EFFECTS OF INERT BODIES. 43 



elementary rapidity of the reactions will go on incessantly 

 increasing, for the twofold reason that the temperature is con- 

 tinually rising and that the pressure of the gases is continually 

 increasing. 



However, the influence of pressure will be more sensible at 

 the beginning than at the end of the experiment, seeing that the 

 non-combined part diminishes more and more, and that there 

 arrives a moment when the tension proper of this part, con- 

 sidered independently of the rest, ceases to go on increasing in 

 consequence of the heating. 



4. The molecular rapidity of reactions in a homogeneous system 

 depends on the relative proportions of the components. 



When operating at constant temperature, the combination is 

 greatly accelerated by the presence of an excess of either of the 

 components. 



At constant temperature, the action is, on the contrary, checked 

 by the presence of an inert substance which acts by diminish- 

 ing the state of condensation of the substance. 



At variable temperature the reactions are a fortiori retarded 

 by the presence of an inert body, such as the nitrogen of the 

 air, or the silica of ordinary dynamite, this inert body absorbing 

 the heat and lowering the temperature of the system without 

 exerting any influence tending to accelerate it by its presence. 



At variable temperature the reaction is generally slower in 

 presence of an excess of one of the components than if equal- 

 equivalents be used, the necessity of heating this excess more 

 than compensating its accelerating influence. 



It is clear that if the proportion of the inert matter be such 

 that the temperature of the system cannot be raised to the 

 degree necessary for the combination to be continued of itself 

 the reaction will cease to be explosive, and even to propagate 

 itself. 



It is in this way that the character of explosive substances 

 may be changed by mixture with an inert body. The follow- 

 ing are some characteristic facts. 



Dynamite of 75 per cent, is less shattering than pure nitrp- 

 glycerin. However, such dynamite cannot be employed in 

 charging shells, as the latter would explode in the bore of the 

 cannon, under the influence of the initial shock of the powder. 

 Dynamite of 50 or 60 per cent, can, on the contrary, be employed 

 in hollow projectiles, which may be fired from cannons without 

 danger. 



This is not all. With dynamite of 60 per cent, the projectile 

 can explode at the point of arrival, even without a special fuse, 

 if it be arrested by a very resisting body, such as an armour 

 plate, the rise of temperature which results from the trans- 

 formation of the energy into heat, produced by the sudden 

 stoppage, being sufficient to cause the explosion. But if the 



