But great as is the danger always attending blasting in coal-mines, it becomes immeasurably greater in the case of a blown-out shot—that is, a shot which blows out the tamping, and does not bring down the coal—for the flame then issues unobstructed from the bore-hole, and extending for some distance, is free to ignite any inflammable mixture with which it may come in contact. To blown-out shots or charges is due the majority of colliery explosions. Before a shot is fired in a seam of coal, a portion of the latter is hewn away at the top to a depth of four or five feet, and is continued down one side, near the bore-hole, so as to decrease the resistance to be overcome by the explosive. If the shot-hole has been properly drilled, the blasting agent does its work; but if the hole has been drilled into the ‘fast’—that is, if it has been bored farther into the seam than the cavity produced by hewing out a portion of the coal extends—a blown-out shot is the result; for the charge of explosive is in such a case placed in the solid bed of coal, and the resistance, consequently, being too great to be overcome, the ramming with which the shot has been fixed in its place is forced out, an outlet being thus formed, through which the propulsive power of the explosive issues without bringing down any of the coal.
From what has been said, it will be seen that the great desideratum of mine-owners has been the discovery of an agent whose propulsive power could be utilised without any attendant flame, or the devising of a method by which the ordinary explosives could be rendered harmless in this respect—that is, that their flame could be extinguished at the moment of its formation. Mining experts, scientists, and others have for years been endeavouring to solve this problem, but without success. At last, however, an invention has been brought forward which leaves but little doubt that all difficulties have now been overcome, and that so soon as the appliance is in general use, colliery explosions resulting from shot-firing will be at an end, and the dreadful loss of life and limb with which they are too frequently attended will be a thing of the past.
The invention, which has been patented, is introduced by Mr Miles Settle, managing director of the Madeley Coal and Iron Company, Staffordshire. The explosive used is gelatine-dynamite (a chemical combination of gun-wood and nitro-glycerine), three ounces of which are equal in explosive power to a pound of gunpowder. It is of a straw colour, and about the consistence of soap. The design of the patent is to inclose the charge of gelatine-dynamite in a tin case or any other material, not necessarily waterproof, and to insert this in a larger case of oiled paper, india-rubber, tin, or anything that is waterproof. Projections from the sides and ends of the inner case keep it in such a position that when the outer vessel is filled with water, the cartridge case is completely surrounded with fluid. A detonator is fixed to the explosive, and this is in turn connected with a magneto-electric machine. When the outer case has been so secured as to prevent the escape of the water, the whole is inserted in the shot-hole, and is fixed there by ramming, as for an ordinary powder shot. The operator then retires to a safe distance and fires the charge by electricity. No flame accompanies its explosion, as at the moment of its formation it is extinguished by the water surrounding the cartridge. In addition to this, the water causes the gelatine-dynamite to exert its power equally in all directions, and it also absorbs the gases formed by the combustion of the explosive, so rendering it possible for men to commence working at the coal immediately after the discharging of the shot. Moreover, the coal dislodged by this method contains a minimum of slack, and there is therefore a great saving to the colliery proprietor in this respect.
The cartridge has recently been put to some very severe tests in some of the most fiery coal-mines in North Staffordshire; in fact, shots have been fired with this explosive in mines which are so gaseous that blasting is strictly prohibited in them, and the coal has to be obtained by the expensive and ancient method of hammer and wedge. In some of these fiery mines, blown-out shots have actually occurred; and all the experts who were present at the time expressed a unanimous opinion that had such a circumstance happened in the ordinary method of blasting, a disastrous explosion would inevitably have been the result. To prove the safety with which one of these cartridges can be fired, they have been exploded in bags of coal-dust, and not the slightest vestige of flame has attended their combustion. Gunpowder has been exploded under similar circumstances, with the result that the coal-dust instantly became ignited, and shot into the air for several yards like one sheet of flame.
All the experts who have witnessed the experiments, both on the surface and down in the mine, have expressed their perfect satisfaction with the invention in every way, and have stated their belief that it can be used with entire safety in the most fiery mines. The government Inspector of Mines for North Staffordshire, who has been present at some of the experiments, has announced that he is prepared to report to the Home Office that the appliance possesses the element of safety which is claimed for it.
A magneto-electric machine is used to fire the shot in preference to an electric battery, as the former is considered much the safer of the two. With a magneto-electric machine, the current, as is well known, is generated by friction, and it can therefore be broken simultaneously with the firing of the shot; whilst in an electric battery it is generated for the most part by means of strong acids, and cannot be broken without disconnecting one of the wires from the battery. It is just possible, therefore, that as the current is continuous in the last-named machine, the two wires might still remain so close together after the discharging of a shot as to allow a spark to pass between them, which in a very fiery mine would certainly cause an explosion.
Looking at the construction of Mr Settle’s patent and at the very severe tests to which it has been subjected, there seems every reason to believe that at last has been solved the difficult problem of shot-firing with safety in coal-mines, and that henceforth explosions arising from this cause will be unknown. Such disasters are among the most dreadful calamities which can overtake a community; and only those who have been eye-witnesses of the widespread sorrow and suffering they entail—whole villages and districts being in a moment plunged into mourning, and dozens of children rendered fatherless or orphans—can form an adequate idea of the boon which the ‘water-cartridge’ promises to be to the mining population. That the highest expectations concerning it may be fully realised, is the devout wish of all who are connected with the management or working of our collieries, and who are so frequently called upon to witness some of the saddest and most heartrending spectacles that it is possible for humanity to gaze upon.
THE HAUNTED JUNGLE.
A LEGEND OF NORTH CEYLON.
IN THREE CHAPTERS.