May 8, 1879] 



NATURE 



43 



detonating agent ; if the particles of absorbent material be, 

 moreoYer, of porous nature, as is the case with the infusorial 

 earth called kieselguhr, used in the production of dynamite, a 

 solid nitro-glycerine preparation may be obtained which contains 

 a very large proportion of the liquid (75 per cent, by weight). 

 In this condition nitro-glycerine may be detonated without any 

 difficulty w hen freely exposed to air ; and although it is diluted 

 with a cons.iderabIe proportion of absolutely inert material, its 

 sensitiveness to detonation is not in the least diminished. Each 

 particle of the diluent is enveloped in the liquid, so that no por- 

 tion of the latter becomes isolated from the remainder by the 

 admixture of inert solid matter ; hence, when the initiative deto- 

 nator is surrounded by such a mass, it is in contact at all points 

 with some portion of the nitro-glycerine, and the latter is in 

 continuous connection throughout, though no longer in a mobile 

 condition ; detonation is consequently as readily established and 

 transmitted through the mass as though it consisted entirely 

 of nitroglycerine. Indeed, while the liquid in its undiluted 

 state, if freely exposed to air in a long layer, transmits detona- 

 tion with difficulty, and very slowly as compared with com- 

 pressed gun-cotton (the observed rate of progression being, in 

 several experiments, below 6,000 feet per second), detonation 

 is transmitted with ease and certainty through very long trains 

 of a solid preparation of nitro-glycerine, such as dynamite, and 

 the rate of transmission is decidedly more rapid than it is with 

 compressed gun-cotton, a result which is in Ijarmony with the 

 greater sensitiveness to detonation tnd the greater violence of 

 action of nitroglycerine. 



It has already been stated that gun-cotton may be detonated 

 if a confined charge of not less than two grains of mercuric 

 fulminate be detonated when closely surrounded by the sub- 

 stance. But in order to attain this result, the cellulose-product 

 must be presented to tte detonating agent in a mechanical con- 

 dition favourable to its action. 



Gun-cotton in a loose flocculent condition, or even if in the 

 n-.ore compact form of a spun yarn or thread, cannot be deto- 

 nated through the agency of a large charge of fulminate buried 

 in the material. It is simply scattered with violence, portions 

 lieing sometimes inflamed by the heat developed where the 

 fulminate is detonated. If however, the gun-cotton be con- 

 verted into a compact form, either by ramming the wool or 

 thread very tightly into a case, or better still, by reducing the 

 gun-cotton fibre to a very fine state of division, and then com- 

 pressing it into compact masses, it becomes susceptible of deto- 

 nation by the initiative action of mercuric fulminate, and the 

 quantity of the latter required to bring about detonation is 

 small in proportion as the compactness or density of the com- 

 pressed material is increased. 



Detonation, when established in compressed gun-cotton, is 

 transmitted with great velocity throughout the mass, as already 

 stated, or from one to another of contiguous masses, and even, 

 though at a reduced rate, if small spaces exist between the 

 individual masses. But, if a small mass of compressed gun- 

 cotton freely exposed to air be detonated when in immediate 

 contact with gun-cotton wool or loosely-tw i-ted yarn, the deto- 

 nation will not be transmitted to these, but they will merely be 

 scattered and perhaps inflamed. 



The difference in the behaviour of nitro-glycerine and of gun- 

 cotton when presented to the action of a so-called initiative de- 

 tonation under the different conditions spoken of above, admits 

 of ready explanation. 



It has been thoroughly established that the action of an ini- 

 tiative detonation is not ascribable to the heat developed within 

 the detonating material itself, in undergoing chemical meta- 

 morphosis. Its action has already been compared to that of a 

 blow from a hammer or falling weight. The readiness and cer- 

 tainty 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, ' :he height of its fall, and to the force with 

 which it is impc. d do\vnwards ; 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 coi.dition 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 w eak blow from the latter. It is very diffi- 

 cult by repeated blows, applied at very brief intervals, to de- 

 tonate 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 condi- 

 tion (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 com- 

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

 for theirdetonation ; 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 appears, therefore, that the detona- 

 tion of an explosive substance by means of a blow is the res«It 

 of the development of heat sufficient to bring about most ener- 

 getic chemical action, or change, by expenditure of force in the 

 compression of the material, or by establishing violent friction 

 between its particles, consequent upon the motion momentarily 

 imparted to them, and that it is brought about with a readiness 

 proportionate to the resistance which they oppose to their motion 

 by the degree of their contiguity to each other. 



The exceedingly violent motion of particles resulting from the 

 sudden or extremely rapid transformation of a solid or liqxiid 

 explosive body into highly heated gas or vapour (which is the 

 effect of a detonation), must obviously exert force which operates 

 upon a body opposed to it in a manner precisely similar to the 

 force applied by opposing a body in the path of a solid mass 

 which is set into very rapid motion. The power of accomplish- 

 injj the detonation of nitro glycerine, gun-cotton, or other highly 

 explosive substances, freely exposed to the air, through the 

 agency of detonation produced in their vicinity or in close con- 

 tact with them, appears therefore correctly ascribable to the heat 

 suddenly developed in some portion of the mass by the mechani- 

 cal effect, or blow exerted by that detonation, and is regulated 

 by the violence and suddenness (either singly or combined) of 

 the detonation, by the extent to which the particles composing 

 the mass of the explosive material are in a condition to oppose 

 resistance to the force, and by the degree of sensitiveness of the 

 substance to detonation, or to sudden metamorphosis, under the 

 influence of heat thus developed. 



It will now be evident why the readily yielding nature of the 

 particles of liquid nitro glycerine tends to counteract its great 

 sensitiveness to detonation, and why, when the motion of the 

 liquid particles is impeded by their admixture with solid matter, 

 and when they are consequently placed in a position to resist 

 mechanical motion by the force applied through the agency of 

 detonation, its natural sensitiveness to detonation, and the 

 rapidity with w hich it can be transmitted from particle to particle 

 become fully developed. 



Again, the reduction of gun-cotton fibre to a fine state of divi- 

 sion, which renders the material readily convertible into very 

 compact and dense masses, places the particles in the condition 

 most favourable to resist mechanical moticm upon the applica- 

 tion of a blow, or of the concussion resulting from a detonation ; 

 hence, compressed gun-cotton is readily susceptible of detona- 

 tion in proportion to the extent of compression, or to its density 

 and compactness, while loose gun-cotton wool, or the lightly 

 twisted or compressed material cannot be readily detonated, 

 because the force applied is expended in imparting motion to 

 the readily yielding particles of the mass. If the force applied 

 through the agency of a detonator to a mass of explosive ma- 

 terial just borders upon that required for the development of 

 the detonation, or if the condition of the mass is such as hardly 

 to present the requisite resistance to mechanical motion essential 

 for its detonation, then, results intermediate between the mecha- 

 nical dispersion of the mass and its violent chemical dispersion 

 or disintegration, i.e., detonation, are obtained. Thus, frequent 

 instances have been observed, especially in the experiments in 

 the transmission of detonation through tubes, in which the 

 initiative detonation has brought about an explosion attended 

 with little, if any, destructive eflfect, portions of the mass being 

 at the same time dispersed and occasionally inflamed. Even 

 silver fulminate, which under ordinary conditions detonates 



