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COALING

STATIONS References.—Most of the detailed information concerning improvements in the practice of coal mining and the improvement in plant and machinery is contained in the published proceedings of the different professional societies, including the Transactions of the Institution of Mining Engineers, the South Wales Institute of Engineers, the British Society of Mining Students, and the American Institute of Mining Engineers. Among special works dealing with modern practice, Professor Galloway’s lectures (published by the South Wales Institute, Cardiff, 1900), and the larger Text-Book on Coal Mining, by Mr H. W. Hughes (fourth edition, London, 1901), are the most notable, the latter being especially valuable for the detailed classified list of original authorities given at the end of each chapter. Yery complete references are also given in the systematic abstracts published in the half-yearly volumes of the Journal of the Iran and Steel Institute. (h. b.)

to the air, where its temperature is reduced, and the tar is condensed and removed. The flow of gas is maintained by rotating exhausters, which force it forward through a series of scrubber towers, where the ammonia vapour is separated by a graduated system of washing with water and ammoniacal liquor. The final removal of benzol is effected by washing the partially purified gas with creosote oil. When the condensible products are removed, the gas is returned by a common supply pipe for distribution to the heating flues of the ovens. In the Otto-Hoffmann oven of the earlier and most generally used form, the gas is fired with heated air in a horizontal flue running along the bottom of the coking chamber; this is divided into two parts by a partition in the middle of its length, and the flame rises through the vertical side passages of the first half of the oven to two horizontal collectors at the top, where the direction being reversed, it passes downwards along the second half to the chimney, after giving up some of the surplus heat to a Siemens regenerator, in which the air for combustion is heated after the next reversal. The gas supply is introduced alternately from the front and back of the oven, there being a regenerator for airheating at either end. In the newer form of this oven the air regenerators and reversal of the flame have been abandoned in favour of a system of continuous heating, the gas distributed by pipes in a chamber below the bottom of the oven supplying a series of large Bunsen burners at equal distances apart along the bottom, whose flames pass continuously upward through the side flues. There is some difference of opinion as to the merits of the two forms, but the new system is generally held to give more uniform heating, as well as being simpler in construction. In the horizontally-heated ovens the flues are arranged as parallel superposed passages along the length of the wall. The gas entering the lowest one is fired, and passes four times backwards and forwards to the chimney flue. This is usually of thin brickwork, so that a portion of the waste heat is transmitted to the air supplied for combustion, which passes in the opposite direction through adjacent parallel flues in the brickwork of the foundation, forming a continuous “ recuperator,” as distinguished from the intermittent Siemens regenerator. The time of coking in retort ovens varies with the quality of the coal and size of the charge, which may be from 51 to 7 tons, about thirty-six hours being required in the newer kinds. The coke produced is not so dense or brilliant as that made in beehive ovens, but the waste being less, there is a decided saving, apart from the value of the condensed products. In one instance the coke was found to be about 5 per cent, less efficient in the blast furnace, while the yield was increased 10 per cent. In the further treatment of the condensed products by distillation the tar gives burning oil and pitch, the benzol is separated from the creosote oil by steam-heated stills, and the ammoniacal liquor, after some lime has been added to decompose fixed ammonium compounds, is heated to vaporize the ammonia, which is condensed in lead or copper lined tanks containing strong sulphuric acid. to produce a crystalline powder of ammonium sulphate, which accumulates in the receiver and is fished out from time to time. The yield of by-products averages about 1 per cent, of sulphate of ammonium, about 3^- per cent, of tar, and 0-6 to 09 per cent, of benzol of the weight of the coal carbonized. Besides heating the ovens and supplying steam for the machinery of the condensing plant and the coke ovens, there is usually a considerable surplus of gas, which may be used for lighting or driving gas-engines. For the latter purpose, however, it is necessary to remove the last traces of tar, which acts very prejudicially in fouling the valves when the gas is not completely purified.

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 Kevolution 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 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 exi-