Amongst the actual coal-fields, that of Pennsylvania stands pre-eminent. The anthracite here is in inexhaustible quant.i.ty, 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 princ.i.p.al 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 a.s.sumes an almost horizontal position. In pa.s.sing 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.

Pa.s.sing 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 Lia.s.sic age. Another important area of production in eastern Virginia contains coal referable to the Jura.s.sic age, and is similar in fossil contents to the Jura.s.sic 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 princ.i.p.al 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 princ.i.p.al 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 quant.i.ties 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. j.a.pan 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 quant.i.ty 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 quant.i.ty.

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. lat.i.tude. 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 quant.i.ties of lignite, described as a hydrous coal, are found and utilised; also an anhydrous coal which may prove to be either of Cretaceous or Jura.s.sic 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 princ.i.p.al coal-fields, it was rumoured, falsely as it appeared, that a collier from America had indeed reached those sh.o.r.es, 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 pa.s.s, 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 a.s.signed as the period during which the coal would last, at the then-existing rate of consumption. The quant.i.ty 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 compet.i.tion 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 quant.i.ty 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 quant.i.ty 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 quant.i.ty 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 const.i.tuents 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 const.i.tuents 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 const.i.tuent 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 compet.i.tion with the old natural dyes.

The isolation of aniline from coal-tar is expensive, in consequence of the small quant.i.ties 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 quant.i.ties. 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 quant.i.ty 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 quant.i.ty 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 quant.i.ty 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 quant.i.ty 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 princ.i.p.al const.i.tuents being pure aniline, para- and meta-toluidine, xylidines, and c.u.midines. They are best known to the colour manufacturer in four qualities--

(_a_) Aniline oil for blue and black.

(_b_) Aniline oil for magenta.