MECHANICS AND USEFUL ARTS. 99 



detonate. The handling of it is now easy, and only slightly 

 dangerous. Spread upon the ground, it is only with difficulty 

 fired by a body in combustion, and then only burns pai-tially ; a 

 flask containing nitroglycerine may be broken upon stones with- 

 out its detonating ; it may be volatilized without decomposition 

 by a regulated heat ; but if it boils, detonation becomes imminent. 



A drop of nitroglycerine falling on a metal place moderately 

 heated volatilizes quietly. If the plate be red-hot, the drop is 

 immediately fired and burns like a grain of powder, only noise- 

 lessly ; but if the plate, without being red-hot, is hot enough to 

 make the drop boil immediately, it decomposes suddenly with a 

 violent detonation. 



Nitroglycerine, especially when impure and acid, decomposes 

 S]5ontaneously after a certain time, with an escape of gas and the 

 production of oxalic and glyceric acid. 



Probably the sjiontaneous explosions of nitroglycerine, with 

 whose disastrous effects the i^apei'S have acquainted us, are owing 

 to the same cause. The nitroglycerine being inclosed in well- 

 corked bottles, the gases produced by its spontaneous combustion 

 cannot escape ; they then excercise an immense pressure on the 

 nitroglycerine, and in this state the least shock and the slightest 

 movement will cause an explosion. 



The flavor of nitroglycerine is at once sweet, piquant, and 

 aromatic ; it is poisonous, and taken in small doses it produces 

 bad headaches. Its vapor produces similar efi'ects, and this reason 

 might well prove an objection to its use in the subterranean gal- 

 leries of mines, where its vapors cannot disperse as they do in 

 oiDen-air quarries. 



Nitrogl}^cerine is not, properly speaking, a nitrated body, such 

 as uitro- or binitro-benzol, or mono-, bi-, and trinitro-phenisic 

 acids. Indeed, under the influence of reducing bodies, such as 

 nascent hydrogen, sulphuretted hydrogen, etc., the glycerine is 

 set at liberty, and the caustic alkalies decompose the nitrogly- 

 cerine into nitrates and glycerine. 



Modes of Employing Nitroglycerine. — Suppose the object is to 

 detach a stratum of rock^ At 2.50 to .3 metres distance from the 

 exterior border, sink a mining hole about 6 or 6 centimetres in 

 diameter, and 2 or 3 metres in depth. 



After having thoroughly cleared all mud, water, and sand out 

 of the hole, pour into it, through a funnel, from 1,500 to 2,000 

 grammes of nitroglycerine. Then immerse in it a little cylinder 

 of wood, pasteboard, or tin, about 4 centimetres in diameter, and 

 from 5 to 6 centimetres in height, and filled with ordinary pow- 

 der. This cylinder is fixed to an ordinary mining fuse, which 

 goes down a certain depth to insure the combustion of the pow- 

 der. The cylinder is lowered by means of the wick or fuse ; 

 the moment the cylinder reaches the surface of the nitrogly- 

 cerine may easily be known by the touch. When it touches 

 the surface, hold it perfectly still, and pour sand into the hole 

 until it is quite full; there is no need to compress or plug the 

 sand. Cut the wick some centimetres from the orifice of the 

 hole, and then set fire to it. In about eight or ten minutes, 



