44 DURATION OF EXPLOSIVE REACTIONS. 



charge of nitroglycerin be lowered to 30 or 40 per cent, the 

 shell charged with such dynamite will require the employment 

 of a percussion fuse in order to explode, as in the case of black 

 powder. It is true that such dynamite scarcely offers any 

 advantage over ordinary powder. 



Another essential point is that not only the molecular 

 rapidity is diminished under these conditions, but also the 

 rapidity of inflammation and the rapidity of combustion of an 

 explosive substance are also extremely retarded when it is 

 mixed with an inert body in proportions approaching those 

 which correspond to the limits of inflammability. Consequently, 

 towards these limits inflammation becomes uncertain, com- 

 bustion is badly propagated, and the explosive character of the 

 phenomenon ceases to be manifest. 



Third Section. A homogeneous system submitted to uniform 

 conditions but capable of losing heat. 



1. These general relations being established for a system 

 where all the heat which it liberates is employed to raise the 

 temperature, we come to the real case, that in which the system 

 still supposed homogeneous and submitted to uniform conditions at 

 the outset yields a portion of its heat to the surrounding bodies by 

 radiation or conduction. The mass of the substances employed, 

 which does not come into question in principle in the first case, 

 here plays an essential part. 



In short, whenever the rapidity of the reactions is not great, 

 a part of the heat produced will be gradually dissipated, and the 

 elevation of temperature will soon attain a certain limit. This 

 limit will be that at which the loss of heat produced by the 

 external actions is equal to the gain due to the internal reactions 

 of the system, the reaction will then take place with a certain 

 rapidity constant or nearly so, without however becoming 

 explosive. 



This is the case of a substance fusing under ordinary con- 

 ditions, and it is also the case, generally in a marked degree of 

 slowness, of a small quantity of an explosive substance which 

 is spontaneously decomposed. 



But if the mass operated upon be increased, supposing it 

 contained in a fixed capacity, the quantity of heat lost by 

 radiation or conduction at a given temperature of the system 

 will be less ; the total quantity of heat retained in the interior 

 at the end of a given time will therefore be increased. Thus 

 the temperature of such a system must be higher whether it 

 tend towards a new limit superior to the preceding or whether 

 its increase becomes more and more rapid and finally explosive, 

 owing to the correlative increase in the pressures. 



This same correlative accelerating of the pressures and of the 

 rapidity of the reactions plays an important part in the inter- 



