"13. Missed shots must not be bored out. "14. Charges in wet ground should be fired directly after charging. "15. Powder must not be charged on top of dynamite or lithofracteur. "16. Charges should always be fired by a detonator. "17. The primer, with a cap affixed, must never be rammed. "18. The cartridge should pass easily to the bottom of the bore-hole. Cartridges that fit the hole tightly must not be forced down by ramming." Experiments have been made in a number of English collieries with the Reuss system of bringing down coal by means of cartridges exploded by compressed air. From a report made on the subject to the North Staffordshire Institute of Mining and Mechanical Engineers, by Mr. Ernest Craig, we take the following data: The cartridge is simply a hollow cast-iron cylinder, varying in strength to suit the class of coal. It is estimated that to burst a cartridge half an inch in thickness a pressure of 6700 pounds per square inch is necessary, and for every additional th of an inch in thickness an increase of 1000 to 1500 pounds per square inch is required. The air-compressor pumps the air into the cartridge, the machine being worked by two men. It is made to run on rails, and stands about 3 feet 6 inches in height. The connection between the machine and the cartridge is made by means of hydraulic tubing which has an internal diameter of d part of an inch, the whole machine and construction being made capable of standing a pressure of 20,000 pounds per square inch. With the air, a small quantity of water is also pumped into the cartridge, to act as a slight check upon the violence of the expansion at the bursting of the cartridge. When the pressure reaches about 6700 pounds the cartridge explodes and the coal is brought down. The explosion is not accompanied by any great noise, and pieces of coal are not thrown any distance. A new method of mining coal by means of lime cartridges is described by Paget Mosley. The method has three objects: First, to take the place of blasting-powder, dynamite, or other explosives, thereby giving absolute immunity from all accidents arising from the use of these agents; secondly, to enable the colliery-owner to secure a greater amount of large coal from a given area, at less cost; thirdly, to lessen the labor of the miner. The mode of operating is to employ lime in a specially caustic state, made from mountain-limestone. This is ground to a fine powder, and consolidated by a pressure of about 40 tons into the form of cartridges 24 inches in diameter, having a groove along the side. These are then packed into air-tight boxes to protect them from damp, and are ready to be conveyed to the mine for use. The shot-holes are first drilled by means of a light boring-machine, and an iron tube about half an inch in diameter, having a small external groove on the upper side, and provided also with perforations, is then inserted along the whole length of the borehole. This tube is enclosed in a bag of calico, covering the perforations and one end, and has a tap fitted on the other end. The cartridge having been inserted, a small forcepump is connected with the tap by a short flexible pipe, and a quantity of water, equal in bulk to the quantity of lime used, is forced in. The water, having reached the end of the hole, escapes along the groove and through the perforations in the tube, flowing into the lime and driving out the air. The tap is then closed, so as to prevent the escape of the steam ge erated by the action of the water on the lime, and the flexible pipe is removed. The action of the steam first takes place, cracking the coal away from the roof, followed by the expansive force of the lime. There is always some little time before the steam attains a high pressure, so that all danger can be avoided. The whole time occupied in drilling a hole 3 feet deep and 24 inches in diameter, setting up the drill, charging the hole, and pumping in the water, is seventeen minutes. The principal advantages of this method are—(1) Absolute freedom from explo sions of gas, there being no fire, no smoke, or smell of any kind. (2) The roof is not shaken, and the coal produces less dust; skilled labor is unnecessary. (3) The apparatus is simple and inexpensive, easily carried about, kept in order, and can be used in thin seams. (4) Any number of holes can be charged, and by applying the water in quick succession a continuous pressure is brought to bear along the face, which causes the coal to fall in large masses. The following tables show interesting comparisons of the accidents in mining in the United States and Great Britain. It should be understood that the statistics for the United States refer only to anthracite mines: TABLE LVII.—Accidents in Anthracite Coal-mines, by H. M. Chance. (ART. "Inst. Mining Engineers.") Roof falling. Explosions Miscellaneous. Totals. Fatal. Nonfatal. Fatal. Nonfatal. Fatal. Nonfatal. Fatal. Nonfatal 100 1873... 1874.. 69 144 26 111 116 200 33 94 53 95 182 223 346 173 27 890 1620 225 902 916 2487 2031 5009 3403 7040 1127 4367 1208 1755 872 8626 436.7 120-8 175.5 87-2862-6 COAL-CUTTING MACHINES.-The accompanying diagram (Plate XVI.) shows a coal-cutting machine described at a meeting of the American Institute of Mir ing Engineers in 1875, as used at the Coal Brook mines. The lateral entry is driven as a base, and, separated Ly a 6-yard rib or pillar, an air-way is carried parallel to the same distance. Leaving a 6-yard rib to suppor the main entry, the wall of the air-way is divided by 6-yard ribs into three 40-yard faces. The machine cuts the most distant face, and is then removed to the second, and repeats the operation while the coal in the first face is taken down. By having a third face always in reserve the machine need not be delayed in case of a Another very important feature recommending nachinery is that, operations being more concentrated, less territory is required to be opened, and the coal is so rapidly removed from the part of the mine worked that much of the annoyance and danger from disintegrated roofing and pillars is escaped. It should also be mentioned that the machine above described can be used very successfully in driving entries and in turning rooms. In entry-work the machine is advanced to the face of the heading, and, moving forward upon a straight track laid along the entry, channels its way in after the manner already described; and when the limit is reached it is swung to the right and to the left. undercutting to the width of 14 feet if desired. COAL-WASHING.-Mechanical processes have been introduced to clean the coal and increase production. Coal-washing has been adopted in places in order to secure these results. The apparatus illustrated (Plate XVII.) first crushes the coal, then separates slate and impurities by reason of their different specific gravities. COAL-BREAKERS.-The large and hard masses in which anthracite coal comes out of the mine, and the popular demand for its reduction to certain specified sizes, mainly for domestic uses, have given rise to the mammoth wooden structures seen all over the anthracite region of Pennsylvania, known as coal-breakers. The following account of these peculiar buildings is from a paper by R. A. Wilder, C. E., of Cressona, Pa.: "The separation of anthracite into lumps of regular size was first done by breaking the coal with hammers on plates of iron having openings a little larger than the size of coal to be made, so that it would readily pass through and preserve something like uniformity of size; the broken coal was shovelled into screens turned by hand or set at an inclination, and the coal thrown against them, so that the waste and small pieces would pass through the meshes and fall behind, and the merchantable sizes roll down the front to the platform, from which it was loaded into wagons for transportation. This preparation increased the sales to such an extent that it was found difficult to meet the demand by the method used, and those interested in the business began to study plans for preparing coal by machinery. The waste and danger of breaking coal by hammers was too great to pass unheeded, and in 1842 crude machinery, driven by steam-power, was tried as an experiment, and failed. Two years later Joseph Batten of Philadelphia patented a machine for breaking coal, consisting of a pair of toothed rollers geared closely together and driven towards each other, through which the coal, not selected for special use as it came from the mines, was passed and broken into irregular sizes. One or two cylindrical screens made of light castings or large wire were placed just below the rollers, and the coal fell from them into the upper end. The screens were inclined at such an angle that the coal would move forward with each revolution. The smallest meshes or openings were in the first section, and they increased in size toward the lower end of the screen. The rotation was graduated to the required movement of coal, so that each particular kind would have time to be separated from the next size. The technical names given to the sizes were 'pea,' 'nut,' 'stove,' egg,' and broken;' 'steamboat and lump' were taken out before going to the breaker. The sections of the screen were about 5 feet in length, and at the lower end of each a division was made in the trough below it, which took the coal to the main storage-chute from which it was loaded into the cars; and this is the system in use now. "The loading is effected by running the railway-cars under the chute and hoisting a small gate by means of a lever connected with it by a chain. There is a gate at each chute, and it is raised just high enough so that the dirt which adhered to it in passing the to permit the coal to run out slowly into the cars, main screen can be separated by means of a small rotary-screen or stationary bars at the end of the loadingchute. "The toothed rollers, screens, and other appliances |