438 DYNAMITES. 



10. Action of shock. Dynamite requires a much more violent 

 shock than nitroglycerin to explode it. It explodes by the 

 shock of iron on iron, or of iron on stone, but not by the shock 

 of wood on wood. 



Dynamite is the more sensitive the more nitroglycerin it 

 contains. 



When dynamite is struck with a hammer, the part directly 

 affected by the shock alone explodes, the surrounding portions 

 being simply dispersed. 



Owing to this circumstance the effects may vary greatly, unless 

 the dynamite be contained in a resisting and completely filled 

 envelope, or placed at the bottom of a receptacle. It explodes 

 by the direct shock of a ball at a distance of 50 m., and even 

 more, a very important matter in military applications. 



11. The detonation of dynamite in tubes entirely filled with 

 this substance propagates itself with a speed of about 5000 mm. 

 per second. 



12. Its explosion, when complete, does not produce noxious 

 gases, like gunpowder ; but if it burn by simple inflammation 

 (miss-fires), it produces nitric oxide, carbonic oxide, and nitrous 

 vapour, which are deleterious (p. 283). 



13. The heat liberated by the sudden decomposition of dyna- 

 mite is the same as its heat of total combustion, and pro- 

 portionate to the weight of nitroglycerin contained in the 

 dynamite. 



It can therefore be easily calculated from the data on page 

 424. 



14. The volume of gases liberated by any dynamite, and the 

 theoretical pressure which it can develop, are also calculated in 

 this way, taking into account the volume occupied by the 

 silica (see p. 425), and the heat absorbed in raising its tem- 

 perature. 



The experiments of Sarrau and Vieille on this question have 

 been described above. 



15. It will be shown in a general way that thermal theories 

 favour the employment of dynamite. In the fii st place, dyna- 

 mite is less shattering than nitroglycerin, because the heat 

 liberated is shared between the products of explosion and 

 the inert- substance. In consequence there is a less rise in 

 temperature, which diminishes the initial pressures propor- 

 tionately. 



For instance, the silica and anhydrous alumina, which may 

 be mixed with nitroglycerin, have nearly the same specific heat 

 (019) as the gaseous products of explosion of the latter at 

 constant volume. Weight for weight, and in a completely filled 

 space, they will lower the temperature, and consequently the 

 initial pressure by half. 



For an equal weight of nitroglycerin the shattering properties 



