RAPIDITY OF PROPAGATION OF REACTIONS. 47 



the weight of the entire explosive matter contained in the 

 amorces amounted to about 64 kgms., and that its force, owing 

 to the composition of this matter, was equal to a force of 

 226 kgms. of black powder. 1 



It is essential, that persons having explosive substances 

 under their charge should never lose sight of the conviction 

 that, from the facts and general truths which have just been 

 stated, preventive measures should always be prescribed on the 

 hypothesis of a total explosion. 



5. KAPIDITY WITH WHICH KEACTIONS ARE PROPAGATED. 



1. Let us now examine the case of a homogeneous system, but 

 subject to different conditions in its various parts, such as those 

 resulting from ignition at one point, or from a local shock, con- 

 ditions to which some of the facts quoted in the preceding 

 paragraph may be ascribed. 



For propagating the transformation in a mass which explodes, 

 and is not subject to the same conditions in all its parts, the 

 physical conditions of temperature, pressure, etc., which have 

 incited the phenomenon at one point must reproduce them- 

 selves successively from layer to layer throughout every part of 

 the whole mass. 



On this head attention may be called to the numerous 

 experiments made by artillerymen, as to the rapidity of the 

 combustion of ordinary powder, and as to that of gun-cotton ; 

 the rapidity varying according to the physical construction and 

 chemical composition of the powders. We will firstly sum 

 up these results, as well as those observed with mixtures of 

 gaseous explosives, that is to say, the observations relating to 

 the rapidity of combustion of mixtures of oxygen and hydrogen, 

 or of carbonic oxide, or of hydrocarbon gases. 



We shall then speak of the new and unexpected results 

 furnished by the study of gun-cotton and nitroglycerin ; describe 

 the new conception of the employment of caps, and the hitherto 

 unknown distinction between the simple ignition and the 

 genuine explosion of explosive matters will be discussed ; a 

 distinction which the author's recent experiments led him to 

 extend to gaseous mixtures themselves. Then it will be 

 attempted to apply these differences to theoretical conceptions. 

 Thus we shall be led on to the notion of the explosive wave, 

 which will form the subject of a special chapter. 



2. According to Piobert, 2 the rapidity of the combustion of 

 powder in the open air, observed on vertically placed prisms of 

 known length, the lateral surfaces of which were greased for the 



1 These facts have been taken from the report presented by the Committee 

 of Inquiry. 



2 Piobert, " Traite d'Artillerie," partie thSorique. 



