68 THE DETONATION PROCESS 



tion as a result of the much less intimate relation between the added 

 reactants and the primary molecules. 



If a high explosive material is to be practical it must obviously be 

 stable under all ordinary conditions of handling and storage, and at the 

 same time be capable of initiation by some external agency. Once a 

 sufficient source of energy is applied, the explosive reaction can be 

 started. The subsequent course of events depends on a large number 

 of factors, both physical and chemical. If the reaction can and is per- 

 mitted to build up, the rate and violence of the reaction will ultimately 

 be limited by the laws of propagation of wave motion and the condi- 

 tions of a steep fronted detonation wave may be realized. It is, how- 

 ever, possible to develop a lower and controllable rate by suitably 

 decreasing the concentration of reacting molecules or by using mixtures 

 such as gunpowder requiring reaction between particles. The practical 

 application of such slow reactions is, of course, in propellants for shells, 

 rockets, etc. where the shattering effect of a high explosive reaction 

 (sometimes termed "brisance") would be more destructive than useful, 

 but where large quantities of energy must be made available in a mod- 

 erately short time (this property being described as the "power" of the 

 explosive) . 



The slower processes in an explosion are usually described as burn- 

 ing, a term made natural by the importance of oxygen in the reaction. 

 The maximum rate at which an explosion can react is the ideal condi- 

 tion of detonation, in which the velocity and final state are determined 

 only by the explosive material and the initial density and temperature 

 (the initial pressure ordinarily being negligible). This ideal condition 

 may not be realized and low-order detonations are possible as a result 

 of any of a number of factors: lack of confinement by the surroundings 

 permitting expansion of the products before the reaction is complete 

 and a falling off of pressure behind the detonation front; insufficient 

 supply or duration of energy initiating the reaction; effects of the physi- 

 cal state of the explosive such as density and homogeneity of the charge. 



From the point of view of underwater explosives, the most impor- 

 tant factors to be considered are perhaps first of all that a reproducible, 

 high order detonation is achieved, and second, that no effects occur 

 peculiar to the particular physical size or condition of the explosive 

 which are not characteristic of the explosive material under ideal con- 

 ditions. As an example of the latter, the failure of some small charges 

 to give results consistent with larger charges may be cited, effects of 

 this kind being attributable to a disproportionate energy supplied for 

 initiation, failure of the surface layer of the charge to react completely 

 before appreciable relief of pressure by the surrounding medium, and 

 other causes. 



