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 princ.i.p.al 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._, c.o.ke.

The ammoniacal liquor which has been pa.s.sing 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 const.i.tuents. 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 quant.i.ty of acid, which converts the princ.i.p.al const.i.tuent 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 quant.i.ties of coal are burned.

c.o.ke, if properly prepared, should consist of pure carbon. Good coal should yield as much as 80 per cent. of c.o.ke, but owing to the unsatisfactory manner of its production, this proportion is seldom yielded, whilst the c.o.ke 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 quant.i.ty of oxygen required in its combustion, it gives rise to feelings of suffocation where insufficient ventilation of the room is provided.

Large quant.i.ties of c.o.ke 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 quant.i.ties of coal are "c.o.ked," a process by which the volatile products are completely combusted, pure c.o.ke 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 c.o.ke 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 princ.i.p.al areas.

The northern coal-field, including those of Fife, Stirling, and Ayr in Scotland; c.u.mberland, 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 pa.s.s 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 princ.i.p.al 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 pa.s.sed through no less than six times.

Germany, on the west side of the Rhine, is exceptionally fortunate in the possession of the famous Pfalz-Saarbrucken 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 quant.i.ty 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 antic.i.p.ate 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 spa.r.s.eness 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 Lia.s.sic 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.