gerous and should be prohibited. The general statements made above do not apply to machine mines, except a few here and there. In some mines the shot firers have fired all the shots in a short time, regardless of the fact that enough time should elapse between the first and the last shot to allow the smoke and fumes to pass off in safety from the mine workings. One case was noted by the writer in which the shots were fired in one-half the time that the fire boss took to make his rounds. Since the shot firer and fire boss both visited the same places, it is reasonable to suppose that they would require an equal length of time to do their work, especially as the shot firer in this case tamped all his holes, cut his own fuse, fitted it to the shots, and fired these shots himself; yet the shot firer was out in onehalf the time that it took the fire boss to make his rounds. Under circumstances such as these it is not strange that explosions occur, mines are wrecked, shot firers are killed, old experienced miners decline to act as shot firers, and that men who do act as shot firers receive a large wage on account of the risk that they assume. However, under the circumstances (except where permissible explosives are used), the introduction of electrical shot firing from without the mine, or the employment of shot firers who are to shoot the shots after all the other men have left the mine, is the only solution of lessening the danger in mines where coal is shot from the solid. DUTIES OF AND NECESSITY FOR SHOT FIRERS. Where coal is shot of the solid and black powder is used, competent shot firers must be employed. These men should examine all shots before they are charged and should charge them. The shot firers should observe the shape and size of the shot; whether it is or is not well balanced; the placing and depth and diameter of the drill hole; whether it is near the cracks left by former shots; whether the shot is in a pillar where it is liable to break through into the next working place and injure the miner working there; and, if the miner is to load the hole, ascertain the quantity of charge that the miner proposes to use. A safe, well-balanced shot is one so laid out that there is every reason to believe, from long experience, that the powder will expend all its energy on the coal and none on the mine air, and that the coal will be brought down in the best possible condition. An unsafe shot, or an unbalanced one, is a shot where some of the powder may be blown out of the drill hole to ignite dust or gas in the mine because the powder has not been so confined that it can do the work or because the shot has not been properly proportioned. As a rule it is dangerous to try to fire the second time any hole that has “missed," meaning by this one that has exploded but has failed to do its work. This is because the natural moisture in the coal has been dried and the sides of the hole have been made smooth by the first blast, so that it is not possible to get the stemming to stick to the sides of the drill hole as it did when the hole was first tamped. Also, the coal about the drill hole may have been so cracked that the powder gases will fly out of these cracks without doing any work. Moreover, the hole having been proved by trial to be useless, it is a waste of time and powder to shoot it again. Time and money will be saved by drilling another hole that is better placed and more to be relied on to do the work. A gripping hole should receive especially careful attention from the shot firer. As a rule these holes are dangerous and unprofitable, and the miner should be taught to avoid drilling them. If the shot firer finds a dependent shot-that is, one which depends for its success on another-he should make sure that the dependent shot is not fired until the first shot has been fired and has done its work properly. This applies more especially to rising holes, which are ordinary holes with a lift or elevation above the horizontal. It is often necessary to drill holes downward to open up the coal face so that other and more practical shots can be fired. These are called "sumping" holes. The following or dependent shots should not be fired until the sumping shots have been fired and have done their work properly. When black powder is used, a flat hole, which is drilled near a parting or soft streak in the coal seam, should be examined very carefully before it is charged and fired. Black powder is slow acting and unless the drill hole is driven so that the powder will be placed across the partings and soft streaks in the seam the powder will blow out of these soft places and not only fail to do its work in bringing down coal but will ignite gas or dust in the air and thus cause an explosion. This is very apt to happen when horizontal holes are placed in or near smooth partings. The black powder hole should have enough lift, or it will not do the work expected of it and will be dangerous. Improperly tamped holes or those in which coal dust has been used for stemming should be rejected. A hole should be well tamped to the mouth. As a rule there should not be more than three shots in each working place, unless the coal seam is thin. In most coal beds three shots will yield enough coal for one day's work. On the other hand, there is a tendency to shoot heavier and more difficult shots and use larger charges when the miner is limited to two or three shots. The shot firer should watch this detail carefully. The shot firer should be especially careful about shots in "tight places," such as at the mouths of entries just breaking off slopes, in "room necks" in pillar-and-room mines, in "crosscuts" in new rooms, and in "break-throughs" near the face of entries. There is not enough room at such points for the gases from the shots to dissipate; and they often collect at these points in such dangerous quantities that they are ignited by succeeding shots; also, the concussions of heavy shots knock down board stoppings, line brattices, and curtains. Even in mines where there is no gas and very little dry coal dust it would be advisable to use permissible explosives in places such as these because their use would prevent explosions 'and also damage to stoppings and curtains. PRECAUTIONS TO BE TAKEN WITH BLACK BLASTING POWDER. Never open a metal keg of powder with a pick or metal object. Use the opening provided by the manufacturer of the keg. Never make up charges or handle cartridges or powder with an open light on your head. Place the light at least 5 feet away on the return air side so that sparks from it will not fall into the powder. Never allow powder or other explosive to remain exposed. Keep it in a well-locked box at least 100 feet from the working face and in an unfrequented place. Never go nearer than 5 feet to a powder box or powder when wearing an open light or when smoking. Never use coal slack or coal spalls for stemming; it is dangerous. Use moistened clay, wet wood pulp, or other noninflammable material. Even wet coal slack may, under some circumstances, cause an explosion. Never withdraw a shot that has missed fire. Drill a fresh hole at least 2 feet from it but parallel to the old hole and fire this new hole. After the shot a careful search should be made for the unexploded charge to prevent its being struck by a pick and perhaps causing an explosion. Never fire the hole the second time. If the first charge proves useless powder and labor are wasted in loading the hole a second time. Moreover, the first shot often cracks the coal so much that the second shot has a chance to blow out of the cracks, and thus a blown-out shot may result. Never use iron or steel tampers or needles. Have at least 6 inches of hard-drawn copper on the tamping end of the bar or, better still, use a hardwood tamping stick. The needle should be made entirely of hard-drawn copper. Never tamp shots with an iron or steel scraper, and do not push a cartridge into the drill hole with the scraper. The scraper rod should be tipped with at least 6 inches of brass or copper on the scraping end. Never allow the point of the coal auger to become dull or to become of less than the standard gage, so that a drill hole may be made with it into which the cartridge may always be pushed freely. Never drill a hole past the "loose end," "chance," or "cutting" in solid shooting. If the coal has been undercut, do not drill beyond the undercutting. It is better to stop at least 6 inches short of the solid coal. Never bore "gripping" holes. Keep the holes parallel to the ribs, or as nearly so as possible. Use the side gear on the machine if you can when boring a hole. Never guess at the quantity of powder to be used. Always measure it. This course is cheaper and better than guessing. Use cartridges rather than loose powder and make them of cartridge paper. Don't use newspaper for cartridge making. Never place black blasting powder in the same drill hole with dynamite or a permissible explosive. Never use short fuse. Always have the fuse long enough to stick out at least 2 inches from the mouth of the drill hole. When the short fuse is lit any gas in the hole may be ignited, and this may result in a premature blast. Never bite a piece of the match off the squib, nor oil it to make it burn faster. Never use sulphur and gas squibs at the same working face. Never fire shots in adjoining working faces at the same time. Never return to a shot that has failed to explode until at least 10 minutes after lighting it, if squibs were used, or 12 hours after lighting if fuse was used. When shots are fired electrically be sure that all wires are disconnected from the battery, and wait at least 5 minutes before returning to the face. Never fire a rib or butt shot before a center or "busting" shot is fired. The opening shots should be fired first, in order to give the succeeding shots a chance to do their work. Never drill a hole near the remaining portion of a former shot, nor near cracks and fissures made by previous shots, because there is great danger of the powder gases on explosion flying out of the loose coal or the cracks and igniting gas or dust in the mine air. Never use squibs or any kind of fuse, except electrical fuse, in mines that make inflammable gases. Never fire a shot without making sure that the coal dust near by is well wet down. Never light a dependent shot at the same time as another shot, and never fire a dependent shot until the first shot has broken properly. 66 Never fire a split shot"; that is, never fire a hole that has been drilled into a mass of coal, cracked and shattered by a previous shot that failed to dislodge the coal. HIGH EXPLOSIVES. In the consideration of the use and misuse of explosives, attention has up to this point been given chiefly to black blasting powder, which burns when touched by a sufficiently hot spark or flame. Like all easily ignited explosives, it is slow to act and on explosion exerts only a pushing or heaving effect. It is therefore called a "low" explosive. There are, however, explosives, of which nitroglycerin and dynamite are familiar examples, that behave differently, for they explode with tremendous speed and power, and therefore shatter things with which they are in contact. These explosives can not easily be exploded by a spark as black blasting powder can, but they require for their certain explosion what is known as a detonator, or copper cap filled with a mixture, such as fulminate of mercury and chlorate of potash, to be detonated in close contact with them to insure their explosion. The detonator itself, fired by a spark or flame from a fuse or by a wire heated by an electric current, explodes violently, and it in turn detonates or explodes the nitroglycerin or dynamite in contact with it. Explosives which behave in this way are known as "high" explosives. Because they can be exploded by a detonator and because they explode with detonation they are known also as detonating explosives. "Permissible" explosives are classed as “high” explosives, because they detonate, but they are so compounded as to be much less dangerous than dynamite for use in dusty or gaseous coal mines. EXPLOSION. An explosive is said to explode when it breaks up chemically and is changed suddenly from a solid into large quantities of highly heated gases. An explosion is accompanied by a noise, due to a concussion or jar on the air and earth, and by flame. The force or strength of the explosion depends on: (1) The length of time it takes the charge to explode; (2) the quantity of gases produced; and (3) the temperature of these gases. Since the force of an explosive depends to a large extent on the quantity of the gases produced, the manufacturers of permissible explosives, while meeting these requirements endeavor so to make the explosives that the quantity of harmful gases produced will be the smallest possible. DYNAMITE. Dynamite is a high explosive, and therefore should be detonated by a detonator "cap" or by an electric detonator. "Straight " dyna |