45 



obtained occupying 280 times the volume of the powder 

 used, and exerting a pressure, if fired in a closed space, of 40 

 tons on the square inch. The violence of this action is 

 shewn when I melt nitre in a glass vessel over a gas flame, 

 and throw on its surface a piece of charcoal slightly kindled 

 at one corner. The charcoal becomes white hot, and is 

 projected violently hither and thither on the surface of 

 the nitre, very great volume of gases passing off into the 

 air. 



The third ingredient, sulphur, lowers the temperature 

 of ignition of the powder, as I will shew by again laying two 

 trains of powder (i) containing nitre, sulphur and charcoal (2) 

 nitre and charcoal only. Firing them both at the same 

 moment (i) burns far more quickly than (2), owing to the 

 lower temperature at which ignition takes place. 



The Explosive force of powder or other explosive depends 

 on 



[a) The volume of gas or vapour produced by the trans- 

 formation, in proportion to the volume of the 

 powder used. 

 {b) The quantity of heat generated during the action 

 which expands the volume of the gases evolved 

 and increases the explosive eifect. 



The explosive effect, however, depends generally upon the 

 rapidity with which the change takes place. 



It may be said that the greater the volume of gases 

 formed, and the heat generated, the greater the explosive 

 effect, whilst the slower the rate of firing the less the e.x- 

 plosive effect. 



Any solids formed on explosion are a waste of energy, for 

 not only do they contribute nothing to the explosive effect, 

 but they actually cool the gaseous products, and so weaken 

 them. 



The gaseous products of gunpowder only amount to 40 

 per cent, of the weight fired, but although in this respect 

 gunpowder is inferior to gun-cotton (which yields about 98 

 per cent, gaseous products), it is a very safe uniform ex- 



