CHAPTER V. 

 DURATION OF EXPLOSIVE REACTIONS. 



1. GENERAL IDEAS. 



1. THE chemical transformation in a mass which explodes, 

 arises and is propagated with a certain rapidity, the knowledge 

 of which is of primary importance for theory, as well as practice. 

 In fact, the rapidity with which the gases are liberated depends 

 upon it, and consequently the velocity communicated to pro- 

 jectiles, as also the effects produced in blasting at the expense of 

 the rocks which it is desired to break up, or the obstacles to be 

 removed in military engineering. Now the heat liberated by a 

 given reaction may be almost entirely employed to heat the 

 gases and increase their pressure, if the reaction be very rapid ; 

 while it is dissipated to no purpose by radiation and conduction 

 if the reaction be slow. 



In the former case the effects may be very various. 



When an instantaneous decomposition takes place, a given 

 quantity of explosive substance crushes on the spot the portions 

 of rock with which it is in contact. Its energy is therefore 

 consumed in a work almost useless from the industrial point of 

 view, but which is sometimes desired in military engineering, 

 with a view to hollowing a primary chamber, destined to contain 

 a larger charge of explosive. If the development of the gases 

 be less sudden, though still extremely rapid, the same quantity 

 of explosive may on the other hand dislocate the rock by 

 producing extended fissures in it, and by hurling abruptly aside 

 the nearest portions of rock, which is in general the result aimed 

 at by miners. 



This action is transformed in certain cases into a general 

 shaking, which causes the ground to tremble and considerably 

 displaces the centres of gravity of stones and other objects, thus 

 destroying the stability of masonry and fortified works. 



Lastly, the same quantity of explosive sometimes reduces its 

 effects to elastic displacements, and an undulating movement 



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