can realise to a certain extent the vast lapses of +years which must have taken place between the existence of each forest; +so that although now an individual passing up a coal-mine shaft may +rapidly pass through the remains of one forest after another, the rise of +the strata above each forest-bed then was tremendously slow, and the +period between the growth of each forest must represent the passing away +of countless ages. Perhaps it would not be too much to say that the +strata between some of the coal-seams would represent a period not less +than that between the formation of the few tertiary coals with which we +are acquainted, and a time which is still to us in the far-away future. + +The actual seams of coal themselves will not yield much information, from +which it will be possible to judge of the contour of the landmasses at +this ancient period. Of one thing we are sure, namely, that at the time +each seam was formed, the spot where it accumulated was dry land. If, +therefore, the seams which appear one above the other coincide fairly +well as to their superficial extent, we can conclude that each time the +land was raised above the sea and the forest again grew, the contour of +the land was very similar. This conclusion will be very useful to go +upon, since whatever decision may be come to as an explanation of one +successive land-period and sea-period on the same spot, will be +applicable to the eighteen or more periods necessary for the completion +of some of the coal-fields. + +We will therefore look at one of the sandstone masses which occur between +the coal-seams, and learn what lessons these have to teach us. In +considering the formation of strata of sand in the seas around our +river-mouths, it was seen that, owing to the greater weight of the +particles of the sand over those of clay, the former the more readily +sank to the bottom, and formed banks not very far away from the land. It +was seen, too, that each successive deposition of sand formed a +wedge-shaped layer, with the point of the wedge pointing away from the +source of origin of the sediment, and therefore of the current which +conveyed the sediment. Therefore, if in the coal-measure sandstones the +layers were found with their wedges all pointing in one direction, we +should be able to judge that the currents were all from one direction, +and that, therefore, they were formed by a single river. But this is just +what we do not find, for instead of it the direction of the wedge-shaped +strata varies in almost every layer, and the current-bedding has been +brought about by currents travelling in every direction. Such diverse +current-bedding could only result from the fact that the spot where the +sand was laid down was subject to currents from every direction, and the +inference is that it was well within the sphere of influence of numerous +streams and rivers, which flowed from every direction. The only condition +of things which would explain this is that the sandstone was originally +formed in a closed sea or large lake, into which numerous rivers flowing +from every direction poured their contents. + +Now, in the sandstones, the remains of numerous plants have been found, +but they do not present the perfect appearance that they do when found in +the shales; in fact they appear to have suffered a certain amount of +damage through having drifted some distance. This, together with the fact +that sandstones are not formed far out at sea, justify the safe +conclusion that the land could not have been far off. Wherever the +current-bedding shows itself in this manner we may be sure we are +examining a spot from which the land in every direction could not have +been at a very great distance, and also that, since the heavy materials +of which sandstone is composed could only be transported by being +impelled along by currents at the bed of the sea, and that in deep water +such currents could not exist, therefore we may safely decide that the +sea into which the rivers fell was a comparatively shallow one. + +Although the present coal-fields of England are divided from one another +by patches of other beds, it is probable that some of them were formerly +connected with others, and a very wide sheet of coal on each occasion was +laid down. The question arises as to what was the extent of the inland +sea or lake, and did it include the area covered by the coal basins of +Scotland and Ireland, of France and Belgium? And if these, why not those +of America and other parts? The deposition of the coal, according to the +theory here advanced, may as well have been brought about in a series of +large inland seas and lakes, as by one large comprehensive sea, and +probably the former is the more satisfactory explanation of the two. But +the astonishing part of it is that the changes in the level of the land +must have been taking place simultaneously over these large areas, +although, of course, while one quarter may have been depressed beneath +the sea, another may have been raised above it. + +In connection with the question of the contour of the land during the +existence of the large lakes or inland seas, Professor Hull has prepared, +in his series of maps illustrative of the Palaeo-Geography of the British +Islands, a map showing on incontestible grounds the existence during the +coal-ages of a great central barrier or ridge of high land stretching +across from Anglesea, south of Flint, Staffordshire, and Shropshire +coal-fields, to the eastern coast of Norfolk. He regards the British +coal-measures as having been laid down in two, or at most three, areas of +deposition--one south of this ridge, the remainder to the north of it. In +regard to the extent of the former deposits of coal in Ireland, there is +every probability that the sister island was just as favourably treated +in this respect as Great Britain. Most unfortunately, Ireland has since +suffered extreme denudation, notably from the great convulsions of nature +at the close of the very period of their deposition, as well as in more +recent times, resulting in the removal of nearly all the valuable upper +carboniferous beds, and leaving only the few unimportant +coal-beds to which reference has been made. + +[Illustration: FIG. 23.--_Cyathophyllum_. Coral in encrinital limestone.] + +We are unable to believe in the continuity of our coal-beds with those of +America, for the great source of sediment in those times was a continent +situated on the site of the Atlantic Ocean, and it is owing to this +extensive continent that the forms of _flora_ found in the coal-beds in +each country bear so close a resemblance to one another, and also that +the encrinital limestone which was formed in the purer depths of the +ocean on the east, became mixed with silt, and formed masses of shaly +impure limestone in the south-western parts of Ireland. + +It must be noted that, although we may attribute to upheaval from beneath +the fact that the bed of the sea became temporarily raised at each period +into dry land, the deposits of sand or shale would at the same time be +tending to shallow the bed, and this alone would assist the process of +upheaval by bringing the land at least very near to the surface of the +water. + +Each upheaval, however, could have been but a temporary arrest of the +great movement of crust subsidence which was going on throughout the coal +period, so that, at its close, when the last coal forest grew upon the +surface of the land, there had disappeared, in the case of South Wales, a +thickness of 11,000 feet of material. + +Of the many remarkable things in connection with coal-beds, not the least +is the state of purity in which coal is found. On the floor of each +forest there would be many a streamlet or even small river which would +wend its way to meet the not very distant sea, and it is surprising at +first that so little sediment found its way into the coal itself. But +this was cleverly explained by Sir Charles Lyell, who noticed, on one of +his visits to America, that the water of the Mississippi, around the rank +growths of cypress which form the "cypress swamps" at the mouths of that +river, was highly charged with sediment, but that, having passed through +the close undergrowth of the swamps, it issued in almost a pure state, +the sediment which it bore having been filtered out of it and +precipitated. This very satisfactorily explained how in some places +carbonaceous matter might be deposited in a perfectly pure state, whilst +in others, where sandstone or shale was actually forming, it might be +impregnated by coaly matter in such a way as to cause it to be stained +black. In times of flood sediment would be brought in, even where pure +coal had been forming, and then we should have a thin "parting" of +sandstone or shale, which was formed when the flood was at its height. Or +a slight sinking of the land might occur, in which case also the +formation of coal would temporarily cease, and a parting of foreign +matter would be formed, which, on further upheaval taking place, would +again give way to another forest growth. Some of the thicker beds have +been found presenting this aspect, such as the South Staffordshire +ten-yard coal, which in some parts splits up into a dozen or so smaller +beds, with partings of sediment between them. + +In the face of the stupendous movements which must have happened in order +to bring about the successive growth of forests one above another on the +same spot, the question at once arises as to how these movements of the +solid earth came about, and what was the cause which operated in such a +manner. We can only judge that, in some way or other, heat, or the +withdrawal of heat, has been the prime motive power. We can perceive, +from what is now going on in some parts of the earth, how great an +influence it has had in shaping the land, for volcanoes owe their +activity to the hidden heat in the earth's interior, and afford us an +idea of the power of which heat is capable in the matter of building up +and destroying continents. No less certain is it that heat is the prime +factor in those more gradual vertical movements of the land to which we +have referred elsewhere, but in regard to the exact manner in which it +acts we are very much in the dark. Everybody knows that, in the majority +of instances, material substances of all kinds expand under the influence +of heat, and contract when the source of heat is withdrawn. If we can +imagine movements in the quantity of heat contained in the solid crust, +the explanation is easy, for if a certain tract of land receive an +accession of heat beneath it, it is certain that the principal effect +will be an elevation of the land, consequent on the expansion of its +materials, with a subsequent depression when the heat beneath the tract +in question becomes gradually lessened. Should the heat be retained for a +long period, the strata would be so uplifted as to form an anticlinal, or +saddle-back, and then, should subsequent denudation take place, more +ancient strata would be brought to view. It was thus in the instance of +the tract bounded by the North and South Downs, which were formerly +entirely covered by chalk, and in the instance of the uprising of the +carboniferous limestone between the coal-fields of Lancashire, +Staffordshire, and Derbyshire. + +How the heat-waves act, and the laws, if any, which they obey in their +subterranean movements, we are unable to judge. From the properties which +heat possesses we know that its presence or absence produces marked +differences in the positions of the strata of the earth, and from +observations made in connection with the closing of some volcanoes, and +the opening up of fresh earth-vents, we have gone a long way towards +establishing the probability that there are even now slow and ponderous +movements taking place in the heat stored in the earth's crust, whose +effects are appreciably communicated to the outside of the thin rind of +solid earth upon which we live. + +Owing to the great igneous and volcanic activity at the close of the +deposition of the carboniferous system of strata, the coal-measures +exhibit what are known as _faults_ in abundance. The mountain limestone, +where it outcrops at the surface, is observed to be much jointed, so much +so that the work of quarrying the limestone is greatly assisted by the +jointed structure of the rock. Faults differ from joints in that, whilst +the strata in the latter are still in relative position on each side of +the joint, they have in the former slipped out of place. In such a case +the continuation of a stratum on the opposite side of a fault will be +found to be depressed, perhaps a thousand feet or more. It will be seen +at once how that, in sinking a new shaft into a coal-seam, the +possibility of an unknown fault has to be brought into consideration, +since the position of the seam may prove to have been depressed to such +an extent as to cause it to be beyond workable depth. Many seams, on the +other hand, which would have remained altogether out of reach of mining +operations, have been brought within workable depth by a series of +_step-faults_, this being a term applied to a series of parallel faults, +in none of which the amount of down-throw is great. + +The amount of the down-throw, or the slipping-down of the beds, is +measured, vertically, from the point of disappearance of a layer to an +imaginary continuation of the same layer from where it again appears +beyond the fault. The plane of a fault is usually more or less inclined, +the amount of the inclination being known as the _hade_ of the fault, and +it is a remarkable characteristic of faults that, as a general rule, they +hade to the down-throw. This will be more clearly understood when it is +explained that, by its action, a seam of coal, which is subject to +numerous faults, can never be pierced more than once by one and the same +boring. In mountainous districts, however, there are occasions when the +hade is to the up-throw, and this kind of fault is known as an _inverted +fault_. + +Lines of faults extend sometimes for hundreds of miles. The great Pennine +Fault of England is 130 miles long, and others extend for much greater +distances. The surfaces on both sides of a fault are often smooth and +highly polished by the movement which has taken place in the strata. They +then show the phenomenon known as _slicken-sides_. Many faults have +become filled with crystalline minerals in the form of veins of ore, +deposited by infiltrating waters percolating through the natural +fissures. + +In considering the formation and structure of the better-known +coal-bearing beds of the carboniferous age, we must not lose sight of the +fact that important beds of coal also occur in strata of much more recent +date. There are important coal-beds in India of Permian age. There are +coal-beds of Liassic age in South Hungary and in Texas, and of Jurassic +age in Virginia, as well as at Brora in Sutherlandshire; there are coals +of Cretaceous age in Moravia, and valuable Miocene Tertiary coals in +Hungary and the Austrian Alps. + +Again, older than the true carboniferous age, are the Silurian +anthracites of Co. Cavan, and certain Norwegian coals, whilst in New +South Wales we are confronted with an assemblage of coal-bearing strata +which extend apparently from the Devonian into Mesozoic times. + +Still, the age we have considered more closely has an unrivalled right to +the title, coal appearing there not merely as an occasional bed, but as a +marked characteristic of the formation. + +The types of animal life which are found in this formation are varied, +and although naturally enough they do not excel in number, there are yet +sufficient varieties to show probabilities of the existence of many with +which we are unfamiliar. The highest forms yet found, show an advance as +compared with those from earlier formations, and exhibit amphibian +characteristics intermediate between the two great classes of fishes and +reptiles. Numerous specimens proper to the extinct order of +_labyrinthodontia_ have been arranged into at least a score of genera, +these having been drawn from the coal-measures of Newcastle, Edinburgh, +Kilkenny, Saärbruck, Bavaria, Pennsylvania, and elsewhere. The +_Archegosaurus,_ which we have figured, and the _Anthracosaurus,_ are +forms which appear to have existed in great numbers in the swamps and +lakes of the age. The fish of the period belong almost entirely to the +ancient orders of the ganoids and placoids. Of the ganoids, the great +_megalichthys Hibberti_ ranges throughout the whole of the system. +Wonderful accumulations of fish remains are found at the base of the +system, in the bone-bed of the Bristol coal-field, as well as in a +similar bed at Armagh. Many fishes were armed with powerful conical +teeth, but the majority, like the existing Port Jackson shark, were +possessed of massive palates, suited in some cases for crushing, and in +others for cutting. + +[Illustration: FIG. 24.--_Archegosaurus minor_. Coal-measures.] + +[Illustration: FIG. 25.--_Psammodus porosus_. Crushing palate of a fish.] + +[Illustration: FIG. 26.--_Orthoceras_. Mountain limestone.] + +In the mountain limestone we see, of course, the predominance of marine +types, encrinital remains forming the greater proportion of the mass. +There are occasional plant remains which bear evidence of having drifted +for some distance from the shore. But next to the _encrinites_, the +corals are the most important and persistent. Corals of most beautiful +forms and capable of giving polished marble-like sections, are in +abundance. _Polyzoa_ are well represented, of which the lace-coral +(_fenestella_) and screw-coral (_archimedopora_) are instances. +_Cephalopoda_ are represented by the _orthoceras_, sometimes five or six +feet long, and _goniatites_, the forerunner of the familiar _ammonite_. +Many species of brachiopods and lammellibranchs are met with. _Lingula_, +most persistent throughout all geological time, is abundant in the +coal-shales, but not in the limestones. _Aviculopecten_ is there abundant +also. In the mountain limestone the last of the trilobites (_Phillipsia_) +is found. + +[Illustration: FIG. 27.--_Fenestella retipora_. Mountain limestone.] + +[Illustration: FIG. 28.--_Goniatites_. Mountain limestone.] + +We have evidence of the existence in the forests of a variety of +_centipede_, specimens having been found in the erect stump of a hollow +tree, although the fossil is an extremely rare one. The same may be said +of the only two species of land-snail which have been found connected +with the coal forests, viz., _pupa vetusta_ and _zonites priscus_, both +discovered in the cliffs of Nova Scotia. These are sufficient to +demonstrate that the fauna of the period had already reached a high stage +of development. In the estuaries of the day, masses of a species of +freshwater mussel (_anthracosia_) were in existence, and these have left +their remains in the shape of extensive beds of shells. They are familiar +to the miner as _mussel-binds_, and are as noticeable a feature of this +long ago period, as are the aggregations of mussels on every coast at +the present day. + +[Illustration: FIG. 29.--_Aviculopecten papyraceus_. Coal-shale.] + + + + +CHAPTER III. + +VARIOUS FORMS OF COAL AND CARBON. + + +In considering the various forms and combinations into which coal enters, +it is necessary that we should obtain a clear conception of what the +substance called "carbon" is, and its nature and properties generally, +since this it is which forms such a large percentage of all kinds of +coal, and which indeed forms the actual basis of it. In the shape of +coke, of course, we have a fairly pure form of carbon, and this being +produced, as we shall see presently, by the driving off of the volatile +or vaporous constituents of coal, we are able to perceive by the residue +how great a proportion of coal consists of carbon. In fact, the two have +almost an identical meaning in the popular mind, and the fact that the +great masses of strata, in which are contained our principal and most +valuable seams of coal, are termed "carboniferous," from the Latin +_carbo_, coal, and _fero_, I bear, tends to perpetuate the existence of +the idea. + +There is always a certain, though slight, quantity of carbon in the air, +and this remains fairly constant in the open country. Small though it may +be in proportion to the quantity of pure air in which it is found, it is +yet sufficient to provide the carbon which is necessary to the growth of +vegetable life. Just as some of the animals known popularly as the +_zoophytes_, which are attached during life to rocks beneath the sea, are +fed by means of currents of water which bring their food to them, so the +leaves, which inhale carbon-food during the day through their +under-surfaces, are provided with it by means of the currents of air +which are always circulating around them; and while the fuel is being +taken in beneath, the heat and light are being received from above, and +the sun supplies the motive power to digestion. + +It is assumed that it is, within the knowledge of all that, for the +origin of the various seams and beds of coaly combinations which exist in +the earth's crust, we must look to the vegetable world. If, however, we +could go so far back in the world's history as the period when our +incandescent orb had only just severed connection with a +gradually-diminishing sun, we should probably find the carbon there, but +locked up in the bonds of chemical affinities with other elements, and +existing therewith in a gaseous condition. But, as the solidifying +process went on, and as the vegetable world afterwards made its +appearance, the carbon became, so to speak, wrenched from its +combinations, and being absorbed by trees and plants, finally became +deposited amongst the ruins of a former vegetable world, and is now +presented to us in the form of coal. + +We are able to trace the gradual changes through which the pasty mass of +decaying vegetation passed, in consequence of the fact that we have this +material locked up in various stages of carbonisation, in the strata +beneath our feet. These we propose to deal with individually, in as +unscientific and untechnical a manner as possible. + +First of all, when a mass of vegetable matter commences to decay, it soon +loses its colour. There is no more noticeable proof of this, than that +when vitality is withdrawn from the leaves of autumn, they at once +commence to assume a rusty or an ashen colour. Let the leaves but fall to +the ground, and be exposed to the early frosts of October, the damp mists +and rains of November, and the rapid change of colour is at once +apparent. Trodden under foot, they soon assume a dirty blackish hue, and +even when removed they leave a carbonaceous trace of themselves behind +them, where they had rested. Another proof of the rapid acquisition of +their coaly hue is noticeable in the spring of the year. When the trees +have burst forth and the buds are rapidly opening, the cases in which the +buds of such trees as the horse-chestnut have been enclosed will be found +cast off, and strewing the path beneath. Moistened by the rains and the +damp night-mists, and trodden under foot, these cases assume a jet black +hue, and are to all appearance like coal in the very first stages of +formation. + +But of course coal is not made up wholly and only of leaves. The branches +of trees, twigs of all sizes, and sometimes whole trunks of trees are +found, the last often remaining in their upright position, and piercing +the strata which have been formed above them. At other times they lie +horizontally on the bed of coal, having been thrown down previously to +the formation of the shale or sandstone, which now rests upon them. They +are often petrified into solid sandstone themselves, whilst leaving a +rind of coal where formerly was the bark. Although the trunk of a tree +looks so very different to the leaves which it bears upon its branches, +it is only naturally to be supposed that, as they are both built up after +the same manner from the juices of the earth and the nourishment in the +atmosphere, they would have a similar chemical composition. One very +palpable proof of the carbonaceous character of tree-trunks suggests +itself. Take in your hand a few dead twigs or sticks from which the +leaves have long since dropped; pull away the dead parts of the ivy which +has been creeping over the summer-house; or clasp a gnarled old monster +of the forest in your arms, and you will quickly find your hand covered +with a black smut, which is nothing but the result of the first stage +which the living plant has made, in its progress towards its condition as +dead coal. But an easy, though rough, chemical proof of the constituents +of wood, can be made by placing a few pieces of wood in a medium-sized +test-tube, and holding it over a flame. In a short time a certain +quantity of steam will be driven off, next the gaseous constituents of +wood, and finally nothing will be left but a few pieces of black brittle +charcoal. The process is of course the same in a fire-grate, only that +here more complete combustion of the wood takes place, owing to its being +intimately exposed to the action of the flames. If we adopt the same +experiment with some pieces of coal, the action is similar, only that in +this case the quantity of gases given off is not so great, coal +containing a greater proportion of carbon than wood, owing to the fact +that, during its long burial in the bowels of the earth, it has been +acted upon in such a way as to lose a great part of its volatile +constituents. + +From processes, therefore, which are to be seen going on around us, it is +easily possible to satisfy ourselves that vegetation will in the long run +undergo such changes as will result in the formation of coal. + +There are certain parts in most countries, and particularly in Ireland, +where masses of vegetation have undergone a still further stage in +metamorphism, namely, in the well-known and famous peat-bogs. Ireland is +_par excellence_ the land of bogs, some three millions of acres being +said to be covered by them, and they yield an almost inexhaustible supply +of peat. One of the peat-bogs near the Shannon is between two and three +miles in breadth and no less than fifty in length, whilst its depth +varies from 13 feet to as much as 47 feet. Peat-bogs have in no way +ceased to be formed, for at their surfaces the peat-moss grows afresh +every year; and rushes, horse-tails, and reeds of all descriptions grow +and thrive each year upon the ruins of their ancestors. The formation of +such accumulations of decaying vegetation would only be possible where +the physical conditions of the country allowed of an abundant rainfall, +and depressions in the surface of the land to retain the moisture. Where +extensive deforesting operations have taken place, peat-bogs have often +been formed, and many of those in existence in Europe undoubtedly owe +their formation to that destruction of forests which went on under the +sway of the Romans. Natural drainage would soon be obstructed by fallen +trees, and the formation of marsh-land would follow; then with the growth +of marsh-plants and their successive annual decay, a peaty mass would +collect, which would quickly grow in thickness without let or hindrance. + +In considering the existence of inland peat-bogs, we must not lose sight +of the fact that there are subterranean forest-beds on various parts of +our coasts, which also rest upon their own beds of peaty matter, and very +possibly, when in the future they are covered up by marine deposits, they +will have fairly started on their way towards becoming coal. + +Peat-bogs do not wholly consist of peat, and nothing else. The trunks of +such trees as the oak, yew, and fir, are often found mingled with the +remains of mosses and reeds, and these often assume a decidedly coaly +aspect. From the famous Bog of Allen in Ireland, pieces of oak, generally +known as "bog-oak," which have been buried for generations in peat, have +been excavated. These are as black as any coal can well be, and are +sufficiently hard to allow of their being used in the manufacture of +brooches and other ornamental objects. Another use to which peat of some +kinds has been put is in the manufacture of yarn, the result being a +material which is said to resemble brown worsted. On digging a ditch to +drain a part of a bog in Maine, U.S., in which peat to a depth of twenty +feet had accumulated, a substance similar to cannel coal itself was +found. As we shall see presently, cannel coal is one of the earliest +stages of true coal, and the discovery proved that under certain +conditions as to heat and pressure, which in this case happened to be +present, the materials which form peat may also be metamorphosed into +true coal. + +Darwin, in his well-known "Voyage in the _Beagle_" gives a peculiarly +interesting description of the condition of the peat-beds in the Chonos +Archipelago, off the Chilian coast, and of their mode of formation. "In +these islands," he says, "cryptogamic plants find a most congenial +climate, and within the forest the number of species and great abundance +of mosses, lichens, and small ferns, is quite extraordinary. In Tierra +del Fuego every level piece of land is invariably covered by a thick bed +of peat. In the Chonos Archipelago where the nature of the climate more +closely approaches that of Tierra del Fuego, every patch of level ground +is covered by two species of plants (_Astelia pumila_ and _Donatia +megellanica_), which by their joint decay compose a thick bed of elastic +peat. + +"In Tierra del Fuego, above the region of wood-land, the former of these +eminently sociable plants is the chief agent in the production of peat. +Fresh leaves are always succeeding one to the other round the central +tap-root; the lower ones soon decay, and in tracing a root downwards in +the peat, the leaves, yet holding their places, can be observed passing +through every stage of decomposition, till the whole becomes blended in +one confused mass. The Astelia is assisted by a few other plants,--here +and there a small creeping Myrtus (_M. nummularia_), with a woody stem +like our cranberry and with a sweet berry,--an Empetrum (_E. rubrum_), +like our heath,--a rush (_Juncus grandiflorus_), are nearly the only ones +that grow on the swampy surface. These plants, though possessing a very +close general resemblance to the English species of the same genera, are +different. In the more level parts of the country the surface of the peat +is broken up into little pools of water, which stand at different +heights, and appear as if artificially excavated. Small streams of water, +flowing underground, complete the disorganisation of the vegetable +matter, and consolidate the whole. + +"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° +to 42°), 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°) 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 £100,000 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 _eozoön_ 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 _eozoön_ 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. + +[Illustration: FIG 30.--_Lepidodendron_. Portion of Sandstone stem after +removal of bark of a giant club-moss] + +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 £150 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° 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. + +[Illustration: FIG. 31.--Engine-House and Buildings at head of a +Coal-Pit.] + +If there be one of these shafts at one end of the mine, and another at a +remote distance from it, a movement of the air will at once begin, and a +rough kind of ventilation will ensue. This is, however, quite +insufficient to provide the necessary 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. + +[Illustration: FIG. 32.--Gas Jet and Davy Lamp.] + +With the complicated improvements which have since been made in the Davy +lamp, a state of almost absolute safety can be guaranteed, but still from +time to time explosions are reported. Of the cause of many we are +absolutely ignorant, but occasionally a light is thrown upon their origin +by a paragraph appearing in a daily paper. Two men are charged before the +magistrates with being in the possession of keys used exclusively for +unlocking their miners' safety-lamps. There is no defence. These men know +that they carry their lives in their hands, yet will risk their own and +those of hundreds of others, in order that they may be able to light +their pipes by means of their safety-lamps. Sometimes in an unexpected +moment there is a great dislodgement of coal, and a tremendous 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. + +[Illustration: Fig. 33--Part of a trunk of _Sigillaria_, showing the thin +outer carbonised bark, with leaf-scars, and the seal-like impressions +where the bark is removed.] + +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 £11,000. 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. + +[Illustration: FIG. 34.--Inside a Gas-Holder.] + +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° 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. + +[Illustration: FIG. 35.--Filling Retorts by Machinery.] + +[Illustration: FIG. 36.--CONDENSERS.] + +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. + +[Illustration: FIG. 37.] + +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. + +[Illustration: FIG. 38.] + +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° 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° 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. + +The term asphalt has been applied to so many and various mixtures, that +one scarcely associates it with natural mineral pitch which is found in +some parts of the world. From time immemorial this compact, bituminous, +resinous mineral has been discovered in masses on the shores of the Dead +Sea, which has in consequence received the well-known title of Lake +Asphaltites. Like the naphthas and petroleums which have been noticed, +this has had its origin in the decomposition of vegetable matter, and +appears to be thrown up in a liquid form by the volcanic energies which, +are still believed to be active in the centre of the lake, and which may +be existent beneath a stratum, or bed, of oil-producing bitumen. + +In connection with the formation of this substance, the remarks of Sir +Charles Lyell, the great geologist, may well be quoted, as showing the +transformation of vegetable matter into petroleum, and afterwards into +solid-looking asphalt. At Trinidad is a lake of bitumen which is a mile +and a half in circumference. "The Orinoco has for ages been rolling down +great quantities of woody and vegetable bodies into the surrounding sea, +where, by the influence of currents and eddies, they may be arrested, and +accumulated in particular places. The frequent occurrence of earthquakes +and other indications of volcanic action in those parts, lend countenance +to the opinion that these vegetable substances may have undergone, by the +agency of subterranean fire, those transformations or chemical changes +which produce petroleum; and this may, by the same causes, be forced up +to the surface, where, by exposure to the air, it becomes inspissated, +and forms those different varieties of earth-pitch or asphaltum so +abundant in the island." + +It is interesting to note also that it was obtained, at an ancient +period, from the oil-fountains of Is, and that it was put to considerable +use in the embalming of the bodies of the Egyptians. It appears, too, to +have been employed in the construction of the walls of Babylon, and thus +from very early times these wonderful products and results of decayed +vegetation have been brought into use for the service of man. + +Aniline has been previously referred (p. 135) to as having been prepared +from nitro-benzole, or _essence de mirbane_, and its preparation, by +treating this substance with iron-filings and acetic acid, was one of the +early triumphs of the chemists who undertook the search after the unknown +contained in gas-tar. It had previously been obtained from oils distilled +from bones. The importance of the substance lies in the fact that, by the +action of various chemical reagents, a series of colouring matters of +very great richness are formed, and these are the well-known _aniline +dyes_. + +As early as 1836, it was discovered that aniline, when heated with +chloride of lime, acquired a beautiful blue tint. This discovery led to +no immediate practical result, and it was not until twenty-one years +after that a further discovery was made, which may indeed be said to have +achieved a world-wide reputation. It was found that, by adding bichromate +of potash to a solution of aniline and sulphuric acid, a powder was +obtained from which the dye was afterwards extracted, which is known as +_mauve_. Since that time dyes in all shades and colours have been +obtained from the same source. _Magenta_ was the next dye to make its +appearance, and in the fickle history of fashion, probably no colours +have had such extraordinary runs of popularity as those of mauve and +magenta. Every conceivable colour was obtained in due course from the +same source, and chemists began to suspect that, in the course of time, +the colouring matter of dyer's madder, which was known as _alizarin_, +would also be obtained therefrom. Hitherto this had been obtained from +the root of the madder-plant, but by dint of careful and well-reasoned +research, it was obtained by Dr Groebe, from a solid crystalline coal-tar +product, known as _anthracene_, (C_{12}H_{14}). This artificial alizarin +yields colours which are purer than those of natural madder, and being +derived from what was originally regarded as a waste product, its cost of +production is considerably cheaper. + +We have endeavoured thus far to deal with (1) gas, and (2) tar, the two +principal products in the distillation of coal. We have yet to say a few +words concerning the useful ammoniacal liquor, and the final residue in +the retorts, _i.e._, coke. + +The ammoniacal liquor which has been passing over during distillation of +the coal, and which has been collecting in the hydraulic main and in +other parts of the gas-making apparatus, is set aside to be treated to a +variety of chemical reactions, in order to wrench from it its useful +constituents. Amongst these, of course, _ammonia_ stands in the first +rank, the others being comparatively unimportant. In order to obtain +this, the liquor is first of all neutralised by being treated with a +quantity of acid, which converts the principal constituent of the liquor, +viz., carbonate of ammonia (smelling salts), into either sulphate of +ammonia, or chloride of ammonia, familiarly known as sal-ammoniac, +according as sulphuric acid or hydrochloric acid is the acid used. Thus +carbonate of ammonia with sulphuric acid will give sulphate of ammonia, +but carbonate of ammonia with hydrochloric acid will give sal-ammoniac +(chloride of ammonia). By a further treatment of these with lime, or, as +it is chemically known, oxide of calcium, ammonia is set free, whilst +chloride of lime (the well-known disinfectant), or sulphate of lime +(gypsum, or "plaster of Paris" ), is the result. + +Thus: + +Sulphate of ammonia + lime = plaster of Paris + ammonia. + +or, + +Sal-ammoniac + lime = chloride of lime + ammonia. + +Ammonia itself is a most powerful gas, and acts rapidly upon the eyes. It +has a stimulating effect upon the nerves. It is not a chemical element, +being composed of three parts of hydrogen by weight to one of nitrogen, +both of which elements alone are very harmless, and, the latter indeed, +very necessary to human life. Ammonia is fatal to life, producing great +irritation of the lungs. + +It has also been called "hartshorn," being obtained by destructive +distillation of horn and bone. The name "ammonia" is said to have been +derived from the fact that it was first obtained by the Arabs near the +temple of Jupiter Ammon, in Lybia, North Africa, from the excrement of +camels, in the form of sal-ammoniac. There are always traces of it in the +atmosphere, especially in the vicinity of large towns and manufactories +where large quantities of coal are burned. + +Coke, if properly prepared, should consist of pure carbon. Good coal +should yield as much as 80 per cent. of coke, but owing to the +unsatisfactory manner of its production, this proportion is seldom +yielded, whilst the coke which is familiar to householders, being the +residue left in the retorts after gas-making, usually contains so large a +proportion of sulphur as to make its combustion almost offensive. No +doubt the result of its unsatisfactory preparation has been that it has +failed to make its way into households as it should have done, but there +is also another objection to its use, namely, the fact that, owing to the +quantity of oxygen required in its combustion, it gives rise to feelings +of suffocation where insufficient ventilation of the room is provided. + +Large quantities of coke are, however, consumed in the feeding of furnace +fires, and in the heating of boilers of locomotives, as well as in +metallurgical operations; and in order to supply the demand, large +quantities of coal are "coked," a process by which the volatile products +are completely combusted, pure coke remaining behind. This process is +therefore the direct opposite to that of "distillation," by which the +volatile products are carefully collected and re-distilled. + +The sulphurous impurities which are always present in the coal, and which +are, to a certain extent, retained in coke made at the gas-works, +themselves have a value, which in these utilitarian days is not long +likely to escape the attention of capitalists. In coal, bands of bright +shining iron pyrites are constantly seen, even in the homely scuttle, and +when coal is washed, as it is in some places, the removal of the pyrites +increases the value of the coal, whilst it has a value of its own. + +The conversion of the sulphur which escapes from our chimneys into +sulphuretted hydrogen, and then into sulphuric acid, or oil of vitriol, +has already been referred to, and we can only hope that in these days +when every available source of wealth is being looked up, and when there +threatens to remain nothing which shall in the future be known as +"waste," that the atmosphere will be spared being longer the receptacle +for the unowned and execrated brimstone of millions of fires and +furnaces. + + + + +CHAPTER VII. + +THE COAL SUPPLIES OF THE WORLD. + + +As compared with some of the American coal-fields, those of Britain are +but small, both in extent and thickness. They can be regarded as falling +naturally into three principal areas. + + The northern coal-field, including those of Fife, Stirling, and Ayr + in Scotland; Cumberland, Newcastle, and Durham in England; Tyrone + in Ireland. + + The middle coal-field, all geologically in union, including those of + Yorkshire, Derbyshire, Shropshire, Staffordshire, Flint, and + Denbigh. + + The southern coal-field, including South Wales, Forest of Dean, + Bristol, Dover, with an offshoot at Leinster, &c., and Millstreet, + Cork. + +Thus it will be seen that while England and Scotland are, in comparison +with their extent of surface, bountifully supplied with coal-areas, in +the sister island of Ireland coal-producing areas are almost absent. The +isolated beds in Cork and Tipperary, in Tyrone and Antrim, are but the +remnants left of what were formerly beds of coal extending the whole +breadth and length of Ireland. Such beds as there remain undoubtedly +belong to the base of the coal-measures, and observations all go to show +that the surface suffered such extreme denudation subsequent to the +growth of the coal-forests, that the wealth which once lay there, has +been swept away from the surface which formerly boasted of it. + +On the continent of Europe the coal-fields, though not occupying so large +a proportion of the surface of the country as in England, are very far +from being slight or to be disregarded. The extent of forest-lands still +remaining in Germany and Austria are sufficing for the immediate needs of +the districts where some of the best seams occur. It is only where there +is a dearth of handy fuel, ready to be had, perhaps, by the simple +felling of a few trees, that man commences to dig into the earth for his +fuel. But although on the continent not yet occupying so prominent a +position in public estimation as do coal-fields in Great Britain, those +of the former have one conspicuous characteristic, viz., the great +thickness of some of the individual seams. + +In the coal-field of Midlothian the seams of coal vary from 2 feet to 5 +feet in thickness. One of them is known as the "great seam," and in spite +of its name attains a thickness only of from 8 to 10 feet thick. There +are altogether about thirty seams of coal. When, however, we pass to the +continent, we find many instances, such as that of the coal-field of +Central France, in which the seams attain vast thicknesses, many of them +actually reaching 40 and 60 feet, and sometimes even 80 feet. One of the +seams in the district of St. Etienne varies from 30 to 70 feet thick, +whilst the fifteen to eighteen workable seams give a thickness of 112 +feet, although the total area of the field is not great. Again, in the +remarkable basin of the Saône-et-Loire, although there are but ten beds +of coal, two of them run from 30 to 60 feet each, whilst at Creusot the +main seam actually runs locally to a thickness varying between 40 and 130 +feet. + +The Belgian coal-field stretches in the form of a narrow strip from 7 to +9 miles wide by about 100 miles long, and is divided into three principal +basins. In that stretching from Liége to Verviers there are eighty-three +seams of coal, none of which are less than 3 feet thick. In the basin of +the Sambre, stretching from Namur to Charleroi, there are seventy-three +seams which are workable, whilst in that between Mons and Thulin there +are no less than one hundred and fifty-seven seams. The measures here are +so folded in zigzag fashion, that in boring in the neighbourhood of Mons +to a depth of 350 yards vertical, a single seam was passed through no +less than six times. + +Germany, on the west side of the Rhine, is exceptionally fortunate in the +possession of the famous Pfalz-Saarbrücken coal-field, measuring about 60 +miles long by 20 miles wide, and covering about 175 square miles. Much of +the coal which lies deep in these coal-measures will always remain +unattainable, owing to the enormous thickness of the strata, but a +careful computation made of the coal which can be worked, gives an +estimate of no less than 2750 millions of tons. There is a grand total of +two hundred and forty-four seams, although about half of them are +unworkable. + +Beside other smaller coal-producing areas in Germany, the coal-fields of +Silesia in the southeastern corner of Prussia are a possession unrivalled +both on account of their extent and thickness. It is stated that there +exist 333 feet of coal, all the seams of which exceed 2-1/2 feet, and +that in the aggregate there is here, within a workable depth, the +scarcely conceivable quantity of 50,000 million tons of coal. + +The coal-field of Upper Silesia, occupying an area about 20 miles long by +15 miles broad, is estimated to contain some 10,000 feet of strata, with +333 feet of good coal. This is about three times the thickness contained +in the South Wales coal-field, in a similar thickness of coal-measures. +There are single seams up to 60 feet thick, but much of the coal is +covered by more recent rocks of New Red and Cretaceous age. In Lower +Silesia there are numerous seams 3-1/2 feet to 5 feet thick, but owing to +their liability to change in character even in the same seam, their value +is inferior to the coals of Upper Silesia. + +When British supplies are at length exhausted, we may anticipate that +some of the earliest coals to be imported, should coal then be needed, +will reach Britain from the upper waters of the Oder. + +The coal-field of Westphalia has lately come into prominence in +connection with the search which has been made for coal in Kent and +Surrey, the strata which are mined at Dortmund being thought to be +continuous from the Bristol coal-field. Borings have been made through +the chalk of the district north of the Westphalian coal-field, and these +have shown the existence of further coal-measures. The coal-field extends +between Essen and Dortmund a distance of 30 miles east and west, and +exhibits a series of about one hundred and thirty seams, with an +aggregate of 300 feet of coal. + +It is estimated that this coal-field alone contains no less than 39,200 +millions of tons of coal. + +Russia possesses supplies of coal whose influence has scarcely yet been +felt, owing to the sparseness of the population and the abundance of +forest. Carboniferous rocks abut against the flanks of the Ural +Mountains, along the sides of which they extend for a length of about a +thousand miles, with inter-stratifications of coal. Their actual contents +have not yet been gauged, but there is every reason to believe that those +coal-beds which have been seen are but samples of many others which will, +when properly worked, satisfy the needs of a much larger population than +the country now possesses. + +Like the lower coals of Scotland, the Russian coals are found in the +carboniferous limestone. This may also be said of the coal-fields in the +governments of Tula and Kaluga, and of those important coal-bearing +strata near the river Donetz, stretching to the northern corner of the +Sea of Azov. In the last-named, the seams are spread over an area of +11,000 square miles, in which there are forty-four workable seams +containing 114 feet of coal. The thickest of known Russian coals occur at +Lithwinsk, where three seams are worked, each measuring 30 feet to 40 +feet thick. + +An extension of the Upper Silesian coal-field appears in Russian Poland. +This is of upper Carboniferous age, and contains an aggregate of 60 feet +of coal. + +At Ostrau, in Upper Silesia (Austria), there is a remarkable coal-field. +Of its 370 seams there are no less than 117 workable ones, and these +contain 350 feet of coal. The coals here are very full of gas, which even +percolates to the cellars of houses in the town. A bore hole which was +sunk in 1852 to a depth of 150 feet, gave off a stream of gas, which +ignited, and burnt for many years with a flame some feet long. + +The Zwickau coal-field in Saxony is one of the most important in Europe. +It contains a remarkable seam of coal, known as Russokohle or soot-coal, +running at times 25 feet thick. It was separated by Geinitz and others +into four zones, according to their vegetable contents, viz.:-- + +1. Zone of Ferns. + +2. Zone of Annularia and Calamites. + +3. Zone of Sigillaria. + +4. Zone of Sagenaria (in Silesia), equivalent to the culm-measures of + Devonshire. + +Coals belonging to other than true Carboniferous age are found in Europe +at Steyerdorf on the Danube, where there are a few seams of good coal in +strata of Liassic age, and in Hungary and Styria, where there are +tertiary coals which approach closely to those of true Carboniferous age +in composition and quality. + +In Spain there are a few small scattered basins. Coal is found overlying +the carboniferous limestone of the Cantabrian chain, the seams being from +5 feet to 8 feet thick. In the Satero valley, near Sotillo, is a single +seam measuring from 60 feet to 100 feet thick. Coal of Neocomian age +appears at Montalban. + +When we look outside the continent of Europe, we may well be astonished +at the bountiful manner in which nature has laid out beds of coal upon +these ancient surfaces of our globe. + +Professor Rogers estimated that, in the United States of America, the +coal-fields occupy an area of no less than 196,850 square miles. + +Here, again, it is extremely probable that the coal-fields which remain, +in spite of their gigantic existing areas, are but the remnants of one +tremendous area of deposit, bounded only on the east by the Atlantic, and +on the west by a line running from the great lakes to the frontiers of +Mexico. The whole area has been subjected to forces which have produced +foldings and flexures in the Carboniferous strata after deposition. These +undulations are greatest near the Alleghanies, and between these +mountains and the Atlantic, whilst the flexures gradually dying out +westward, cause the strata there to remain fairly horizontal. In the +troughs of the foldings thus formed the coal-measures rest, those +portions which had been thrown up as anticlines having suffered loss by +denudation. Where the foldings are greatest there the coal has been +naturally most altered; bituminous and caking-coals are characteristic of +the broad flat areas west of the mountains, whilst, where the contortions +are greatest, the coal becomes a pure anthracite. + +It must not be thought that in this huge area the coal is all uniformly +good. It varies greatly in quality, and in some districts it occurs in +such thin seams as to be worthless, except as fuel for consumption by the +actual coal-getters. There are, too, areas of many square miles in +extent, where there are now no coals at all, the formation having been +denuded right down to the palaeozoic back-bone of the country. + +Amongst the actual coal-fields, that of Pennsylvania stands +pre-eminent. The anthracite here is in inexhaustible quantity, its output +exceeding that of the ordinary bituminous coal. The great field of which +this is a portion, extends in an unbroken length for 875 miles N.E. and +S.W., and includes the basins of Ohio, Maryland, Virginia, Kentucky, and +Tennessee. The workable seams of anthracite about Pottsville measure in +the aggregate from 70 to 207 feet. Some of the lower seams individually +attain an exceptional thickness, that at Lehigh Summit mine containing a +seam, or rather a bed, of 30 feet of good coal. + +A remarkable seam of coal has given the town of Pittsburg its name. This +is 8 feet thick at its outcrop near the town, and although its thickness +varies considerably, Professor Rogers estimates that the sheet of coal +measures superficially about 14,000 square miles. What a forest there +must have existed to produce so widespread a bed! Even as it is, it has +at a former epoch suffered great denudation, if certain detached basins +should be considered as indicating its former extent. + +The principal seam in the anthracite district of central Pennsylvania, +which extends for about 650 miles along the left bank of the Susquehanna, +is known as the "Mammoth" vein, and is 29-1/2 feet thick at Wilkesbarre, +whilst at other places it attains to, and even exceeds, 60 feet. + +On the west of the chain of mountains the foldings become gentler, and +the coal assumes an almost horizontal position. In passing through Ohio +we find a saddle-back ridge or anticline of more ancient strata than the +coal, and in consequence of this, we have a physical boundary placed upon +the coal-fields on each side. + +Passing across this older ridge of denuded Silurian and other rocks, we +reach the famous Illinois and Indiana coal-field, whose +coal-measures lie in a broad trough, bounded on the west by the uprising +of the carboniferous limestone of the upper Mississippi. This limestone +formation appears here for the first time, having been absent on the +eastern side of the Ohio anticline. The area of the coal-field is +estimated at 51,000 square miles. + +In connection with the coal-fields of the United States, it is +interesting to notice that a wide area in Texas, estimated at 3000 square +miles, produces a large amount of coal annually from strata of the +Liassic age. Another important area of production in eastern Virginia +contains coal referable to the Jurassic age, and is similar in fossil +contents to the Jurassic of Whitby and Brora. The main seam in eastern +Virginia boasts a thickness of from 30 to 40 feet of good coal. + +Very serviceable lignites of Cretaceous age are found on the Pacific +slope, to which age those of Vancouver's Island and Saskatchewan River +are referable. + +Other coal-fields of less importance are found between Lakes Huron and +Erie, where the measures cover an area of 5000 square miles, and also in +Rhode Island. + +In British North America we find extensive deposits of valuable +coal-measures. Large developments occur in New Brunswick and Nova Scotia. +At South Joggins there is a thickness of 14,750 feet of strata, in which +are found seventy-six coal-seams of 45 feet in total thickness. At Picton +there are six seams with a total of 80 feet of coal. In the lower +carboniferous group is found the peculiar asphaltic coal of the Albert +mine in New Brunswick. Extensive deposits of lignite are met with both in +the Dominion and in the United States, whilst true coal-measures flank +both sides of the Rocky Mountains. Coal-seams are often encountered in +the Arctic archipelago. + +The principal areas of deposit in South America are in Brazil, Uruguay, +and Peru. The largest is the Candiota coal-field, in Brazil, where +sections in the valley of the Candiota River show five good seams with a +total of 65 feet of coal. It is, however, worked but little, the +principal workings being at San Jeronimo on the Jacahahay River. + +In Peru the true carboniferous coal-seams are found on the higher ground +of the Andes, whilst coal of secondary age is found in considerable +quantities on the rise towards the mountains. At Porton, east of +Truxillo, the same metamorphism which has changed the ridge of sandstone +to a hard quartzite has also changed the ordinary bituminous coal into an +anthracite, which is here vertical in position. The coals of Peru usually +rise to more than 10,000 feet above the sea, and they are practically +inaccessible. + +Cretaceous coals have been found at Lota in Chili, and at Sandy Point, +Straits of Magellan. + +Turning to Asia, we find that coal has been worked from time to time at +Heraclea in Asia Minor. Lignites are met with at Smyrna and Lebanon. + +The coal-fields of Hindoostan are small but numerous, being found in all +parts of the peninsula. There is an important coal-field at Raniganj, +near the Hooghly, 140 miles north of Calcutta. It has an area of 500 +square miles. In the Raniganj district there are occasional seams 20 feet +to 80 feet in thickness, but the coals are of somewhat inferior quality. + +The best quality amongst Indian coals has come from a small coal-field of +about 11 square miles in extent, situated at Kurhurbali on the East +Indian Railway. Other coal-fields are found at Jherria and on the Sone +River, in Bengal, and at Mopani on the Nerbudda. Much is expected in +future from the large coal-field of the Wardha and Chanda districts, in +the Central Provinces, the coal of which may eventually prove to be of +Permian age. + +The coal-deposits of China are undoubtedly of tremendous extent, although +from want of exploration it is difficult to form any satisfactory +estimate of them. Near Pekin there are beds of coal 95 feet thick, which +afford ample provision for the needs of the city. In the mountainous +districts of western China the area over which carboniferous strata are +exposed has been estimated at 100,000 square miles. The coal-measures +extend westward to the Mongolian frontier, where coal-seams 30 feet thick +are known to lie in horizontal plane for 200 miles. Most of the Chinese +coal-deposits are rendered of small value, either owing to the +mountainous nature of the valleys in which they outcrop, or to their +inaccessibility from the sea. Japan is not lacking in good supplies of +coal. A colliery is worked by the government on the island of Takasima, +near Nagasaki, for the supply of coals for the use of the navy. + +The British possession of Labuan, off the island of Borneo, is rich in a +coal of tertiary age, remarkable for the quantity of fossil resin which, +it contains. Coal is also found in Sumatra, and in the Malayan +Archipelago. + +In Cape Colony and Natal the coal-bearing Karoo beds are probably of New +Red age. The coal is reported to be excellent in quantity. + +In Abyssinia lignites are frequently met with in the high lands of the +interior. + +Coal is very extensively developed throughout Australasia. In New South +Wales, coal-measures occur in large detached portions between 29° and 35° +S. latitude. The Newcastle district, at the mouth of the Hunter river, is +the chief seat of the coal trade, and the seams are here found up to 30 +feet thick. Coal-bearing strata are found at Bowen River, in Queensland, +covering an area of 24,000 square miles, whilst important mines of +Cretaceous age are worked at Ipswich, near Brisbane. In New Zealand +quantities of lignite, described as a hydrous coal, are found and +utilised; also an anhydrous coal which may prove to be either of +Cretaceous or Jurassic age. + +We have thus briefly sketched the supplies of coal, so far as they are +known, which are to be found in various countries. But England has of +late years been concerned as to the possible failure of her home supplies +in the not very distant future, and the effects which such failure would +be likely to produce on the commercial prosperity of the country. + +Great Britain has long been the centre of the universe in the supply of +the world's coal, and as a matter of fact, has been for many years +raising considerably more than one half of the total amount of coal +raised throughout the whole world. There is, as we have seen, an +abundance of coal elsewhere, which will, in the course of time, compete +with her when properly worked, but Britain seems to have early taken the +lead in the production of coal, and to have become the great universal +coal distributor. Those who have misgivings as to what will happen when +her coal is exhausted, receive little comfort from the fact that in North +America, in Prussia, in China and elsewhere, there are tremendous +supplies of coal as yet untouched, although a certain sense of relief is +experienced when that fact becomes generally known. + +If by the time of exhaustion of the home mines Britain is still dependent +upon coal for fuel, which, in this age of electricity, scarcely seems +probable, her trade and commerce will feel with tremendous effect the +blow which her prestige will experience when the first vessel, laden with +foreign coal, weighs anchor in a British harbour. In the great coal +lock-out of 1893, when, for the greater part of sixteen weeks scarcely a +ton of coal reached the surface in some of her principal coal-fields, it +was rumoured, falsely as it appeared, that a collier from America had +indeed reached those shores, and the importance which attached to the +supposed event was shown by the anxious references to it in the public +press, where the truth or otherwise of the alarm was actively discussed. +Should such a thing at any time actually come to pass, it will indeed be +a retribution to those who have for years been squandering their +inheritance in many a wasteful manner of coal-consumption. + +Thirty years ago, when so much small coal was wasted and wantonly +consumed in order to dispose of it in the easiest manner possible at the +pitmouths, and when only the best and largest coal was deemed to be of +any value, louder and louder did scientific men speak in protest against +this great and increasing prodigality. Wild estimates were set on foot +showing how that, sooner or later, there would be in Britain no native +supply of coal at all, and finally a Royal Commission was appointed in +1866, to collect evidence and report upon the probable time during which +the supplies of Great Britain would last. + +This Commission reported in 1871, and the outcome of it was that a period +of twelve hundred and seventy-three years was assigned as the period +during which the coal would last, at the then-existing rate of +consumption. The quantity of workable coal within a depth of 4000 feet +was estimated to be 90,207 millions of tons, or, including that at +greater depths, 146,480 millions of tons. Since that date, however, there +has been a steady annual increase in the amount of coal consumed, and +subsequent estimates go to show that the supplies cannot last for more +than 250 years, or, taking into consideration a possible decrease in +consumption, 350 years. Most of the coal-mines will, indeed, have been +worked out in less than a hundred years hence, and then, perhaps, the +competition brought about by the demand for, and the scarcity of, coal +from the remaining mines, will have resulted in the dreaded importation +of coal from abroad. + +In referring to the outcome of the Royal Commission of 1866, although the +Commissioners fixed so comparatively short a period as the probable +duration of the coal supplies, it is but fair that it should be stated +that other estimates have been made which have materially differed from +their estimate. Whereas one estimate more than doubled that of the Royal +Commission, that of Sir William Armstrong in 1863 gave it as 212 years, +and Professor Jevons, speaking in 1875 concerning Armstrong's estimate, +observed that the annual increase in the amount used, which was allowed +for in the estimate, had so greatly itself increased, that the 212 years +must be considerably reduced. + +One can scarcely thoroughly appreciate the enormous quantity of coal that +is brought to the surface annually, and the only wonder is that there are +any supplies left at all. The Great Pyramid which is said by Herodotus to +have been twenty years in building, and which took 100,000 men to build, +contains 3,394,307 cubic yards of stone. The coal raised in 1892 would +make a pyramid which would contain 181,500,000 cubic yards, at the low +estimate that one ton could be squeezed into one cubic yard. + +The increase in the quantity of coal which has been raised in succeeding +years can well be seen from the following facts. + +In 1820 there were raised in Great Britain about 20 millions of tons. By +1855 this amount had increased to 64-1/2 millions. In 1865 this again had +increased to 98 millions, whilst twenty years after, viz., in 1885, this +had increased to no less than 159 millions, such were the giant strides +which the increase in consumption made. + +In the return for 1892, this amount had farther increased to 181-1/2 +millions of tons, an advance in eight years of a quantity more than equal +to the total raised in 1820, and in 1894 the total reached +199-1/2 millions; this was produced by 795,240 persons, employed in and +about the mines. + + + + +CHAPTER VIII. + +THE COAL-TAR COLOURS. + + +In a former chapter some slight reference has been made to those +bye-products of coal-tar which have proved so valuable in the production +of the aniline dyes. It is thought that the subject is of so interesting +a nature as to deserve more notice than it was possible to bestow upon it +in that place. With abstruse chemical formulae and complex chemical +equations it is proposed to have as little as possible to do, but even +the most unscientific treatment of the subject must occasionally +necessitate a scientific method of elucidation. + +The dyeing industry has been radically changed during the last half +century by the introduction of what are known as the _artificial_ dyes, +whilst the _natural_ colouring matters which had previously been the sole +basis of the industry, and which had been obtained by very simple +chemical methods from some of the constituents of the animal kingdom, or +which were found in a natural state in the vegetable kingdom, have very +largely given place to those which have been obtained from coal-tar, a +product of the mineralised vegetation of the carboniferous age. + +The development and discovery of the aniline colouring matters were not, +of course, possible until after the extensive adoption of +house-gas for illuminating purposes, and even then it was many years +before the waste products from the gas-works came to have an appreciable +value of their own. This, however, came with the increased utilitarianism +of the commerce of the present century, but although aniline was first +discovered in 1826 by Unverdorben, in the materials produced by the dry +distillation of indigo (Portuguese, _anil_, indigo), it was not until +thirty years afterwards, namely, in 1856, that the discovery of the +method of manufacture of the first aniline dye, mauveine, was announced, +the discovery being due to the persistent efforts of Perkin, to whom, +together with other chemists working in the same field, is due the great +advance which has been made in the chemical knowledge of the carbon, +hydrogen, and oxygen compounds. Scientists appeared to work along two +planes; there were those who discovered certain chemical compounds in the +resulting products of reactions in the treatment of _existing_ +vegetation, and there were those who, studying the wonderful constituents +in coal-tar, the product of a _past_ age, immediately set to work to find +therein those compounds which their contemporaries had already +discovered. Generally, too, with signal success. + +The discovery of benzene in 1825 by Faraday was followed in the course of +a few years by its discovery in coal-tar by Hofmann. Toluene, which was +discovered in 1837 by Pelletier, was recognised in the fractional +distillation of crude naphtha by Mansfield in 1848. Although the method +of production of mauveine on a large scale was not accomplished until +1856, yet it had been noticed in 1834, the actual year of its recognition +as a constituent of coal-tar, that, when brought into contact with +chloride of lime, it gave brilliant colours, but it required a +considerable cheapening of the process of aniline manufacture before the +dyes commenced to enter into competition with the old natural dyes. + +The isolation of aniline from coal-tar is expensive, in consequence of +the small quantities in which it is there found, but it was discovered by +Mitscherlich that by acting upon benzene, one of the early distillates of +coal-tar, for the production of nitro-benzole, a compound was produced +from which aniline could be obtained in large quantities. There were thus +two methods of obtaining aniline from tar, the experimental and the +practical. + +In producing nitrobenzole (nitrobenzene), chemically represented as +(C_{6}H_{5}NO_{2}), the nitric acid used as the reagent with benzene, is +mixed with a quantity of sulphuric acid, with the object of absorbing +water which is formed during the reaction, as this would tend to dilute +the efficiency of the nitric acid. The proportions are 100 parts of +purified benzene, with a mixture of 115 parts of concentrated nitric acid +(HNO_{3}) and 160 parts of concentrated sulphuric acid. The mixture is +gradually introduced into the large cast-iron cylinder into which the +benzene has been poured. The outside of the cylinder is supplied with an +arrangement by which fine jets of water can be made to play upon it in +the early stages of the reaction which follows, and at the end of from +eight to ten hours the contents are allowed to run off into a storage +reservoir. Here they arrange themselves into two layers, the top of which +consists of the nitrobenzene which has been produced, together with some +benzene which is still unacted upon. The mixture is then freed from the +latter by treatment with a current of steam. Nitrobenzene presents itself +as a yellowish oily liquid, with a peculiar taste as of bitter almonds. +It was formerly in great demand by perfumers, but its poisonous +properties render it a dangerous substance to deal with. In practice a +given quantity of benzene will yield about 150 per cent of nitrobenzene. +Stated chemically, the reaction is shown by the following equation:-- + +C_{6}H_{6} + HNO_{3} = C_{6}H_{5}NO_{2}, + H_{2}O +(Benzene) (Nitric acid) (Nitrobenzene) (Water). + +The water which is thus formed in the process, by the freeing of one of +the atoms of hydrogen in the benzene, is absorbed by the sulphuric acid +present, although the latter takes no actual part in the reaction. + +From the nitrobenzene thus obtained, the aniline which is now used so +extensively is prepared. The component atoms of a molecule of aniline are +shown in the formula C_{6}H_{5}NH_{2}. It is also known as phenylamine or +amido-benzole, or commercially as aniline oil. There are various methods +of reducing nitrobenzene for aniline, the object being to replace the +oxygen of the former by an equivalent number of atoms of hydrogen. The +process generally used is that known as Béchamp's, with slight +modifications. Equal volumes of nitrobenzene and acetic acid, together +with a quantity of iron-filings rather in excess of the weight of the +nitrobenzene, are placed in a capacious retort. A brisk effervescence +ensues, and to moderate the increase of temperature which is caused by +the reaction, it is found necessary to cool the retort. Instead of acetic +acid hydrochloric acid has been a good deal used, with, it is said, +certain advantageous results. From 60 to 65 per cent. of aniline on the +quantity of nitrobenzene used, is yielded by Béchamp's process. + +Stated in a few words, the above is the process adopted on all hands for +the production of commercial aniline, or aniline oil. The details of the +distillation and rectification of the oil are, however, as varied as they +can well be, no two manufacturers adopting the same process. Many of the +aniline dyes depend entirely for their superiority, on the quality of the +oil used, and for this reason it is subject to one or more processes of +rectification. This is performed by distilling, the distillates at the +various temperatures being separately collected. + +When pure, aniline is a colourless oily liquid, but on exposure rapidly +turns brown. It has strong refracting powers and an agreeable aromatic +smell. It is very poisonous when taken internally; its sulphate is, +however, sometimes used medicinally. It is by the action upon aniline of +certain oxidising agents, that the various colouring matters so well +known as aniline dyes are obtained. + +Commercial aniline oil is not, as we have seen, the purest form of +rectified aniline. The aniline oils of commerce are very variable in +character, the principal constituents being pure aniline, para- and +meta-toluidine, xylidines, and cumidines. They are best known to the +colour manufacturer in four qualities-- + +(_a_) Aniline oil for blue and black. + +(_b_) Aniline oil for magenta. + +(_c_) Aniline oil for safranine. + +(_d_) _Liquid toluidine. + +From the first of these, which is almost pure aniline, aniline black is +derived, and a number of organic compounds which are further used for the +production of dyes. The hydrochloride of aniline is important and is +known commercially as "aniline salt." + +The distillation and rectification of aniline oil is practised on a +similar principle to the fractional distillation which we have noticed as +being used for the distillation of the naphthas. First, light aniline +oils pass over, followed by others, and finally by the heavy oils, or +"aniline-tailings." It is a matter of great necessity to those engaged in +colour manufacture to apply that quality oil which is best for the +production of the colour required. This is not always an easy matter, and +there is great divergence of opinion and in practice on these points. + +The so-called aniline colours are not all derived from aniline, such +colouring matters being in some cases derived from other coal-tar +products, such as benzene and toluene, phenol, naphthalene, and +anthracene, and it is remarkable that although the earlier dyes were +produced from the lighter and more easily distilled products of +coal-tar, yet now some of the heaviest and most stubborn of the +distillates are brought under requisition for colouring matters, those +which not many years ago were regarded as fit only to be used as +lubricants or to be regarded as waste. + +It is scarcely necessary or advisable in a work of this kind to pursue +the many chemical reactions, which, from the various acids and bases, +result ultimately in the many shades and gradations of colour which are +to be seen in dress and other fabrics. Many of them, beautiful in the +extreme, are the outcome of much careful and well-planned study, and to +print here the complicated chemical formulae which show the great changes +taking place in compounds of complex molecules, or to mention even the +names of these many-syllabled compounds, would be to destroy the purpose +of this little book. The Rosanilines, the Indulines, and Safranines; the +Oxazines, the Thionines: the Phenol and Azo dyes are all substances which +are of greater interest to the chemical students and to the colour +manufacturer than to the ordinary reader. Many of the names of the bases +of various dyes are unknown outside the chemical dyeworks, although each +and all have complicated; reactions of their own. In the reds are +rosanilines, toluidine xylidine, &c.; in the blues--phenyl-rosanilines, +diphenylamine, toluidine, aldehyde, &c.; violets--rosaniline, mauve, +phenyl, ethyl, methyl, &c.; greens--iodine, aniline, leucaniline, +chrysotoluidine, aldehyde, toluidine, methyl-anilinine, &c.; yellows and +orange--leucaniline, phenylamine, &c.; browns--chrysotoluidine, &c.; +blacks--aniline, toluidine, &c. + +To take the rosanilines as an instance of the rest. + +Aniline red, magenta, azaleine, rubine, solferino, fuchsine, chryaline, +roseine, erythrobenzine, and others, are colouring matters in this group +which are salts of rosaniline, and which are all recognised in commerce. + +The base rosaniline is known chemically by the formula C_{20}H_{l9}N_{3}, +and is prepared by heating a mixture of magenta aniline, toluidine, and +pseudotoluidine, with arsenic acid and other oxidising agents. It is +important that water should be used in such quantities as to prevent the +solution of arsenic acid from depositing crystals on cooling. Unless +carefully crystallised rosaniline will contain a slight proportion of the +arseniate, and when articles of clothing are dyed with the salt, it is +likely to produce an inflammatory condition of skin, when worn. Some +years ago there was a great outcry against hose and other articles dyed +with aniline dyes, owing to the bad effects which were produced, and this +has no doubt proved very prejudicial to aniline dyes as a whole. + +Again, the base known as mauve, or mauveine, has a composition shown by +the formula C_{27}H_{24}N_{4}. It is produced from the sulphate of +aniline by mixing it with a cold saturated solution of bichromate of +potash, and allowing the mixture to stand for ten or twelve hours. A +blue-black precipitate is then formed, which, after undergoing a process +of purification, is dissolved in alcohol and evaporated to dryness. A +metallic-looking powder is then obtained, which constitutes this +all-important base. Mauve forms with acids a series of well-defined salts +and is capable of expelling ammonia from its combinations. Mauve was the +first aniline dye which was produced on a large scale, this being +accomplished by Perkin in 1856. + +The substance known as carbolic acid is so useful a product of a piece of +coal that a description of the method of its production must necessarily +have a place here. It is one of the most powerful antiseptic agents with +which we are acquainted, and has strong anaesthetic qualities. Some +useful dyes are also obtained from it. It is obtained in quantities from +coal-tar, that portion of the distillate known as the light oils being +its immediate source. The tar oil is mixed with a solution of caustic +soda, and the mixture is violently agitated. This results in the caustic +soda dissolving out the carbolic acid, whilst the undissolved oils +collect upon the surface, allowing the alkaline solution to be drawn from +beneath. The soda in the solution is then neutralised by the addition of +a suitable quantity of sulphuric acid, and the salt so formed sinks while +the carbolic acid rises to the surface. + +Purification of the product is afterwards carried out by a process of +fractional distillation. There are various other methods of preparing +carbolic acid. + +Carbolic acid is known chemically as C_{6}H_{5}(HO). When pure it appears +as colourless needle-like crystals, and is exceedingly poisonous. It has +been used with marked success in staying the course of disease, such as +cholera and cattle plague. It is of a very volatile nature, and its +efficacy lies in its power of destroying germs as they float in the +atmosphere. Modern science tells us that all diseases have their origin +in certain germs which are everywhere present and which seek only a +suitable _nidus_ in which to propagate and flourish. Unlike mere +deodorisers which simply remove noxious gases or odours; unlike +disinfectants which prevent the spread of infection, carbolic acid +strikes at the very root and origin of disease by oxidising and consuming +the germs which breed it. So powerful is it that one part in five +thousand parts of flour paste, blood, &c., will for months prevent +fermentation and putrefaction, whilst a little of its vapour in the +atmosphere will preserve meat, as well as prevent it from becoming +fly-blown. Although it has, in certain impure states, a slightly +disagreeable odour, this is never such as to be in any way harmful, +whilst on the other hand it is said to act as a tonic to those connected +with its preparation and use. + +The new artificial colouring matters which are continually being brought +into the market, testify to the fact that, even with the many beautiful +tints and hues which have been discovered, finality and perfection have +not yet been reached. A good deal of popular prejudice has arisen against +certain aniline dyes on account of their inferiority to many of the old +dye-stuffs in respect to their fastness, but in recent years the +manufacture of many which were under this disadvantage of looseness of +dye, has entirely ceased, whilst others have been introduced which are +quite as fast, and sometimes even faster than the natural dyes. + +It is convenient to express the constituents of coal-tar, and the +distillates of those constituents, in the form of a genealogical chart, +and thus, by way of conclusion, summarise the results which we have +noticed. + + COAL. + | + .----------+-----------+----+-------------------+--------+----. + | | | | | | + Water House-gas Coal-tar Ammoniacal Coke | + | liquor | + .---------+-------+---------+---------. | Sulphur + | | | | | | (sulphurreted + First Second Heavy Anthracene Pitch | hydrogen: + light light oils (green | sulphurous + oils oils (creosote oils) | acid: oil + | (crude oils) | | of vitriol) + .----+----. naphtha) | Anthracene | + | | | | | | +Ammoniacal Benzene | | Alizarin or | + liquor toluene,| | dyer's madder | + &c. | | | + | | | + | | Sulphuric acid=Carbonate of=Hydrochloric + | | | ammonia acid + | | | (smelling + | | | salts) + | | | + | | Lime=Sulphate of Lime=Chloride of + | | | ammonia | ammonia (sal + | | | | ammoniac) + | | | | + | | .----+----. .----+----. + | | | | | | + | | Ammonia Sulphate Ammonia Chloride + | | of lime of lime. + | | (Plaster of Paris) + | | + | .--+-----+----------. + | | | | + | Crude Carbolic Naphthalin + | Creosote acid + | + .--------------+---+--+-------+--------+-----------. + | | | | | + Benzene=Nitric Acid Toluene Nylene Artificial Burning + | turpentine oils + Nitrobenzene= } Iron filings oil (solvent + (Essence de | } and acetic acid naphtha) + mirbane) | + | + Aniline=Various reagents + | + Aniline dyes + + + + + + +INDEX. + +A. + +Accidents, causes of mining +"Age of _Acrogens_" +_Alethopteris_ +Alizarin +American coal-fields +Ammoniacal liquor +Aniline +Aniline dyes +Aniline oil, commercial +Aniline salt +Aniline "tailings" +Anthracene +Anthracite +Artificial turpentine oil +Asphalt +Australian coals +_Aviculopecten_ + +B. + +Béchamp's process +Benzene +Bind +Bitumen in Trinidad +"Blower" a +Boghead coal +Bog-oak +Boring diamonds +Borrowdale graphite mine +Bovey Tracey lignite +British coal-fields +British North-American coal-measures +Briquettes + +C. + +_Calamites_, extinct horsetails +Carbolic acid +Carboniferous formation, the +_Cardiocarpum_, fossil fruit +Carelessness of miners +Causes of earth-movements +Changes of level +Charcoal as a disinfectant +Chemistry of a gas-flame +Chinese coals +Clanny's safety-lamp +Clayton's experiments with gas +Clay, regularity in deposition of +Club-mosses, great height of fossil +Coal-dust, danger from +Coal formed in large lakes or closed seas +Coal formation, geological position of +Coal formed by escape of gases +Coal-mine, the +Coal not the result of drifted vegetation +Coal-period, climate of +"Coal-pipes" +Coal-plants, classification of +Coal-seam, each, a forest growth +Coals of non-carboniferous age +Coal, vegetable origin of +Coke +"Cole" +"Condensers" +Cones of _Lepidodendra_ +Conifers in coal-measures +Current-bedding in sandstone + +D. + +Davy-lamp +Dangers of benzene +Darwin on the Chonos Archipelago +Diamonds, how made artificially +Disintegration of vegetable substances +Disproportion in relative thickness of coal and coal-measures + +E. + +Early use of coal +Effects of an explosion +Encrinital limestone +_Equiseta_ +"Essence de mirbane" +European coal-fields +Evelyn on the use of coal +Experiments illustrating fossilisation + +F. + +Filling retorts by machinery +Firedamp +Fire, mines on +First light oils +First record of an explosion +Flashing-point of oil +Flooding of pits +Fog and smoke +_Foraminifera_ +Fossil ferns +Fructification on fossil-ferns +Furnace, ventilating + +G. + +Gas, coal +Gasholder, the +Gas, house, constituents of +_Glossopteris_ +Graphite +"Green Grease" + +H. + +Hannay, of Glasgow +Heavy oils +Humboldt's safety-lamp +Hydraulic Main + +I. + +Impurities in house-gas +Indian coals +Insertion of rootlets of _stigmaria_ +Insufficiency of modern forest growths +Ireland denuded of coal-beds +Iron, supplies of + +L. + +_Lepidodendra_ +_Lepidostrobi_ +Lignite +London lit by gas + +M. + +Mammoth trees +Marco Polo +Marsh gas +Medium oils +Metamorphism of coal by igneous agency +Methods of ventilation +Mountain limestone +Murdock's use of gas +Mussel beds + +N. + +Napthalin +_Neuropteris_ +Newcastle, charters to +Nitro-benzole + +O. + +Objections to use of coal +Oils from coal and lignite +Oil-wells of America +Olefiant gas +_Orthoceras_ + +P. + +Paraffins +Peat +_Pecopteris_ +Pennsylvanian anthracite +Persian fire-worshippers +Pitch +Plumbago +_Polyzoa_ +Prejudice against aniline dyes +Prohibitions of the use of coal +Proportions of explosive mixtures +_Psaronius_ +"Purifiers" +Pyrites in coal + +Q. + +Quantity of coal raised in Great Britain + +R. + +Reptiles of the coal-era +Resemblance of American and British coal-_flora_ +Retorts +Roman use of coal +Rosanilines, the +Royal Commission of 1866 + +S. + +Sandstone, how formed +Shales +_Sigillaria_ +South American coals +Spores of _lepidodrendron_ +Spores, resinous matter in +Spores, inflammability of +Steel-mill +_Sternbergia_ +_Stigmaria_ +Subsidence throughout coal-era +Surturbrand at Brighton +Sussex iron-works + +T. + +Tar +Testing pits by the candle +Texas coal +Toluene, discovery of +Torbanehill mineral +Trappers + +U. + +Underclays +Uses to which coal is put + +V. + +Vaseline +Vegetation of the coal age +Ventilation of coal-pits + +W. + +"Washers" +Waste of fuel +Wealden lignite +Westphalian coal-field + +Y. + +Young's Paraffin Oil + +Z. + +Zoroastrians + + + + + +End of Project Gutenberg's The Story of a Piece of Coal, by Edward A. 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Donations are accepted in a number of other +ways including including checks, online payments and credit card +donations. To donate, please visit: https://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart was the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + https://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. diff --git a/old/12762-8.zip b/old/12762-8.zip Binary files differnew file mode 100644 index 0000000..8e7effa --- /dev/null +++ b/old/12762-8.zip diff --git a/old/12762.txt b/old/12762.txt new file mode 100644 index 0000000..e086774 --- /dev/null +++ b/old/12762.txt @@ -0,0 +1,4781 @@ +Project Gutenberg's The Story of a Piece of Coal, by Edward A. Martin + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Story of a Piece of Coal + What It Is, Whence It Comes, and Whither It Goes + +Author: Edward A. Martin + +Release Date: June 28, 2004 [EBook #12762] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK THE STORY OF A PIECE OF COAL *** + + + + +Produced by Miranda van de Heijning, Luiz Antonio de Souza and PG +Distributed Proofreaders + + + + + +THE STORY OF +A PIECE OF COAL + +WHAT IT IS, WHENCE IT COMES, +AND WHITHER IT GOES + +BY +EDWARD A. MARTIN, F.G.S. + +1896 + + + + + +PREFACE. + + +The knowledge of the marvels which a piece of coal possesses within +itself, and which in obedience to processes of man's invention it is +always willing to exhibit to an observant enquirer, is not so widespread, +perhaps, as it should be, and the aim of this little book, this record of +one page of geological history, has been to bring together the principal +facts and wonders connected with it into the focus of a few pages, where, +side by side, would be found the record of its vegetable and mineral +history, its discovery and early use, its bearings on the great +fog-problem, its useful illuminating gas and oils, the question of the +possible exhaustion of British supplies, and other important and +interesting bearings of coal or its products. + +In the whole realm of natural history, in the widest sense of the term, +there is nothing which could be cited which has so benefited, so +interested, I might almost say, so excited mankind, as have the wonderful +discoveries of the various products distilled from gas-tar, itself a +distillate of coal. + +Coal touches the interests of the botanist, the geologist, and the +physicist; the chemist, the sanitarian, and the merchant. + +In the little work now before the reader I have endeavoured to recount, +without going into unnecessary detail, the wonderful story of a piece of +coal. + +E.A.M. + +THORNTON HEATH, + +_February_, 1896. + + + + +CONTENTS. + + + I. THE ORIGIN OF COAL AND THE PLANTS OF WHICH IT IS COMPOSED + + II. A GENERAL VIEW OF THE COAL-BEARING STRATA + + III. VARIOUS FORMS OF COAL AND CARBON + + IV. THE COAL-MINE AND ITS DANGERS + + V. EARLY HISTORY--ITS USE AND ITS ABUSE + + VI. HOW GAS IS MADE--ILLUMINATING OILS AND BYE-PRODUCTS + + VII. THE COAL SUPPLIES OF THE WORLD + +VIII. THE COAL-TAR COLOURS + +CHART SHEWING THE PRODUCTS OF COAL + +GENERAL INDEX + + + +LIST OF ILLUSTRATIONS. + +FIG. 1. _Stigmaria_ + " 2. _Annularia radiata_ + " 3. _Rhacopteris inaequilatera_ + " 4. Frond of _Pecopteris_ + " 5. _Pecopteris Serlii_ + " 6. _Sphenopteris affinis_ + " 7. _Catamites Suckowii_ + " 8. _Calamocladus grandis_ + " 9. _Asterophyllites foliosa_ + " 10. _Spenophyllum cuneifolium_ + " 11. Cast of _Lepidodendron_ + " 12. _Lepidodendron longifolium_ + " 13. _Lepidodendron aculeatum_ + " 14. _Lepidostrobus_ + " 15. _Lycopodites_ + " 16. _Stigmaria ficoides_ + " 17. Section of _Stigmaria_ + " 18. Sigillarian trunks in sandstone + " 19. _Productus_ + " 20. _Encrinite_ + " 21. Encrinital limestone + " 22. Various _encrinites_ + " 23. _Cyathophyllum_ + " 24. _Archegosaurus minor_ + " 25. _Psammodus porosus_ + " 26. _Orthoceras_ + " 27. _Fenestella retepora_ + " 28. _Goniatites_ + " 29. _Aviculopecten papyraceus_ + " 30. Fragment of _Lepidodendron_ + " 31. Engine-house at head of a Coal-Pit + " 32. Gas Jet and Davy Lamp + " 33. Part of a Sigillarian trunk + " 34. Inside a Gas-holder + " 35. Filling Retorts by Machinery + " 36. "Condensers" + " 37. "Washers" + " 38. "Purifiers" + + + + +CHAPTER I. + +THE ORIGIN OF COAL AND THE PLANTS OF +WHICH IT IS COMPOSED. + + +From the homely scuttle of coal at the side of the hearth to the +gorgeously verdant vegetation of a forest of mammoth trees, might have +appeared a somewhat far cry in the eyes of those who lived some fifty +years ago. But there are few now who do not know what was the origin of +the coal which they use so freely, and which in obedience to their demand +has been brought up more than a thousand feet from the bowels of the +earth; and, although familiarity has in a sense bred contempt for that +which a few shillings will always purchase, in all probability a stray +thought does occasionally cross one's mind, giving birth to feelings of a +more or less thankful nature that such a store of heat and light was long +ago laid up in this earth of ours for our use, when as yet man was not +destined to put in an appearance for many, many ages to come. We can +scarcely imagine the industrial condition of our country in the absence +of so fortunate a supply of coal; and the many good things which are +obtained from it, and the uses to which, as we shall see, it can be put, +do indeed demand recognition. + +Were our present forests uprooted and overthrown, to be covered by +sedimentary deposits such as those which cover our coal-seams, the amount +of coal which would be thereby formed for use in some future age, would +amount to a thickness of perhaps two or three inches at most, and yet, in +one coal-field alone, that of Westphalia, the 117 most important seams, +if placed one above the other in immediate succession, would amount to no +less than 294 feet of coal. From this it is possible to form a faint idea +of the enormous growths of vegetation required to form some of our +representative coal beds. But the coal is not found in one continuous +bed. These numerous seams of coal are interspersed between many thousands +of feet of sedimentary deposits, the whole of which form the +"coal-measures." Now, each of these seams represents the growth of a +forest, and to explain the whole series it is necessary to suppose that +between each deposit the land became overwhelmed by the waters of the sea +or lake, and after a long subaqueous period, was again raised into dry +land, ready to become the birth-place of another forest, which would +again beget, under similarly repeated conditions, another seam of coal. +Of the conditions necessary to bring these changes about we will speak +later on, but this instance is sufficient to show how inadequate the +quantity of fuel would be, were we dependent entirely on our own existing +forest growths. + +However, we will leave for the present the fascinating pursuit of +theorising as to the how and wherefore of these vast beds of coal, +relegating the geological part of the study of the carboniferous system +to a future chapter, where will be found some more detailed account of +the position of the coal-seams in the strata which contain them. At +present the actual details of the coal itself will demand our attention. + +Coal is the mineral which has resulted, after the lapse of thousands of +thousands of years, from the accumulations of vegetable material, caused +by the steady yearly shedding of leaves, fronds and spores, from forests +which existed in an early age; these accumulated where the trees grew +that bore them, and formed in the first place, perhaps, beds of peat; the +beds have since been subjected to an ever-increasing pressure of +accumulating strata above them, compressing the sheddings of a whole +forest into a thickness in some cases of a few inches of coal, and have +been acted upon by the internal heat of the earth, which has caused them +to part, to a varying degree, with some of their component gases. If we +reason from analogy, we are compelled to admit that the origin of coal is +due to the accumulation of vegetation, of which more scattered, but more +distinct, representative specimens occur in the shales and clays above +and below the coal-seams. But we are also able to examine the texture +itself of the various coals by submitting extremely thin slices to a +strong light under the microscope, and are thus enabled to decide whether +the particular coal we are examining is formed of conifers, horse-tails, +club-mosses, or ferns, or whether it consists simply of the accumulated +sheddings of all, or perhaps, as in some instances, of innumerable +spores. + +In this way the structure of coal can be accurately determined. Were we +artificially to prepare a mass of vegetable substance, and covering it up +entirely, subject it to great pressure, so that but little of the +volatile gases which would be formed could escape, we might in the course +of time produce something approaching coal, but whether we obtained +lignite, jet, common bituminous coal, or anthracite, would depend upon +the possibilities of escape for the gases contained in the mass. + +Everybody has doubtless noticed that, when a stagnant pool which contains +a good deal of decaying vegetation is stirred, bubbles of gas rise to the +surface from the mud below. This gas is known as marsh-gas, or light +carburetted hydrogen, and gives rise to the _ignis fatuus_ which hovers +about marshy land, and which is said to lure the weary traveller to his +doom. The vegetable mud is here undergoing rapid decomposition, as there +is nothing to stay its progress, and no superposed load of strata +confining its resulting products within itself. The gases therefore +escape, and the breaking-up of the tissues of the vegetation goes on +rapidly. + +The chemical changes which have taken place in the beds of vegetation of +the carboniferous epoch, and which have transformed it into coal, are +even now but imperfectly understood. All we know is that, under certain +circumstances, one kind of coal is formed, whilst under other conditions, +other kinds have resulted; whilst in some cases the processes have +resulted in the preparation of large quantities of mineral oils, such as +naphtha and petroleum. Oils are also artificially produced from the +so-called waste-products of the gas-works, but in some parts of the world +the process of their manufacture has gone on naturally, and a yearly +increasing quantity is being utilised. In England oil has been pumped up +from the carboniferous strata of Coalbrook Dale, whilst in Sussex it has +been found in smaller quantities, where, in all probability, it has had +its origin in the lignitic beds of the Wealden strata. Immense quantities +are used for fuel by the Russian steamers on the Caspian Sea, the Baku +petroleum wells being a most valuable possession. In Sicily, Persia, and, +far more important, in the United States, mineral oils are found in great +quantity. + +In all probability coniferous trees, similar to the living firs, pines, +larches, &c., gave rise for the most part to the mineral oils. The class +of living _coniferae_ is well known for the various oils which it +furnishes naturally, and for others which its representatives yield on +being subjected to distillation. The gradually increasing amount of heat +which we meet the deeper we go beneath the surface, has been the cause of +a slow and continuous distillation, whilst the oil so distilled has found +its way to the surface in the shape of mineral-oil springs, or has +accumulated in troughs in the strata, ready for use, to be drawn up when +a well has been sunk into it. + +The plants which have gone to make up the coal are not at once apparent +to the naked eye. We have to search among the shales and clays and +sandstones which enclose the coal-seams, and in these we find petrified +specimens which enable us to build up in our mind pictures of the +vegetable creation which formed the jungles and forests of these +immensely remote ages, and which, densely packed together on the old +forest floor of those days, is now apparent to us as coal. + +[Illustration: Fig. 2.--_Annularia radiata._ Carboniferous sandstone.] + +A very large proportion of the plants which have been found in the +coal-bearing strata consists of numerous species of ferns, the number of +actual species which have been preserved for us in our English coal, +being double the number now existing in Europe. The greater part of these +do not seem to have been very much larger than our own living ferns, and, +indeed, many of them bear a close resemblance to some of our own living +species. The impressions they have left on the shales of the +coal-measures are most striking, and point to a time when the sandy clay +which imbedded them was borne by water in a very tranquil manner, to be +deposited where the ferns had grown, enveloping them gradually, and +consolidating them into their mass of future shale. In one species known +as the _neuropteris_, the nerves of the leaves are as clear and as +apparent as in a newly-grown fern, the name being derived from two Greek +words meaning "nerve-fern." It is interesting to consider the history of +such a leaf, throughout the ages that have elapsed since it was part of a +living fern. First it grew up as a new frond, then gradually unfolded +itself, and developed into the perfect fern. Then it became cut off by +the rising waters, and buried beneath an accumulation of sediment, and +while momentous changes have gone on in connection with the surface of +the earth, it has lain dormant in its hiding-place exactly as we see it, +until now excavated, with its contemporaneous vegetation, to form fuel +for our winter fires. + +[Illustration: FIG. 3.--_Rhacopteris inaequilatera._ Carboniferous +limestone.] + +Although many of the ferns greatly resembled existing species, yet there +were others in these ancient days utterly unlike anything indigenous to +England now. There were undoubted tree-ferns, similar to those which +thrive now so luxuriously in the tropics, and which throw out their +graceful crowns of ferns at the head of a naked stem, whilst on the bark +are the marks at different levels of the points of attachment of former +leaves. These have left in their places cicatrices or scars, showing the +places from which they formerly grew. Amongst the tree-ferns found are +_megaphyton_, _paloeopteris_, and _caulopteris_, all of which have these +marks upon them, thus proving that at one time even tree-ferns had a +habitat in England. + +[Illustration: Fig. 4.--Frond of _Pecopteris._ Coal-shale.] + +One form of tree-fern is known by the name of _Psaronius_, and this was +peculiar in the possession of masses of aerial roots grouped round the +stem. Some of the smaller species exhibit forms of leaves which are +utterly unknown in the nomenclature of living ferns. Most have had names +assigned to them in accordance with certain characteristics which they +possess. This was the more possible since the fossilised impressions had +been retained in so distinct a manner. Here before us is a specimen in a +shale of _pecopteris_, as it is called, (_pekos_, a comb). The leaf in +some species is not altogether unlike the well-known living fern +_osmunda_. The position of the pinnules on both sides of the central +stalk are seen in the fossil to be shaped something like a comb, or a +saw, whilst up the centre of each pinnule the vein is as prominent and +noticeable as if the fern were but yesterday waving gracefully in the +air, and but to-day imbedded in its shaly bed. + +[Illustration: FIG. 5.--_Pecopteris Serlii_. Coal-shale.] + +_Sphenopteris_, or "wedge-fern," is the name applied to another +coal-fern; _glossopteris_, or "tongue-leaf"; _cyclopteris_, or +"round-leaf"; _odonlopteris,_ or "tooth-leaf," and many others, show +their chief characteristics in the names which they individually bear. +_Alethopteris_ appears to have been the common brake of the coal-period, +and in some respects resembles _pecopteris_. + +[Illustration: Fig. 6.--_Sphenopteris Affinis._ Coal-shale.] + +In some species of ferns so exact are the representations which they have +impressed on the shale which contains them, that not only are the veins +and nerves distinctly visible, but even the fructification still remains +in the shape of the marks left by the so-called seeds on the backs of the +leaves. Something more than a passing look at the coal specimens in a +good museum will well repay the time so spent. + +What are known as septarian nodules, or snake-stones, are, at certain +places, common in the carboniferous strata. They are composed of layers +of ironstone and sandstone which have segregated around some central +object, such as a fern-leaf or a shell. When the leaf of a fern has been +found to be the central object, it has been noticed that the leaf can +sometimes be separated from the stone in the form of a carbonaceous film. + +Experiments were made many years ago by M. Goppert to illustrate the +process of fossilisation of ferns. Having placed some living ferns in a +mass of clay and dried them, he exposed them to a red heat, and obtained +thereby striking resemblances to fossil plants. According to the degree +of heat to which they were subjected, the plants were found to be either +brown, a shining black, or entirely lost. In the last mentioned case, +only the impression remained, but the carbonaceous matter had gone to +stain the surrounding clay black, thus indicating that the dark colour of +the coal-shales is due to the carbon derived from the plants which they +included. + +Another very prominent member of the vegetation of the coal period, was +that order of plants known as the _Calamites_. The generic distinctions +between fossil and living ferns were so slight in many cases as to be +almost indistinguishable. This resemblance between the ancient and the +modern is not found so apparent in other plants. The Calamites of the +coal-measures bore indeed a very striking resemblance, and were closely +related, to our modern horse-tails, as the _equiseta_ are popularly +called; but in some respects they differed considerably. + +Most people are acquainted with the horse-tail (_equisetum fluviatile)_ +of our marshes and ditches. It is a somewhat graceful plant, and stands +erect with a jointed stem. The foliage is arranged in whorls around the +joints, and, unlike its fossil representatives, its joints are protected +by striated sheaths. The stem of the largest living species rarely +exceeds half-an-inch in diameter, whilst that of the calamite attained a +thickness of five inches. But the great point which is noticeable in the +fossil calamites and _equisetites_ is that they grew to a far greater +height than any similar plant now living, sometimes being as much as +eight feet high. In the nature of their stems, too, they exhibited a more +highly organised arrangement than their living representatives, having, +according to Dr Williamson, a "fistular pith, an exogenous woody stem, +and a thick smooth bark." The bark having almost al ways disappeared has +left the fluted stem known to us as the calamite. The foliage consisted +of whorls of long narrow leaves, which differed only from the fern +_asterophyllites_ in the fact that they were single-nerved. Sir William +Dawson assigns the calamites to four sub-types: _calamite_ proper, +_calamopitus, calamodendron_, and _eucalamodendron_. + +[Image: FIG. 7.--Root of _Catamites Suckowii_. Coal-shale.] + +[Image: FIG 8.--_Calamocladus grandis_. Carboniferous sandstone.] + +Having used the word "exogenous," it might be as well to pay a little +attention, in passing, to the nomenclature and broad classification of +the various kinds of plants. We shall then doubtless find it far easier +thoroughly to understand the position in the scale of organisation to +which the coal plants are referable. + +[Illustration: FIG. 9.--_Asterophyllites foliosa_. Coal-measures.] + +The plants which are lowest in organisation are known as _Cellular_. They +are almost entirely composed of numerous cells built up one above the +other, and possess none of the higher forms of tissue and organisation +which are met with elsewhere. This division includes the lichens, +sea-weeds, confervae (green aquatic scum), fungi (mushrooms, dry-rot), +&c. + +The division of _Vascular_ plants includes the far larger proportion of +vegetation, both living and fossil, and these plants are built up of +vessels and tissues of various shapes and character. + +All plants are divided into (1) Cryptogams, or Flowerless, such as +mosses, ferns, equisetums, and (2) Phanerogams, or Flowering. Flowering +plants are again divided into those with naked seeds, as the conifers and +cycads (gymnosperms), and those whose seeds are enclosed in vessels, or +ovaries (angiosperms). + +Angiosperms are again divided into the monocotyledons, as the palms, and +dicotyledons, which include most European trees. + +Thus:-- + +------------------------------------------------------------------- +| (M.A. Brongniart). | |(Lindley). | +|CELLULAR | | | +| _Cryptogams_ (Flowerless) |Fungi, seaweeds, |Thallogens | +| | lichens | | +| | | | +|VASCULAR | | | +| _Cryptogams_ (Flowerless) |Ferns, equisetums, |Acrogens | +| | mosses, lycopodiums| | +| _Phanerogams_ (Flowering) | | | +| Gymnosperms (having |Conifers and |Gymnogens | +| naked seeds) | cycads | | +| Two or more Cotyledons | | | +| Angiosperms (having | | | +| enclosed seeds) | | | +| Monocotyledons |Palms, lilies, |Endogens | +| | grasses | | +| Dicotyledons |Most European |Exogens | +| | trees and shrubs | | +------------------------------------------------------------------- + +Adolphe Brongniart termed the coal era the "Age of Acrogens," because, as +we shall see, of the great predominance in those times of vascular +cryptogamic plants, known in Dr Lindley's nomenclature as "Acrogens." + +[Illustration: FIG. 10.--_Spenophyllum cuneifolium._ Coal-shale.] + +Two of these families have already been dealt with, viz., the ferns +(_felices_), and the equisetums, (_calamites_ and _equisetites_), and we +now have to pass on to another family. This is that which includes the +fossil representatives of the Lycopodiums, or Club-mosses, and which goes +to make up in some coals as much as two-thirds of the whole mass. +Everyone is more or less familiar with some of the living Lycopodiums, +those delicate little fern-like mosses which are to be found in many a +home. They are but lowly members of our British flora, and it may seem +somewhat astounding at first sight that their remote ancestors occupied +so important a position in the forests of the ancient period of which we +are speaking. Some two hundred living species are known, most of them +being confined to tropical climates. They are as a rule, low creeping +plants, although some few stand erect. There is room for astonishment +when we consider the fact that the fossil representatives of the family, +known as _Lepidodendra_, attained a height of no less than fifty feet, +and, there is good ground for believing, in many cases, a far greater +magnitude. They consist of long straight stems, or trunks which branch +considerably near the top. These stems are covered with scars or scales, +which have been caused by the separation of the petioles or leaf-stalks, +and this gives rise to the name which the genus bears. The scars are +arranged in a spiral manner the whole of the way up the stem, and the +stems often remain perfectly upright in the coal-mines, and reach into +the strata which have accumulated above the coal-seam. + +[Illustration: FIG. 11.--Cast of _lepidodendron_ in sandstone.] + +Count Sternberg remarked that we are unacquainted with any existing +species of plant, which like the _Lepidodendron_, preserves at all ages, +and throughout the whole extent of the trunk, the scars formed by the +attachment of the petioles, or leaf-stalks, or the markings of the leaves +themselves. The yucca, dracaena, and palm, entirely shed their scales +when they are dried up, and there only remain circles, or rings, arranged +round the trunk in different directions. The flabelliform palms preserve +their scales at the inferior extremity of the trunk only, but lose them +as they increase in age; and the stem is entirely bare, from the middle +to the superior extremity. In the ancient _Lepidodendron_, on the other +hand, the more ancient the scale of the leaf-stalk, the more apparent it +still remains. Portions of stems have been discovered which contain +leaf-scars far larger than those referred to above, and we deduce from +these fragments the fact that those individuals which have been found +whole, are not by any means the largest of those which went to form so +large a proportion of the ancient coal-forests. The _lepidodendra_ bore +linear one-nerved leaves, and the stems always branched dichotomously and +possessed a central pith. Specimens variously named _knorria, +lepidophloios, halonia_, and _ulodendron_ are all referable to this +family. + +[Illustration: FIG. 12.--_Lepidodendron longifolium._ Coal-shale.] + +[Illustration: FIG. 13.--_Lepidodendron aculeatum_ in sandstone.] + +In some strata, as for instance that of the Shropshire coalfield, +quantities of elongated cylindrical bodies known as _lepidostrobi_ have +been found, which, it was early conjectured, were the fruit of the giant +club-mosses about which we have just been speaking. Their appearance can +be called to mind by imagining the cylindrical fruit of the maize or +Indian corn to be reduced to some three or four inches in length. The +sporangia or cases which contained the microscopic spores or seeds were +arranged around a central axis in a somewhat similar manner to that in +which maize is found. These bodies have since been found actually +situated at the end of branches of _lepidodendron_, thus placing their +true nature beyond a doubt. The fossil seeds (spores) do not appear to +have exceeded in volume those of recent club-mosses, and this although +the actual trees themselves grew to a size very many times greater than +the living species. This minuteness of the seed-germs goes to explain the +reason why, as Sir Charles Lyell remarked, the same species of +_lepidodendra_ are so widely distributed in the coal measures of Europe +and America, their spores being capable of an easy transportation by the +wind. + +[Illustration: FIG. 14.--_Lepidostrobus._ Coal-shale.] + +One striking feature in connection with the fruit of the _lepidodendron_ +and other ancient representatives of the club-moss tribe, is that the +bituminous coals in many, if not in most, instances, are made up almost +entirely of their spores and spore-cases. Under a microscope, a piece of +such coal is seen to be thronged with the minute rounded bodies of the +spores interlacing one another and forming almost the whole mass, whilst +larger than these, and often indeed enclosing them, are flattened +bag-like bodies which are none other than the compressed sporangia which +contained the former. + +[Illustration: FIG. 15.--_Lycopodites_. Coal sandstone.] + +Now, the little Scottish or Alpine club-moss which is so familiar, +produces its own little cones, each with its series of outside scales or +leaves; these are attached to the bags or spore-cases, which are crowded +with spores. Although in miniature, yet it produces its fruit in just the +same way, at the terminations of its little branches, and the spores, the +actual germs of life, when examined microscopically, are scarcely +distinguishable from those which are contained in certain bituminous +coals. And, although ancient club-mosses have been found in a fossilised +condition at least forty-nine feet high, the spores are no larger than +those of our miniature club-mosses of the present day. + +The spores are more or less composed of pure bitumen, and the bituminous +nature of the coal depends largely on the presence or absence of these +microscopic bodies in it. The spores of the living club-mosses contain so +much resinous matter that they are now largely used in the making of +fireworks, and upon the presence of this altered resinous matter in coal +depends its capability of providing a good blazing coal. + +At first sight it seems almost impossible that such a minute cause should +result in the formation of huge masses of coal, such an inconceivable +number of spores being necessary to make even the smallest fragment of +coal. But if we look at the cloud of spores that can be shaken from a +single spike of a club-moss, then imagine this to be repeated a thousand +times from each branch of a fairly tall tree, and then finally picture a +whole forest of such trees shedding in due season their copious showers +of spores to earth, we shall perhaps be less amazed than we were at first +thought, at the stupendous result wrought out by so minute an object. + +Another well-known form of carboniferous vegetation is that known as the +_Sigillaria_, and, connected with this form is one, which was long +familiar under the name of _Stigmaria_, but which has since been +satisfactorily proved to have formed the branching root of the +sigillaria. The older geologists were in the habit of placing these +plants among the tree-ferns, principally on account of the cicatrices +which were left at the junctions of the leaf-stalks with the stem, after +the former had fallen off. No foliage had, however, been met with which +was actually attached to the plants, and hence, when it was discovered +that some of them had long attenuated leaves not at all like those +possessed by ferns, geologists were compelled to abandon this +classification of them, and even now no satisfactory reference to +existing orders of them has been made, owing to their anomalous +structure. The stems are fluted from base to stem, although this is not +so apparent near the base, whilst the raised prominences which now form +the cicatrices, are arranged at regular distances within the vertical +grooves. + +When they have remained standing for some length of time, and the strata +have been allowed quietly to accumulate around the trunks, they have +escaped compression. They were evidently, to a great extent, hollow like +a reed, so that in those trees which still remain vertical, the interior +has become filled up by a coat of sandstone, whilst the bark has become +transformed into an envelope of an inch, or half an inch of coal. But +many are found lying in the strata in a horizontal plane. These have been +cast down and covered up by an ever-increasing load of strata, so that +the weight has, in the course of time, compressed the tree into simply +the thickness of the double bark, that is, of the two opposite sides of +the envelope which covered it when living. + +_Sigillarae_ grew to a very great height without branching, some +specimens having measured from 60 to 70 feet long. In accordance with +their outside markings, certain types are known as _syringodendron_, +_favularia_, and _clathraria_. _Diploxylon_ is a term applied to an +interior stem referable to this family. + +[Illustration: FIG. 16.--_Stigmaria ficoides_. Coal-shale.] + +But the most interesting point about the _sigillariae_ is the root. This +was for a long time regarded as an entirely distinct individual, and the +older geologists explained it in their writings as a species of succulent +aquatic plant, giving it the name of _stigmaria_. They realized the fact +that it was almost universally found in those beds which occur +immediately beneath the coal seams, but for a long time it did not strike +them that it might possibly be the root of a tree. In an old edition of +Lyell's "Elements of Geology," utterly unlike existing editions in +quality, quantity, or comprehensiveness, after describing it as an +extinct species of water-plant, the author hazarded the conjecture that +it might ultimately be found to have a connection with some other +well-known plant or tree. It was noticed that above the coal, in the +roof, stigmariae were absent, and that the stems of trees which occurred +there, had become flattened by the weight of the overlying strata. The +stigmariae on the other hand, abounded in the _underclay_, as it is +called, and were not in any way compressed but retained what appeared to +be their natural shape and position. Hence to explain their appearance, +it was thought that they were water-plants, ramifying the mud in every +direction, and finally becoming overwhelmed and covered by the mud +itself. On botanical grounds, Brongniart and Lyell conjectured that they +formed the roots of other trees, and this became the more apparent as it +came to be acknowledged that the underclays were really ancient soils. +All doubt was, however, finally dispelled by the discovery by Mr Binney, +of a sigillaria and a stigmaria in actual connection with each other, in +the Lancashire coal-field. + +Stigmariae have since been found in the Cape Breton coal-field, attached +to Lepidodendra, about which we have already spoken, and a similar +discovery has since been made in the British coal-fields. This, +therefore, would seem to shew the affinity of the sigillaria to the +lepidodendron, and through it to the living lycopods, or +club-mosses. + +Some few species of stigmarian roots had been discovered, and various +specific names had been given to them before their actual nature was made +out. What for some time were thought to be long cylindrical leaves, have +now been found to be simply rootlets, and in specimens where these have +been removed, the surface of the stigmaria has been noticed to be covered +with large numbers of protuberant tubercles, which have formed the bases +of the rootlets. There appears to have also been some special kind of +arrangement in their growth, since, unlike the roots of most living +plants, the tubercles to which these rootlets were attached, were +arranged spirally around the main root. Each of these tubercles was +pitted in the centre, and into these the almost pointed ends of the +rootlets fitted, as by a ball and socket joint. + +[Illustration: FIG. 17--_Section of stigmaria_.] + +"A single trunk of _sigillaria_ in an erect forest presents an epitome of +a coal-seam. Its roots represent the _stigmaria_ underclay; its bark the +compact coal; its woody axis, the mineral charcoal; its fallen leaves and +fruits, with remains of herbaceous plants growing in its shade, mixed +with a little earthy matter, the layers of coarse coal. The condition of +the durable outer bark of erect trees, concurs with the chemical theory +of coal, in showing the especial suitableness of this kind of tissue for +the production of the purer compact coals."--(Dawson, "Structures in +Coal.") + +There is yet one other family of plants which must be mentioned, and +which forms a very important portion of the constituent _flora_ of the +coal period. This is the great family of the _coniferae_, which although +differing in many respects from the highly organised dicotyledons of the +present day, yet resembled them in some respects, especially in the +formation of an annual ring of woody growth. + +The conifers are those trees which, as the name would imply, bear their +fruit in the form of cones, such as the fir, larch, cedar, and others. +The order is one which is familiar to all, not only on account of the +cones they bear, and their sheddings, which in the autumn strew the +ground with a soft carpet of long needle-like leaves, but also because of +the gum-like secretion of resin which is contained in their tissues. Only +a few species have been found in the coal-beds, and these, on examination +under the microscope, have been discovered to be closely related to the +araucarian division of pines, rather than to any of our common firs. The +living species of this tree is a native of Norfolk Island, in the +Pacific, and here it attains a height of 200 feet, with a girth of 30 +feet. From the peculiar arrangement of the ducts in the elongated +cellular tissue of the tree, as seen under the microscope, the fossil +conifers, which exhibit this structure, have been placed in the same +division. + +The familiar fossil known to geologists as _Sternbergia_ has now been +shown to be the cast of the central pith of these conifers, amongst which +may be mentioned _cordaites, araucarites_, and _dadoxylon._. The central +cores had become replaced with inorganic matter after the pith had shrunk +and left the space empty. This shrinkage of the pith is a process which +takes place in many plants even when living, and instances will at once +occur, in which the stems of various species of shrubs when broken open +exhibit the remains of the shrunken pith, in the shape of thin discs +across the interval cavity. + +We might reasonably expect that where we find the remains of fossil +coniferous trees, we should also meet with the cones or fruit which they +bear. And such is the case. In some coal-districts fossil fruits, named +_cardiocarpum_ and _trigonocarpum_, have been found in great quantities, +and these have now been decided by botanists to be the fruits of certain +conifers, allied, not to those which bear hard cones, but to those which +bear solitary fleshy fruits. Sir Charles Lyell referred them to a Chinese +genus of the yew tribe called _salisburia_. Dawson states that they are +very similar to both _taxus_ and _salisburia._. They are abundant in some +coal-measures, and are contained, not only in the coal itself, but also +in the sandstones and shales. The under-clays appear to be devoid of +them, and this is, of course, exactly what might have been expected, +since the seeds would remain upon the soil until covered up by vegetable +matter, but would never form part of the clay soil itself. + +In connection with the varieties which have been distinguished in the +families of the conifers, calamites, and sigillariae, Sir William Dawson +makes the following observations: "I believe that there was a +considerably wide range of organisation in _cordaitinae_ as well as in +_calamites_ and _sigillariae_, and that it will eventually be found that +there were three lines of connection between the higher cryptogams +(flowerless) and the phaenogams (flowering), one leading from the +lycopodes by the _sigillariae_, another leading by the _cordaites_, and +the third leading from the _equisetums_ by the _calamites_. Still further +back the characters, afterwards separated in the club-mosses, +mare's-tails, and ferns, were united in the _rhizocarps_, or, as some +prefer to call them, the heterosporous _filicinae_." + +In concluding this chapter dealing with the various kinds of plants which +have been discovered as contributing to the formation of +coal-measures, it would be as well to say a word or two concerning the +climate which must have been necessary to permit of the growth of such an +abundance of vegetation. It is at once admitted by all botanists that a +moist, humid, and warm atmosphere was necessary to account for the +existence of such an abundance of ferns. The gorgeous waving +tree-ferns which were doubtless an important feature of the landscape, +would have required a moist heat such as does not now exist in this +country, although not necessarily a tropical heat. The magnificent giant +lycopodiums cast into the shade all our living members of that class, the +largest of which perhaps are those that flourish in New Zealand. In New +Zealand, too, are found many species of ferns, both those which are +arborescent and those which are of more humble stature. Add to these the +numerous conifers which are there found, and we shall find that a forest +in that country may represent to a certain extent the appearance +presented by a forest of carboniferous vegetation. The ferns, lycopods, +and pines, however, which appear there, it is but fair to add, are mixed +with other types allied to more recent forms of vegetation. + +There are many reasons for believing that the amount of carbonic acid gas +then existing in the atmosphere was larger than the quantity which we now +find, and Professor Tyndall has shown that the effect of this would be to +prevent radiation of heat from the earth. The resulting forms of +vegetation would be such as would be comparable with those which are now +reared in the green-house or conservatory in these latitudes. The gas +would, in fact, act as a glass roof, extending over the whole world. + + + + +CHAPTER II. + +A GENERAL VIEW OF THE COAL-BEARING STRATA. + + +In considering the source whence coal is derived, we must be careful to +remember that coal itself is but a minor portion of the whole formation +in which it occurs. The presence of coal has indeed given the name to the +formation, the word "carboniferous" meaning "coal-bearing," but in taking +a comprehensive view of the position which it occupies in the bowels of +the earth, it will be necessary to take into consideration the strata in +which it is found, and the conditions, so far as are known, under which +these were deposited. + +Geologically speaking, the Carboniferous formation occurs near the close +of that group of systems which have been classed as "palaeozoic," younger +in point of age than the well known Devonian and Old Red Sandstone +strata, but older by far than the Oolites, the Wealden, or the Cretaceous +strata. + +In South Wales the coal-bearing strata have been estimated at between +11,000 and 12,000 feet, yet amongst this enormous thickness of strata, +the whole of the various coal-seams, if taken together, probably does not +amount to more than 120 feet. This great disproportion between the total +thickness and the thickness of coal itself shows itself in every +coal-field that has been worked, and when a single seam of coal is +discovered attaining a thickness of 9 or 10 feet, it is so unusual a +thing in Great Britain as to cause it to be known as the "nine" or +"ten-foot seam," as the case may be. Although abroad many seams are found +which are of greater thicknesses, yet similarly the other portions of the +formation are proportionately greater. + +It is not possible therefore to realise completely the significance of +the coal-beds themselves unless there is also a knowledge of the +remaining constituents of the whole formation. The strata found in the +various coal-fields differ considerably amongst themselves in character. +There are, however, certain well-defined characteristics which find +representation in most of the principal coal-fields, whether British or +European. Professor Hull classifies these carboniferous beds as +follows:-- + + UPPER CARBONIFEROUS. + _Upper coal-measures._ + Reddish and purple sandstones, red and grey clays and shales, + thin bands of coal, ironstone and limestone, with _spirorbis_ + and fish. + + _Middle coal-measures._ + Yellow and gray sandstones, blue and black clays and shales, + bands of coal and ironstone, fossil plants, bivalves + and fish, occasional marine bands. + + MIDDLE CARBONIFEROUS. + _Gannister beds_ or _Lower coal-measures._ + _Millstone grit._ Flagstone series in Ireland. + _Yoredale beds._ Upper shale series of Ireland. + + LOWER CARBONIFEROUS. + _Mountain limestone_. + _Limestone shale_. + +Each of the three principal divisions has its representative in Scotland, +Belgium, and Ireland, but, unfortunately for the last-named country, the +whole of the upper coal-measures are there absent. It is from these +measures that almost all our commercial coals are obtained. + +This list of beds might be further curtailed for all practical purposes +of the geologist, and the three great divisions of the system would thus +stand:-- + + Upper Carboniferous, or Coal-measures proper. + + Millstone grit. + + Lower Carboniferous, or Mountain limestone. + +In short, the formation consists of masses of sandstone, shale, limestone +and coal, these also enclosing clays and ironstones, and, in the +limestone, marbles and veins of the ores of lead, zinc, and antimony, and +occasionally silver. + +[Illustration: FIG. 18.--Sigillarian trunks in current-bedded sandstone. +St Etienne.] + +As the most apparent of the rocks of the system are sandstone, shale, +limestone, and coal, it will be necessary to consider how these were +deposited in the waters of the carboniferous ages, and this we can best +do by considering the laws under which strata of a similar nature are now +being deposited as sedimentary beds. + +A great proportion consists of sandstone. Now sandstone is the result of +sand which has been deposited in large quantities, having become +indurated or hardened by various processes brought to bear upon it. It is +necessary, therefore, first to ascertain whence came the sand, and +whether there are any peculiarities in its method of deposition which +will explain its stratification. It will be noticed at once that it bears +a considerable amount of evidence of what is called "current-bedding," +that is to say, that the strata, instead of being regularly deposited, +exhibit series of wedge-shaped masses, which are constantly thinning out. + +Sand and quartz are of the same chemical composition, and in all +probability the sand of which every sandstone in existence is composed, +appeared on this earth in its first solid form in the shape of quartz. +Now quartz is a comparatively heavy mineral, so also, therefore, will +sand be. It is also very hard, and in these two respects it differs +entirely from another product of sedimentary deposition, namely, mud or +clay, with which we shall have presently to deal when coming to the +shales. Since quartz is a hard mineral it necessarily follows that it +will suffer, without being greatly affected, a far greater amount of +wearing and knocking about when being transported by the agency of +currents and rivers, than will a softer substance, such as clay. An equal +amount of this wearing action upon clay will reduce it to a fine +impalpable silt. The grains of sand, however, will still remain of an +appreciable average size, and where both sand and clay are being +transported to the sea in one and the same stream, the clay will be +transported to long distances, whilst the sand, being heavier, bulk for +bulk, and also consisting of grains larger in size than grains of clay, +will be rapidly deposited, and form beds of sand. Of course, if the +current be a violent one, the sand is transported, not by being held in +suspension, but rather by being pushed along the bed of the river; such +an action will then tend to cause the sand to become powdered into still +finer sand. + +When a river enters the sea it soon loses its individuality; it becomes +merged in the body of the ocean, where it loses its current, and where +therefore it has no power to keep in suspension the sediment which it had +brought down from the higher lands. When this is the case, the sand borne +in suspension is the first to be deposited, and this accumulates in banks +near the entrance of the river into the sea. We will suppose, for +illustration, that a small river has become charged with a supply of +sand. As it gradually approaches the sea, and the current loses its +force, the sand is the more sluggishly carried along, until finally it +falls to the bottom, and forms a layer of sand there. This layer +increases in thickness until it causes the depth of water above it to +become comparatively shallow. On the shallowing process taking place, the +current will still have a certain, though slighter, hold on the sand in +suspension, and will transport it yet a little further seaward, when it +will be thrown down, at the edge of the bank or layer already formed, +thus tending to extend the bank, and to shallow a wider space of +river-bed. + +As a result of this action, strata would be formed, shewing +stratification diagonally as well as horizontally, represented in section +as a number of banks which had seemingly been thrown down one above the +other, ending in thin wedge-shaped terminations where the particular +supply of sediment to which each owed its formation had failed. + +The masses of sandstone which are found in the carboniferous formation, +exhibit in a large degree these wedge-shaped strata, and we have +therefore a clue at once, both as to their propinquity to sea and land, +and also as to the manner in which they were formed. + +[Illustration: FIG. 19.--_Productus_. Coal-measures.] + +There is one thing more, too, about them. Just as, in the case we were +considering, we could observe that the wedge-shaped strata always pointed +away from the source of the material which formed them, so we can +similarly judge that in the carboniferous strata the same deduction holds +good, that the diagonally-pointing strata were formed in the same way, +and that their thinning out was simply owing to temporary failure of +sediment, made good, however, by a further deposition of strata when the +next supply was borne down. + +It is scarcely likely, however, that sand in a pure state was always +carried down by the currents to the sea. Sometimes there would be some +silt mixed with it. Just as in many parts large masses of almost pure +sandstone have been formed, so in other places shales, or, as they are +popularly known by miners, "bind," have been formed. Shales are formed +from the clays which have been carried down by the rivers in the shape of +silt, but which have since become hardened, and now split up easily into +thin parallel layers. The reader has no doubt often handled a piece of +hard clay when fresh from the quarry, and has remembered how that, when +he has been breaking it up, in order, perhaps, to excavate a +partially-hidden fossil, it has readily split up in thin flakes or layers +of shaly substance. This exhibits, on a small scale, the chief +peculiarity of the coal shales. + +The formation of shales will now demand our attention. When a river is +carrying down with it a quantity of mud or clay, it is transported as a +fine, dusty silt, and when present in quantities, gives the muddy tint to +the water which is so noticeable. We can very well see how that silt will +be carried down in greater quantities than sand, since nearly all rivers +in some part of their course will travel through a clayey district, and +finely-divided clay, being of a very light nature, will be carried +forward whenever a river passes over such a district. And a very slight +current being sufficient to carry it in a state of suspension, it follows +that it will have little opportunity of falling to the bottom, until, by +some means or other, the current, which is the means of its conveyance, +becomes stopped or hindered considerably in its flow. + +When the river enters a large body of water, such as the ocean or a lake, +in losing its individuality, it loses also the velocity of its current, +and the silt tends to sink down to the bottom. But being less heavy than +the sand, about which we have previously spoken, it does not sink all at +once, but partly with the impetus it has gained, and partly on account of +the very slight velocity which the current still retains, even after +having entered the sea, it will be carried out some distance, and will +the more gradually sink to the bottom. The deeper the water in which it +falls the greater the possibility of its drifting farther still, since in +sinking, it would fall, not vertically, but rather as the drops of rain +in a shower when being driven before a gale of wind. Thus we should +notice that clays and shales would exhibit a regularity and uniformity of +deposition over a wide area. Currents and tides in the sea or lake would +tend still further to retard deposition, whilst any stoppages in the +supply of silt which took place would give the former layer time to +consolidate and harden, and this would assist in giving it that bedded +structure which is so noticeable in the shales, and which causes it to +split up into fine laminae. This uniformity of structure in the shales +over wide areas is a well ascertained characteristic of the coal-shales, +and we may therefore regard the method of their deposition as given here +with a degree of certainty. + +There is a class of deposit found among the coal-beds, which is known as +the "underclay," and this is the most regular of all as to the position +in which it is found. The underclays are found beneath every bed of coal. +"Warrant," "spavin," and "gannister" are local names which are sometimes +applied to it, the last being a term used when the clay contains such a +large proportion of silicious matter as to become almost like a hard +flinty rock. Sometimes, however, it is a soft clay, at others it is mixed +with sand, but whatever the composition of the underclays may be, they +always agree in being unstratified. They also agree in this respect that +the peculiar fossils known as _stigmariae_ abound in them, and in some +cases to such an extent that the clay is one thickly-matted mass of the +filamentous rootlets of these fossils. We have seen how these gradually +came to be recognised as the roots of trees which grew in this age, and +whose remains have subsequently become metamorphosed into coal, and it is +but one step farther to come to the conclusion that these underclays are +the ancient soils in which the plants grew. + +No sketch of the various beds which go to form the coal-measures would be +complete which did not take into account the enormous beds of mountain +limestone which form the basis of the whole system, and which in thinner +bands are intercalated amongst the upper portion of the system, or the +true coal-measures. + +Now, limestones are not formed in the same way in which we have seen that +sandstones and shales are formed. The last two mentioned owe their origin +to their deposition as sediment in seas, estuaries or lakes, but the +masses of limestone which are found in the various geological formations +owe their origin to causes other than that of sedimentary deposition. + +In carboniferous times there lived numberless creatures which we know +nowadays as _encrinites_. These, when growing, were fixed to the bed of +the ocean, and extended upward in the shape of pliant stems composed of +limestone joints or plates; the stem of each encrinite then expanded at +the top in the shape of a gorgeous and graceful starfish, possessed of +numberless and lengthy arms. These encrinites grew in such profusion that +after death, when the plates of which their stems consisted, became +loosened and scattered over the bed of the sea, they accumulated and +formed solid beds of limestone. Besides the encrinites, there were of +course other creatures which were able to create the hard parts of their +structures by withdrawing lime from the sea, such as _foraminifera_, +shell-fish, and especially corals, so that all these assisted after death +in the accumulation of beds of limestone where they had grown and lived. + +[Illustration: FIG. 20.--Encrinite.] + +[Illustration: FIG. 21.--Encrinital limestone.] + +There is one peculiarity in connection with the habitats of the +encrinites and corals which goes some distance in supplying us with a +useful clue as to the conditions under which this portion of the +carboniferous formation was formed. These creatures find it a difficult +matter, as a rule, to live and secrete their calcareous skeleton in any +water but that which is clear, and free from muddy or sandy sediment. +They are therefore not found, generally speaking, where the other +deposits which we have considered, are forming, and, as these are always +found near the coasts, it follows that the habitats of the creatures +referred to must be far out at sea where no muddy sediments, borne by +rivers, can reach them. We can therefore safely come to the conclusion +that the large masses of encrinital limestone, which attain such an +enormous thickness in some places, especially in Ireland, have been +formed far away from the land of the period; we can at the same time draw +the conclusion that if we find the encrinites broken and snapped asunder, +and the limestone deposits becoming impure through being mingled with a +proportion of clayey or sandy deposits, that we are approaching a +coast-line where perhaps a river opened out, and where it destroyed the +growth of encrinites, mixing with their dead remains the sedimentary +debris of the land. + +[Illustration: FIG. 22.--Encrinites: various. Mountain limestone.] + +We have lightly glanced at the circumstances attending the deposition of +each of the principal rocks which form the beds amongst which coal is +found, and have now to deal with the formation of the coal itself. We +have already considered the various kinds of plants and trees which have +been discovered as contributing their remains to the formation of coal, +and have now to attempt an explanation of how it came to be formed in so +regular a manner over so wide an area. + +Each of the British coal-fields is fairly extensive. The Yorkshire and +Derbyshire coal-fields, together with the Lancashire coal-field, with +which they were at one time in geological connection, give us an area of +nearly 1000 square miles, and other British coal-fields show at least +some hundreds of square miles. And yet, spread over them, we find a +series of beds of coal which in many cases extend throughout the whole +area with apparent regularity. If we take it, as there seems every reason +to believe was the case, that almost all these coal-fields were not only +being formed at the same time, but were in most instances in continuation +with one another, this regularity of deposition of comparatively narrow +beds of coal, appears all the more remarkable. + +The question at once suggests itself, Which of two things is probable? +Are we to believe that all this vegetable matter was brought down by some +mighty river and deposited in its delta, or that the coal-plants grew +just where we now find the coal? + +Formerly it was supposed that coal was formed out of dead leaves and +trees, the refuse of the vegetation of the land, which had been carried +down by rivers into the sea and deposited at their mouths, in the same +way that sand and mud, as we have seen, are swept down and deposited. If +this were so, the extent of the deposits would require a river with an +enormous embouchure, and we should be scarcely warranted in believing +that such peaceful conditions would there prevail as to allow of the +layers of coal to be laid down with so little disturbance and with such +regularity over these wide areas. But the great objection to this theory +is, that not only do the remains still retain their perfection of +structure, but they are comparatively _pure,--i.e.,_ unmixed with +sedimentary depositions of clay or sand. Now, rivers would not bring down +the dead vegetation alone; their usual burden of sediment would also be +deposited at their mouths, and thus dead plants, sand, and clay would be +mixed up together in one black shaly or sandy mass, a mixture which would +be useless for purposes of combustion. The only theory which explained +all the recognised phenomena of the coal-measures was that the plants +forming the coal actually grew where the coal was formed, and where, +indeed, we now find it. When the plants and trees died, their remains +fell to the ground of the forest, and these soon turned to a black, +pasty, vegetable mass, the layer thus formed being regularly increased +year by year by the continual accumulation of fresh carbonaceous matter. +By this means a bed would be formed with regularity over a wide area; the +coal would be almost free from an admixture of sandy or clayey sediment, +and probably the rate of formation would be no more rapid in one part of +the forest than another. Thus there would be everywhere uniformity of +thickness. The warm and humid atmosphere, which it is probable then +existed, would not only have tended towards the production of an abnormal +vegetation, but would have assisted in the decaying and disintegrating +processes which went on amongst the shed leaves and trees. + +When at last it was announced as a patent fact that every bed of coal +possessed its underclay, and that trees had been discovered actually +standing upon their own roots in the clay, there was no room at all for +doubt that the correct theory had been hit upon--viz., that coal is now +found just where the trees composing it had grown in the past. + +But we have more than one coal-seam to account for. We have to explain +the existence of several layers of coal which have been formed over one +another on the same spot at successive periods, divided by other periods +when shale and sandstones only have been formed. + +A careful estimate of the Lancashire coal-field has been made by +Professor Hull for the Geological Survey. Of the 7000 feet of +carboniferous strata here found, spread out over an area of 217 square +miles, there are on the average eighteen seams of coal. + +This is only an instance of what is to be found elsewhere. Eighteen +coal-seams! what does this mean? It means that, during carboniferous +times, on no less than eighteen occasions, separate and distinct forests +have grown on this self-same spot, and that between each of these +occasions changes have taken place which have brought it beneath the +waters of the ocean, where the sandstones and shales have been formed +which divide the coal-seams from each other. We are met here by a +wonderful demonstration of the instability of the surface of the earth, +and we have to do our best to show how the changes of level have been +brought about, which have allowed of this game of geological see-saw to +take place between sea and land. Changes of level! Many a hard geological +nut has only been overcome by the application of the principle of changes +of level in the surface of the earth, and in this we shall find a sure +explanation of the phenomena of the coal-measures. + +Great changes of the level of the land are undoubtedly taking place even +now on the earth's surface, and in assuming that similar changes took +place in carboniferous times, we shall not be assuming the former +existence of an agent with which we are now unfamiliar. And when we +consider the thicknesses of sandstone and shale which intervene beneath +the coal-seams, we can realise to a certain extent the vast lapses of +years which must have taken place between the existence of each forest; +so that although now an individual passing up a coal-mine shaft may +rapidly pass through the remains of one forest after another, the rise of +the strata above each forest-bed then was tremendously slow, and the +period between the growth of each forest must represent the passing away +of countless ages. Perhaps it would not be too much to say that the +strata between some of the coal-seams would represent a period not less +than that between the formation of the few tertiary coals with which we +are acquainted, and a time which is still to us in the far-away future. + +The actual seams of coal themselves will not yield much information, from +which it will be possible to judge of the contour of the landmasses at +this ancient period. Of one thing we are sure, namely, that at the time +each seam was formed, the spot where it accumulated was dry land. If, +therefore, the seams which appear one above the other coincide fairly +well as to their superficial extent, we can conclude that each time the +land was raised above the sea and the forest again grew, the contour of +the land was very similar. This conclusion will be very useful to go +upon, since whatever decision may be come to as an explanation of one +successive land-period and sea-period on the same spot, will be +applicable to the eighteen or more periods necessary for the completion +of some of the coal-fields. + +We will therefore look at one of the sandstone masses which occur between +the coal-seams, and learn what lessons these have to teach us. In +considering the formation of strata of sand in the seas around our +river-mouths, it was seen that, owing to the greater weight of the +particles of the sand over those of clay, the former the more readily +sank to the bottom, and formed banks not very far away from the land. It +was seen, too, that each successive deposition of sand formed a +wedge-shaped layer, with the point of the wedge pointing away from the +source of origin of the sediment, and therefore of the current which +conveyed the sediment. Therefore, if in the coal-measure sandstones the +layers were found with their wedges all pointing in one direction, we +should be able to judge that the currents were all from one direction, +and that, therefore, they were formed by a single river. But this is just +what we do not find, for instead of it the direction of the wedge-shaped +strata varies in almost every layer, and the current-bedding has been +brought about by currents travelling in every direction. Such diverse +current-bedding could only result from the fact that the spot where the +sand was laid down was subject to currents from every direction, and the +inference is that it was well within the sphere of influence of numerous +streams and rivers, which flowed from every direction. The only condition +of things which would explain this is that the sandstone was originally +formed in a closed sea or large lake, into which numerous rivers flowing +from every direction poured their contents. + +Now, in the sandstones, the remains of numerous plants have been found, +but they do not present the perfect appearance that they do when found in +the shales; in fact they appear to have suffered a certain amount of +damage through having drifted some distance. This, together with the fact +that sandstones are not formed far out at sea, justify the safe +conclusion that the land could not have been far off. Wherever the +current-bedding shows itself in this manner we may be sure we are +examining a spot from which the land in every direction could not have +been at a very great distance, and also that, since the heavy materials +of which sandstone is composed could only be transported by being +impelled along by currents at the bed of the sea, and that in deep water +such currents could not exist, therefore we may safely decide that the +sea into which the rivers fell was a comparatively shallow one. + +Although the present coal-fields of England are divided from one another +by patches of other beds, it is probable that some of them were formerly +connected with others, and a very wide sheet of coal on each occasion was +laid down. The question arises as to what was the extent of the inland +sea or lake, and did it include the area covered by the coal basins of +Scotland and Ireland, of France and Belgium? And if these, why not those +of America and other parts? The deposition of the coal, according to the +theory here advanced, may as well have been brought about in a series of +large inland seas and lakes, as by one large comprehensive sea, and +probably the former is the more satisfactory explanation of the two. But +the astonishing part of it is that the changes in the level of the land +must have been taking place simultaneously over these large areas, +although, of course, while one quarter may have been depressed beneath +the sea, another may have been raised above it. + +In connection with the question of the contour of the land during the +existence of the large lakes or inland seas, Professor Hull has prepared, +in his series of maps illustrative of the Palaeo-Geography of the British +Islands, a map showing on incontestible grounds the existence during the +coal-ages of a great central barrier or ridge of high land stretching +across from Anglesea, south of Flint, Staffordshire, and Shropshire +coal-fields, to the eastern coast of Norfolk. He regards the British +coal-measures as having been laid down in two, or at most three, areas of +deposition--one south of this ridge, the remainder to the north of it. In +regard to the extent of the former deposits of coal in Ireland, there is +every probability that the sister island was just as favourably treated +in this respect as Great Britain. Most unfortunately, Ireland has since +suffered extreme denudation, notably from the great convulsions of nature +at the close of the very period of their deposition, as well as in more +recent times, resulting in the removal of nearly all the valuable upper +carboniferous beds, and leaving only the few unimportant +coal-beds to which reference has been made. + +[Illustration: FIG. 23.--_Cyathophyllum_. Coral in encrinital limestone.] + +We are unable to believe in the continuity of our coal-beds with those of +America, for the great source of sediment in those times was a continent +situated on the site of the Atlantic Ocean, and it is owing to this +extensive continent that the forms of _flora_ found in the coal-beds in +each country bear so close a resemblance to one another, and also that +the encrinital limestone which was formed in the purer depths of the +ocean on the east, became mixed with silt, and formed masses of shaly +impure limestone in the south-western parts of Ireland. + +It must be noted that, although we may attribute to upheaval from beneath +the fact that the bed of the sea became temporarily raised at each period +into dry land, the deposits of sand or shale would at the same time be +tending to shallow the bed, and this alone would assist the process of +upheaval by bringing the land at least very near to the surface of the +water. + +Each upheaval, however, could have been but a temporary arrest of the +great movement of crust subsidence which was going on throughout the coal +period, so that, at its close, when the last coal forest grew upon the +surface of the land, there had disappeared, in the case of South Wales, a +thickness of 11,000 feet of material. + +Of the many remarkable things in connection with coal-beds, not the least +is the state of purity in which coal is found. On the floor of each +forest there would be many a streamlet or even small river which would +wend its way to meet the not very distant sea, and it is surprising at +first that so little sediment found its way into the coal itself. But +this was cleverly explained by Sir Charles Lyell, who noticed, on one of +his visits to America, that the water of the Mississippi, around the rank +growths of cypress which form the "cypress swamps" at the mouths of that +river, was highly charged with sediment, but that, having passed through +the close undergrowth of the swamps, it issued in almost a pure state, +the sediment which it bore having been filtered out of it and +precipitated. This very satisfactorily explained how in some places +carbonaceous matter might be deposited in a perfectly pure state, whilst +in others, where sandstone or shale was actually forming, it might be +impregnated by coaly matter in such a way as to cause it to be stained +black. In times of flood sediment would be brought in, even where pure +coal had been forming, and then we should have a thin "parting" of +sandstone or shale, which was formed when the flood was at its height. Or +a slight sinking of the land might occur, in which case also the +formation of coal would temporarily cease, and a parting of foreign +matter would be formed, which, on further upheaval taking place, would +again give way to another forest growth. Some of the thicker beds have +been found presenting this aspect, such as the South Staffordshire +ten-yard coal, which in some parts splits up into a dozen or so smaller +beds, with partings of sediment between them. + +In the face of the stupendous movements which must have happened in order +to bring about the successive growth of forests one above another on the +same spot, the question at once arises as to how these movements of the +solid earth came about, and what was the cause which operated in such a +manner. We can only judge that, in some way or other, heat, or the +withdrawal of heat, has been the prime motive power. We can perceive, +from what is now going on in some parts of the earth, how great an +influence it has had in shaping the land, for volcanoes owe their +activity to the hidden heat in the earth's interior, and afford us an +idea of the power of which heat is capable in the matter of building up +and destroying continents. No less certain is it that heat is the prime +factor in those more gradual vertical movements of the land to which we +have referred elsewhere, but in regard to the exact manner in which it +acts we are very much in the dark. Everybody knows that, in the majority +of instances, material substances of all kinds expand under the influence +of heat, and contract when the source of heat is withdrawn. If we can +imagine movements in the quantity of heat contained in the solid crust, +the explanation is easy, for if a certain tract of land receive an +accession of heat beneath it, it is certain that the principal effect +will be an elevation of the land, consequent on the expansion of its +materials, with a subsequent depression when the heat beneath the tract +in question becomes gradually lessened. Should the heat be retained for a +long period, the strata would be so uplifted as to form an anticlinal, or +saddle-back, and then, should subsequent denudation take place, more +ancient strata would be brought to view. It was thus in the instance of +the tract bounded by the North and South Downs, which were formerly +entirely covered by chalk, and in the instance of the uprising of the +carboniferous limestone between the coal-fields of Lancashire, +Staffordshire, and Derbyshire. + +How the heat-waves act, and the laws, if any, which they obey in their +subterranean movements, we are unable to judge. From the properties which +heat possesses we know that its presence or absence produces marked +differences in the positions of the strata of the earth, and from +observations made in connection with the closing of some volcanoes, and +the opening up of fresh earth-vents, we have gone a long way towards +establishing the probability that there are even now slow and ponderous +movements taking place in the heat stored in the earth's crust, whose +effects are appreciably communicated to the outside of the thin rind of +solid earth upon which we live. + +Owing to the great igneous and volcanic activity at the close of the +deposition of the carboniferous system of strata, the coal-measures +exhibit what are known as _faults_ in abundance. The mountain limestone, +where it outcrops at the surface, is observed to be much jointed, so much +so that the work of quarrying the limestone is greatly assisted by the +jointed structure of the rock. Faults differ from joints in that, whilst +the strata in the latter are still in relative position on each side of +the joint, they have in the former slipped out of place. In such a case +the continuation of a stratum on the opposite side of a fault will be +found to be depressed, perhaps a thousand feet or more. It will be seen +at once how that, in sinking a new shaft into a coal-seam, the +possibility of an unknown fault has to be brought into consideration, +since the position of the seam may prove to have been depressed to such +an extent as to cause it to be beyond workable depth. Many seams, on the +other hand, which would have remained altogether out of reach of mining +operations, have been brought within workable depth by a series of +_step-faults_, this being a term applied to a series of parallel faults, +in none of which the amount of down-throw is great. + +The amount of the down-throw, or the slipping-down of the beds, is +measured, vertically, from the point of disappearance of a layer to an +imaginary continuation of the same layer from where it again appears +beyond the fault. The plane of a fault is usually more or less inclined, +the amount of the inclination being known as the _hade_ of the fault, and +it is a remarkable characteristic of faults that, as a general rule, they +hade to the down-throw. This will be more clearly understood when it is +explained that, by its action, a seam of coal, which is subject to +numerous faults, can never be pierced more than once by one and the same +boring. In mountainous districts, however, there are occasions when the +hade is to the up-throw, and this kind of fault is known as an _inverted +fault_. + +Lines of faults extend sometimes for hundreds of miles. The great Pennine +Fault of England is 130 miles long, and others extend for much greater +distances. The surfaces on both sides of a fault are often smooth and +highly polished by the movement which has taken place in the strata. They +then show the phenomenon known as _slicken-sides_. Many faults have +become filled with crystalline minerals in the form of veins of ore, +deposited by infiltrating waters percolating through the natural +fissures. + +In considering the formation and structure of the better-known +coal-bearing beds of the carboniferous age, we must not lose sight of the +fact that important beds of coal also occur in strata of much more recent +date. There are important coal-beds in India of Permian age. There are +coal-beds of Liassic age in South Hungary and in Texas, and of Jurassic +age in Virginia, as well as at Brora in Sutherlandshire; there are coals +of Cretaceous age in Moravia, and valuable Miocene Tertiary coals in +Hungary and the Austrian Alps. + +Again, older than the true carboniferous age, are the Silurian +anthracites of Co. Cavan, and certain Norwegian coals, whilst in New +South Wales we are confronted with an assemblage of coal-bearing strata +which extend apparently from the Devonian into Mesozoic times. + +Still, the age we have considered more closely has an unrivalled right to +the title, coal appearing there not merely as an occasional bed, but as a +marked characteristic of the formation. + +The types of animal life which are found in this formation are varied, +and although naturally enough they do not excel in number, there are yet +sufficient varieties to show probabilities of the existence of many with +which we are unfamiliar. The highest forms yet found, show an advance as +compared with those from earlier formations, and exhibit amphibian +characteristics intermediate between the two great classes of fishes and +reptiles. Numerous specimens proper to the extinct order of +_labyrinthodontia_ have been arranged into at least a score of genera, +these having been drawn from the coal-measures of Newcastle, Edinburgh, +Kilkenny, Saaerbruck, Bavaria, Pennsylvania, and elsewhere. The +_Archegosaurus,_ which we have figured, and the _Anthracosaurus,_ are +forms which appear to have existed in great numbers in the swamps and +lakes of the age. The fish of the period belong almost entirely to the +ancient orders of the ganoids and placoids. Of the ganoids, the great +_megalichthys Hibberti_ ranges throughout the whole of the system. +Wonderful accumulations of fish remains are found at the base of the +system, in the bone-bed of the Bristol coal-field, as well as in a +similar bed at Armagh. Many fishes were armed with powerful conical +teeth, but the majority, like the existing Port Jackson shark, were +possessed of massive palates, suited in some cases for crushing, and in +others for cutting. + +[Illustration: FIG. 24.--_Archegosaurus minor_. Coal-measures.] + +[Illustration: FIG. 25.--_Psammodus porosus_. Crushing palate of a fish.] + +[Illustration: FIG. 26.--_Orthoceras_. Mountain limestone.] + +In the mountain limestone we see, of course, the predominance of marine +types, encrinital remains forming the greater proportion of the mass. +There are occasional plant remains which bear evidence of having drifted +for some distance from the shore. But next to the _encrinites_, the +corals are the most important and persistent. Corals of most beautiful +forms and capable of giving polished marble-like sections, are in +abundance. _Polyzoa_ are well represented, of which the lace-coral +(_fenestella_) and screw-coral (_archimedopora_) are instances. +_Cephalopoda_ are represented by the _orthoceras_, sometimes five or six +feet long, and _goniatites_, the forerunner of the familiar _ammonite_. +Many species of brachiopods and lammellibranchs are met with. _Lingula_, +most persistent throughout all geological time, is abundant in the +coal-shales, but not in the limestones. _Aviculopecten_ is there abundant +also. In the mountain limestone the last of the trilobites (_Phillipsia_) +is found. + +[Illustration: FIG. 27.--_Fenestella retipora_. Mountain limestone.] + +[Illustration: FIG. 28.--_Goniatites_. Mountain limestone.] + +We have evidence of the existence in the forests of a variety of +_centipede_, specimens having been found in the erect stump of a hollow +tree, although the fossil is an extremely rare one. The same may be said +of the only two species of land-snail which have been found connected +with the coal forests, viz., _pupa vetusta_ and _zonites priscus_, both +discovered in the cliffs of Nova Scotia. These are sufficient to +demonstrate that the fauna of the period had already reached a high stage +of development. In the estuaries of the day, masses of a species of +freshwater mussel (_anthracosia_) were in existence, and these have left +their remains in the shape of extensive beds of shells. They are familiar +to the miner as _mussel-binds_, and are as noticeable a feature of this +long ago period, as are the aggregations of mussels on every coast at +the present day. + +[Illustration: FIG. 29.--_Aviculopecten papyraceus_. Coal-shale.] + + + + +CHAPTER III. + +VARIOUS FORMS OF COAL AND CARBON. + + +In considering the various forms and combinations into which coal enters, +it is necessary that we should obtain a clear conception of what the +substance called "carbon" is, and its nature and properties generally, +since this it is which forms such a large percentage of all kinds of +coal, and which indeed forms the actual basis of it. In the shape of +coke, of course, we have a fairly pure form of carbon, and this being +produced, as we shall see presently, by the driving off of the volatile +or vaporous constituents of coal, we are able to perceive by the residue +how great a proportion of coal consists of carbon. In fact, the two have +almost an identical meaning in the popular mind, and the fact that the +great masses of strata, in which are contained our principal and most +valuable seams of coal, are termed "carboniferous," from the Latin +_carbo_, coal, and _fero_, I bear, tends to perpetuate the existence of +the idea. + +There is always a certain, though slight, quantity of carbon in the air, +and this remains fairly constant in the open country. Small though it may +be in proportion to the quantity of pure air in which it is found, it is +yet sufficient to provide the carbon which is necessary to the growth of +vegetable life. Just as some of the animals known popularly as the +_zoophytes_, which are attached during life to rocks beneath the sea, are +fed by means of currents of water which bring their food to them, so the +leaves, which inhale carbon-food during the day through their +under-surfaces, are provided with it by means of the currents of air +which are always circulating around them; and while the fuel is being +taken in beneath, the heat and light are being received from above, and +the sun supplies the motive power to digestion. + +It is assumed that it is, within the knowledge of all that, for the +origin of the various seams and beds of coaly combinations which exist in +the earth's crust, we must look to the vegetable world. If, however, we +could go so far back in the world's history as the period when our +incandescent orb had only just severed connection with a +gradually-diminishing sun, we should probably find the carbon there, but +locked up in the bonds of chemical affinities with other elements, and +existing therewith in a gaseous condition. But, as the solidifying +process went on, and as the vegetable world afterwards made its +appearance, the carbon became, so to speak, wrenched from its +combinations, and being absorbed by trees and plants, finally became +deposited amongst the ruins of a former vegetable world, and is now +presented to us in the form of coal. + +We are able to trace the gradual changes through which the pasty mass of +decaying vegetation passed, in consequence of the fact that we have this +material locked up in various stages of carbonisation, in the strata +beneath our feet. These we propose to deal with individually, in as +unscientific and untechnical a manner as possible. + +First of all, when a mass of vegetable matter commences to decay, it soon +loses its colour. There is no more noticeable proof of this, than that +when vitality is withdrawn from the leaves of autumn, they at once +commence to assume a rusty or an ashen colour. Let the leaves but fall to +the ground, and be exposed to the early frosts of October, the damp mists +and rains of November, and the rapid change of colour is at once +apparent. Trodden under foot, they soon assume a dirty blackish hue, and +even when removed they leave a carbonaceous trace of themselves behind +them, where they had rested. Another proof of the rapid acquisition of +their coaly hue is noticeable in the spring of the year. When the trees +have burst forth and the buds are rapidly opening, the cases in which the +buds of such trees as the horse-chestnut have been enclosed will be found +cast off, and strewing the path beneath. Moistened by the rains and the +damp night-mists, and trodden under foot, these cases assume a jet black +hue, and are to all appearance like coal in the very first stages of +formation. + +But of course coal is not made up wholly and only of leaves. The branches +of trees, twigs of all sizes, and sometimes whole trunks of trees are +found, the last often remaining in their upright position, and piercing +the strata which have been formed above them. At other times they lie +horizontally on the bed of coal, having been thrown down previously to +the formation of the shale or sandstone, which now rests upon them. They +are often petrified into solid sandstone themselves, whilst leaving a +rind of coal where formerly was the bark. Although the trunk of a tree +looks so very different to the leaves which it bears upon its branches, +it is only naturally to be supposed that, as they are both built up after +the same manner from the juices of the earth and the nourishment in the +atmosphere, they would have a similar chemical composition. One very +palpable proof of the carbonaceous character of tree-trunks suggests +itself. Take in your hand a few dead twigs or sticks from which the +leaves have long since dropped; pull away the dead parts of the ivy which +has been creeping over the summer-house; or clasp a gnarled old monster +of the forest in your arms, and you will quickly find your hand covered +with a black smut, which is nothing but the result of the first stage +which the living plant has made, in its progress towards its condition as +dead coal. But an easy, though rough, chemical proof of the constituents +of wood, can be made by placing a few pieces of wood in a medium-sized +test-tube, and holding it over a flame. In a short time a certain +quantity of steam will be driven off, next the gaseous constituents of +wood, and finally nothing will be left but a few pieces of black brittle +charcoal. The process is of course the same in a fire-grate, only that +here more complete combustion of the wood takes place, owing to its being +intimately exposed to the action of the flames. If we adopt the same +experiment with some pieces of coal, the action is similar, only that in +this case the quantity of gases given off is not so great, coal +containing a greater proportion of carbon than wood, owing to the fact +that, during its long burial in the bowels of the earth, it has been +acted upon in such a way as to lose a great part of its volatile +constituents. + +From processes, therefore, which are to be seen going on around us, it is +easily possible to satisfy ourselves that vegetation will in the long run +undergo such changes as will result in the formation of coal. + +There are certain parts in most countries, and particularly in Ireland, +where masses of vegetation have undergone a still further stage in +metamorphism, namely, in the well-known and famous peat-bogs. Ireland is +_par excellence_ the land of bogs, some three millions of acres being +said to be covered by them, and they yield an almost inexhaustible supply +of peat. One of the peat-bogs near the Shannon is between two and three +miles in breadth and no less than fifty in length, whilst its depth +varies from 13 feet to as much as 47 feet. Peat-bogs have in no way +ceased to be formed, for at their surfaces the peat-moss grows afresh +every year; and rushes, horse-tails, and reeds of all descriptions grow +and thrive each year upon the ruins of their ancestors. The formation of +such accumulations of decaying vegetation would only be possible where +the physical conditions of the country allowed of an abundant rainfall, +and depressions in the surface of the land to retain the moisture. Where +extensive deforesting operations have taken place, peat-bogs have often +been formed, and many of those in existence in Europe undoubtedly owe +their formation to that destruction of forests which went on under the +sway of the Romans. Natural drainage would soon be obstructed by fallen +trees, and the formation of marsh-land would follow; then with the growth +of marsh-plants and their successive annual decay, a peaty mass would +collect, which would quickly grow in thickness without let or hindrance. + +In considering the existence of inland peat-bogs, we must not lose sight +of the fact that there are subterranean forest-beds on various parts of +our coasts, which also rest upon their own beds of peaty matter, and very +possibly, when in the future they are covered up by marine deposits, they +will have fairly started on their way towards becoming coal. + +Peat-bogs do not wholly consist of peat, and nothing else. The trunks of +such trees as the oak, yew, and fir, are often found mingled with the +remains of mosses and reeds, and these often assume a decidedly coaly +aspect. From the famous Bog of Allen in Ireland, pieces of oak, generally +known as "bog-oak," which have been buried for generations in peat, have +been excavated. These are as black as any coal can well be, and are +sufficiently hard to allow of their being used in the manufacture of +brooches and other ornamental objects. Another use to which peat of some +kinds has been put is in the manufacture of yarn, the result being a +material which is said to resemble brown worsted. On digging a ditch to +drain a part of a bog in Maine, U.S., in which peat to a depth of twenty +feet had accumulated, a substance similar to cannel coal itself was +found. As we shall see presently, cannel coal is one of the earliest +stages of true coal, and the discovery proved that under certain +conditions as to heat and pressure, which in this case happened to be +present, the materials which form peat may also be metamorphosed into +true coal. + +Darwin, in his well-known "Voyage in the _Beagle_" gives a peculiarly +interesting description of the condition of the peat-beds in the Chonos +Archipelago, off the Chilian coast, and of their mode of formation. "In +these islands," he says, "cryptogamic plants find a most congenial +climate, and within the forest the number of species and great abundance +of mosses, lichens, and small ferns, is quite extraordinary. In Tierra +del Fuego every level piece of land is invariably covered by a thick bed +of peat. In the Chonos Archipelago where the nature of the climate more +closely approaches that of Tierra del Fuego, every patch of level ground +is covered by two species of plants (_Astelia pumila_ and _Donatia +megellanica_), which by their joint decay compose a thick bed of elastic +peat. + +"In Tierra del Fuego, above the region of wood-land, the former of these +eminently sociable plants is the chief agent in the production of peat. +Fresh leaves are always succeeding one to the other round the central +tap-root; the lower ones soon decay, and in tracing a root downwards in +the peat, the leaves, yet holding their places, can be observed passing +through every stage of decomposition, till the whole becomes blended in +one confused mass. The Astelia is assisted by a few other plants,--here +and there a small creeping Myrtus (_M. nummularia_), with a woody stem +like our cranberry and with a sweet berry,--an Empetrum (_E. rubrum_), +like our heath,--a rush (_Juncus grandiflorus_), are nearly the only ones +that grow on the swampy surface. These plants, though possessing a very +close general resemblance to the English species of the same genera, are +different. In the more level parts of the country the surface of the peat +is broken up into little pools of water, which stand at different +heights, and appear as if artificially excavated. Small streams of water, +flowing underground, complete the disorganisation of the vegetable +matter, and consolidate the whole. + +"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. + +[Illustration: FIG 30.--_Lepidodendron_. Portion of Sandstone stem after +removal of bark of a giant club-moss] + +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. + +[Illustration: FIG. 31.--Engine-House and Buildings at head of a +Coal-Pit.] + +If there be one of these shafts at one end of the mine, and another at a +remote distance from it, a movement of the air will at once begin, and a +rough kind of ventilation will ensue. This is, however, quite +insufficient to provide the necessary 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. + +[Illustration: FIG. 32.--Gas Jet and Davy Lamp.] + +With the complicated improvements which have since been made in the Davy +lamp, a state of almost absolute safety can be guaranteed, but still from +time to time explosions are reported. Of the cause of many we are +absolutely ignorant, but occasionally a light is thrown upon their origin +by a paragraph appearing in a daily paper. Two men are charged before the +magistrates with being in the possession of keys used exclusively for +unlocking their miners' safety-lamps. There is no defence. These men know +that they carry their lives in their hands, yet will risk their own and +those of hundreds of others, in order that they may be able to light +their pipes by means of their safety-lamps. Sometimes in an unexpected +moment there is a great dislodgement of coal, and a tremendous 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. + +[Illustration: Fig. 33--Part of a trunk of _Sigillaria_, showing the thin +outer carbonised bark, with leaf-scars, and the seal-like impressions +where the bark is removed.] + +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. + +[Illustration: FIG. 34.--Inside a Gas-Holder.] + +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. + +[Illustration: FIG. 35.--Filling Retorts by Machinery.] + +[Illustration: FIG. 36.--CONDENSERS.] + +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. + +[Illustration: FIG. 37.] + +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. + +[Illustration: FIG. 38.] + +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. + +The term asphalt has been applied to so many and various mixtures, that +one scarcely associates it with natural mineral pitch which is found in +some parts of the world. From time immemorial this compact, bituminous, +resinous mineral has been discovered in masses on the shores of the Dead +Sea, which has in consequence received the well-known title of Lake +Asphaltites. Like the naphthas and petroleums which have been noticed, +this has had its origin in the decomposition of vegetable matter, and +appears to be thrown up in a liquid form by the volcanic energies which, +are still believed to be active in the centre of the lake, and which may +be existent beneath a stratum, or bed, of oil-producing bitumen. + +In connection with the formation of this substance, the remarks of Sir +Charles Lyell, the great geologist, may well be quoted, as showing the +transformation of vegetable matter into petroleum, and afterwards into +solid-looking asphalt. At Trinidad is a lake of bitumen which is a mile +and a half in circumference. "The Orinoco has for ages been rolling down +great quantities of woody and vegetable bodies into the surrounding sea, +where, by the influence of currents and eddies, they may be arrested, and +accumulated in particular places. The frequent occurrence of earthquakes +and other indications of volcanic action in those parts, lend countenance +to the opinion that these vegetable substances may have undergone, by the +agency of subterranean fire, those transformations or chemical changes +which produce petroleum; and this may, by the same causes, be forced up +to the surface, where, by exposure to the air, it becomes inspissated, +and forms those different varieties of earth-pitch or asphaltum so +abundant in the island." + +It is interesting to note also that it was obtained, at an ancient +period, from the oil-fountains of Is, and that it was put to considerable +use in the embalming of the bodies of the Egyptians. It appears, too, to +have been employed in the construction of the walls of Babylon, and thus +from very early times these wonderful products and results of decayed +vegetation have been brought into use for the service of man. + +Aniline has been previously referred (p. 135) to as having been prepared +from nitro-benzole, or _essence de mirbane_, and its preparation, by +treating this substance with iron-filings and acetic acid, was one of the +early triumphs of the chemists who undertook the search after the unknown +contained in gas-tar. It had previously been obtained from oils distilled +from bones. The importance of the substance lies in the fact that, by the +action of various chemical reagents, a series of colouring matters of +very great richness are formed, and these are the well-known _aniline +dyes_. + +As early as 1836, it was discovered that aniline, when heated with +chloride of lime, acquired a beautiful blue tint. This discovery led to +no immediate practical result, and it was not until twenty-one years +after that a further discovery was made, which may indeed be said to have +achieved a world-wide reputation. It was found that, by adding bichromate +of potash to a solution of aniline and sulphuric acid, a powder was +obtained from which the dye was afterwards extracted, which is known as +_mauve_. Since that time dyes in all shades and colours have been +obtained from the same source. _Magenta_ was the next dye to make its +appearance, and in the fickle history of fashion, probably no colours +have had such extraordinary runs of popularity as those of mauve and +magenta. Every conceivable colour was obtained in due course from the +same source, and chemists began to suspect that, in the course of time, +the colouring matter of dyer's madder, which was known as _alizarin_, +would also be obtained therefrom. Hitherto this had been obtained from +the root of the madder-plant, but by dint of careful and well-reasoned +research, it was obtained by Dr Groebe, from a solid crystalline coal-tar +product, known as _anthracene_, (C_{12}H_{14}). This artificial alizarin +yields colours which are purer than those of natural madder, and being +derived from what was originally regarded as a waste product, its cost of +production is considerably cheaper. + +We have endeavoured thus far to deal with (1) gas, and (2) tar, the two +principal products in the distillation of coal. We have yet to say a few +words concerning the useful ammoniacal liquor, and the final residue in +the retorts, _i.e._, coke. + +The ammoniacal liquor which has been passing over during distillation of +the coal, and which has been collecting in the hydraulic main and in +other parts of the gas-making apparatus, is set aside to be treated to a +variety of chemical reactions, in order to wrench from it its useful +constituents. Amongst these, of course, _ammonia_ stands in the first +rank, the others being comparatively unimportant. In order to obtain +this, the liquor is first of all neutralised by being treated with a +quantity of acid, which converts the principal constituent of the liquor, +viz., carbonate of ammonia (smelling salts), into either sulphate of +ammonia, or chloride of ammonia, familiarly known as sal-ammoniac, +according as sulphuric acid or hydrochloric acid is the acid used. Thus +carbonate of ammonia with sulphuric acid will give sulphate of ammonia, +but carbonate of ammonia with hydrochloric acid will give sal-ammoniac +(chloride of ammonia). By a further treatment of these with lime, or, as +it is chemically known, oxide of calcium, ammonia is set free, whilst +chloride of lime (the well-known disinfectant), or sulphate of lime +(gypsum, or "plaster of Paris" ), is the result. + +Thus: + +Sulphate of ammonia + lime = plaster of Paris + ammonia. + +or, + +Sal-ammoniac + lime = chloride of lime + ammonia. + +Ammonia itself is a most powerful gas, and acts rapidly upon the eyes. It +has a stimulating effect upon the nerves. It is not a chemical element, +being composed of three parts of hydrogen by weight to one of nitrogen, +both of which elements alone are very harmless, and, the latter indeed, +very necessary to human life. Ammonia is fatal to life, producing great +irritation of the lungs. + +It has also been called "hartshorn," being obtained by destructive +distillation of horn and bone. The name "ammonia" is said to have been +derived from the fact that it was first obtained by the Arabs near the +temple of Jupiter Ammon, in Lybia, North Africa, from the excrement of +camels, in the form of sal-ammoniac. There are always traces of it in the +atmosphere, especially in the vicinity of large towns and manufactories +where large quantities of coal are burned. + +Coke, if properly prepared, should consist of pure carbon. Good coal +should yield as much as 80 per cent. of coke, but owing to the +unsatisfactory manner of its production, this proportion is seldom +yielded, whilst the coke which is familiar to householders, being the +residue left in the retorts after gas-making, usually contains so large a +proportion of sulphur as to make its combustion almost offensive. No +doubt the result of its unsatisfactory preparation has been that it has +failed to make its way into households as it should have done, but there +is also another objection to its use, namely, the fact that, owing to the +quantity of oxygen required in its combustion, it gives rise to feelings +of suffocation where insufficient ventilation of the room is provided. + +Large quantities of coke are, however, consumed in the feeding of furnace +fires, and in the heating of boilers of locomotives, as well as in +metallurgical operations; and in order to supply the demand, large +quantities of coal are "coked," a process by which the volatile products +are completely combusted, pure coke remaining behind. This process is +therefore the direct opposite to that of "distillation," by which the +volatile products are carefully collected and re-distilled. + +The sulphurous impurities which are always present in the coal, and which +are, to a certain extent, retained in coke made at the gas-works, +themselves have a value, which in these utilitarian days is not long +likely to escape the attention of capitalists. In coal, bands of bright +shining iron pyrites are constantly seen, even in the homely scuttle, and +when coal is washed, as it is in some places, the removal of the pyrites +increases the value of the coal, whilst it has a value of its own. + +The conversion of the sulphur which escapes from our chimneys into +sulphuretted hydrogen, and then into sulphuric acid, or oil of vitriol, +has already been referred to, and we can only hope that in these days +when every available source of wealth is being looked up, and when there +threatens to remain nothing which shall in the future be known as +"waste," that the atmosphere will be spared being longer the receptacle +for the unowned and execrated brimstone of millions of fires and +furnaces. + + + + +CHAPTER VII. + +THE COAL SUPPLIES OF THE WORLD. + + +As compared with some of the American coal-fields, those of Britain are +but small, both in extent and thickness. They can be regarded as falling +naturally into three principal areas. + + The northern coal-field, including those of Fife, Stirling, and Ayr + in Scotland; Cumberland, Newcastle, and Durham in England; Tyrone + in Ireland. + + The middle coal-field, all geologically in union, including those of + Yorkshire, Derbyshire, Shropshire, Staffordshire, Flint, and + Denbigh. + + The southern coal-field, including South Wales, Forest of Dean, + Bristol, Dover, with an offshoot at Leinster, &c., and Millstreet, + Cork. + +Thus it will be seen that while England and Scotland are, in comparison +with their extent of surface, bountifully supplied with coal-areas, in +the sister island of Ireland coal-producing areas are almost absent. The +isolated beds in Cork and Tipperary, in Tyrone and Antrim, are but the +remnants left of what were formerly beds of coal extending the whole +breadth and length of Ireland. Such beds as there remain undoubtedly +belong to the base of the coal-measures, and observations all go to show +that the surface suffered such extreme denudation subsequent to the +growth of the coal-forests, that the wealth which once lay there, has +been swept away from the surface which formerly boasted of it. + +On the continent of Europe the coal-fields, though not occupying so large +a proportion of the surface of the country as in England, are very far +from being slight or to be disregarded. The extent of forest-lands still +remaining in Germany and Austria are sufficing for the immediate needs of +the districts where some of the best seams occur. It is only where there +is a dearth of handy fuel, ready to be had, perhaps, by the simple +felling of a few trees, that man commences to dig into the earth for his +fuel. But although on the continent not yet occupying so prominent a +position in public estimation as do coal-fields in Great Britain, those +of the former have one conspicuous characteristic, viz., the great +thickness of some of the individual seams. + +In the coal-field of Midlothian the seams of coal vary from 2 feet to 5 +feet in thickness. One of them is known as the "great seam," and in spite +of its name attains a thickness only of from 8 to 10 feet thick. There +are altogether about thirty seams of coal. When, however, we pass to the +continent, we find many instances, such as that of the coal-field of +Central France, in which the seams attain vast thicknesses, many of them +actually reaching 40 and 60 feet, and sometimes even 80 feet. One of the +seams in the district of St. Etienne varies from 30 to 70 feet thick, +whilst the fifteen to eighteen workable seams give a thickness of 112 +feet, although the total area of the field is not great. Again, in the +remarkable basin of the Saone-et-Loire, although there are but ten beds +of coal, two of them run from 30 to 60 feet each, whilst at Creusot the +main seam actually runs locally to a thickness varying between 40 and 130 +feet. + +The Belgian coal-field stretches in the form of a narrow strip from 7 to +9 miles wide by about 100 miles long, and is divided into three principal +basins. In that stretching from Liege to Verviers there are eighty-three +seams of coal, none of which are less than 3 feet thick. In the basin of +the Sambre, stretching from Namur to Charleroi, there are seventy-three +seams which are workable, whilst in that between Mons and Thulin there +are no less than one hundred and fifty-seven seams. The measures here are +so folded in zigzag fashion, that in boring in the neighbourhood of Mons +to a depth of 350 yards vertical, a single seam was passed through no +less than six times. + +Germany, on the west side of the Rhine, is exceptionally fortunate in the +possession of the famous Pfalz-Saarbruecken coal-field, measuring about 60 +miles long by 20 miles wide, and covering about 175 square miles. Much of +the coal which lies deep in these coal-measures will always remain +unattainable, owing to the enormous thickness of the strata, but a +careful computation made of the coal which can be worked, gives an +estimate of no less than 2750 millions of tons. There is a grand total of +two hundred and forty-four seams, although about half of them are +unworkable. + +Beside other smaller coal-producing areas in Germany, the coal-fields of +Silesia in the southeastern corner of Prussia are a possession unrivalled +both on account of their extent and thickness. It is stated that there +exist 333 feet of coal, all the seams of which exceed 2-1/2 feet, and +that in the aggregate there is here, within a workable depth, the +scarcely conceivable quantity of 50,000 million tons of coal. + +The coal-field of Upper Silesia, occupying an area about 20 miles long by +15 miles broad, is estimated to contain some 10,000 feet of strata, with +333 feet of good coal. This is about three times the thickness contained +in the South Wales coal-field, in a similar thickness of coal-measures. +There are single seams up to 60 feet thick, but much of the coal is +covered by more recent rocks of New Red and Cretaceous age. In Lower +Silesia there are numerous seams 3-1/2 feet to 5 feet thick, but owing to +their liability to change in character even in the same seam, their value +is inferior to the coals of Upper Silesia. + +When British supplies are at length exhausted, we may anticipate that +some of the earliest coals to be imported, should coal then be needed, +will reach Britain from the upper waters of the Oder. + +The coal-field of Westphalia has lately come into prominence in +connection with the search which has been made for coal in Kent and +Surrey, the strata which are mined at Dortmund being thought to be +continuous from the Bristol coal-field. Borings have been made through +the chalk of the district north of the Westphalian coal-field, and these +have shown the existence of further coal-measures. The coal-field extends +between Essen and Dortmund a distance of 30 miles east and west, and +exhibits a series of about one hundred and thirty seams, with an +aggregate of 300 feet of coal. + +It is estimated that this coal-field alone contains no less than 39,200 +millions of tons of coal. + +Russia possesses supplies of coal whose influence has scarcely yet been +felt, owing to the sparseness of the population and the abundance of +forest. Carboniferous rocks abut against the flanks of the Ural +Mountains, along the sides of which they extend for a length of about a +thousand miles, with inter-stratifications of coal. Their actual contents +have not yet been gauged, but there is every reason to believe that those +coal-beds which have been seen are but samples of many others which will, +when properly worked, satisfy the needs of a much larger population than +the country now possesses. + +Like the lower coals of Scotland, the Russian coals are found in the +carboniferous limestone. This may also be said of the coal-fields in the +governments of Tula and Kaluga, and of those important coal-bearing +strata near the river Donetz, stretching to the northern corner of the +Sea of Azov. In the last-named, the seams are spread over an area of +11,000 square miles, in which there are forty-four workable seams +containing 114 feet of coal. The thickest of known Russian coals occur at +Lithwinsk, where three seams are worked, each measuring 30 feet to 40 +feet thick. + +An extension of the Upper Silesian coal-field appears in Russian Poland. +This is of upper Carboniferous age, and contains an aggregate of 60 feet +of coal. + +At Ostrau, in Upper Silesia (Austria), there is a remarkable coal-field. +Of its 370 seams there are no less than 117 workable ones, and these +contain 350 feet of coal. The coals here are very full of gas, which even +percolates to the cellars of houses in the town. A bore hole which was +sunk in 1852 to a depth of 150 feet, gave off a stream of gas, which +ignited, and burnt for many years with a flame some feet long. + +The Zwickau coal-field in Saxony is one of the most important in Europe. +It contains a remarkable seam of coal, known as Russokohle or soot-coal, +running at times 25 feet thick. It was separated by Geinitz and others +into four zones, according to their vegetable contents, viz.:-- + +1. Zone of Ferns. + +2. Zone of Annularia and Calamites. + +3. Zone of Sigillaria. + +4. Zone of Sagenaria (in Silesia), equivalent to the culm-measures of + Devonshire. + +Coals belonging to other than true Carboniferous age are found in Europe +at Steyerdorf on the Danube, where there are a few seams of good coal in +strata of Liassic age, and in Hungary and Styria, where there are +tertiary coals which approach closely to those of true Carboniferous age +in composition and quality. + +In Spain there are a few small scattered basins. Coal is found overlying +the carboniferous limestone of the Cantabrian chain, the seams being from +5 feet to 8 feet thick. In the Satero valley, near Sotillo, is a single +seam measuring from 60 feet to 100 feet thick. Coal of Neocomian age +appears at Montalban. + +When we look outside the continent of Europe, we may well be astonished +at the bountiful manner in which nature has laid out beds of coal upon +these ancient surfaces of our globe. + +Professor Rogers estimated that, in the United States of America, the +coal-fields occupy an area of no less than 196,850 square miles. + +Here, again, it is extremely probable that the coal-fields which remain, +in spite of their gigantic existing areas, are but the remnants of one +tremendous area of deposit, bounded only on the east by the Atlantic, and +on the west by a line running from the great lakes to the frontiers of +Mexico. The whole area has been subjected to forces which have produced +foldings and flexures in the Carboniferous strata after deposition. These +undulations are greatest near the Alleghanies, and between these +mountains and the Atlantic, whilst the flexures gradually dying out +westward, cause the strata there to remain fairly horizontal. In the +troughs of the foldings thus formed the coal-measures rest, those +portions which had been thrown up as anticlines having suffered loss by +denudation. Where the foldings are greatest there the coal has been +naturally most altered; bituminous and caking-coals are characteristic of +the broad flat areas west of the mountains, whilst, where the contortions +are greatest, the coal becomes a pure anthracite. + +It must not be thought that in this huge area the coal is all uniformly +good. It varies greatly in quality, and in some districts it occurs in +such thin seams as to be worthless, except as fuel for consumption by the +actual coal-getters. There are, too, areas of many square miles in +extent, where there are now no coals at all, the formation having been +denuded right down to the palaeozoic back-bone of the country. + +Amongst the actual coal-fields, that of Pennsylvania stands +pre-eminent. The anthracite here is in inexhaustible quantity, its output +exceeding that of the ordinary bituminous coal. The great field of which +this is a portion, extends in an unbroken length for 875 miles N.E. and +S.W., and includes the basins of Ohio, Maryland, Virginia, Kentucky, and +Tennessee. The workable seams of anthracite about Pottsville measure in +the aggregate from 70 to 207 feet. Some of the lower seams individually +attain an exceptional thickness, that at Lehigh Summit mine containing a +seam, or rather a bed, of 30 feet of good coal. + +A remarkable seam of coal has given the town of Pittsburg its name. This +is 8 feet thick at its outcrop near the town, and although its thickness +varies considerably, Professor Rogers estimates that the sheet of coal +measures superficially about 14,000 square miles. What a forest there +must have existed to produce so widespread a bed! Even as it is, it has +at a former epoch suffered great denudation, if certain detached basins +should be considered as indicating its former extent. + +The principal seam in the anthracite district of central Pennsylvania, +which extends for about 650 miles along the left bank of the Susquehanna, +is known as the "Mammoth" vein, and is 29-1/2 feet thick at Wilkesbarre, +whilst at other places it attains to, and even exceeds, 60 feet. + +On the west of the chain of mountains the foldings become gentler, and +the coal assumes an almost horizontal position. In passing through Ohio +we find a saddle-back ridge or anticline of more ancient strata than the +coal, and in consequence of this, we have a physical boundary placed upon +the coal-fields on each side. + +Passing across this older ridge of denuded Silurian and other rocks, we +reach the famous Illinois and Indiana coal-field, whose +coal-measures lie in a broad trough, bounded on the west by the uprising +of the carboniferous limestone of the upper Mississippi. This limestone +formation appears here for the first time, having been absent on the +eastern side of the Ohio anticline. The area of the coal-field is +estimated at 51,000 square miles. + +In connection with the coal-fields of the United States, it is +interesting to notice that a wide area in Texas, estimated at 3000 square +miles, produces a large amount of coal annually from strata of the +Liassic age. Another important area of production in eastern Virginia +contains coal referable to the Jurassic age, and is similar in fossil +contents to the Jurassic of Whitby and Brora. The main seam in eastern +Virginia boasts a thickness of from 30 to 40 feet of good coal. + +Very serviceable lignites of Cretaceous age are found on the Pacific +slope, to which age those of Vancouver's Island and Saskatchewan River +are referable. + +Other coal-fields of less importance are found between Lakes Huron and +Erie, where the measures cover an area of 5000 square miles, and also in +Rhode Island. + +In British North America we find extensive deposits of valuable +coal-measures. Large developments occur in New Brunswick and Nova Scotia. +At South Joggins there is a thickness of 14,750 feet of strata, in which +are found seventy-six coal-seams of 45 feet in total thickness. At Picton +there are six seams with a total of 80 feet of coal. In the lower +carboniferous group is found the peculiar asphaltic coal of the Albert +mine in New Brunswick. Extensive deposits of lignite are met with both in +the Dominion and in the United States, whilst true coal-measures flank +both sides of the Rocky Mountains. Coal-seams are often encountered in +the Arctic archipelago. + +The principal areas of deposit in South America are in Brazil, Uruguay, +and Peru. The largest is the Candiota coal-field, in Brazil, where +sections in the valley of the Candiota River show five good seams with a +total of 65 feet of coal. It is, however, worked but little, the +principal workings being at San Jeronimo on the Jacahahay River. + +In Peru the true carboniferous coal-seams are found on the higher ground +of the Andes, whilst coal of secondary age is found in considerable +quantities on the rise towards the mountains. At Porton, east of +Truxillo, the same metamorphism which has changed the ridge of sandstone +to a hard quartzite has also changed the ordinary bituminous coal into an +anthracite, which is here vertical in position. The coals of Peru usually +rise to more than 10,000 feet above the sea, and they are practically +inaccessible. + +Cretaceous coals have been found at Lota in Chili, and at Sandy Point, +Straits of Magellan. + +Turning to Asia, we find that coal has been worked from time to time at +Heraclea in Asia Minor. Lignites are met with at Smyrna and Lebanon. + +The coal-fields of Hindoostan are small but numerous, being found in all +parts of the peninsula. There is an important coal-field at Raniganj, +near the Hooghly, 140 miles north of Calcutta. It has an area of 500 +square miles. In the Raniganj district there are occasional seams 20 feet +to 80 feet in thickness, but the coals are of somewhat inferior quality. + +The best quality amongst Indian coals has come from a small coal-field of +about 11 square miles in extent, situated at Kurhurbali on the East +Indian Railway. Other coal-fields are found at Jherria and on the Sone +River, in Bengal, and at Mopani on the Nerbudda. Much is expected in +future from the large coal-field of the Wardha and Chanda districts, in +the Central Provinces, the coal of which may eventually prove to be of +Permian age. + +The coal-deposits of China are undoubtedly of tremendous extent, although +from want of exploration it is difficult to form any satisfactory +estimate of them. Near Pekin there are beds of coal 95 feet thick, which +afford ample provision for the needs of the city. In the mountainous +districts of western China the area over which carboniferous strata are +exposed has been estimated at 100,000 square miles. The coal-measures +extend westward to the Mongolian frontier, where coal-seams 30 feet thick +are known to lie in horizontal plane for 200 miles. Most of the Chinese +coal-deposits are rendered of small value, either owing to the +mountainous nature of the valleys in which they outcrop, or to their +inaccessibility from the sea. Japan is not lacking in good supplies of +coal. A colliery is worked by the government on the island of Takasima, +near Nagasaki, for the supply of coals for the use of the navy. + +The British possession of Labuan, off the island of Borneo, is rich in a +coal of tertiary age, remarkable for the quantity of fossil resin which, +it contains. Coal is also found in Sumatra, and in the Malayan +Archipelago. + +In Cape Colony and Natal the coal-bearing Karoo beds are probably of New +Red age. The coal is reported to be excellent in quantity. + +In Abyssinia lignites are frequently met with in the high lands of the +interior. + +Coal is very extensively developed throughout Australasia. In New South +Wales, coal-measures occur in large detached portions between 29 deg. and 35 deg. +S. latitude. The Newcastle district, at the mouth of the Hunter river, is +the chief seat of the coal trade, and the seams are here found up to 30 +feet thick. Coal-bearing strata are found at Bowen River, in Queensland, +covering an area of 24,000 square miles, whilst important mines of +Cretaceous age are worked at Ipswich, near Brisbane. In New Zealand +quantities of lignite, described as a hydrous coal, are found and +utilised; also an anhydrous coal which may prove to be either of +Cretaceous or Jurassic age. + +We have thus briefly sketched the supplies of coal, so far as they are +known, which are to be found in various countries. But England has of +late years been concerned as to the possible failure of her home supplies +in the not very distant future, and the effects which such failure would +be likely to produce on the commercial prosperity of the country. + +Great Britain has long been the centre of the universe in the supply of +the world's coal, and as a matter of fact, has been for many years +raising considerably more than one half of the total amount of coal +raised throughout the whole world. There is, as we have seen, an +abundance of coal elsewhere, which will, in the course of time, compete +with her when properly worked, but Britain seems to have early taken the +lead in the production of coal, and to have become the great universal +coal distributor. Those who have misgivings as to what will happen when +her coal is exhausted, receive little comfort from the fact that in North +America, in Prussia, in China and elsewhere, there are tremendous +supplies of coal as yet untouched, although a certain sense of relief is +experienced when that fact becomes generally known. + +If by the time of exhaustion of the home mines Britain is still dependent +upon coal for fuel, which, in this age of electricity, scarcely seems +probable, her trade and commerce will feel with tremendous effect the +blow which her prestige will experience when the first vessel, laden with +foreign coal, weighs anchor in a British harbour. In the great coal +lock-out of 1893, when, for the greater part of sixteen weeks scarcely a +ton of coal reached the surface in some of her principal coal-fields, it +was rumoured, falsely as it appeared, that a collier from America had +indeed reached those shores, and the importance which attached to the +supposed event was shown by the anxious references to it in the public +press, where the truth or otherwise of the alarm was actively discussed. +Should such a thing at any time actually come to pass, it will indeed be +a retribution to those who have for years been squandering their +inheritance in many a wasteful manner of coal-consumption. + +Thirty years ago, when so much small coal was wasted and wantonly +consumed in order to dispose of it in the easiest manner possible at the +pitmouths, and when only the best and largest coal was deemed to be of +any value, louder and louder did scientific men speak in protest against +this great and increasing prodigality. Wild estimates were set on foot +showing how that, sooner or later, there would be in Britain no native +supply of coal at all, and finally a Royal Commission was appointed in +1866, to collect evidence and report upon the probable time during which +the supplies of Great Britain would last. + +This Commission reported in 1871, and the outcome of it was that a period +of twelve hundred and seventy-three years was assigned as the period +during which the coal would last, at the then-existing rate of +consumption. The quantity of workable coal within a depth of 4000 feet +was estimated to be 90,207 millions of tons, or, including that at +greater depths, 146,480 millions of tons. Since that date, however, there +has been a steady annual increase in the amount of coal consumed, and +subsequent estimates go to show that the supplies cannot last for more +than 250 years, or, taking into consideration a possible decrease in +consumption, 350 years. Most of the coal-mines will, indeed, have been +worked out in less than a hundred years hence, and then, perhaps, the +competition brought about by the demand for, and the scarcity of, coal +from the remaining mines, will have resulted in the dreaded importation +of coal from abroad. + +In referring to the outcome of the Royal Commission of 1866, although the +Commissioners fixed so comparatively short a period as the probable +duration of the coal supplies, it is but fair that it should be stated +that other estimates have been made which have materially differed from +their estimate. Whereas one estimate more than doubled that of the Royal +Commission, that of Sir William Armstrong in 1863 gave it as 212 years, +and Professor Jevons, speaking in 1875 concerning Armstrong's estimate, +observed that the annual increase in the amount used, which was allowed +for in the estimate, had so greatly itself increased, that the 212 years +must be considerably reduced. + +One can scarcely thoroughly appreciate the enormous quantity of coal that +is brought to the surface annually, and the only wonder is that there are +any supplies left at all. The Great Pyramid which is said by Herodotus to +have been twenty years in building, and which took 100,000 men to build, +contains 3,394,307 cubic yards of stone. The coal raised in 1892 would +make a pyramid which would contain 181,500,000 cubic yards, at the low +estimate that one ton could be squeezed into one cubic yard. + +The increase in the quantity of coal which has been raised in succeeding +years can well be seen from the following facts. + +In 1820 there were raised in Great Britain about 20 millions of tons. By +1855 this amount had increased to 64-1/2 millions. In 1865 this again had +increased to 98 millions, whilst twenty years after, viz., in 1885, this +had increased to no less than 159 millions, such were the giant strides +which the increase in consumption made. + +In the return for 1892, this amount had farther increased to 181-1/2 +millions of tons, an advance in eight years of a quantity more than equal +to the total raised in 1820, and in 1894 the total reached +199-1/2 millions; this was produced by 795,240 persons, employed in and +about the mines. + + + + +CHAPTER VIII. + +THE COAL-TAR COLOURS. + + +In a former chapter some slight reference has been made to those +bye-products of coal-tar which have proved so valuable in the production +of the aniline dyes. It is thought that the subject is of so interesting +a nature as to deserve more notice than it was possible to bestow upon it +in that place. With abstruse chemical formulae and complex chemical +equations it is proposed to have as little as possible to do, but even +the most unscientific treatment of the subject must occasionally +necessitate a scientific method of elucidation. + +The dyeing industry has been radically changed during the last half +century by the introduction of what are known as the _artificial_ dyes, +whilst the _natural_ colouring matters which had previously been the sole +basis of the industry, and which had been obtained by very simple +chemical methods from some of the constituents of the animal kingdom, or +which were found in a natural state in the vegetable kingdom, have very +largely given place to those which have been obtained from coal-tar, a +product of the mineralised vegetation of the carboniferous age. + +The development and discovery of the aniline colouring matters were not, +of course, possible until after the extensive adoption of +house-gas for illuminating purposes, and even then it was many years +before the waste products from the gas-works came to have an appreciable +value of their own. This, however, came with the increased utilitarianism +of the commerce of the present century, but although aniline was first +discovered in 1826 by Unverdorben, in the materials produced by the dry +distillation of indigo (Portuguese, _anil_, indigo), it was not until +thirty years afterwards, namely, in 1856, that the discovery of the +method of manufacture of the first aniline dye, mauveine, was announced, +the discovery being due to the persistent efforts of Perkin, to whom, +together with other chemists working in the same field, is due the great +advance which has been made in the chemical knowledge of the carbon, +hydrogen, and oxygen compounds. Scientists appeared to work along two +planes; there were those who discovered certain chemical compounds in the +resulting products of reactions in the treatment of _existing_ +vegetation, and there were those who, studying the wonderful constituents +in coal-tar, the product of a _past_ age, immediately set to work to find +therein those compounds which their contemporaries had already +discovered. Generally, too, with signal success. + +The discovery of benzene in 1825 by Faraday was followed in the course of +a few years by its discovery in coal-tar by Hofmann. Toluene, which was +discovered in 1837 by Pelletier, was recognised in the fractional +distillation of crude naphtha by Mansfield in 1848. Although the method +of production of mauveine on a large scale was not accomplished until +1856, yet it had been noticed in 1834, the actual year of its recognition +as a constituent of coal-tar, that, when brought into contact with +chloride of lime, it gave brilliant colours, but it required a +considerable cheapening of the process of aniline manufacture before the +dyes commenced to enter into competition with the old natural dyes. + +The isolation of aniline from coal-tar is expensive, in consequence of +the small quantities in which it is there found, but it was discovered by +Mitscherlich that by acting upon benzene, one of the early distillates of +coal-tar, for the production of nitro-benzole, a compound was produced +from which aniline could be obtained in large quantities. There were thus +two methods of obtaining aniline from tar, the experimental and the +practical. + +In producing nitrobenzole (nitrobenzene), chemically represented as +(C_{6}H_{5}NO_{2}), the nitric acid used as the reagent with benzene, is +mixed with a quantity of sulphuric acid, with the object of absorbing +water which is formed during the reaction, as this would tend to dilute +the efficiency of the nitric acid. The proportions are 100 parts of +purified benzene, with a mixture of 115 parts of concentrated nitric acid +(HNO_{3}) and 160 parts of concentrated sulphuric acid. The mixture is +gradually introduced into the large cast-iron cylinder into which the +benzene has been poured. The outside of the cylinder is supplied with an +arrangement by which fine jets of water can be made to play upon it in +the early stages of the reaction which follows, and at the end of from +eight to ten hours the contents are allowed to run off into a storage +reservoir. Here they arrange themselves into two layers, the top of which +consists of the nitrobenzene which has been produced, together with some +benzene which is still unacted upon. The mixture is then freed from the +latter by treatment with a current of steam. Nitrobenzene presents itself +as a yellowish oily liquid, with a peculiar taste as of bitter almonds. +It was formerly in great demand by perfumers, but its poisonous +properties render it a dangerous substance to deal with. In practice a +given quantity of benzene will yield about 150 per cent of nitrobenzene. +Stated chemically, the reaction is shown by the following equation:-- + +C_{6}H_{6} + HNO_{3} = C_{6}H_{5}NO_{2}, + H_{2}O +(Benzene) (Nitric acid) (Nitrobenzene) (Water). + +The water which is thus formed in the process, by the freeing of one of +the atoms of hydrogen in the benzene, is absorbed by the sulphuric acid +present, although the latter takes no actual part in the reaction. + +From the nitrobenzene thus obtained, the aniline which is now used so +extensively is prepared. The component atoms of a molecule of aniline are +shown in the formula C_{6}H_{5}NH_{2}. It is also known as phenylamine or +amido-benzole, or commercially as aniline oil. There are various methods +of reducing nitrobenzene for aniline, the object being to replace the +oxygen of the former by an equivalent number of atoms of hydrogen. The +process generally used is that known as Bechamp's, with slight +modifications. Equal volumes of nitrobenzene and acetic acid, together +with a quantity of iron-filings rather in excess of the weight of the +nitrobenzene, are placed in a capacious retort. A brisk effervescence +ensues, and to moderate the increase of temperature which is caused by +the reaction, it is found necessary to cool the retort. Instead of acetic +acid hydrochloric acid has been a good deal used, with, it is said, +certain advantageous results. From 60 to 65 per cent. of aniline on the +quantity of nitrobenzene used, is yielded by Bechamp's process. + +Stated in a few words, the above is the process adopted on all hands for +the production of commercial aniline, or aniline oil. The details of the +distillation and rectification of the oil are, however, as varied as they +can well be, no two manufacturers adopting the same process. Many of the +aniline dyes depend entirely for their superiority, on the quality of the +oil used, and for this reason it is subject to one or more processes of +rectification. This is performed by distilling, the distillates at the +various temperatures being separately collected. + +When pure, aniline is a colourless oily liquid, but on exposure rapidly +turns brown. It has strong refracting powers and an agreeable aromatic +smell. It is very poisonous when taken internally; its sulphate is, +however, sometimes used medicinally. It is by the action upon aniline of +certain oxidising agents, that the various colouring matters so well +known as aniline dyes are obtained. + +Commercial aniline oil is not, as we have seen, the purest form of +rectified aniline. The aniline oils of commerce are very variable in +character, the principal constituents being pure aniline, para- and +meta-toluidine, xylidines, and cumidines. They are best known to the +colour manufacturer in four qualities-- + +(_a_) Aniline oil for blue and black. + +(_b_) Aniline oil for magenta. + +(_c_) Aniline oil for safranine. + +(_d_) _Liquid toluidine. + +From the first of these, which is almost pure aniline, aniline black is +derived, and a number of organic compounds which are further used for the +production of dyes. The hydrochloride of aniline is important and is +known commercially as "aniline salt." + +The distillation and rectification of aniline oil is practised on a +similar principle to the fractional distillation which we have noticed as +being used for the distillation of the naphthas. First, light aniline +oils pass over, followed by others, and finally by the heavy oils, or +"aniline-tailings." It is a matter of great necessity to those engaged in +colour manufacture to apply that quality oil which is best for the +production of the colour required. This is not always an easy matter, and +there is great divergence of opinion and in practice on these points. + +The so-called aniline colours are not all derived from aniline, such +colouring matters being in some cases derived from other coal-tar +products, such as benzene and toluene, phenol, naphthalene, and +anthracene, and it is remarkable that although the earlier dyes were +produced from the lighter and more easily distilled products of +coal-tar, yet now some of the heaviest and most stubborn of the +distillates are brought under requisition for colouring matters, those +which not many years ago were regarded as fit only to be used as +lubricants or to be regarded as waste. + +It is scarcely necessary or advisable in a work of this kind to pursue +the many chemical reactions, which, from the various acids and bases, +result ultimately in the many shades and gradations of colour which are +to be seen in dress and other fabrics. Many of them, beautiful in the +extreme, are the outcome of much careful and well-planned study, and to +print here the complicated chemical formulae which show the great changes +taking place in compounds of complex molecules, or to mention even the +names of these many-syllabled compounds, would be to destroy the purpose +of this little book. The Rosanilines, the Indulines, and Safranines; the +Oxazines, the Thionines: the Phenol and Azo dyes are all substances which +are of greater interest to the chemical students and to the colour +manufacturer than to the ordinary reader. Many of the names of the bases +of various dyes are unknown outside the chemical dyeworks, although each +and all have complicated; reactions of their own. In the reds are +rosanilines, toluidine xylidine, &c.; in the blues--phenyl-rosanilines, +diphenylamine, toluidine, aldehyde, &c.; violets--rosaniline, mauve, +phenyl, ethyl, methyl, &c.; greens--iodine, aniline, leucaniline, +chrysotoluidine, aldehyde, toluidine, methyl-anilinine, &c.; yellows and +orange--leucaniline, phenylamine, &c.; browns--chrysotoluidine, &c.; +blacks--aniline, toluidine, &c. + +To take the rosanilines as an instance of the rest. + +Aniline red, magenta, azaleine, rubine, solferino, fuchsine, chryaline, +roseine, erythrobenzine, and others, are colouring matters in this group +which are salts of rosaniline, and which are all recognised in commerce. + +The base rosaniline is known chemically by the formula C_{20}H_{l9}N_{3}, +and is prepared by heating a mixture of magenta aniline, toluidine, and +pseudotoluidine, with arsenic acid and other oxidising agents. It is +important that water should be used in such quantities as to prevent the +solution of arsenic acid from depositing crystals on cooling. Unless +carefully crystallised rosaniline will contain a slight proportion of the +arseniate, and when articles of clothing are dyed with the salt, it is +likely to produce an inflammatory condition of skin, when worn. Some +years ago there was a great outcry against hose and other articles dyed +with aniline dyes, owing to the bad effects which were produced, and this +has no doubt proved very prejudicial to aniline dyes as a whole. + +Again, the base known as mauve, or mauveine, has a composition shown by +the formula C_{27}H_{24}N_{4}. It is produced from the sulphate of +aniline by mixing it with a cold saturated solution of bichromate of +potash, and allowing the mixture to stand for ten or twelve hours. A +blue-black precipitate is then formed, which, after undergoing a process +of purification, is dissolved in alcohol and evaporated to dryness. A +metallic-looking powder is then obtained, which constitutes this +all-important base. Mauve forms with acids a series of well-defined salts +and is capable of expelling ammonia from its combinations. Mauve was the +first aniline dye which was produced on a large scale, this being +accomplished by Perkin in 1856. + +The substance known as carbolic acid is so useful a product of a piece of +coal that a description of the method of its production must necessarily +have a place here. It is one of the most powerful antiseptic agents with +which we are acquainted, and has strong anaesthetic qualities. Some +useful dyes are also obtained from it. It is obtained in quantities from +coal-tar, that portion of the distillate known as the light oils being +its immediate source. The tar oil is mixed with a solution of caustic +soda, and the mixture is violently agitated. This results in the caustic +soda dissolving out the carbolic acid, whilst the undissolved oils +collect upon the surface, allowing the alkaline solution to be drawn from +beneath. The soda in the solution is then neutralised by the addition of +a suitable quantity of sulphuric acid, and the salt so formed sinks while +the carbolic acid rises to the surface. + +Purification of the product is afterwards carried out by a process of +fractional distillation. There are various other methods of preparing +carbolic acid. + +Carbolic acid is known chemically as C_{6}H_{5}(HO). When pure it appears +as colourless needle-like crystals, and is exceedingly poisonous. It has +been used with marked success in staying the course of disease, such as +cholera and cattle plague. It is of a very volatile nature, and its +efficacy lies in its power of destroying germs as they float in the +atmosphere. Modern science tells us that all diseases have their origin +in certain germs which are everywhere present and which seek only a +suitable _nidus_ in which to propagate and flourish. Unlike mere +deodorisers which simply remove noxious gases or odours; unlike +disinfectants which prevent the spread of infection, carbolic acid +strikes at the very root and origin of disease by oxidising and consuming +the germs which breed it. So powerful is it that one part in five +thousand parts of flour paste, blood, &c., will for months prevent +fermentation and putrefaction, whilst a little of its vapour in the +atmosphere will preserve meat, as well as prevent it from becoming +fly-blown. Although it has, in certain impure states, a slightly +disagreeable odour, this is never such as to be in any way harmful, +whilst on the other hand it is said to act as a tonic to those connected +with its preparation and use. + +The new artificial colouring matters which are continually being brought +into the market, testify to the fact that, even with the many beautiful +tints and hues which have been discovered, finality and perfection have +not yet been reached. A good deal of popular prejudice has arisen against +certain aniline dyes on account of their inferiority to many of the old +dye-stuffs in respect to their fastness, but in recent years the +manufacture of many which were under this disadvantage of looseness of +dye, has entirely ceased, whilst others have been introduced which are +quite as fast, and sometimes even faster than the natural dyes. + +It is convenient to express the constituents of coal-tar, and the +distillates of those constituents, in the form of a genealogical chart, +and thus, by way of conclusion, summarise the results which we have +noticed. + + COAL. + | + .----------+-----------+----+-------------------+--------+----. + | | | | | | + Water House-gas Coal-tar Ammoniacal Coke | + | liquor | + .---------+-------+---------+---------. | Sulphur + | | | | | | (sulphurreted + First Second Heavy Anthracene Pitch | hydrogen: + light light oils (green | sulphurous + oils oils (creosote oils) | acid: oil + | (crude oils) | | of vitriol) + .----+----. naphtha) | Anthracene | + | | | | | | +Ammoniacal Benzene | | Alizarin or | + liquor toluene,| | dyer's madder | + &c. | | | + | | | + | | Sulphuric acid=Carbonate of=Hydrochloric + | | | ammonia acid + | | | (smelling + | | | salts) + | | | + | | Lime=Sulphate of Lime=Chloride of + | | | ammonia | ammonia (sal + | | | | ammoniac) + | | | | + | | .----+----. .----+----. + | | | | | | + | | Ammonia Sulphate Ammonia Chloride + | | of lime of lime. + | | (Plaster of Paris) + | | + | .--+-----+----------. + | | | | + | Crude Carbolic Naphthalin + | Creosote acid + | + .--------------+---+--+-------+--------+-----------. + | | | | | + Benzene=Nitric Acid Toluene Nylene Artificial Burning + | turpentine oils + Nitrobenzene= } Iron filings oil (solvent + (Essence de | } and acetic acid naphtha) + mirbane) | + | + Aniline=Various reagents + | + Aniline dyes + + + + + + +INDEX. + +A. + +Accidents, causes of mining +"Age of _Acrogens_" +_Alethopteris_ +Alizarin +American coal-fields +Ammoniacal liquor +Aniline +Aniline dyes +Aniline oil, commercial +Aniline salt +Aniline "tailings" +Anthracene +Anthracite +Artificial turpentine oil +Asphalt +Australian coals +_Aviculopecten_ + +B. + +Bechamp's process +Benzene +Bind +Bitumen in Trinidad +"Blower" a +Boghead coal +Bog-oak +Boring diamonds +Borrowdale graphite mine +Bovey Tracey lignite +British coal-fields +British North-American coal-measures +Briquettes + +C. + +_Calamites_, extinct horsetails +Carbolic acid +Carboniferous formation, the +_Cardiocarpum_, fossil fruit +Carelessness of miners +Causes of earth-movements +Changes of level +Charcoal as a disinfectant +Chemistry of a gas-flame +Chinese coals +Clanny's safety-lamp +Clayton's experiments with gas +Clay, regularity in deposition of +Club-mosses, great height of fossil +Coal-dust, danger from +Coal formed in large lakes or closed seas +Coal formation, geological position of +Coal formed by escape of gases +Coal-mine, the +Coal not the result of drifted vegetation +Coal-period, climate of +"Coal-pipes" +Coal-plants, classification of +Coal-seam, each, a forest growth +Coals of non-carboniferous age +Coal, vegetable origin of +Coke +"Cole" +"Condensers" +Cones of _Lepidodendra_ +Conifers in coal-measures +Current-bedding in sandstone + +D. + +Davy-lamp +Dangers of benzene +Darwin on the Chonos Archipelago +Diamonds, how made artificially +Disintegration of vegetable substances +Disproportion in relative thickness of coal and coal-measures + +E. + +Early use of coal +Effects of an explosion +Encrinital limestone +_Equiseta_ +"Essence de mirbane" +European coal-fields +Evelyn on the use of coal +Experiments illustrating fossilisation + +F. + +Filling retorts by machinery +Firedamp +Fire, mines on +First light oils +First record of an explosion +Flashing-point of oil +Flooding of pits +Fog and smoke +_Foraminifera_ +Fossil ferns +Fructification on fossil-ferns +Furnace, ventilating + +G. + +Gas, coal +Gasholder, the +Gas, house, constituents of +_Glossopteris_ +Graphite +"Green Grease" + +H. + +Hannay, of Glasgow +Heavy oils +Humboldt's safety-lamp +Hydraulic Main + +I. + +Impurities in house-gas +Indian coals +Insertion of rootlets of _stigmaria_ +Insufficiency of modern forest growths +Ireland denuded of coal-beds +Iron, supplies of + +L. + +_Lepidodendra_ +_Lepidostrobi_ +Lignite +London lit by gas + +M. + +Mammoth trees +Marco Polo +Marsh gas +Medium oils +Metamorphism of coal by igneous agency +Methods of ventilation +Mountain limestone +Murdock's use of gas +Mussel beds + +N. + +Napthalin +_Neuropteris_ +Newcastle, charters to +Nitro-benzole + +O. + +Objections to use of coal +Oils from coal and lignite +Oil-wells of America +Olefiant gas +_Orthoceras_ + +P. + +Paraffins +Peat +_Pecopteris_ +Pennsylvanian anthracite +Persian fire-worshippers +Pitch +Plumbago +_Polyzoa_ +Prejudice against aniline dyes +Prohibitions of the use of coal +Proportions of explosive mixtures +_Psaronius_ +"Purifiers" +Pyrites in coal + +Q. + +Quantity of coal raised in Great Britain + +R. + +Reptiles of the coal-era +Resemblance of American and British coal-_flora_ +Retorts +Roman use of coal +Rosanilines, the +Royal Commission of 1866 + +S. + +Sandstone, how formed +Shales +_Sigillaria_ +South American coals +Spores of _lepidodrendron_ +Spores, resinous matter in +Spores, inflammability of +Steel-mill +_Sternbergia_ +_Stigmaria_ +Subsidence throughout coal-era +Surturbrand at Brighton +Sussex iron-works + +T. + +Tar +Testing pits by the candle +Texas coal +Toluene, discovery of +Torbanehill mineral +Trappers + +U. + +Underclays +Uses to which coal is put + +V. + +Vaseline +Vegetation of the coal age +Ventilation of coal-pits + +W. + +"Washers" +Waste of fuel +Wealden lignite +Westphalian coal-field + +Y. + +Young's Paraffin Oil + +Z. + +Zoroastrians + + + + + +End of Project Gutenberg's The Story of a Piece of Coal, by Edward A. 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