COMBUSTION AND DETONATION. 55 



properly so called. Pure mercury fulminate is especially em- 

 ployed in this respect ; it is the most powerful of detonators, that 

 is to say, its shock is more violent and more sudden than that 

 of any other substance, which is explained by the suddenness of 

 its decomposition, together with the extraordinary magnitude 

 of the pressure which it would develop when detonating in its 

 own volume (almost 26000atm.). At page 52 a certain number 

 of characteristic facts nave been cited relative to this specific 

 influence of primers. We shall return to this subject. 



7. COMBUSTION AND DETONATION. 



1. Progressive combustion has particularly preserved the 

 name of combustion; the name detonation being reserved to 

 almost instantaneous combustion with expansion of gas. From 

 this, again, we get the distinction proposed by Sarrau between 

 the explosions termed of the first order, such as those of black 

 powder, which are really ordinary combustions, and the ex- 

 plosions termed of the second order, or detonations properly so 

 called, such as that of nitroglycerin, produced by a strong 

 priming of mercury fulminate. 



Nevertheless, the facts known do not, in the author's opinion, 

 compel us to admit a difference in the nature, and a line of 

 absolute demarcation between the two orders of phenomena; 

 they tend rather to place these latter under an aspect showing 

 an indefinite variety comprised between two extreme limits : 



(a) The detonation of the explosive substance in its own 

 volume reaching the maximum of temperature and pressure, 

 and consequently the maximum of speed which chemical 

 reaction realised under these conditions involves. This effect is 

 produced when the substance retains the totality of its energy, 

 that is to say, of the heat developed in the chemical transforma- 

 tion up to the moment when this latter propagates itself to the 

 adjacent portions. Detonation is especially produced by a very 

 sudden shock. Gases formed at the point where the shock is 

 produced at first have not, so to speak, time to become dis- 

 placed, and they immediately communicate their energy to the 

 parts in contact ; the action is thus propagated into the entire 

 mass with a sort of regularity, producing in it a veritable 

 explosive wave. 



, The velocities of propagation which have been measured with 

 dynamite and compressed gun-cotton belong to this order of 

 detonations, and they are very different from those of combustion 

 of black powder. For instance, the Austrian artillerists have 

 observed a velocity exceeding 6000 metres per second when 

 detonating a dynamite cylinder 67 metres in length ; Colonel 

 Se'bert has observed velocities of 5000 to 7000 metres (a mean 

 velocity of 6138 metres) in pulverulent gun-cotton compressed 



