474 iSir Heiinj Ciuiijiyjiwme [Feb. 19v 



to use is gunpowder, so far as the getting- of the coal is concerned, for its 

 action is more of a gentle push than an explosion, whereas the explo- 

 sives made with gun-cotton and similar compounds are very sharp 

 and shattering in their action, and thus make the coal into dust. 

 This is the reason why it is so difficult to adapt high explosives for 

 use in ordinary fowling-pieces. The old black powder is dirty, but 

 is the safest. 



But in a mine quite the contrary is the truth. For gunpowder 

 has the greatest capacity of all explosives for igniting gas. When a 

 shot is to be fired in a mine, the requisite quantity of the explosive 

 with the fuse or detonator is put in the hole, whicli is then filled up. 

 and rammed or stemmed with clay. The fuse is then ignited either 

 l)y means of a train of powder contained in a long paper tube like a 

 firework, or else according to the more modern and better methods,, 

 fired by electricity. Here is an ordinary electric fuse. 



[Experiment.] 



The efficacy of the action of the shot in bringing down the coal 

 is dependent on the hole ])eing well rammed or " stemmed " with 

 good clay. If the stemming is insufficient, the explosion blows it 

 out like a charge from a gun, and little work is done on the coal. 

 This is called a " blown-out " shot. And, moreover, it is a curious 

 thing tliat the more you keep an explosive to its work the less oppor- 

 tunity is given it of setting light to gas. I was almost tempted ta 

 say that Satan finds some miscliief still for blown-out shots to do ; 

 for it is almost always the blown-out shots by which gas is fired. 

 This fact has led in France, England and Germany to the use of a 

 machine for testing explosives. It consists of a tunnel of iron 2 ft. 6 in. 

 in diameter and 2S feet long. This is supposed to represent a gallery 

 in a mine. At the end of the gallery is a gun made with small bore 

 and tremendous sirength, being wound with steel wire. The explo- 

 sive to be tested is put into the gun, which is then rammed full of 

 fine clean clay. The tunnel is filled with an explosive mixture of 

 15 per cent, of air ; a paper diaphragm being put over the end to 

 keep the gas in. 



The operators then retire behind a screen and fire the shot. If 

 the quality of the explosive is unsuitable, the gas explodes as well as 

 the charge, and with a loud report, and flame can be seen through 

 small glass windows fixed in the side of the tube. 



An explosive must pass this test successfully 20 times. Inasmuch 

 as blown-out shots only occur rarely, perhaps once in five or ten 

 thousand firings, with a safety explosive one should only get a 

 blown-out shot capable of firing gas on an average once in 120,000 

 times. If you add to this, that it is strictly incumbent on men to 

 test carefully so that no trace of gas is present when the shot is fired, 

 you will see that explosions of gas ought to be exceedingly rare, and 



