528 CONCLUSIONS. 



accomplish otherwise, except by the aid of complicated, bulky 

 machinery, necessitating considerable hard labour and expendi- 

 ture. By this means also we have replaced with unspeakable 

 advantage the energy afforded by the old war appliances based 

 on the use of the lever and the sling, while at the same time 

 the range and the power of the new weapons are extended far 

 beyond the dreams of former days. 



Such mechanical effects are produced by the act of explosion 

 and by the energy of gaseous molecules, and even this energy 

 results from chemical reactions, these latter, in fact, determining 

 the volume of the gases, the quantity of heat, and consequently 

 the explosive force. 



2. Two orders of effects should here be distinguished: the 

 one due to pressure, the other to the work developed. Thus the 

 rupture of hollow projectiles and the dislocation of rocks is due 

 more especially to pressure ; whereas the clearing away of 

 materials in mines and the projection of missiles in firearms 

 represent more especially work due to expansion. Now, pressure 

 depends both on the nature of the gases formed and on their 

 volume and temperature. Work, on the contrary, depends 

 especially on the heat liberated, which is the measure of the 

 potential energy of the explosive substance. 



The time necessary for the realisation and the propagation of 

 chemical reactions plays an essential part in the applications, as 

 the terms shattering powders, slow powders, and rapid powders 

 themselves indicate. These various characters do not depend 

 merely on the structure of the powders and of the nature of the 

 reactions ; but we may observe, even with the same explosive 

 substance, taken in an identical form, extremely unequal 

 durations of combustion, and consequently of its effects. 



This, for instance, is what is exemplified in dynamite. Such 

 diversities are observable in a substance which is identical in its 

 chemical composition and in its physical structure. They result 

 from the establishment of two very different laws : the law of 

 ordinary combustion slowly communicated, and the law of 

 detonation, that is to say, the law of the explosive wave which 

 propagates itself with a lightning-like velocity. 



These notions on the velocity of the propagation of pheno- 

 mena, added to the knowledge of the heat liberated and of the 

 volume of gases, characterise the comparison which may be 

 made between the old black powder and the new substances 

 now practically used, such as dynamite and gun-cotton. 



From this it follows that, in order to define the force of an 

 explosive substance, we should know the following data : first, 

 the nature of the chemical reaction which determines the heat 

 developed and the volume of gases, and secondly, the rapidity of 

 the reaction. 



3. Chemical reaction is characterised by the initial composi- 



