THE DETONATION PROCESS 69 



The process of initiation is also of importance. The more stable 

 explosives from the point of view of shock or impact are more difficult 

 to initiate and for satisfactory "triggering" of these relatively safest 

 explosives it is necessary to use a small "booster" charge of more sensi- 

 tive material. The booster is set off by a percussion or electrical de- 

 tonator composition which can be initiated by a small quantity of heat 

 from mechanical impact or by an electrical current. 



Explosives materials, exclusive of propellants, have been roughly 

 divided into two general classes: primary or initiating explosives for 

 which detonation can be achieved in small quantities with a nominal 

 supply of energy from, say, a detonator cap, and high explosives for 

 which detonation is achieved only in larger quantities and is initiated 

 by a booster charge. The distinction does not imply that a primary 

 explosive is "lower" than a high explosive (the reverse may be true), 

 but rather is made on the basis of difficulty in establishing detonation. 

 The distinction is of course a somewhat arbitrary one, as taken literally 

 it would make propellants, which do not detonate at all, the limiting 

 cases of high explosives. It does, however, differentiate between the 

 explosives used in quantity for destructive purposes and those used in 

 small amounts to start the process. 



The list of explosives which have been used or tested is a very long 

 one and only a few will be considered here. The available data on 

 these few are likewise numerous and all that will be attempted is to 

 give the formulas and an indication of their primary interest for under- 

 water explosion phenomena. 



A. TNT (C7H5O6N3), trinitrotoluene. TNT has for many years been 

 the standard high explosive. Its usefulness is the result of extreme lack 

 of sensitivity (and consequent safety), considerable energy, and low 

 melting point (80° C.) which makes it ideal as the liquid component in 

 preparing mixtures. The density of crystalline TNT is about 1.65gm./ 

 cm.^, but densities of 1.50-1.55 are ordinarily realized in cast charges 

 prepared by melting granular TNT and pouring. Although cast TNT 

 has been used as the standard filling for more high explosive munitions 

 than anything else, a number of more effective mixed explosives have 

 been developed, in which TNT is a primary component. 



B. Tetryl {CiE.^O^^^)2,^fitrinitrophenylmethylnitramine. A more 

 sensitive explosive than TNT, tetryl is extensively used as a primary 

 charge or booster for initiating TNT and other less sensitive explosives. 

 For this purpose, the granular powder product is formed into a solid 

 pellet by pressures of 2,000-4,000 kg./cm.^ 



C. RDX or cyclonite (CsHeNeOe), cyclomethylene trinitramine. RDX 

 is extensively used in mixtures with TNT and other components to 

 produce more powerful high explosives. The mixture Composition B, 



