EXPLOSIVES.
13. No military mining operations of note have been carried on since the introduction of dynamite and other high explosives; consequently our knowledge of their value for work of this kind rests entirely upon the results obtained from experimental mines. Unfortunately but few experiments seem to have been made, and the published results of these are very meagre.
14. Two mines fired at Krems in 1873 with L. L. R. of 12 ft. in earth weighing 100 lbs. per cubic foot and charged, one with 173 lbs. gunpowder, the other with 58 lbs. dynamite (kind not stated), gave crater radii, respectively, of 12.75 and 10.25 feet. Lebrun’s formulas applied to these give to gunpowder and dynamite the ratio 1 : 1.688.
Two powder-mines and one dynamite-mine, each of 12 ft. L. L. R., were fired at Willet’s Point in 1878. The powder-mines were each charged with 200 lbs. cannon-powder and the dynamite mine with 82 lbs. dynamite No. 1.
No. 1 powder-mine gave a crater radius of 15½ ft.
No. 2 powder-mine gave a crater radius of 15¼ ft., or a mean of 15⅜ ft.
The dynamite-mine gave a crater radius of 14½ ft.
The relative values of cannon powder and dynamite resulting from the application of the same formulas to these mines is 1 : 1.997.[11]
15. Choice of Explosive.—From these experimental mines it may be concluded that for forming craters in ordinary earth dynamite is not quite so efficient as double its weight of good gunpowder. For breaking up hard rock, blowing up strong masonry, and especially in demolitions where tamping is usually defective, this ratio does not hold; but the relative effect of the high explosive increases continually with the lack of tamping and the intensity of the local blow desired, until a point is reached at which the effect of gunpowder is almost imperceptible, while the high explosive does efficient work. This property of the high explosives renders them extremely valuable for use in hasty demolitions, such as blowing up palisades or barriers, destroying guns, etc., etc.
Owing to their varying values in different conditions the choice of explosive to be used in any particular case must evidently depend upon the circumstances attending it.
In underground explosions both gunpowder and high explosives give out noxious gases which penetrate the soil, and which entering a gallery in sufficient quantity would suffocate the miners. Of these gases the carbonic oxide given off by some of the high explosives is probably the most dangerous to human life, and if mixed with the proper proportion of air forms an explosive mixture, resembling in this respect the fire-damp of the coal-mines. Whether in practical mining operations it would ever be retained in the soil in such quantities as to produce this effect remains to be seen.
Some of the high explosives, on the other hand, seem to produce relatively small quantities of noxious gases. The gases produced by gunpowder, while suffocating in their nature, have the advantage of always making their presence known by their odor.
16. For use in overcharged mines designed to break in the enemy’s galleries, the high explosives, from the violent character of their explosion and from the phenomena exhibited in submarine mining, promise to give relatively greater radii of rupture than gunpowder; but sufficient data are not available to state this positively.[12]
17. Beside the considerations above stated, which refer to the effects produced by the explosive when fired, there are others equally important relating to the safety and facility with which the explosive may be transported, handled, and placed in the mines. The latter will frequently have greater weight than the former in determining the explosive to be used in any particular case which may arise in the practical operations of mining. Of the latter considerations some of the most important in deciding whether to use gunpowder or high explosives are the following, viz.:
Gunpowder is easily obtained, and most enlisted men are more or less familiar with its properties.
It explodes when ignited by fire.
It does not ordinarily explode when struck by a bullet.
It is injured by moisture and destroyed by thorough wetting.
It is not affected by ordinary changes of temperature.
It requires thorough tamping to produce good effects.
Many high explosives are not injured by moisture, and some are unaffected by total immersion in water.
They generally burn without detonation if ignited by flame.
Some of them do not explode when struck by a bullet. The more sensitive ones do.
The properties of some of them are materially changed by freezing.
On account of their greater strength, the same effects may be produced by smaller charges, requiring smaller chambers and cases.
By reason of the violence of their action they produce good results even if imperfectly tamped.
The last two considerations, together with the possibility of using them in wet places without protection against moisture, lessen greatly the time required to excavate, charge, and tamp a mine, and may frequently enable the one using them to anticipate an enemy using gunpowder and thus secure success, when the use of gunpowder would reverse the situation. In mining operations and in expert hands the high explosives, upon the whole, seem to cause fewer accidents than gunpowder.
CHAPTER II.
PRACTICAL OPERATIONS AND DETAILS.
18. Tools and Appliances.—The different operations of mining are carried on by the use of picks, shovels, bars, saws, axes, hammers (large and small), chisels, wheel and hand barrows, windlasses, ropes, wooden or leather buckets, gauge-sticks, mason’s levels ([Pl. XI], Fig. 4), plumb-lines, candles, closed lanterns, tin pipes, rubber and canvas hose, canvas, nails, etc., etc., of the kinds in common use; and the following special tools and appliances, viz.:
The Miner’s Pick. Smaller and lighter than the common pick. Neither its head nor its handle exceeds 2 feet in length.
The Miner’s Shovel. Similar in shape to a common shovel, but not exceeding 2 feet in length.
The Push Pick ([Pl. XI], Fig 5), which has a lance-shaped blade about 3½ in. wide and 6 in. long attached to a handle about 2 feet long.
The Field Level ([Pl. XI], Fig 6), which consists of three strips of wood about 2" × ½", arranged as shown. The strip A is 4' between centres of pins; B and C are 2', 915/16"; the angle at a = 90°. A spirit-level is inserted in piece C, and a plumb-line attached as shown. The markings on A are used for gentle slopes, those on B for steep ones.
The other sides of B and C are divided into degrees of arc, the centre being at the middle point of the outside edge of A.
The Slope Block, which is a wooden cube used in connection with a mason’s level for fixing slopes.
Angle Templets ([Pl. XI], Fig. 7), making a definite angle, used in laying out galleries.
The Miner’s Truck or Car. A small, four-wheeled wagon with fixed axles and very short wheel-base; exterior dimensions about 20" wide, 18" to 20" high, and 30" long. Used for carrying earth through galleries, and usually hoisted up the shaft and dumped outside, replacing the buckets used in sinking the shaft.
The Miner’s Bellows ([Pl. XI], Fig. 8). A leather bag with wooden top and bottom, provided with inlet and outlet valves, from the latter of which the air is led off in pipes or hose. In using the bellows the miner stands upon the lower handles and works the bellows with his hands by the upper ones.
This is frequently replaced by a common blacksmith’s bellows or the rotary blower from a portable forge; and sometimes by an improvised air-pump, consisting of a large open cask filled with water and another smaller one, with one head removed and the other provided with outlet and inlet valves and an air-tube, inverted over the large cask, supported by a spring-pole and worked up and down by hand in the water of the lower cask.
The Miner’s Candlestick ([Pl. XI], Fig. 9), which holds a candle, and may be driven into the side or bottom of a gallery.
Miner’s Lamps ([Pl. XI], Fig. 10), can be used only when the ventilation is good, as they give off more smoke than candles.
When an electric-light plant is available, incandescent lamps will be used for mining.
Earth Augers, similar to those used for boring post-holes, but of different diameters, are sometimes used for placing camouflets. Their shanks are made in short lengths, which can be joined together to allow of boring a deep hole from a narrow shaft or gallery.