Blasting powder

“ All powder, whether it is intended for blasting, hunting, rifle-shooting, or warfare purposes, is made in the same general way, and so, in telling of a visit I recently made to the Du Pont Works, near Wilmington, I shall reveal no secrets if I describe the various mills and processes which practically all powder goes through before it is finished. Ordinary powder is composed of three ingredients—saltpetre, sulphur, and charcoal, or nitrate of soda, sulphur, and charcoal. Powder intended for blasting is generally made with soda; powder intended for shooting is generally made with saltpetre. ”

“ The greatest number of men employed in one pair of shafts was about eighty, and the quantity of blasting powder used by that number in the course of a day averaged 1 cwt. Safety fuses were seldom used, the charge being fired by a straw filled with fine powder, which was lighted from a candle. ”

“ The low and high explosives are differentiated, and the sensitiveness of fulminate of mercury and other detonators is clearly pointed out. The various explosives, such as gunpowder, black blasting powder, potassium chlorate powders, nitro-glycerine powders, etc., are described, and their peculiarities and suitability for different purposes are set forth. The character and method of using the different explosives, both in opening up work and in enclosed work in coal mines, follow, with information as to the proper method of handling, transporting, storing, and thawing the same. ”

“ Explosives may be either mere mixtures, such as gunpowder, or chemical compounds, such as nitroglycerin. They may all be made to explode under sufficient heat; for example, dynamite or nitroglycerin at 180°C., blasting powder at 270°C. and rifle-powder at 270°C. The oldest of the explosives is gunpowder, which is a mixture of potassium nitrate, sulphur and charcoal, in some such proportion as 75 per cent., 10 per cent. and 15 per cent. respectively. The principle of explosives is to bring oxygen into very close contact with combustible substances. ”

“ Some raise a weight, and others throw a shot, to certain heights and distances. As a test of gunpowder the eprouvette is comparatively worthless, and it has been generally superseded by instruments for measuring the initial velocity obtained by firing the powder in the particular gun for which it is intended. A short mortar is, however, still used, to a certain extent, for testing the power of modern blasting powders, such as the mixtures of nitro-glycerine. A very small charge and a heavy shot of chilled iron which enters two or three inches only into the mortar are used. ”

“ The fullest benefit of modern explosives, such as dynamite, gun-cotton and yonite, can be obtained only by the use of strong detonators fired by electricity, by which it is impossible to place a number of bore-holes in such a manner that when fired simultaneously they shall help one another. Blasting powder is still used for removing coal and millions of tons are obtained by its aid. ”

“ At the East heading, partly owing to the rock being softer than either at the West End or in the Central Shaft, partly to the miners being accustomed to powder, partly to the heavy battery of drills enabling twelve drilling machines to work at once, and thus make progress satisfactory to the contractors, who, wisely, let well enough alone, the holes when drilled to a depth of from two feet six inches to three feet, are each charged with from one to two and one-half pounds of blasting powder, then tamped ”

“ Whenever possible, a new method or a new machine should be so constructed as to apply to as large a proportion of the whole work as possible, and every effort should be made toward the standardization of materials and apparatus.
In attempting work in blasting, it should be remembered that the use of new and untried explosives is attended with peculiar dangers. The men are familiar with the use of the standard grades of powder; and while they are ignorant of how dangerous it is to take liberties with dynamite, they are at a great disadvantage when a new explosive is given to them for trial. ”

“ But if once a blast is shewn, and they have to hoist out the rock, their obstinacy succumbs, and in three months, men, who knew it was poison, and so dangerous it was wicked to ask them to drill holes to receive it, have positively refused to descend a shaft if powder was attempted to be used merely in a comparative experiment, alleging, that the powder was unhealthy and not fit to be used at the bottom of a shaft, where the air was confined. ”

“ Better to face the difficulty, construct efficient electric apparatus, convey the electricity along wires of perfect insulation to a safe priming, and by complete and violent explosion of the Nitro-Glycerin, or powder, make such effective blasting as not to throw away the labor of drilling, candles, power, and blasting materials. I believe this the true economy. These details may seem wearisome, but the casualties of blasting can best be diminished by avoiding missed holes, a result only attainable by using materials absolutely reliable ”

“ There was no one at the quarry who really knew how to blast efficiently. But then one day a man came out and showed Earl how to use electric blasting caps instead of the fuses he had been using. By drilling shallow holes, placing less explosives in each hole, and setting them off all at once, electrically, the blasting was much more efficient and a lot safer. Before that time, the custom was to set off a small blast in the bottom of a deep hole for the purpose of opening up a "pocket" large enough to hold as many as eight cans of powder and 80 sticks of dynamite. ”

“ Hence in all blasting operations there will be two things to determine, the line of least resistance and the quantity of powder requisite to overcome the resistance along that line. For it is obvious that all excess of powder is waste; and, moreover, as the force developed by this excess must be expended upon something, it will probably be employed in doing mischief. Charges of powder of uniform strength produce effects varying with their weight, that is, a double charge will move a double mass. ”

“ The test has to be applied in the following way:—The explosives that have to be tested are finely subdivided, gun-cotton, nitro-glycerine, dynamite, blasting gelatine, &c., in the same way as at present directed by the Home Office regulations. Smokeless powders are all to be ground in a bell-shaped coffee mill as finely as possible, and sifted as hitherto. 1.5 grm. of the explosive (from the second sieve in the case of smokeless powder) is to be weighed off and put into a test tube as hitherto used. Strips of well-washed filter paper, 25 mm. wide, are to be hung on a hooked glass rod as usual. ”

“ The caps used in exploding giant-powder and nitro-glycerine are filled with a powerful fulminating powder, and are very dangerous. They explode with the slightest scratch upon their contents. They are about half an inch in length, and their interior diameter is sufficient to admit the end of a piece of ordinary blasting fuse. Persons unacquainted with their uses always appear to be overcome by an ungovernable curiosity in regard to the nature of their contents, the moment they by any means get hold of any of these caps. ”

“ The detonation of an explosive is caused by the shock or heat of the explosion of a more sensitive substance which has been exploded by a powder fuse or electric spark. The common method of detonating explosive charges is by the firing of a blasting 299cap. These caps are copper cylinders, closed at one end, about 11⁄2 inches long and 1⁄4 to 3⁄8 of an inch in diameter, or larger. They contain a mixture of about 85 per cent fulminate of mercury and 15 per cent potassium chlorate held in place by a wad of shellac, collodion, or paper. ”

“ Gunpowder, or black powder, is seldom used for rock-blasting, except in quarrying building-stone, where slow explosives of relatively low power are desirable to avoid shattering the stone, and in such collieries as do not require the use of safety explosives. Gunpowder is exploded by deflagration, by means of a fuze, and exerts a comparatively slow and rending force. The high explosives, on the other hand, are exploded by detonation, through the agency of a fuze and fulminating cap, exerting a quick, shattering, rather than a rending force. ”

“ It has also been ascertained that the greater the pressure, the higher is the proportion of carbonic acid produced, so that the more work the powder has to do, the more perfect will be the combustion, and, consequently, the greater will be the force developed. ”

“ Opposite to the village, another awkward snag, in the shape of a large tree sticking up in 30 feet of water, was destroyed by tying a 70-lb. charge at its [183] base. A charge of 50 lb. of powder under this head of water, or even a smaller amount, might have been sufficient, but as the work had to be done quickly, not much account was taken of a few pounds of powder more or less, provided the object was attained. ”

“ With Nitro-Glycerin the holes need not be drilled at so acute an angle to the face of the rock, and need no tamping, that is, the drilled hole is left entirely open, and no time is occupied therefore in ramming materials over the explosive, and no risk is incurred in cutting the fuse or electric wire, as with powder, dualin or dynamite, all of which must be tamped. ”

“ Moreover, as the depth of the holes is increased, so must the diameter be increased in proportion to the depth when powder is the blasting agent, but when the drilled hole is to be blasted out with Nitro-Glycerin, a diameter of 13⁄4 inches is sufficient for a hole having a depth of ten feet, and a line of least resistance of eight feet, a depth wholly inadmissible for powder, because the rock at that depth would act like the breech of a cannon, and the explosion would issue direct from the hole, only fracturing the edge, i. ”

“ If pure, the danger in the use of Nitro-Glycerin is no greater than that of powder, and the premature explosions that have proved so fatal in many instances, have without doubt been caused by decomposition, which was the result of imperfect manufacture. If regularly manufactured, accidents will be the result only of inexperience or the neglect of instructions from those having experience. In the manufacture, the nitrous vapours that are disengaged at the time of mixing, if not entirely expelled, will make it liable to explosion from any concussion, and from Mr. ”

“ Thirty per cent. more blasting power is evolved, when the Nitro-Glycerin reaches the bare rock of the drill hole, than when, by insertion in cartridge, the metal of the cartridge and a layer of air or water are interposed between the blasting gases and the rock. ”

“ The relative strength, bulk for bulk, is, however, of greater importance in rock blasting. This is easily computed from the foregoing table and the specific gravity of the substances, which is 1·00 for gunpowder and compressed gun-cotton, 1·60 for nitro-glycerine, and 1·65 for dynamite. Compared in this way, bulk for bulk, these explosives range as follows:—
Hence, for a given height of charge in a bore-hole, gun-cotton exerts about 21⁄2 times the force of gunpowder, and dynamite about 41⁄4 times that force. ”

“ In addition to the difference in chemical composition of these Schultze powders, I would point out that there is a difference in density—the Blissett being heaviest, the Bland next, and the New the lightest of the three. I think this fact also has some bearing on the violence of the explosion. In black powders, I believe, a dense powder, speaking generally, is stronger than a lighter one; and the Schultze patent states that hard woods make more explosive powders—not, I take it, because the composition is thereby altered, but because a denser powder is produced. ”

“ But this classification is very rough; because although some of the better known purely military powders are not suited for use in sporting guns, nearly all the manufacturers of sporting powders also manufacture a special variety of their particular explosive, fitted for use in modern rifles or machine guns, and occasionally, it is claimed, for big guns also.
Of the purely military powders, the best known are cordite, ballistite, and the French B.N. powder, the German smokeless (which contains nitro- glycerine and nitro-cotton) ”

“ In the combustion of all explosive materials, great heat is generated, and the force of the explosion is dependent upon the volume of gases and the high temperature to which they are raised.
The smokeless powder used in the United States is made by dissolving a special kind of guncotton or nitrocellulose in ether and alcohol, just sufficient of the solvent being used to gelatinate the nitrocellulose, which is then stuffed through a forming die into rods. ”

“ In all cases, ample power should be possessed by the firing machine or battery.
The shattering class of explosives are very suitable for subaqueous-rock blasting. In many cases, their employment renders the boring of shot-holes unnecessary, an advantage of obviously great importance. When detached or projecting masses of rock have to be broken up, it is sufficient to place the charges upon them. Of course, when so applied, larger quantities of the explosive are required; but though the method is wasteful of explosive, it is very [170] economical of labour and time. ”

“ It will be observed, from a consideration of the foregoing facts, that a very large proportion of the force developed by an explosion is due to the heat liberated by the chemical reactions which take place. And hence it will plainly appear that, in the practical application of explosive agents to rock blasting, care should be taken to avoid a loss of the heat upon which the effects of the explosion manifestly so largely depend. ”