72 Professor Abel [March 21, 



exploding temperature of gun-cotton, yet a very much smaller charge 

 is required for the detonation of nitro-glycerine than is needed for the 

 detonation of gun-cotton. On the other hand, a quantity of confined 

 percussion cap composition which, if it were pure mercuric fulminate, 

 would be altogether inadequate for the detonation of gun-cotton, 

 suffices for the detonation of nitro-glycerine. 



The action of an initiative detonation has already been compared 

 to that of a blow from a hammer or falling weight. The readiness 

 and certainty with which gunpowder, gun-cotton, and other explosive 

 agents are detonated by the latter agency are regulated by several 

 circumstances; they are in direct proportion to the weight of the 

 falling body, to the height of its fall, and to the force with which it 

 is impelled downwards ; to the velocity of its motion ; to the mass 

 and rigidity or hardness of the support upon which the substance to 

 be detonated rests ; lastly, to the quantity and mechanical condition 

 of the explosive agent struck, and to its sensitiveness. 



Gunpowder is much more readily detonated by a sharp blow from 

 a small hammer, than by the simple fall of a heavy hammer, or by 

 a comparatively weak blow from the latter. It is very difficult by 

 repeated blows, applied at very brief intervals, to detonate gun- 

 cotton if placed upon a support of wood or lead, both of which 

 materials yield to a blow, the force applied by that blow being 

 transferred through the explosive agent and absorbed in work done 

 upon the material composing the support. But if the latter be of 

 iron, which does not yield permanently to the blow of the hammer, 

 the detonation of those substances is easily accomplished. If the 

 quantity of the explosive agent employed be so considerable as to 

 form a thick layer between the hammer and support, the force 

 applied is to so great an extent expended in imparting motion to the 

 particles of the compressible mass, that there remains little or none 

 by which its detonation can be accomplished, and if the material be 

 in a loose or porous condition (as in the case of a powder or of loose 

 wool), much work has to be accomplished in moving particles of the 

 mass through a comparatively considerable space, in the operation of 

 compressing them, so that a second or even a third blow is required 

 for their detonation ; whereas if, by blows or pressure previously 

 applied, the explosive material will be presented in the form of a 

 compact mass, the particles of which have little tendency to motion 

 when force is applied to them, detonation will be much more readily 

 developed. It ajjpears therefore that the detonation of an exj^losive 

 substance by means of a blow is the result of the development of heat 

 sufficient to bring about most energetic chemical action, or change, by 

 expenditure of force in the compression of the material, or by esta- 

 blishing violent friction between its particles, cons(;qucnt upon the 

 motion momentarily imparted to them, and that it is brought about 

 with a readiness proportionate to the resistance wliich they o})pose to 

 their motion by the degree of their contiguity to each other. 



The exceedingly violent motion of particles resulting from the 



