DIFFERENT MODES OF DECOMPOSITION. 57 



the one being mechanical and the other more particularly 

 chemical. 



3. From a mechanical point of view it is conceivable that 

 between the two limits of progressive combustion and detona- 

 tion the intermediate modes of propagation and reaction may, 

 according to circumstances, be produced (p. 53), combustion 

 tending to transform itself more or less quickly into detonation. 

 But only the two limits should be regarded as constituting 

 regular standards. This will be more fully defined in the 

 chapter relating to the explosive wave. 



4. Chemical phenomena themselves may vary, at any rate 

 under certain conditions. In fact, the mode of decomposition is 

 not unique, unless the explosive substance contains sufficient 

 oxygen to cause a total combustion, as happens in the case of 

 nitroglycerin and nitromannite. It is further essential that 

 this total combustion should have really taken place; which 

 does not necessarily occur, especially in slow inflammations, 

 effected at as low a temperature as possible and in which in- 

 complete reactions may at first become developed. 



5. But it often happens that oxygen is deficient, or that the 

 first reaction gives rise to a bad distribution of this oxygen, as 

 in the case where nitroglycerin burns slowly, producing a 

 nitrous vapour, and fixed or gaseous matters, incompletely 

 burned. Under these circumstances the possible decompositions 

 are manifold; their number depends on the temperature, on the 

 pressure, and on the quickness of the heating. We have already 

 pointed out this case for ammonium nitrate (p. 6) ; it is 

 generally observed in organic substances decomposable by 

 heating. 1 Mixtures such as black powder are equally susceptible 

 of it. 



6. Among the numerous decompositions of the same sub- 

 stance, those which develop the greatest heat are those which 

 also generate the most violent explosive effects, all things else 

 being equal. This is evident, since the volume of gases (re- 

 duced to and 760 mm.) reaches its maximum value at the 

 same time. But it takes place in other cases, the decomposition 

 being always followed by a diminution of pressure, as has been 

 elsewhere shown (p. 8). 



On the other hand, these are not generally the reactions 

 which manifest themselves at the lowest temperature possible. 

 If, therefore, the explosive body receive in a given time a 

 quantity of heat which is insufficient to carry its temperature 

 up to a degree which corresponds to the most violent reactions, 

 it will experience a decomposition capable of disengaging less 

 heat, or even of absorbing it ; and it will by this decomposition 

 become completely destroyed without developing its most 

 energetic effects. 



1 " Essai de M&anique Chimique," torn. n. p. 45. 



