VENTILATION.] MINING 459 surmounted by pumps, and the bucket with its rod. The whole works like any ordinary pump, and needs no special explanation. The force-pump used in mines, known as the plunger-pump, consists of a solid piston (plunger) (fig. 88) 1 working through a stuffing-box in a pump standing on the H-piece. This has a valve which communicates with the windbore resting in the cistern. Above the H-piece comes the door-piece with another valve, and then a series of pipes, generally of cast iron, but occasionally of wrought iron, constituting the column. The upward motion of the plunger, which is attached to the main rod, causes an inflow of water, which is forced into the column when the plunger descends. It is usual to fix a drawing lift at tho bottom of the shaft, which raises the water into a first cistern, and thence a plunger forces it into a second cistern some 60 yards higher up; and it is continually forced up from cistern to cistern until it reaches the adit or the surface. There are numerous important matters which require special attention, such as tho valves, catches, balance-bobs, guiding arrangements for the rod in inclined shafts, the V-bobs, fend-off bobs, and running loops, which have to bo used when there are bends in the shaft; but space will not permit of more than mere mention of these details. Such then is tho standard arrangement worked by steam or water power for pumping from mines. The great advantage of the system consists in the employment of the plunger, because it is simply necessary for the machine to raise a weight slightly greater than that of the water, which is forced up afterwards by the down- stroke of the rods. Leaks are readily discovered, and the stuffing- box can be easily screwed up as the packing wears ; this is one great reason of the superiority of the plunger compared with a piston working in a barrel. The modifications of this system relate more to the engines em ployed than to the actual pumps themselves. The cylinder of the Cornish engine is sometimes reversed and stands over the shaft, the main rod being attached directly to the piston. This type of engine, known as the Bull engine in Corn wall, dispenses with the ponderous beam, but it has the great disadvantage of obstructing the mouth of the shaft. The use of two cylinders combined, as invented by Woolf, causes less strain upon the main rod and pumps (pit-ioork) and machinery generally, as the initial velocity of the piston is smaller and the engine starts with less jerk. The cylinders are placed side by side or one above the other. jr s Kley, of Bonn, has constructed engines on the "Woolf system with ines. steam acting on both sides of the pistons. He makes the excess of the weight of the rod over that of the counterbalances sufficient to raise only half the weight of the water and to overcome the friction; and then in the descending stroke the. steam acts on the top of the piston and so makes up for the insufficiency in force of the rods. As the steam acts on both sides of the piston the same amount is con sumed, it is true, but a smaller cylinder will do the work, and the original cost of the engine is lessened. The same engineer of late years has put up several pumping engines in Belgium, Germany, and France of 30 to 560 horse-power, with a fly-wheel which serves simply to regulate the stroke of the piston, so that the crank always stops before or after the dead point till the cataract starts another stroke. The engines are double-acting, with two cylinders and beam. The advantage of working with the fly-wheel is that the main rod and pumps are set in motion without the injurious jerk unavoidable with a Cornish engine worked at a high rate of expansion. Juinotte s M. Guinotte, the well-known Belgian engineer, also adopts a engine. fly-wheel, and the engines he has erected at Mariemont and else where are single-acting rotary engines with one cylinder. The peculiarity of the fly-wheel is that he can weight it in any way he pleases ; and he so overcomes the difficulty, which occurs in other rotary machines, of its being impossible to work them below a certain speed. His object has been to make the speed slow at the beginning and end of a stroke, so as to avoid the injurious shocks to the valves and machinery generally from sudden starts and stoppages. In order to make the main rod act by traction only and not compression, which may be advisable with iron rods, the plungers are sometimes reversed ; whilst Kraft of Seraing has introduced the Rittinger pump, which consists of a hollow moving plunger with a valve inside, and a plunger case above it working over a hollow fixed plunger. By this arrangement both the up and the down stroke of the engine cause water to be forced up; and this pump is used with a double-acting rotary engine. B. We must now speak of the second class of pumps, viz., force- pumps worked by steam, water-power, or compressed air at the bottom of the shaft. The steam pumps are of very various descriptions, 2 but they mostly consist of one or two plungers, or rams, set in motion by a rotary or a non-rotary engine, which may or may not work with 1 Michell and Letcher on " Cornish Mine Drainage," Forty-Third Annual Report of the Royal Cornwall Polytechnic Society, p. 211. 2 Stephen Michell, Mine Drainage, London, 1881. expansion and condensation. The plunger or ram is generally fixed directly on to the piston, and works in the same line, con sequently the power is transmitted to the plunger with the least possible loss. The water is forced up the shaft in one long column. Engines and pumps of this kind are easily kept in order; all the parts are readily accessible. The miner is able to dispense with the heavy beam, the massive engine-house, the long main rod and its connexions and bobs, the various cisterns and plungers, and instead he has a compact and easily supervised machine and a simple line of pipes taking up but little space in the shaft; the pump can therefore be erected and set to work very quickly, and this is a matter of the utmost importance in emergencies. It is true that these direct-acting steam-pumps, even when worked by a compound engine, cause a greater consumption of coal than the Cornish engine ; but, as a set off, there is the economy in first cost, erection, and repairs which has led to their adoption more especially in collieries. The steam is generated by boilers underground, or is conveyed from the surface in well-jacketed pipes. If natural water-power is available water-pressure engines working the plunger directly are often employed, and indeed such water-power may be created artificially for use in workings where steam-power is objectionable on account of the heat. There arc other reasons too for employing water for transmitting power ; where the length of the rods is very great, and they have to be worked quickly, there is a great liability to breakages; in order to overcome these difficulties at the mines on the Comstock lode, Mr Joseph Moore 3 uses a steam- engine at the surface to work an hydraulic accumulator, and then by pipes conveys the water under pressure to hydraulic engines working plungers. These are fixed at 2400 feet from the surface, and force the water in one column, 813 feet high, to the level of the Sutro tunnel. The exhaust water is returned to the surface in pipes and used over again. The pumps are now raising 1600 to 1700 gallons per minute. Where compressed air is being supplied to a mine for drilling and winding purposes, it is often convenient to employ it, by means of direct-acting pumps, such as are generally used with steam, for the drainage of small temporary sinkings ; and occasion ally large pumps raising considerable quantities of water are worked in this way. 11. Ventilation and Lighting. The composition of the air of the atmosphere is about one-fifth by volume of oxygen and four-fifths of nitrogen, with a little carbonic acid gas ; more exactly, the standard amount of oxygen may be taken at 20 9 per cent., and that of the carbonic acid gas at 03 per cent. The atmosphere of mines is subject to various deteriorating influences : not only do noxious gases escape from the rocks into the underground excavations, but also the very agents employed in the execution of the work itself pollute the air considerably. The dangerous emanations of fire-damp in collieries have Deleteri been already described (CoAL, vol. vi. p. 72) ; and with ous reference to this gas it is simply necessary to say that its presence is not entirely confined to coal mines. Large quantities have been observed in Silver Islet mine, 4 Lake Superior, where several explosions have occurred, whilst small quantities are met with in the stratified ironstone of Cleveland, and also in the Cheshire salt mines ; jets of the gas may be seen constantly burning in the salt mine at Bex in Switzerland ; a little has been noticed also in lead mines in Wales and Derbyshire. In the Sicilian mines the amount given off by the black carbonaceous shales inter- stratified with the sulphur beds is sufficient to cause dangerous explosions. It has been pointed out (vol. vi. p. 72) that carbonic acid gas exudes from coal; 5 it escapes also from some mineral veins. At the lead mines of Pontgibaud in central France it is so abundant that special fans have to be provided for getting rid of it ; very distinct issues of this gas may be observed at the Foxdale mines in the Isle of Man, and in the Alston Moor district it is not 3 Trans. Inst. Engineers and Shipbuilders in Scotland, 1882. 4 Engineering and Mining Journal, vol. xxxiv. p. 322. 5 A. Schondorff, " Untersuchung der auszielienclen Wetterstrome in den Steinkohlenbergwerken des Saarbeckens," Zeitschrift fur das Berg-, H Men-, und Salinen- Wesen im Preussischen Staate, vol. xxiv. p. 73; and Cl. Winkler, "Die chemische Untersuchung derbei verschiedenen Steir.kohlengruben Sachsens ausziehenden Wetterotrome und ihre Ergebnisse," Jahrbuch fttr das Berg- und Hiittenwesen im Kirnigreiche
Sachsen auf das Jahr 1882, p. 65.