Elliott Multiple Wedge. The construction and method of using these can be readily seen from Fig. 94, the advantage claimed being that only a small-sized hole is required, and that the weight of the whole apparatus, including boring machine and wedge, is very small, while the expansive force developed is large, owing to the fact that the impact of a blow is more effective than other means of applying wedging power. Haswell Mechanical Coal-getter.*-In this machine the rending action is accomplished by a wedge between two feathers, the wedge being drawn out by a combination of a screw and lever. The bursting action takes place towards the back of the hole, and not at the face, where least required. Burnett's Roller Wedge.-The amount of friction between the sides of the wedge and feathers, in ordinary systems, is very great. To overcome this difficulty, Mr. Burnett† designed a roller wedge, in which rolling is substituted for sliding friction. It consists of two external plugs, or feathers, with an internal wedge running on roller bearings. This wedge is drawn out by the action of a screw and nut, driven by a ratchet and pawl arrangement. Hydraulic Wedges.-To increase the power of these machines hydraulic pressure has been called into requisition. A man's strength, acting on a lever working the piston of a small hydraulic pump, is capable of producing an enormous pressure, which can be applied to driving in wedges. Instead of applying the hydraulic apparatus directly to the wedge, which compels the operator to stand close to the face, in some designs the pressure pump is fixed a considerable distance away, and the water is conveyed to the wedge through a pipe. Lime Cartridges.-Messrs. Smith and Moore designed a process for bringing down coal by utilising the expansion of quicklime, when water is applied to it. Ordinary mountain limestone is calcined and ground to a fine powder, and compressed by hydraulic power into a cartridge, having a groove running along its full length. The cartridge is about 5 inches long and 2 inches diameter, and when taken from the press is wrapped in a sheet of paper, and placed in an air-tight box to keep away damp. Coal is holed and shot-holes drilled in the ordinary way, and cartridges placed in them. An iron tube inch diameter, having a small external channel on the upper side, and provided with perforations, is inserted along the full length of the hole. Several cartridges are placed in each hole, the grooves formed in them during the process of manufacture lying against the tube just referred to, and the mouth of the hole is tamped in the usual way. A small force-pump is connected by suitable means to the end of the tube projecting from the hole, and water forced in. The hand pump is then detached and carried away to another hole. The water acting on the lime greatly expands its bulk, and the coal is forced down. This system has been employed and gave good results at Shipley Colliery for a considerable time, but has not met with much favour elsewhere. It can only be used for certain classes of coal, and great care has to be exercised to keep the cartridges dry. They readily absorb moisture from the atmosphere, and completely lose their efficiency. * N. E. I., xxxiii., 37. + Min. Inst. Scot., viii., 2. Bosseyeuse. For a considerable length of time an apparatus has been in use at the Marihaye Colliery, Belgium, which consists of a rock drill of the Dubois-François type, boring a series of holes grouped. in a certain pattern in the face of the work. The drilling tool is removed and replaced by a hammer head, a number of plug and feather wedges are then put in the holes, and driven in by the battering ram till the rock is broken down and split up. No explosives are used, and trials over a period of many years show that the employment of the machine has not increased the cost of working. Oxy-hydrogen Gas.-The decomposition of water into its elements by electricity is a comparatively easy matter, and the resulting mixture of oxyhydrogen gas forms a powerful explosive. The idea of substituting this gas for the explosives ordinarily used is fascinating, as it may be obtained from water by a slight expenditure of electrical. power. 3 32 At Mont Cennis Colliery, Westphalia,* experiments were made with about ounce of distilled water, containing a small quantity of soda lye (added to increase conductibility) enclosed in a steel cylinder 7 inches long, 1 inches diameter, and inch thick, capable of standing a pressure of 1200 atmospheres. Two conductors were passed through the steel lid, and the electrodes were made of ordinary iron nails. The electric current of about 1 ampère and 10 volts was passed through for some forty hours, when about ounce of water was decomposed and the pressure within the cylinder had risen to 450 atmospheres. When blasting, the cartridge is connected to two electric conducting wires, introduced into the shot hole, tamped in the usual manner, and exploded by a spark, produced by a Bornhardt or other igniting apparatus, leaping from one electrode to the other. Experiments demonstrated that such cartridges produced the same blasting effect as 5 ounces of the ordinary nitrate of ammonia explosive, such as westphalite, &c., and it was also hoped that the idea would provide a safe method of blasting for fiery and dusty collieries, but the ignition of a gaseous mixture of fire-damp was caused several times. The cost of generating the oxyhydrogen gas is small, but the cylinders themselves have to be so carefully made that they are costly. It also remains to be proved that the internal pressure of over 6500 lbs. in the cartridges is unattended with danger. Prohibition of Blasting.-From time to time suggestions are made that blasting should be prohibited in mines. Undoubtedly, there are seams of coal which can be economically worked by wedges, but such are few and far between. With a seam that is thin, hard, and blocky, and adheres tenaciously to the roof, wedging is of no use; the coal breaks short, and wedge after wedge is inserted with little effect. On the other hand, where the coal is soft, the wedge, on expanding, simply widens the sides of the bore-hole. As in too many cases the direct causes of explosions can only be conjectured, every cause to which explosions have been traced shares a prejudice which evidently does not rightly belong to them all. Although the occurrence of some explosions can be directly traced to blasting, it must not be assumed that all are due to this cause, or that if it was stopped entirely they would cease. When a large explosion takes place the *Coll. Guard., 1897, lxxiv., 1065. loss of life is so serious that public attention is directed to it, and the other accidents which happen in mines are apt to be lost sight of. Statistics, however, show that the death-rate is higher from several other causes than from explosions; for instance, falls of roofs and sides. Now, with blasting, the men are away from the working face, but with wedging they must be there, and are liable to be injured by falls which take place, especially in thick seams. Wedges are claimed to produce more round coal than when shots are used, but such is not necessarily the case. If the charge employed is properly proportioned it can be made to do what is required; all that has to be done to produce the coal in a large round state is to vary the amount of explosive. To show the increase in cost due to prohibition of blasting, Mr. W. Y. Craig arranged for the best miners at Podmore Hall Colliery to be employed to work at day wages on two places for one month with, and one month without, powder. In a 12 yards drift, working one month without powder, the wages paid were £16 os. 10d., quantity produced 233 tons II cwts. 3 qrs., cost per ton Is. 4d; same worked with powder, wages £17 98. 3d., including 8s. for powder and fuse, coal produced 327 tons 16 cwts., cost per ton Is. To this has to be added the increased cost per ton of the fixed charges, such as superintendence, timber, and road maintenance due to the diminution in quantity. In each shift 1064 tons were got without powder, 14:26 tons with powder, the difference being 3'2 tons per shift, so that the quantity was 24 per cent. less than when worked with blasting. The total increase of cost, minutely and carefully calculated, was Is. 2 d. per ton by working without powder. Experiments in narrow heading with the Hardy Pick Company's wedge instead of explosives, at the König and Wellesweiler Collieries † in the Saar district, proved that the cost was increased 49 per cent., and in long-wall work 56 per cent. The financial results of a diminution in blasting at Maybach Colliery, and partly substituting wedging, was that the cost increased by nearly twopence per ton as a minimum. At Blackwell experiments were made on a length of 114 feet of the Alfreton deep, soft coal face, with roburite, carbonite, and gunpowder. In each case the face was holed 5 feet deep, with the result that the cost of getting round coal was increased a halfpenny per ton by using high explosives over gunpowder, while 1 to 2 per cent. more slack was obtained by carbonite, and 3 per cent. by roburite, than by gunpowder. It was also stated that the increased quantity of slack produced by high explosives reduced the average selling price by one penny per ton. The accidents due to firing can be best prevented by careful supervision of the work, by placing the operations under the control of a well-regulated staff with a steady and attentive person at the head, by careful examination of the working face before firing, and, above all, by good ventilation. The number of shots required can be decreased by deep undercutting. Finally, the loss of life may be entirely removed by firing all the shots simultaneously from the surface when all the workmen are out of the pit, this being the procedure at some of the South Wales collieries. *N. Staff. Inst., iv., 53. + Coll. Guard., 1896, lxxii., 723. Bibliography.-The following is a list of the more important memoirs dealing with the subject-matter of this chapter : :- MIN. INST. SCOT.: Notes on Coal-Cutting Machinery, G. B. Begg, i., 269; The ENG. AND MIN. JOURN. : Edison Electric Percussion Drill, li., 400; Electric Soc. IND. MIN. Notes sur l'application des moyens mécaniques au creusement des puits et des galeries au rocher, A. Pernolet (2o Série), i., 381, ii., 5, and iii., 595; Appareils de perforation mécanique à l'Exposition de Paris, 1878, Ch. Buisson (2o Série), viii., 873; L'air comprimé aux mines de Blanzy, F. Mathet (3 Série), ii., 65; Appareils de perforation à la main, MM. Dinoire et Maillard (3° Série), ii., 305; Note sur la perforation mécanique à l'air comprimé aux mines de Blanzy, J. Druge (3o Série), vii., 387; Sur les compresseurs des Alouettes, mines des Blanzy, M. de Boisset (3o Série), vii., 395. N. E. I. On the Application of Machines worked by Compressed Air at the Collieries of Saars Longchamps, J. Dalglish, xxi., 199; Dangers of Sparks produced from Prickers and Stemmers used for Blasting Purposes, H. Lawrence, xxxiii., 3 (see also Colliery Guardian, lxi., 207, Jan., 1891); The Haswell Mechanical Coal-Getter, W. F. Hall, xxxiii., 37; Transmission of Power by Steam, Messrs. Liddell & Merivale, xxxv., 159, and xxxvi., 13; System of Working Ironstone at Lumpsey Mine with Hydraulic Drills, A. L. Steavenson, xxxvi., 67; Bornét's Hand-Boring Machine, E. L. Dumas, xxxvii., 117. FED. INST. The Distribution of Electrical Energy over Extended Areas in Mines, A. T. Snell, i., 141; Coal-Getting by Machinery, G. B. Walker, i., 123; Experiments with Explosives, used in Mines, M. Walton Brown, ii., 49; Experiments with Carbonite, M. Walton Brown and W. Foggin, ii., 85; An Investigation as to whether the Fumes produced by the use of Roburite and Tonite in Coal Mines are injurious to health, with Appendices, ii., 368; The Low Tension System of Shot Firing, T. M. Winstanley-Wallis, ii., 553; Notes on work done by the Stanley Heading Machine at Hamilton Colliery, J. S. Dixon, vi., 4; The Transmission of Power by Compressed Air, T. Goodman, vii., 234; Electric Machinery for Mines, R. Kennedy, X., 98; Coal-Cutting by Machinery, W. Blakemore, xi., 179; Electric Coal-Cutting on Longwall Faces, T. B. A. Clarke, xi., 492; The Danger of employing Safety Fuses for Blasting in Fiery Mines, F. Winkhaus, xii., 169; High Grade Gunpowder, A. F. Hargraves, xiv., 2; Electric Blasting, W. Maurice, xiv., 142 and 445, and xv., 189; The Walker Hollow Needle for Firing High Explosives, J. Mein, xiv., 164; Latest Developments and the Practical Application of Alternating Multiphase Machinery for Electric Power Transmission, W. Dixon, xiv., 328; Explosions in Air Compressors and Receivers, T. G. Lees, xiv., 554; Machine Mining and Pick Mining Compared, W. D. C. Hardie, xvii., 171. AMER. INST. M.E.: A new Rock Drill without Cushion, A. C. Rand, xiii., 249; Electric Power Transmission in Mining Operations, H. C. Spaulding, xix., 258; A Twelve Mile Transmission of Power by Electricity, T. H. Leggett, xxiv., 315; Additions to the Power Plant of the Standard Consolidated Mining Co., R. G. Brown, xxvi., 319; Electric Mining in the Rocky Mountain Region, J. Hale, xxvi., 402. CHES. INST.: On Compressing Air, J. Sturgeon, viii., 290; Stanley's Coal Heading Machine, R. Stanley, xvi., 192. MID. INST. Simultaneous Blasting in Sinking Pits, C. Walker, vi., 196 and 261; Hydro-carbon Explosives, G. B. Walker, xi., 101 and 138. N. STAFF. INST.: Prohibition of Blasting in Coal Mines; its Effect on the Cost of Production, W. Y. Craig, iv., 53; The Compressed Air Power System, J. Sturgeon, ix., 45; Mechanical Coal-Getter, E. Mould, ix., 186. REV. UNIV.: Note sur l'établissement de machines à comprimer l'air au charbonnages du Levant-du-Flénu, H. Mativa (2o Série), i., 269; Rapport sur les expériences faites au Levant-du-Flénu sur la perforation mécanique, H. Mativa (2 Série), iii., 652; Note sur la perforation mécanique aux mines de Ramsbeck (Westphalie), C. Haber (2o Série), xii., 557; Notes sur des expériences faites sur les nouveaux explosifs et notamment sur la grisoutite en présence des poussières de charbon et du gaz, E Braive (3o Série), iv., 248, and v., 67; Note sur les nouveaux explosifs hydro-carbonés, J. Henrotte (3 Série), v., 87; Expériences faites le 11 Septembre 1890, au charbonnage de Marchienne sur divers explosifs en présence du grisou et de la poussière de charbon, E Larmoyéux (3 Série), xiii., 193; Transmission du travail à distance par l'air comprimé, G. Hanarte (3o Série), xvi., 113. ANN. DES. MINES: Note sur l'emploi de l'air comprimé pour le percement des long tunnels, D. Colladon (8° Série), xii., 469; Rapport sur l'étude des questions relatives à l'emploi des explosifs en presence du grisou (8° Série), xiv., 197; Essais pratique faites dans quelques exploitations des mines sur divers explosifs indiqués par la commission des substance explosifs, M. Mallard (8 Série), xvi., 15; Note relative à des essais faites aux mines de Liévin sur les explosifs de sureté, A. Simon (8° Série), xviii., 580. Machine Mining in the St. Louis Coal Region, H. A. Wheeler, School of Mines Quarterly, New York, vol. ix., 299. APPENDIX. List of Permitted Explosives under the order of the British Secretary of State.* Albionite, consisting of the following mixture: the wood-meal to contain not more than 15 per cent. and not less than 5 per cent. by weight of moisture. This list is subject to revision in accordance with the results of experiments made from time to time in the Government Testing Station at Woolwich. |