by steam per minute, circulates 47,000 cubic feet of air through the The comparative merits of furnace and machine ventilation have long been discussed without any definite result. The former was at one time regarded in England as practically superior in every respect, but this opinion has been modified since the introduction of the improved forms of fans which have been worked to a considerable extent. In France and Belgium, on the contrary, machine ventilation has been more generally in favor. For a deep and extensive mine where the coal is not fiery, the furnace is undoubtedly the simplest and most efficacious method of producing a large circulation of air; but for moderate depths, especially with fiery return air, a ventilating machine at the surface is in many cases to be preferred. There is also an important advantage procured by the latter, namely, that of reserve power, so that a large circulation may be obtained immediately in case of need, e. g., when the barometer falls suddenly, by merely increasing the speed of rotation, which cannot so readily be done with the furnace, which has a tendency to slacken at the time when the increased work is wanted. Distribution of air underground. cloth, specially made for the purpose, is used instead of Lighting. The lighting of underground workings in collieries is closely connected with the subject of ventilation. In many of the smaller pits in the Midland districts, and generally in South Staffordshire, the coals are sufficiently free from gas, or rather the gases are not liable to become explosive when mixed with air, to allow the use of naked lights, candles being generally used. Oil lamps are employed in many of the Scotch collieries, and are almost universally used in Belgium and other Continental countries. The buildings near the pit bottom, such as the stables and lamp cabin, and even the main roads for some distance, are often in large collieries lighted with gas brought from the surface, or in some cases the gas given off by the coal is used for the same purpose. Where the gases are fiery, the use of protected lights or safety lamps becomes a necessity. tion of gas The nature of the gases evolved by coal when freshly exposed to the atmosphere has been in- Composivestigated by several chemists, more particularly evolved by by Playfair and Meyer. The latter observer coal. found the gases given off by coal from the district of Newcastle and Durham to contain carbonic acid (anhydride), marsh gas or light carburetted hydrogen (the fire-damp of the miner), oxygen, and nitrogen. A newer investigation, by Mr. J. W. Thomas, of the gases dissolved or occluded in coals from South Wales basin shows them to vary considerably with the class of coal. The results given below, which are selected from a much larger series published in the Journal of the Chemical Society, were obtained by heating samples of the different coals in vacuo for several hours at the temperature of boiling water. The quantity of air required for a large colliery depends upon the number of men employed, as for actual respiration from 100 to 200 cubic feet per minute should be allowed. In fiery mines, however, a very much larger amount must be provided in order to dilute the gas to the point of safety. Even with the best arrangements a dangerous increase in the amount of gas is not unfrequent from the sudden release of stored up masses in the coal, which, overpowering the ventilation, produce magazines of explosive material ready for ignition when brought into contact with the flame of a lamp or the blast of a shot. The management of such places, therefore, requires the most constant vigilance on the part of the workmen, especially in the examination of the working places that have been standing Steam........ empty during the night, in which gas may have accumulated, to see that they are properly cleared before the new shift commences. Quality. Bituminous 66 Anthracite..... Court 19.72 5:44 1.05 63.76 29.75 14.34 9.43 2.25 31.95 56.34 89.62 13.21 0.49 81.64 4.66 198.95 2.62 93.13 4.25 In one instance, about 1 per cent. of hydride of ethyl was The actual conveyance or coursing of the air from the found in the gas from a blower in a pit in the Rhondda disintake to the working faces is effected by splitting or trict, which was collected in a tube and brought to the surface dividing the current at different points in its course, so as to be used in lighting the engine-room and pit-bank. The to carry it as directly as possible to the places where it is gases from the bituminous house coals of South Wales are required. In laying out the mine, it is customary to drive comparatively free from marsh gas, as compared with those the levels or roads in pairs, communication being made be- from the steam coal and anthracite pits. The latter class tween them at intervals by cutting through the intermediate of coal contains the largest proportion of this dangerous pillar, the air then passes along one, and returns by the gas, but holds it more tenaciously than do the steam coals, other. As the roads advance other pillars are driven thus rendering the workings comparatively safer. It was through in the same manner, the passages first made being found that, of the entire volume of occluded gas in an anclosed by stoppings of broken rock, or built up with brick thracite, only one-third could be expelled at the temperand mortar walls, or both. When it is desired to preserve ature of boiling water, and that the whole quantity, amounta way from one road or similar class of working to another, ing to 650 cubic feet per ton, was only to be driven out by double doors placed at sufficient intervals apart to take in a heat of 300° C. Steam coals being softer and more one or more trams between them when closed are used, porous give off enormous volumes of gas from the workforming a kind of lock or sluice. These are made to shuting face in most of the deep pits, many of which have been air-tight against their frames, so as to prevent the air from taking a short cut back to the upcast, while preserving free access between the different districts without following the whole round of the airways. The ventilation of ends is effected by means of brattices or temporary partitions of thin boards placed midway in the drift, and extending to within a few feet of the face. The air passes along one side of the brattice, courses round the free end, and returns on the other side. In many cases a light but air-proof the scene of disastrous explosions. The gases evolved from the sudden outbursts or blowers in coal, which are often given off at a considerable tension, are the most dangerous enemy that the collier has to contend with. They consist almost entirely of marsh gas, with only a small quantity of carbonic acid, usually under 1 per cent., and from 1 to 4 per cent. of nitrogen. Fire-damp when mixed with from four to twelve times its volume of atmospheric air is explosive; but when the proportion is above or below these limits, it is inflammable, burning quietly with a pale blue flame. When a lighted candle is exposed in a non-explosive mixture of this gas, the flame gradually elongates, forming a conical cap, floating above the wick, which may be extinguished by cautious withdrawal without communicating the fire to the surrounding atmosphere. This method of testing for gas in the working places and wastes, which is obviously only to be trusted in skilled hands, used to be commonly practised, but since the introduction of safety-lamps it has fallen into disuse. Safetylamps. The principle involved in the construction of safety-lamps consists in surrounding the flame of a lamp by a protecting metal case, perforated with numerous small holes, through which the air for feeding the flame may freely enter, and the products of combustion pass out, while the passage of flame, or gases sufficiently heated to cause the ignition of the external air when laden with explosive gases, is prevented. In 1816 Sir Humphry Davy made the great discovery that these conditions are fulfilled by the use of tubes reduced to a mere section, such as the apertures in wire gauze, when the substance of the wire is rightly proportioned to the size of the aperture. The standard adopted as the limit for safety at that time was a gauze of 28 iron wires to the linear inch, having 784 apertures per square inch, which has been used ever since. The common safety or Davy lamp consists of a small cylindrical oil lamp, covered with a cylinder of wire gauze about six inches long and 1 inches in diameter, with a flat gauze top. The upper part of the gauze is doubled to prevent its being worn into holes by the products of combustion, and the air for feeding the flame enters round the wick. The gauze is mounted in a cage, consisting of three upright wires, screwed into a flat brass ring at each end. A handle is attached to the upper ring, while the lower one screws on to a collar on the oil-vessel of the lamp. When the two parts are screwed together the lamp is locked by a bolt passing through both parts, which is screwed down flush with or below the surface of the outer ring, so that the gauze cannot be removed without the use of a key. In Stephenson's safety-lamp, generally known as the "Geordie," from the inventor George Stephenson, the light is covered by a glass chimney, surrounded by an outer casing and top of wire gauze. The feed air is admitted through numerous small holes in a copper ring a little below the level of the wick. This is one of the safest forms of lamp, but requires considerable care in use, especially in keeping the small feed holes clear from dust and oil; the glass protects the gauze from becoming overheated, and when the air is dangerously charged with gas the light is extinguished. Various forms of safety-lamps have been introduced at different times, for the purpose of increasing the amount of light by substituting a glass cylinder for the lower portion of the wire gauze. The oldest of these is that of Dr. Clanny, contemporary with those of Davy and Stephenson. The air for supplying the flame, entering at the bottom of the gauze, and passing down the inner side of the glass, protects the latter to some extent from becoming overheated, but a large amount of light is lost by absorption in the glass, so that there is no great advantage over the ordinary Davy lamp to compensate for the extra weight and cost, especially as the safety property of the lamp depends upon the glass cylinder, which may be readily broken when subjected to the ordinary accidents of working. A more perfect form of lamp of the same character is that of Museler, which is extensively used in Belgium. It differs from Clanny's lamp by the addition of a conical chimney above the flame, which produces a rapid draught, and consequently a more perfect cooling of the glass cylinder by the down-draught of feed air for the flame. Boty's lamp, which was recommended by a commission of the Belgian Government as being safe in use, is essentially that of Dr. Clanny with Stephenson's perforated ring for admitting air at the level of the wick. Another Belgian variety is that of Eloin, in which the glass is shaped to the surface produced by the revolution of a parabolic arc, so as to disperse the light in parallel lines. The air is admitted by a Stephenson ring, combined with an Argand cap, the glass being surrounded by a brass chimney with a gauze top. In another form of the same lamp Museler's chimney is added. The locking of safety lamps, so as to render them incapable of being opened by the miners when at work, is a point that has given play to a large amount of ingenuity. One of the most favorite devices is a combination of the wick-holder with the locking-bolt, so that the latter cannot be withdrawn without lowering the wick and extinguishing the flame. Another method consists in the use of a lead rivet, uniting the two parts of the lamp, impressed with a seal, which cannot be removed without defacing the device. All this class of contrivances have the defect of only being efficacious when the miners are not provided with matches, or other means of obtaining a light. A more physically perfect method is that adopted by Bidder, where the locking-bolt is magnetized and held in place by a force which can only be overcome by the application of a battery of heavy and powerful steel magnets. These are kept in the lamp cabin at the pit bottom, where the lamps are cleaned and served out lighted to the miners at the commencement of the shift, and are collected before they return to the surface. When a Davy lamp is exposed to an atmosphere containing less than 8 per cent. of marsh gas, the flame lengthens and becomes smoky; when that amount is reached the flame returns to its usual size, but a column of blue flame rises to the top of the gauze. With 10 per cent. the flame of the wick is extinguished, the whole of the space within the gauze being filled with a blue flame of burning gas. If the lamp is allowed to remain too long in a fiery atmosphere it becomes dangerous, as the gauze being heated to redness may fire the gas. The safety of the lamp is also endangered by an exposure to a current of gas moving at the rate of more than 6 or 8 feet per second, as the flame can then be readily driven through the gauze. It is therefore usual to protect the flame by a sliding shield of tin plate, horn, or mica from the direct action of any sudden outburst of gas in the workings. Lamps with glass cylinders are generally very safe, except from the risk of accidental breakage, which, however, is less frequent than might be imagined, and those taking air through a feed ring, such as Stephenson's, are readily extinguished in a foul atmosphere. The danger arising from gas in the workings may be considerably increased by the presence of coal dust in the air. This point has been the subject of investigation by Galloway, who found that an explosion may be produced by igniting particles of coal dust through the agency of a safety-lamp which under ordinary circumstances would be perfectly trustworthy. At Blanzy, in France, several fatal explosions have been traced to the firing of coal dust from the flame of a shot, even in cases where no fire-damp was present in the workings. Electric An electric lamp, where the light is obtained from the discharge in a Geissler vacuum tube, lamps. has been proposed by Benoit-Dumas, instead of the ordinary safety-lamps, or for use in exploring after explosions or in bad air-ways. This consists of a box containing a galvanic battery, consisting of two Bunsen cells, and a small induction coil, with connecting wires which convey the current to the lamp. The Bunsen cells may be conveniently replaced by a single bottle-shaped bichromate battery. The cost and complication of this apparatus must necessarily limit its use. Aero Apparatus, originating in France, known as aerophores, which enable the miner to carry phores. sufficient fresh air for his own respiration, and to keep a lamp alight for a short time in a totally irrespirable atmosphere, have of late years come into use for the purpose of saving life after explosions, and repairing shafts and pit-work under water. There are two principal patterns, those of Galibert and Denayrouze. The former, which is the simplest, consists of an air-tight bag of about 12 cubic feet capacity, containing air at a little above atmospheric pressure, which is carried on the miner's back like a knapsack. The air, after being used, is returned with the products of respiration into the bag, and can be used over again until it becomes too impure for further use. It is obvious, therefore, that such an apparatus must be of very limited application, but its sim plicity and cheapness are points in its favor for use in sudden emergencies. The Denayrouze apparatus consists of a series of sheet metal cylinders, containing air compressed to 300 or 350 lb to the square inch, which can be carried on the back, and served out at a pressure very slightly above that of the atmosphere by means of a reducing valve, whose construction is essentially the same in principle as that of the ordinary pressure regulator used in gas-works, i. e., a conical plug closed against its seat by the pressure of the air in the reservoir, which is constantly opposed by an external force tending to open it. This force is supplied by a disc of vulcanized india-rubber, which opens the valve at each inspiration, and allows a fresh supply of air to escape into the chamber of the regulator through the small aperture of the valve. Of course, all communication with the external air must be cut off, so that respiration can only take place through the mouth, the air-tube being attached by an india-rubber mask called a mouth-closer, and the nostrils closed by a spring clip. A similar regulator valve, so constructed as to keep the india-rubber spring under a slight excess pressure in order to maintain a flow of air, is in connection with the lamp. This is of the ordinary Museler construction, with the addition of a chamber outside the gauze to receive the products of combustion, which are discharged through a conical valve at the top, a reflux of the exterior gases being prevented by the pressure of a counter spring. The air is carried to the lamp by an india-rubber tube, which is sufficiently flexible to allow a certain freedom of motion. The distance that an explorer can penetrate with this apparatus is obviously limited by the capacity of the aircylinders. These have been made large enough to supply air to a man with a lamp for an hour, but this is an inconvenient size, being too large to be carried on the back. mines. Underground fires are not uncommon acciFires in dents in coal-mines. In the thick coal workings in South Staffordshire the slack left behind | in the sides of work is especially liable to fire from socalled spontaneous combustion, due to the rapid oxidization that is set up, when finely-divided coal is brought in contact with air. The best remedy in such cases is to prevent the air from gaining access to the coal by building a wall round the burning portion, which can in this way be isolated from the remainder of the working, and the fire prevented from spreading, even if it cannot be extinguished. When the coal is fired by the blast of an explosion it is often necessary to completely isolate the mine by stopping up the mouths of the pits with earth, or in extreme cases it must be flooded with water or carbonic acid before the fire can be brought under. There have been several instances of this being done in the fiery pits in the Barnsley district, notably at the great explosion at the Oaks colliery in 1866, when 360 lives were lost. winding. The drawing or winding of the coal from the Methods of pit bottom to the surface is one of the most important operations in coal mining, and probably the department in which mechanical appliances have been brought to the highest state of development. In the simplest case where the mine is worked by levels, the trains of coal may be drawn from the working faces directly to the level mouth by horse power, or in some exceptional cases locomotives worked by compressed air are used. In South Wales the power for lifting the load in the shaft is still in some small workings furnished by a water balance, that is, a box which is filled with water at a high level, and in descending raises the loaded trucks by a rope passing over a pulley at the surface. This method is only available when there is a free drainage level for the water to run off when the box reaches the lowest point. Other hydraulic motors, such as wheels, pressure engines, &c., are used in different localities as well as animal power, where the amount of coal to be drawn is small, but as a general rule it is necessary to have recourse to steam power to maintain an adequate output. The old custom of drawing the coals in tubs or hutches (cuffat of the French miner), swinging freely from the end of the drawing rope, is now almost entirely superseded by the adoption of cages sliding between fixed guides, which allow the load to move freely up and down while checking lateral oscillation. This improvement, which is due to Mr. John Curr of Sheffield, was originally introduced in 1798, but made surprisingly little progress for nearly half a century. It was first brought into general use in the North of England, but in many of the smaller pits of the Midland counties the older custom prevailed until recently. Cage. The different elements making up the drawing arrangements of a colliery are (1) the cage, (2) the shaft or pit fittings, (3) the drawing-rope, (4) the engine, and (5) the surface arrangements. The cage, as its name implies, consists of one or more platforms connected by an open framework of vertical bars of wrought iron or steel, with a top bar to which the drawing-rope is attached. It is customary to have a curved sheet-iron roof or bonnet when the cage is used for raising or lowering the miners, to prevent them from injury by falling materials. The number of platforms or decks varies considerably; in small mines only a single one may be used, but in the larger modern pits two, three, or even fourdecked cages are used. The use of several decks is necessary in old pits of small section, where only a single tram can be carried on each. In the large shafts of the Northern and Wigan districts the cages are made about 8 feet long and 3 feet broad, being sufficient to carry two large trams on one deck. These are received upon a railway made of two strips of angle iron of the proper gauge for the wheels, and are locked fast by a latch falling over their ends. Guides. The guides or conductors in the pit may be constructed of wood, in which case rectangular fir beams, about 3 by 4 inches, are used, attached at intervals of a few feet to buntons or cross-beams, built into the lining of the pit. Two guides are required for each cage; they may be placed opposite each other, either on the long or short sides-the latter being preferable. The cage is guided by shoes of wrought iron, a few inches long and bell-mouthed at the ends, attached to the horizontal bars of the framing, which pass loosely over the guides on three sides. In some of the large collieries in Northumberland wrought iron guides have been adopted with advantage. They are applied on one side of the cage only, forming a complete vertical railway,-light flange rails such as are used for the roadways underground being used instead of wooden rods and iron cross sleepers, with proper seats for the rails instead of wooden buntons; the cage is guided by curved shoes of a proper section to cover the heads of the rails. Rigid guides connected with the walling of the pit are probably the best and safest, but they have the disadvantage of being liable to distortion, in case of the pit altering its form, owing to irregular movements of the ground, or other causes. Wooden guides being of considerable size, block up a certain portion of the area of the pit, and thus offer an impediment to the ventilation, especially in upcast shafts, where the high temperature, when furnace ventilation is used, is also against their use. In the Wigan district, wire-rope guides have been introduced to a very considerable extent, with a view of meeting the above objections. These are simply wire-ropes, from 4 to 14 inches in diameter, hanging from a cross-bar connected with the pit-head framing at the surface, and attached to a similar bar at the bottom, which are kept straight by a stretching weight of from 30 cwt. to 4 tons attached to the lower bar. In some cases four guides are used-two to each of the long sides of the cage; but a more general arrangement is to have three-two on one side, and the third in an intermediate position on the opposite side. Many colliery managers, however, prefer to have only two opposite guides, as being safer. The cage is connected by tubular clips, made in two pieces and bolted together, which slide over the ropes. In addition to this, it is necessary to have an extra system of fixed guides at the surface and at the bottom, where it is necessary to keep the cage steady during the operations of loading and landing, there being a much greater amount of oscillation during the passage of the cage than with fixed guides. For the same reason it is necessary to give a considerable clearance between the two lines of guides, which are kept from 15 to 18 inches apart, to prevent the possibility of the two cages striking each other in passing. With proper precautions, however, wire guides are perfectly safe for use at the highest travelling speed. The cage is connected with the drawing-rope by short lengths of chain from the Ropes and corners chains. known as tackling chains, gathered into a central ring, to which the rope is attached. Round steel wire-ropes, about 2 inches in diameter, are now commonly used; but in very deep pits they are sometimes tapered in section to reduce the dead weight lifted. Flat ropes of steel or iron wire were and are still used to a great extent, but round ones are now generally preferred. In Belgium flat ropes of aloe fibre are in high repute, being considered preferable by many colliery managers to wire, in spite of their great weight. In South Staffordshire, flat link chains made with three or more parallel links, with a stud of wood filling up the hollow, are or were in general use in the numerous shallow pits working the thick coal in the neighborhood of Dudley, &c. Winding The best modern engines for drawing in colengines. lieries are usually direct-acting, with either horizontal or vertical cylinders. In the north of England a single engine with a heavy fly-wheel is often used, but the more general arrangement is to have two engines coupled to the opposite ends of the winding drumshaft. In almost all cases steam is used at high pressure without condensation. The drum, when round ropes are used, is a plain broad cylinder, with flanged rims, and cased with soft wood packing, upon which the rope is coiled; the breadth is made sufficient to take the whole length of the rope at two laps. One drum is usually fixed to the shaft, while the other is loose, with a screw link or other means of coupling, in order to be able to adjust the two ropes to exactly the same length, so that one cage may be at the surface when the other is at the bottom, without having to pay out or take up any slack rope by the engine. For flat ropes, the drum or bobbin consists of a solid disc, of the width of the rope fixed upon the shaft, with numerous parallel pairs of arms or horns, arranged radially on both sides, the space between being just sufficient to allow the rope to enter and coil regularly upon the preceding lap. This method has the advantage of equalizing the work of the engine throughout the journey, for when the load is greatest, with the full cage at the bottom and the whole length of rope out, the duty required in the first revolution of the engine is measured by the length of the smallest circumference; while the assistance derived from gravitating action of the descending cage in the same period is equal to the weight of the falling mass through a height corresponding to the length of the largest lap, and so on, the speed being increased as the weight diminishes, and vice versa. The same thing can be effected in a more perfect manner by the use of spiral or scroll drums, in which the rope is made to coil in a spiral groove upon the surface of the drum, which is formed by the frusta of two obtuse cones placed with their smaller diameters outwards. This plan, though mechanically a very good one, has certain defects, especially in the possibility of danger resulting from the rope slipping sideways, if the grooves in the bed are not perfectly true. The great size and weight of such drums are also disadvantages, as giving rather unmanageable dimensions in a very deep pit. The use of a counterbalance chain for the winding engines is common in the collieries of the Midland districts of England. In this method a third drum is used to receive a heavy flat link chain, shorter than the main drawing-ropes, the end of which hangs down a special or balance pit. At starting, when the full load is to be lifted, the balance chain uncoils, and continues to do so until the desired equilibrium between the working loads is attained, when it is coiled up again in the reverse direction, to be again given out on the return trip. Surface arrange ments. The surface arrangements of a modern colliery are often of considerable extent and complexity, the most important feature being the pit-frame carrying the guide-pulleys or roperolls which lead the drawing-ropes from the vertical line of the pit to the engine-drum. This consists essentially of an upright framework, carefully braced together, and strutted by diagonal beams against the wall of the enginehouse, or other solid abutment. It is generally necessary to have a clear head-room, 10 or 20 feet or more, for the working arrangements at the surface above the level of the ground, especially in flat countries; the pit-frames are made of considerable height, from 50 to 70 feet being not uncommon; and when, as is generally the case, they are made of wood, they afford opportunities for the exercise of skilful carpentry. Of late years, however, wrought-iron pit-frames have been adopted to some extent, which allows of a comparatively simpler construction being used, the main elements of the frame consisting of hollow latticed pillars and beams, similar to the construction now generally adopted for the pillars of railway signals, but of course of a more solid construction. They have one great advan tage over wooden frames, in not being liable to destruction by fire, an accident which has occasionally happened with the latter. The guide-pulleys for iron or steel wire-ropes are made of very large dimensions, to avoid strain upon the wires by sudden change of direction when moving at a high speed. The usual construction is a deep channeled rim or tire of cast-iron, from 7 to 20 feet in diameter, supported by numerous thin wrought-iron arms, inclining inwards from a central cast-iron boss, a form combining rigidity with comparative lightness. They are in fact very similar to the driving wheels of the large modern bicycles, supposing a channeled rim to be substituted for the Indiarubber tire. To prevent accidents from the breakage of the rope on the shaft, or from overwinding catches. Safety when the engine is not stopped at the right moment, whereby the cage may be dragged up to the head pulleys (both which kinds of accident are unhappily not uncommon), various forms of safety catch and disengaging hooks have been proposed. These consist of variously. constructed toothed levers, cams, or eccentrics, mounted α FIG. 20. upon transverse axes, attached to the top of the cage, whose function is to take hold of the guides, and support the cage in the event of its becoming detached from the rope. They are generally applied by means of springs acting agains. the pull of the rope. Figs. 19-21 represent a form of safety catch, introduced some years since by Messrs. White and Grant of Glasgow. The catches BB consist of partially toothed eccentrics, which when released are forced inwards C against the wooden guide a by the coiled springs d d, as shown in fig. 21. When the rope is drawing, the catches are lifted by the pull of the chains attached to the pulleys cc, which turn the broad-toothed portions outwards, and away from the B d d FIG. 21. FIGS. 19-21.-White and Grant's Safety Catch. guides. The connection with the rope is made by the slide bar C and spring catch h having a projecting trig ger, which, if the cage is lifted too high, strikes against the cross-bar of the framing k, and detaches the cage, which is then left hanging by the catches to the guides in the pit. The use of safety catches is more common in the collieries of France, Belgium, and Germany than in Eng land, where they are not generally popular, owing to their uncertainty in action, as they are often found to fail FIGS. 22-24.-Surface arrangements of Colliery. accidents in winding are to be found in constant vigilance, in maintaining the ropes in working efficiency, and in the use of proper signals and brake power in the engine house. The speed attained by the load in the shaft in the bestappointed English collieries is very considerable, and may be paralleled with that of a fast railway train. At Shireoaks Colliery, Nottinghamshire, the cage with a load of 34 cwts. of coal in five tubs, and weighing in all 60 cwts., or with the rope at the bottom 92 cwts., is raised from a depth of 516 yards in 45 seconds, corresponding to an average of 35 feet per second, or 24 miles per hour, the maximum speed when the load is midway being 50 feet per second, or nearly 35 miles an hour. The ropes used are round, of steel wire, weighing 13 lbs. to the yard, winding on to a spiral drum, increasing from 17 to 20 feet in diameter. There are two engines with vertical cylinders, 32 inches diameter and 6 feet stroke, develop ing a useful effect of about 320 horse-power. The guide pulleys are 12 feet in diameter. The above may be taken as a good example of the modern class of winding engines, such as are required to draw from 600 to 1200 tons in the shift of 10 hours. When the pits are of small depth it is better to increase the weight of the load than to draw at a very high speed, as the loss of time in filling and unloading or striking the cages is the same for a short as for a long journey, so that it becomes advantageous to diminish the number of journeys for a given quantity of coal drawn. X The great amount of dead weight required to be raised in the ordinary system of winding (e.g., in the instance given above, the total weight moved is nearly four times that of the net load drawn, that of the ropes being nearly 14 times as much as the latter) has led to the proposal of various plans to obtain a more mechanically economical method, but none of these have at present been brought into successful use. One of the latest is that of M. Blanchet, who proposes to draw a number of tubs linked together into a long vertical train in a closed tube about 5 feet in diameter, by exhausting the air above them in the manner adopted in the pneumatic tubes used for the transmission of parcels. An experimental apparatus of this class has been recently constructed at Creusot, in France, designed to lift a cage with 9 tubs, attached to a piston, weighing in all about 12 tons. and When the cage arrives at the surface, or rather the platform forming the working Striking top above the mouth of the pit, it is re- screening. ceived upon the keeps, a pair of hinged gratings which are kept in an inclined position over the pit-top by counterbalance weights, so that they are pushed aside to allow the cage to pass upwards, but fall back and receive it when the engine is reversed. The tubs are then removed or struck by the landers, who pull them forward on to the platform, which is covered with cast-iron plates; at the same time empty ones are pushed in from the opposite side. The cage is then lifted by the engine clear of the keeps, which are opened by a lever worked by hand, and the empty tubs start on the return trip. When the cage has several decks, it is necessary to repeat this operation for each, unless there is a special provision made for loading and discharging the tubs at different levels. An arrangement of this kind for shifting the load from a large cage at one operation has recently been introduced by Mr. Fowler at Hucknall, in Leicestershire, where the trains are received into a framework with a number of platforms corresponding to those of the cage, carried on the head of a plunger movable by hydraulic pressure in a vertical cylinder. The empty tubs are carried by a corresponding arrangement on the opposite side. By this means the time of stoppage is reduced to a minimum, 8 seconds for a threedecked cage as against 28 seconds, as the operations of lowering the tubs to the level of the pit-top, discharging and replacing them are performed during the time that the following load is being drawn up the pit. The tub when brought to the surface, after passing over a weigh-bridge, where it is weighed and tallied by a weigher specially appointed for the purpose by the men and the owner jointly, is run into a tipping cage, and the contents are discharged into an inclined screen with bars about 1 inch to 1 inches apart. The large coal remaining passes through a spout into a railway wagon placed below, the discharge being regulated by a valve at the lower end. The small coal passing through is either sold as such, or may be lifted by an elevator to a second series of screens, either fixed or rotating, with half-inch apertures. These make a further separation of larger pieces, which are sold as "nuts," while the small, or slack, passing through is sent to the coke ovens, if the quality of the coal is suitable. As a rule, non-caking coals are not very closely screened, as the small is of comparatively little value, and therefore must have a proportion of larger sizes mixed with it to form salable slack. ments. Figs. 22-24, representing the surface arrange- Illustraments adopted at a pair of pits in the Wigan tions of district, may be taken as fairly representative surface of the fittings of a large modern colliery, where arrangea considerable output of coal has to be screened and loaded in an ordinary working day of less than twelve hours. The details, of course, will vary, according to the nature of the outlet or vend, which may be by retailing into carts sent by purchasers, or by canals or rail. |