Chapter XVI: Part 16

COALING STATIONS. Maritime war in all ages has required that the ships of the belligerents should have the use of sheltered waters for repairs and for replenishment of supplies. The operations of commerce from the earliest days demanded natural harbours, round which, as in the conspicuous instance of Syracuse, large populations gathered. Such points, where wealth and resources of all kinds accumulated, became objects of attack, and great efforts were expended upon their capture. As maritime operations extended, the importance of a seaboard increased, and the possession of good natural harbours became more and more advantageous. At the same time, the growing size of ships and the complexity of fitments caused by the development of the sailing art imposed new demands upon the equipment of ports alike for purposes of construction and for repairs; while the differentiation between warships and the commercial marine led to the establishment of naval bases and dockyards provided with special resources. From the days when the great sailors of Elizabeth carried war into distant seas, remote harbours began to assume naval importance. Expeditionary forces required temporary bases, such as Guantanamo Bay, in Cuba, which was so utilized by Admiral Vernon in 1741. As outlying territories began to be occupied, and jurisdiction to be exercised over their ports, the harbours available for the free use of a belligerent were gradually reduced in number, and it became occasionally necessary to take them by force. Thus, in 1782, the capture of Trincomalee was an object of sufficient importance to justify special effort, and Suffren gained a much-needed refuge for his ships, at the same time compelling his opponent to depend upon the open roadstead of Madras, and even to send ships to Bombay. In this case a distant harbour acquired strategic importance, mainly because sheltered waters, in the seas where Hughes and Suffren strove for naval supremacy, were few and far between. A sailing man-of-war usually carried from five to six months' provisions and water for 100 to 120 days. Other needs required to be met, and during the wars of the French Revolution it was usual, when possible, to allow ships engaged in blockade to return to port every five or six weeks "to refresh." For a sailing fleet acting on the offensive, a port from which it could easily get to sea was a great advantage. Thus Raleigh protested against the use of closely landlocked harbours. "Certain it is," he wrote, "that these ships are purposely to serve His Majesty and to defend the kingdom from danger, and not to be so penned up from casualitie as that they should be less able or serviceable in times of need." Nelson for this reason made great use of Maddalena Bay, in Sardinia, and was not greatly impressed with the strategic value of Malta in spite of its fine natural harbour. The introduction of steam gave rise to a new naval requirement--coal--which soon became vital. Commerce under steam quickly settled down upon fixed routes, and depots of coal were established to meet its needs. Coaling stations thus came into existence by a natural process, arising from the exigencies of trade, and began later to supply the needs of navies.

British coaling stations.

For many years there was no inquiry into the war requirements of the British fleet as regards coal, and no attempt to regularize or to fortify the ports at which it was stored. Successful naval war had won for Great Britain many points of vantage throughout the world, and in some cases the strategic value of ports had been proved by actual experience. The extreme importance of the Cape of Good Hope, obscured for a time after the opening of the Suez Canal, was fully realized in sailing days, and the naval conditions of those days to some extent determined the choice of islands and harbours for occupation. There does not, however, appear to have been any careful study of relative strategic values. Treaties were occasionally drafted by persons whose geographical knowledge was at fault, and positions were, in some cases, abandoned which ought to have been retained, or tenaciously held when they might have been abandoned. It was left to the personal exertions of Sir Stamford Raffles to secure such a supremely important roadstead as that of Singapore for the empire. Although, therefore, the relative values of positions was not always recognized, Great Britain obtained as a legacy from sailing days a large number of harbours admirably adapted for use as coaling stations. Since the dawn of the era of steam, she has acquired Aden, Perim, Hong-Kong, North Borneo, Fiji, part of New Guinea, Fanning Island, and many other islands in the Pacific, while the striking development of Australia and New Zealand has added to the long roll of British ports. The coaling stations, actual and potential, of the empire are unrivalled in number, in convenience of geographical distribution, and in resources. Of the numerous British ports abroad which contained coal stores, only the four so-called "fortresses"--Gibraltar, Malta, Halifax and Bermuda--were at first fortified as naval stations after the introduction of rifled ordnance. The term fortress is a misnomer in every case except Gibraltar, which, being a peninsula separated only by a neck of neutral ground from the territory of a foreign power, exists under fortress conditions. Large sums were expended on these places with little regard to principles, and the defences of Bermuda, which were very slowly constructed, are monuments of misapplied ingenuity.

Carnarvon Commission.

In 1878 great alarm arose from strained relations with Russia. Rumours of the presence of Russian cruisers in many waters, and of hostile projects, were readily believed, although the Russian navy, which had just shown itself unable to face that of Turkey, would at this period have been practically powerless. Widespread fears for the security of coaling stations led to the appointment of a strong royal commission, under the presidency of the earl of Carnarvon, which was instructed to inquire into and report upon the protection of British commerce at sea. This was the first attempt to formulate any principles, or to determine which of the many ports where coal was stored should be treated as coaling stations essential for the purposes of war. The terms of the reference to the commission were ill-conceived. The basis of all defence of sea-borne commerce is a mobile navy. It is the movement of commerce upon the sea during war, not its security in port, that is essential to the British empire, and a navy able to protect commerce at sea must evidently protect ports and coaling stations. The first object of inquiry should, therefore, have been to lay down the necessary standard of naval force. The vital question of the navy was not referred to the royal commission, and the four fortresses were also strangely excluded from its purview. It followed inevitably that the protection of commerce was approached at the wrong end, and that the labours of the commission were to a great extent vitiated by the elimination of the principal factor. Voluminous and important evidence, which has not been made public, was, however, accumulated, and the final report was completed in 1881. The commissioners recalled attention to the extreme importance of the Cape route to the East; they carefully examined the main maritime communications of the empire, and the distribution of trade upon each; they selected certain harbours for defence, and they obtained from the War Office and endorsed projects of fortification in every case; lastly, they condemned the great dispersion of troops in the West Indies, which had arisen in days when it was a political object to keep the standing army out of sight of the British people, and had since been maintained by pure inadvertence. Although the principal outcome of the careful inquiries of the commission was to initiate a great system of passive defence, the able reports were a distinct gain. Some principles were at last formulated by authority, and the information collected, if it had been rendered accessible to the public, would have exercised a beneficial influence upon opinion. Moreover, the commissioners, overstepping the bounds of their charter, delivered a wise and statesmanlike warning as to the position of the navy.

Meanwhile, the impulse of the fears of 1878 caused indifferent armaments to be sent to Cape Town, Singapore and Hong-Kong, there to be mounted after much delay in roughly designed works. At the same time, the great colonies of Australasia began to set about the defence of their ports with commendable earnestness. There is no machinery for giving effect to the recommendations of a royal commission, and until 1887, when extracts were laid before the first colonial Conference, the valuable report was veiled in secrecy. After several years, during which Lord Carnarvon persistently endeavoured to direct attention to the coaling stations, the work was begun. In 1885 a fresh panic arose out of the Panjdeh difficulty, which supplied an impetus to the belated proceedings. Little had then been accomplished and the works were scarcely completed before the introduction of long breech-loading guns rendered their armaments obsolete.

The fortification of the coaling stations for the British empire is still proceeding on a scale which, in some cases, cannot easily be reconciled with the principles laid down by the president of the cabinet committee of defence. At the Guildhall, London, on the 3rd of December 1896, the duke of Devonshire stated that "The maintenance of sea supremacy has been assumed as the basis of the system of imperial defence against attack from over the sea. This is the determining factor in fixing the whole defensive policy of the empire." It was, however, he added, necessary to provide against "the predatory raids of cruisers"; but "it is in the highest degree improbable that this raiding attack would be made by more than a few ships, nor could it be of any permanent effect unless troops were landed." This is an unexceptionable statement of the requirements of passive defence in the case of the coaling stations of the British empire. Their protection must depend primarily on the navy. Their immobile armaments are needed to ward off a raiding attack, and a few effective guns, well mounted, manned by well-trained men, and kept in full readiness, will amply suffice.

Modern conditions.

Secondary bases.

If the command of the sea is lost, large expeditionary forces can be brought to bear upon coaling stations, and their security will thus depend upon their mobile garrisons, not upon their passive defences. In any case, where coal is stored on shore, it cannot be destroyed by the fire of a ship, and it can only be appropriated by landing men. A small force, well armed and well handled, can effectually prevent a raid of this nature without any assistance from heavy guns. In war, the possession of secure coal stores in distant ports may be a great advantage, but it will rarely suffice for the needs of a fleet engaged in offensive operations, and requiring to be accompanied or met at prearranged rendezvous by colliers from which coal can be transferred in any sheltered waters. In the British naval manoeuvres of 1892, Admiral Sir Michael Seymour succeeded in coaling his squadron at sea, and by the aid of mechanical appliances this is frequently possible. In the Spanish-American War of 1898 some coaling was thus accomplished; but Guantanamo Bay served the purpose of a coaling station during the operations against Santiago. Watering at sea was usually carried out by means of casks in sailing days, and must have been almost as difficult as coaling. As, however, it is certainty of coaling in a given time that is of primary importance, the utilization of sheltered waters as improvised coaling stations is sure to be a marked feature of future naval wars. Although coaling stations are now eagerly sought for by all powers which cherish naval ambitions, the annexation of the Hawaiian Islands by the United States being a case in point, it is probable that they will play a somewhat less important part than has been assumed. A fleet which is able to assert and to maintain the command of the sea, will not find great difficulty in its coal supply. Moreover, the increased coal endurance of ships of war tends to make their necessary replenishment less frequent. On the other hand, the modern warship, being entirely dependent upon a mass of complex machinery, requires the assistance of workshops to maintain her continuous efficiency, and unless docked at intervals suffers a material reduction of speed. Prolonged operations in waters far distant from home bases will therefore be greatly facilitated in the case of the Power which possesses local docks and means of executing repairs. Injuries received in action, which might otherwise disable a ship during a campaign, may thus be remedied. During the hostilities between France and China in 1884, the French ship "La Galissonniere" was struck by a shell from one of the Min forts, which, though failing to burst, inflicted serious damage. As, by a technical fiction, a state of war was not considered to exist, the "La Galissonniere" was repaired at Hong-Kong and enabled again to take the sea. Local stores of reserve ammunition and of spare armaments confer evident advantages. Thus, independently of the question of coal supply, modern fleets employed at great distances from their bases require the assistance of ports furnished with special resources, and a power like Japan with well-equipped naval bases in the China Sea, and possessing large sources of coal, occupies, for that reason, a favoured position in regard to naval operations in the Far East. As the term "coaling station" refers only to a naval need which can often be satisfied without a visit to any port, it appears less suitable to modern conditions than "secondary base." Secondary bases, or coaling stations, when associated with a powerful mobile navy, are sources of maritime strength in proportion to the services they can render, and to their convenience of geographical position. In the hands of an inferior naval power, they may be used, as was Mauritius in 1809-1810, as points from which to carry on operations against commerce; but unless situated near to trade routes, which must be followed in war, they are probably less useful for this purpose than in sailing days, since convoys can now be more effectively protected, and steamers have considerable latitude of courses. Isolated ports dependent on sea-borne resources, and without strong bodies of organized fighting men at their backs are now, as always, hostages offered to the power which obtains command of the sea. (G. S. C.)

COALITION (Lat. _coalitio_, the verbal substantive of _coalescere_, to grow together), a combination of bodies or parts into one body or whole. The word is used, especially in a political sense, of an alliance or temporary union for joint action of various powers or states, such as the coalition of the European powers against France, during the wars of the French Revolution; and also of the union in a single government of distinct parties or members of distinct parties. Of the various coalition ministries in English history, those of Fox and North in 1782, of the Whigs and the Peelites, under Lord Aberdeen in 1852-1853, and of the Liberal Unionists and Conservatives in Lord Salisbury's third ministry in 1895, may be instanced.

COAL-TAR, the black, viscous, sometimes semi-solid, fluid of peculiar smell, which is condensed together with aqueous "gas liquor" when the volatile products of the destructive distillation of coal are cooled down. It is also called "gas-tar," because it was formerly exclusively, and even now is mostly, obtained as a by-product in the manufacture of coal-gas, but the tar obtained from the modern coke-ovens, although not entirely identical with gas-tar, resembles it to such an extent that it is worked up with the latter, without making any distinction in practice between the two kinds. Some descriptions of gas-tar indeed differ very much more than coke-oven tar from pure coal-tar, viz. those which are formed when bituminous shale or other materials, considerably deviating in their nature from coal, are mixed with the latter for the purpose of obtaining gas of higher illuminating power.

It may be generally said that for the purpose of tar-distillers the tar is all the more valuable the less other materials than real coal have been used by the gas-maker. All these materials--bog-head shale, bituminous lignite and so forth--by destructive distillation yield more or less paraffinoid oils, which render the purification of the benzols very difficult and sometimes nearly impossible for the purposes of the manufacturer of coal-tar colours.

Neither too high nor too low a temperature should have been observed in gas-making in order to obtain a good quality of tar. Since in recent times most gas retorts have been provided with heating arrangements based on the production of gaseous fuel from coke, which produce higher temperatures than direct firing and have proved a great economy in the process of gas-making itself, the tar has become of decidedly inferior quality for the purposes of the tar-distillers, and in particular yields much less benzol than formerly.

Entirely different from gas-tar is the tar obtained as a by-product from those (Scottish) blast furnaces which are worked with splint-coal. This tar contains very little aromatic hydrocarbons, and the phenols are of quite a different character from those obtained in the working of gas-tar. The same holds good of oil-gas tars and similar substances. These should not be worked up like gas-tars.

The ordinary yield of tar in the manufacture of coal-gas is between 4 and 5% of the weight of the coal. Rather more is obtained when passing the gas through the apparatus of E. Pelouze and P. Audouin, where it is exposed to several shocks against solid surfaces, or by carrying on the process at the lowest possible temperature, as proposed by H. J. Davis, but this "carbonizing process" can only pay under special circumstances, and is probably no longer in practical use.

All coal-tars have a specific gravity above that of water, in most cases between 1.12 and 1.20, but exceptionally up to 1.25. The heavier tars contain less benzol than the lighter tars, and more "fixed carbon," which remains behind when the tars are exhausted of benzol and is a decidedly objectionable constituent. All tars also mechanically retain a certain quantity of water (or rather gas-liquor), say, 4% on the average, which is very obnoxious during the process of distillation, as it leads to "bumping," and therefore ought to be previously removed by prolonged settling, preferably at a slightly elevated temperature, which makes the tar more fluid. The water then rises to the top, and is removed in the ordinary way or by special "separators."

The tar itself is a mixture of exceedingly complex character. The great bulk of its constituents belongs to the class of "aromatic" hydrocarbons, of very different composition and degrees of volatility, beginning with the simplest and most volatile, benzene (C6H6), and ending with an entirely indistinguishable mass of non-volatile bodies, which compose the pitch left behind in the tar-stills. The hydrocarbons mostly belong to the benzene series CnH2n-6, the naphthalene series CnH2n-12, and the anthracene and phenanthrene series CnH2n-18. Small quantities of "fatty" ("aliphatic") hydrocarbons are never absent, even in pure tars, and are found in considerable quantities when shales and similar matters have been mixed with the coal in the gas-retorts. They belong mostly to the paraffins CnH2n+2, and the olefines CnH2n. The "asphalt" or soluble part of the pitch is also a mixture of hydrocarbons, of the formula CnH2n; even the "carbon," left behind after treating the pitch with all possible solvents is never pure carbon, but contains a certain quantity of hydrogen, although less than any of the volatile and soluble constituents of the tar.

Besides the hydrocarbons, coal-tar contains about 2% of the simpler phenols CnH2n-7OH, the best known and most valuable of which is the first of the series, carbolic acid (q.v.) C6H5OH, besides another interesting oxygenized substance, cumarone C8H6O. The phenols, especially the carbolic acid, are among the more valuable constituents of coal-tar. Numerous sulphur compounds also occur in coal-tar, some of which impart to it their peculiar nauseous smell, but they are of no technical importance or value.

Still more numerous are the nitrogenated compounds contained in coal-tar. Most of these are of a basic character, and belong to the pyridine and the quinoline series. Among these we find a somewhat considerable quantity of aniline, which, however, is never obtained from the tar for commercial purposes, as its isolation in the pure state is too difficult. The pyridines are now mostly recovered from coal-tar, but only in the shape of a mixture of all members of the series which is principally employed for denaturing alcohol. Some of these nitrogenated compounds possess considerable antiseptic properties, but on the whole they are only considered as a contamination of the tar-oils.

_Applications of Coal-Tar in the Crude State._--Large quantities of coal-tar are employed for various purposes without submitting it to the process of distillation. It is mostly advisable to dehydrate the tar as much as possible for any one of its applications, and in some cases it is previously boiled in order to remove its more volatile constituents.

No preparation whatever is needed if the tar is to be used as _fuel_, either for heating the gas-retorts or for other purposes. Its heating-value is equal to the same weight of best coal, but it is very difficult to burn it completely without producing a great deal of evil-smelling smoke. This drawback has been overcome by employing the same means as have been found suitable for the combustion of the heavy petroleum residues, called "masut," viz. converting the tar into a fine spray by means of steam or compressed air. When the gas-maker cannot conveniently or profitably dispose of his tar for other purposes, he burns it by the above means under his retorts.

Several processes have also been patented for producing _illuminating gas_ from tar, the most notable of which is the Dinsmore process. This process has been adversely criticized by very competent gas-makers, and no great success can be expected in this line.

Coal-tar is very much employed for painting wood, iron, brickwork, or stone, as a preventive against the influence of weather or the far more potent action of corrosive chemicals. This, of course, can be done only where appearance is no object, for instance in chemical works, where all kinds of erections and apparatus are protected by this cheap kind of paint. Coal-tar should not be used for tarring the woodwork and ropes of ships, a purpose for which only wood-tar has been found suitable.

One of the most considerable outlets for crude tar is in the manufacture of _roofing-felt_. This industry was introduced in Germany upwards of a hundred years ago, even before coal-tar was available, and has reached a very large extension both in that country and in the United States, where most of the gas-tar seems to be devoted to this purpose. In the United Kingdom it is much less extensive. For this manufacture a special fabric is made from pure woollen fibre, on rolls of about 3 ft. width and of considerable length. The tar must be previously dehydrated, and is preferably deprived of its more volatile portions by heating in a still. It is heated in an iron pan to about 90 deg. or 100 deg.C.; the fabric is drawn through it by means of rollers which at the same time squeeze out the excess of tar; on coming out of these, the tarred felt is covered with a layer of sand on both sides by means of a self-acting apparatus; and is ultimately wound round wooden rolls, in which state it is sent out into the trade. This roofing-felt is used as a cheap covering, both by itself and as a grounding for tiles or slates. In the former case it must be kept in repair by repainting with tar from time to time, a top covering of sand or small gravel being put on after every coat of paint.

Coal-tar is also employed for the manufacture of _lamp-black_. This is done by burning the tar in ovens, connected with brick-chambers in which the large quantity of soot, formed in this process, deposits before the gases escape through the chimney. Numerous patents have been taken out for more efficiently collecting this soot. Most of it is employed without further manipulation for the manufacture of electric carbons, printing inks, shoe-blacking, patent leather and so forth. A finer quality of lamp-black, free from oily and empyreumatic parts, is obtained by calcining the soot in closed iron pots at a red heat.

_Distillation of Coal-Tar._--Much more important than all applications of crude coal-tar is the industry of separating its constituents from it in a more or less pure form by fractional distillation, mostly followed by purifying processes. Most naturally this industry took its rise in Great Britain, where coal-gas was invented and made on a large scale before any other nation took it up, and up to this day both the manufacture of coal-gas and the distillation of the tar, obtained as a by-product thereof, are carried out on a much larger scale in that than in any other country. The first attempts in this line were made in 1815 by F. C. Accum, and in 1822 by Dr G. D. Longstaff and Dr Dalston. At first the aim was simply to obtain "naphtha," used in the manufacture of india-rubber goods, for burning in open lamps and for some descriptions of varnish; the great bulk of the tar remained behind and was used as fuel or burned for the purpose of obtaining lamp-black.

It is not quite certain who first discovered in the coal-naphtha the presence of benzene (q.v.), which had been isolated from oil-gas by M. Faraday as far back as 1825. John Leigh claims to have shown coal-tar benzene and nitro-benzene made from it at the British Association meeting held at Manchester in 1842, but the report of the meeting says nothing about it, and the world in general learned the presence of benzene in coal-tar only from the independent discovery of A. W. Hofmann, published in 1845. And it was most assuredly in Hofmann's London laboratory that Charles Mansfield worked out that method of fractional distillation of the coal-tar and of isolating the single hydrocarbons which laid the foundation of that industry. His patent, numbered 11,960 and dated November 11th, 1847, is the classical land-mark of it. About the same time, in 1846, Bronner, at Frankfort, brought his "grease-remover" into the trade, which consisted of the most volatile coal-tar oils, of course not separated into the pure hydrocarbons; he also sold water-white "creosote" and heavy tar-oils for pickling railway timbers, and used the remainder of the tar for the manufacture of roofing-felt. The employment of heavy oils for pickling timber had already been patented in 1838 by John Bethell, and from this time onward the distillation of coal-tar seems to have been developed in Great Britain on a larger scale, but the utilization of the light oils in the present manner naturally took place only after Sir W. H. Perkin, in 1856, discovered the first aniline colour which suddenly created a demand for benzene and its homologues. The isolation of carbolic acid from the heavier oils followed soon after; that of naphthalene, which takes place almost automatically, went on simultaneously, although the uses of this hydrocarbon for a long time remained much behind the quantities which are producible from coal-tar, until the manufacture of synthetic indigo opened out a wide field for it. The last of the great discoveries in that line was the preparation of alizarine from anthracene by C. Graebe and C. T. Liebermann, in 1868, soon followed by patents for its practical manufacture by Sir W. H. Perkin in England, and by Graebe, Liebermann and H. Caro in Germany.

The present extension of the industry of coal-tar distilling can be only very roughly estimated from the quantity of coal-tar produced in various countries. Decidedly at the head is Great Britain, where about 700,000 tons are produced per annum, most of which probably finds its way into the tar-distilleries, whilst in Germany and the United States much less gas-tar is produced and a very large proportion of it is used for roofing-felt and other purposes.

We shall now give an outline of the processes used in the distillation of tar.

_Dehydration._--The first operation in coal-tar distilling is the
removal of the mechanically enclosed water. Some water is chemically
combined with the bases, phenols, &c., and this, of course, cannot be
removed by mechanical means, but splits off only during the
distillation itself, when a certain temperature has been reached. The
water mechanically present in the tar is separated by long repose in
large reservoirs. Very thick viscous tars are best mixed with thinner
tars, and the whole is gently heated by coils of pipes through which
the heated water from the oil-condensers is made to flow. Sometimes
special "tar-separators" are employed, working on the centrifugal
principle. The water rises to the top and is worked up like ordinary
gas-liquor. More water is again separated during the heating-up of the
tar in the still itself, and can be removed there by a special
overflow.

]

_Tar-Stills._--The tar is now pumped into the tar-still, fig. 1. This
is usually, as shown, an upright wrought-iron cylinder, with an arched
top, and with a bottom equally vaulted upwards for the purpose of
increasing the heating surface and of raising the level of the pitch
remaining at the end of the operation above the fire-flues. The fuel
is consumed on the fire-grate a, and, after having traversed the holes
bb in the annular wall e built below the still, the furnace gases are
led around the still by means of the flue d, whence they pass to the
chimney. Cast-iron necks are provided in the top for the outlet of the
vapours, for a man-hole, supply-pipe, thermometer-pipe, safety valve,
and for air and steam-pipes reaching down to the bottom and branching
out into a number of distributing arms. Near the top there is an
overflow pipe which comes into action on filling the still. In the
lowest part of the bottom there is a running-off valve or tap. In some
cases (but only exceptionally) a perpendicular shaft is provided, with
horizontal arms, and chains hanging down from these drag along the
bottom for the purpose of keeping it clean and of facilitating the
escape of the vapours. This arrangement is quite unnecessary where the
removal of the vapours is promoted by the injection of steam, but this
steam must be carefully dried beforehand, or, better, slightly
superheated, in order to prevent explosions, which might be caused by
the entry of liquid water into the tar during the later stages of the
work, when the temperature has arisen far above the boiling-point of
water. The steam acts both by stirring up the tar and by rapidly
carrying off the vapours formed in distillation. The latter object is
even more thoroughly attained by the application of a vacuum,
especially during the later stage of distillation. For this purpose
the receivers, in which the liquids condensed in the cooler are
collected, are connected with an air pump or an ejector, by which a
vacuum of about 4 in., say 1/8 atmosphere, is made which lowers the
boiling process by about 80 deg. C.; this not merely hastens the process,
but also produces an improvement of the quality and yield of the
products, especially of the anthracene, and, moreover, lessens or
altogether prevents the formation of coke on the still-bottom, which
is otherwise very troublesome.

Most manufacturers employ ordinary stills as described. A few of them
have introduced continuously acting stills, of which that constructed
by Frederic Lennard has probably found a wider application than any of
the others. They all work on the principle of gradually heating the
tar in several compartments, following one after the other. The fresh
tar is run in at one end and the pitch is run out from the other. The
vapours formed in the various compartments are separately carried away
and condensed, yielding at one and the same time those products which
are obtained in the ordinary stills at the different periods of the
distillation. Although in theory this continuous process has great
advantages over the ordinary style of working, the complication of the
apparatus and practical difficulties arising in the manipulation have
deterred most manufacturers from introducing it.

The tar-stills are set in brickwork in such a manner that there is no
over-heating of their contents. For this purpose the fire-grate is
placed at a good distance from the bottom or even covered by a brick
arch so that the flame does not touch the still-bottom at all and acts
only indirectly, but the sides of the still are always directly
heated. The fire-flue must not be carried up to a greater height than
is necessary to provide against the overheating of any part of the
still not protected inside by liquid tar, or, at the end of the
operation, by liquid pitch. The outlet pipe is equally protected
against overheating and also against any stoppage by pitch solidifying
therein. The capacity of tar-stills ranges from 5 to 50 tons. They
hold usually about 10 tons, in which case they can be worked off
during one day.

The vapours coming from the still are condensed in coolers of various
shapes, one of which is shown in figs. 2 and 3. The cooling-pipes are
best made of cast-iron, say 4 in. wide inside and laid so as to have a
continuous fall towards the bottom. A steam-pipe (b) is provided for
heating the cooling water, which is necessary during the later part of
the operation to prevent the stopping up of the pipes by the
solidification of the distillates. A cock (a) allows steam to be
injected into the condensing worm in order to clear any obstruction.

The cooling-pipe is at its lower end connected with receivers for the
various distillates in such a manner that by the turning of a cock the
flow of the distillates into the receivers can be changed at will. In
a suitable place provision is made for watching the colour, the
specific gravity, and the general appearance of the distillates. At
the end of the train of apparatus, and behind the vacuum pump or
ejector, when one is provided, there is sometimes a purifier for the
gases which remain after condensation; or these gases are carried back
into the fire, in which case a water-trap must be interposed to
prevent explosions.

_Distillation of the Tar._--The number of fractions taken during the
distillation varies from four to six. Sometimes a first fraction is
taken as "first runnings," up to a temperature of 105 deg. C. in the
still, and a second fraction as "light oil," up to 210 deg. C., but more
usually these two are not separated in the first distillation, and the
first or "light oil" fraction then embraces everything which comes
over until the drops no longer float on, but show the same specific
gravity as water. The specific gravity of this fraction varies from
0.91 to 0.94. The next fraction is the "middle oil" or "carbolic oil,"
of specific gravity 1.01, boiling up to 240 deg. C.; it contains most of
the carbolic acid and naphthalene. The next fraction is the "heavy
oil" or "creosote oil," of specific gravity 1.04. Where the nature of
the coals distilled for gas is such that the tar contains too little
anthracene to be economically recovered, the creosote-oil fraction is
carried right to the end; but otherwise, that is in most cases, a last
fraction is made at about the temperature 270 deg. C., above which the
"anthracene oil" or "green oil" is obtained up to the finish of the
distillation.

During the light-oil period the firing must be performed very
cautiously, especially where the water has not been well removed, to
prevent bumping and boiling over. It has been observed that, apart
from the water, those tars incline most to boiling over which contain
an unusual quantity of "fixed carbon." During this period cold water
must be kept running through the cooler. The distillate at once
separates into water (gas-liquor) and light oil, floating at the top.
Towards the end of this fraction the distillation seems to cease, in
spite of increasing the fires, and a rattling noise is heard in the
still. This is caused by the combined water splitting off from the
bases and phenols and causing slight explosions in the tar.

As soon as the specific gravity approaches 1.0, the supply of cold
water to the cooler is at least partly cut off, so that the
temperature of the water rises up to 40 deg. C. This is necessary because
otherwise some naphthalene would crystallize out and plug up the
pipes. If a little steam is injected into the still during this period
no stoppage of the pipes need be feared in any case, but this must be
done cautiously.

When the carbolic oil has passed over and the temperature in the still
has risen to about 240 deg. C., the distillate can be run freely by always
keeping the temperature in the cooler at least up to 40 deg. C. The
"creosote oil" which now comes over often separates a good deal of
solid naphthalene on cooling.

The last fraction is made, either when the thermometer indicates 270 deg.
C., or when "green grease" appears in the distillate, or simply by
judging from the quantity of the distillate. What comes over now is
the "anthracene oil." The firing may cease towards the end as the
steam (with the vacuum) will finish the work by itself. The water in
the cooler should now approach the boiling-point.

The point of finishing the distillation is different in various places
and for various objects. It depends upon the fact whether _soft_ or
_hard_ pitch is wanted. The latter must be made where it has to be
sold at a distance, as soft pitch cannot be easily carried during the
warmer season in railway trucks and not at all in ships, where it
would run into a single lump. Hard pitch is also always made where as
much anthracene as possible is to be obtained. For hard pitch the
distillation is carried on as far as practicable without causing the
residue in the still to "coke." The end cannot be judged by the
thermometer, but by the appearance and quantity of the distillate and
its specific gravity. If carried too far, not merely is coke formed,
but the pitch is porous and almost useless, and the anthracene oil is
contaminated with high-boiling hydrocarbons which may render it almost
worthless as well. Hard pitch proper should soften at 100 deg. C., or
little above.

Where the distillation is to stop at soft pitch it is, of course, not
carried up to the same point, but wherever the pitch can be disposed
of during the colder season or without a long carriage, even the hard
pitch is preferably softened within the still by pumping back a
sufficient quantity of heavy oil, previously deprived of anthracene.
This makes it much easier to discharge the still. When the contents
consist of soft pitch they are run off without much trouble, but hard
pitch not merely emits extremely pungent vapours, but is mostly at so
high a temperature that it takes fire in the air. Hard pitch must,
therefore, always be run into an iron or brick cooler where it cools
down out of contact with air, until it can be drawn out into the open
pots where its solidification is completed.

Most of the pitch is used for the manufacture of "briquettes" ("patent
fuel"), for which purpose it should soften between 55 deg. and 80 deg. C.
according to the requirements of the buyer. In Germany upwards of
50,000 tons are used annually in that industry; much of it is imported
from the United Kingdom, whence also France and Belgium are provided.
Apart from the softening point the pitch is all the more valued the
more constituents it contains which are soluble in xylene. The portion
insoluble in this is denoted as "fixed carbon." If the briquette
manufacturer has bought the pitch in the hard state he must himself
bring it down to the proper softening point by re-melting it with
heavy coal-tar oils.

We now come to the treatment of the various fractions obtained from
the tar-stills. These operations are frequently not carried out at the
smaller tar-works, which sell their oils in the crude state to the
larger tar-distillers.

_Working up of the Light-Oil Fraction._--The greatest portion of the
light-oil fraction consists of aromatic hydrocarbons, about one-fifth
being naphthalene, four-fifths benzene and its homologues, in the
proportion of about 100 benzene, 30 toluene, 15 xylenes, 10
trimethylbenzenes, 1 tetramethylbenzene. Besides these the light-oil
contains 5-15% phenols, 1-3% bases, 0.1 sulphuretted compounds,
0.2-0.3% nitriles, &c. It is usually first submitted to a preliminary
distillation in directly fired stills, similar to the tar-stills, but
with a dephlegmating head. Here we obtain (1) first runnings (up to
O.89 spec. grav.), (2) heavy benzols (up to O.95), (3) carbolic oil
(up to 1.00). The residue remaining in the still (chiefly naphthalene)
goes to the middle-oil fraction.

The "first runnings" are now "washed" in various ways, of which we
shall describe one of the best. The oil is mixed with dilute caustic
soda solution, and the solution of phenols thus obtained is worked up
with that obtained from the next fractions. After this follows a
treatment with dilute sulphuric acid (spec. grav. 1.3), to extract the
pyridine bases, and lastly with concentrated sulphuric acid (1.84),
which removes some of the aliphatic hydrocarbons and "unsaturated"
compounds. After this the crude benzol is thoroughly washed with water
and dilute caustic soda solution, until its reaction is neutral. The
mixing of the basic, acid and aqueous washing-liquids with the oils is
performed by compressed air, or more suitably by mechanical stirrers,
arranged on a perpendicular, or better, a horizontal shaft. Precisely
the same treatment takes place with the next fraction, the "heavy
benzols," and the oils left behind after the washing operations now go
to the steam-stills. The heaviest hydrocarbons are sometimes twice
subjected to the operation of washing.

The washed crude benzols are now further fractionated by distillation
with steam. The _steam-stills_ are in nearly all details on the
principle of the "column apparatus" employed in the distillation of
alcoholic liquids, as represented in fig. 4. They are usually made of
cast iron. The still itself is either an upright or a horizontal
cylinder, heated by a steam-coil, of a capacity of from 1000 to 2000
gallons. The superposed columns contain from 20 to 50 compartments of
a width of 2-1/2 or 3 ft. The vapours pass into a cooler, and from this
the distillate runs through an apparatus, where the liquor can be seen
and tested, into the receivers. The latter are so arranged that the
water passing over at the same time is automatically removed. This is
especially necessary, because the last fraction is distilled by means
of pure steam.

The fractions made in the steam distillation vary at different works.
In some places the pure hydrocarbons are net extracted and here only
the articles called: "90 per cent. benzol," "50 per cent. benzol,"
"solvent naphtha," "burning naphtha" are made, or any other commercial
articles as they are ordered. The expression "per cent." in this case
does not signify the percentage of real benzene, but that portion
which distills over up to the temperature of 100 deg. C., when a certain
quantity of the article is heated in glass retorts of a definite
shape, with the thermometer inserted in the liquid itself. By the
application of well-constructed rectifying-columns and with proper
care it is, however, possible to obtain in this operation nearly pure
benzene, toluene, xylene, and cumene (in the two last cases a mixture
of the various isomeric hydrocarbons). These hydrocarbons contain only
a slight proportion of thiophene and its isomers, which can be removed
only by a treatment with fuming sulphuric acid, but this is only
exceptionally done.

Sometimes the _pyridine bases_ are recovered from the tarry acid which
is obtained in the treatment of the light oil with sulphuric acid, and
which contains from 10 to 30% of bases, chiefly pyridine and its
homologues with a little aniline, together with resinous substances.
The latter are best removed by a partial precipitation with ammonia,
either in the shape of gas or of concentrated ammoniacal liquor. This
reagent is added until the acid reaction has just disappeared and a
faint smell of pyridine is perceived. The mixture is allowed to
settle, and it then separates into two layers. The upper layer,
containing the impurities, is run off; the lower layer, containing the
sulphates of ammonia and of the pyridine bases, is treated with
ammonia in excess, where it separates into a lower aqueous layer of
ammonium sulphate solution and an oil, consisting of crude pyridine.
This is purified by fractionation in iron stills and distillation over
caustic soda. Most of it is used for denaturing spirit of wine in
Germany, for which purpose it is required to contain 90% of bases
boiling up to 140 deg. C. (see ALCOHOL).

_Working up of the Middle-Oil Fraction (Carbolic Oil
Fraction)._--Owing to its great percentage of naphthalene (about 40%)
this fraction is solid or semi-solid at ordinary temperatures. Its
specific gravity is about 1.2; its colour may vary from light yellow
to dark brown or black. In the latter case it must be re-distilled
before further treatment. On cooling down, about four-fifths of the
naphthalene crystallizes out on standing from three to ten days. The
crystals are freed from the mother oils by draining and cold or hot
pressing; they are then washed at 100 deg. C. with concentrated
sulphuric acid, afterwards with water and re-distilled or sublimed.
About 10,000 tons of naphthalene are used annually in Germany, mostly
for the manufacture of many azo-colours and of synthetic indigo.

The oils drained from the crude naphthalene are re-distilled and
worked for carbolic acid and its isomers. For this purpose the oil is
washed with a solution of caustic soda, of specific gravity 1.1; the
solution thus obtained is treated with sulphuric acid or with carbon
dioxide, and the crude phenols now separated are fractionated in a
similar manner as is done in the case of crude benzol. The pure phenol
crystallizes out and is again distilled in iron stills with a silver
head and cooling worm; the remaining oils, consisting mainly of
cresols, are sold as "liquid carbolic acid" or under other names.

Most of the oil which passes as the "creosote-oil fraction" is sold in
the crude state for the purpose of pickling timber. It is at the
ordinary temperature a semi-solid mixture of about 20% crystallized
hydrocarbons (chiefly naphthalene), and 80% of a dark brown, nauseous
smelling oil, of 1.04 spec. grav., and boiling between 200 deg. and
300 deg. C. The liquid portion contains phenols, bases, and a great
number of hydrocarbons. Sometimes it is redistilled, when most of the
naphthalene passes over in the first fraction, between 180 deg. and
230 deg. C., and crystallizes out in a nearly pure state. The oily
portion remaining behind, about 60% of this distillate, contains about
30% phenols and 3% bases. It has highly disinfectant properties and is
frequently converted into special disinfectants, e.g. by mixing it
with four times its volume of slaked lime, which yields "disinfectant
powder" for stables, railway cars, &c. Mixtures of potash soaps (soft
soaps) with this oil have the property of yielding with water
emulsions which do not settle for a long time and are found in the
trade as "creolin," "sapocarbol," "lysol," &c.

That description of creosote oil which is sold for the purpose of
pickling railway sleepers, telegraph posts, timber for the erection of
wharves and so forth, must satisfy special requirements which are laid
down in the specifications for tenders to public bodies. These vary to
a considerable extent. They always stipulate (1) a certain specific
gravity (e.g. not below 1.035 and not above 1.065); (2) certain limits
of boiling points (e.g. to yield at most 3% up to 150 deg., at most
30% between 150 deg. and 255 deg., and at least 85% between 150 deg.
and 355 deg.); (3) a certain percentage of phenols, as shown by
extraction with caustic soda solution, say 8 to 10%.

Much of this creosote oil is obtained by mixing that which has
resulted in the direct distillation of the tar with the liquid portion
of the anthracene oils after separating the crude anthracene (see
below). It is frequently stipulated that the oil should remain clear
at the ordinary temperature, say 15 deg. C., which means that no
naphthalene should crystallize out.

_Working up the Anthracene Oil Fraction._--The crude oil boils between
280 deg. and 400 deg. C. It is liquid at 60 deg. C., but on cooling
about 6 to 10% of crude anthracene separates as greenish-yellow, sandy
crystals, containing about 30% of real anthracene, together with a
large percentage of carbazol and phenanthrene. This crystallization
takes about a week. The crude anthracene is separated from the mother
oils by filter presses, followed by centrifugals or by hot hydraulic
presses. The liquid oils are redistilled, in order to obtain more
anthracene, and the last oils go back to the creosote oil, or are
employed for softening the hard pitch (_vide supra_). The crude
anthracene is brought up to 50 or 60, sometimes to 80%, by washing
with solvent naphtha, or more efficiently with the higher boiling
portion of the pyridine bases. The naphtha removes mostly only the
phenanthrene, but the carbazol can be removed only by pyridine, or by
subliming or distilling the anthracene over caustic potash. The whole
of the anthracene is sold for the manufacture of artificial alizarine.

BIBLIOGRAPHY.--The principal work on Coal-tar is G. Lunge's _Coal-tar
and Ammonia_ (3rd ed., 1900). Consult also G. P. Sadtler, _Handbook of
Industrial Organic Chemistry_ (1891), and the article
"Steinkohlentheer," Kraemer and Spreker, in _Encyklopadisches Handbuch
der technischen Chemie_ (4th ed., 1905, viii. 1). (G. L.)

FOOTNOTE:

[1] The illustrations in this article are from Prof. G. Lunge's _Coal
Tar and Ammonia_, by permission of Friedrich Vieweg u. Sohn.

COALVILLE, a town in the Loughborough parliamentary division of Leicestershire, England, 112 m. N.N.W. from London. Pop. of urban district (1901) 15,281. It is served by the Midland railway, and there is also a station (Coalville East) on the Nuneaton-Loughborough branch of the London & North-Western railway. This is a town of modern growth, a centre of the coal-mining district of north Leicestershire. There are also iron foundries and brick-works. A mile north of Coalville is Whitwick, with remains of a castle of Norman date, while to the north again are slight remains of the nunnery of Gracedieu, founded in 1240, where, after its dissolution, Francis Beaumont, the poet-colleague of John Fletcher, was born about 1586. In the neighbourhood is the Trappist abbey of Mount St Bernard, founded in 1835, possessing a large domain, with buildings completed from the designs of A. W. Pugin in 1844.

COAST (from Lat. _costa_, a rib, side), the part of the land which meets the sea in a line of more or less regular form. The word is sometimes applied to the bank of a river or lake, and sometimes to a region (cf. Gold Coast, Coromandel Coast) which may include the hinterland. If the coast-line runs parallel to a mountain range, such as the Andes, it has usually a more regular form than when, as in the _rias_ coast of west Brittany, it crosses the crustal folds. Again, a recently elevated coast is more regular than one that has been long exposed to wave action. A recently depressed coast will show the irregularities that were impressed upon the surface before submergence. Wave erosion and the action of marine currents are the chief agents in coast sculpture. A coast of homogeneous rock exposed to similar action will present a regular outline, but if exposed to differential action it will be embayed where that action is greatest. A coast consisting of rocks of unequal hardness or of unequal structure will present headlands, "stacks" and "needles" of hard rocks, and bays of softer or more loosely aggregated rocks, when the wave and current action is similar throughout. The southern shore-line of the Isle of Wight and the western coast of Wales are simple examples of this differential resistance. In time the coast becomes "mature" and its outline undergoes little change as it gradually recedes, for the hard rock being now more exposed is worn away faster, but the softer rock more slowly because it is protected in the bays and re-entrants.

COAST DEFENCE, a general term for the military and naval protection and defence of a coast-line, harbours, dockyards, coaling-stations, &c., against serious attack by a strong naval force of the enemy, bombardment, torpedo boat or destroyer raids, hostile landing parties, or invasion by a large or small army. The principal means employed by the defender to cope with these and other forms of attack which may be expected in time of war or political crisis are described below. See also for further details NAVY; ARMY; FORTIFICATION AND SIEGE-CRAFT; AMMUNITION; ORDNANCE; SUBMARINE MINES; TORPEDO. The following is a general description of modern coast defences as applied in the British service.