52 DURATION OF EXPLOSIVE REACTIONS. 



6. MULTIPLICITY OF THE MODES OF COMBUSTION. 



1. According to the method employed for ignition, dynamite 

 may be quietly decomposed without any flame ; or it may burn 

 briskly ; or, again, give rise to an explosion properly so called, 

 either moderate, or capable of dislocating rocks, or even of 

 locally crushing them and of producing the most violent 

 effects. 



2. The substances which determine these latter effects have 

 received more especially the name of detonators. Noble was 

 the first to recognise the character of these when experimenting 

 on nitroglycerin in 1864, and from thence he deduced the con- 

 venient method of exploding this substance effectually by 

 means of a priming of mercury fulminate. 



Gun-cotton does not present less variety. Abel has published, 

 with reference to this matter, since the year 1868, some very 

 curious experiments, which similarly tend to establish a great 

 diversity between the conditions of deflagration in this substance 

 according to the mode of detonating it. 1 Eoux and Sarrau 

 have generalised these phenomena by distinguishing what they 

 have termed the explosions of the first and of the second order, 

 a real distinction, yet one which appears insufficient, by reason 

 of its too absolute character. 



3. However strange this diversity may appear at first sight, 

 the author holds nevertheless that thermo-dynamic theories are 

 capable of accounting for it by a suitable analysis of the 

 phenomena of shock. 



In fact, the variety of explosive phenomena depends on the 

 speed with which the reaction is propagated, and on the more 

 or less intense pressures which result therefrom. 



Take the simplest case, that of an explosion determined by 

 the fall of a weight from a certain height. At first one would 

 be inclined to attribute the effects observed to the heat dis- 

 engaged by the compression due to the shock of the suddenly 

 arrested weight. But calculation shows that the stoppage 

 of a weight of several kgms. falling from a height of 

 0*25 metre or 0*50 metre cannot raise the temperature of the 

 explosive mass more than a fraction of a degree, if the resultant 

 heat be uniformly distributed throughout the entire mass. 

 Such mass could therefore never reach to a high temperature, 

 such as 190 and 200, for instance, in the case of nitroglycerin, 

 a temperature to which it would seem necessary to raise the 

 entire mass suddenly in order to produce explosion. 



It is by a different mechanism that the energy of the weight 

 transformed into heat becomes the origin of the effects observed. 



1 "Comptes rendus des stances de I'Acad&nie des Sciences," torn. Ixix. 

 pp. 105 a 121. 1869. 





