70 THE DETONATION PROCESS 



containing sixty per cent RDX and forty per cent TNT, is a form in 

 which RDX is often employed either as an explosive or in preparation 

 of other mixtures. 



D. PETN (C5H8O12N4), pentaerythritol tetranitrate. PETN is a 

 more sensitive explosive than tetryl but is less convenient for general 

 use as a booster charge. An important application of PETN is in 

 primacord, a detonating high velocity fuse much used in demolition 

 work for firing a number of charges nearly simultaneously; it consists of 

 a waterproof, flexible cord with a small amount of PETN (approx. 

 3 g./ft.) as a core. The velocity of detonation in primacord is about 

 6,000 m./sec, the exact value depending on the production lot. This 

 high and quite reproducible velocity has been extensively employed in 

 experimental work to provide time intervals accurate to within a few 

 microseconds. Mixtures of PETN and TNT are called pentolites, the 

 most common being a 50/50 mixture. Cast pentolite charges can be 

 initiated by a detonator cap plus a few grams at most of loose (granular) 

 tetryl, and have been found highly reproducible and convenient charges 

 for small scale explosion tests. 



E. Other explosives. A number of military explosives have been 

 developed as the result of efforts to improve upon the performance of 

 TNT. The necessary properties of any military explosive, such as 

 safety, stability, and ease of production, and the desirable feature of 

 greater power, are more easily specified than achieved. It is thus un- 

 derstandable that data on the composition and performance of success- 

 ful developments have not been made freely available. The addition 

 to TNT of such components as aluminum, to increase the heat of reac- 

 tion, and ammonium nitrate or other oxygen rich materials, to improve 

 oxygen balance, are two possible modifications by which the perform- 

 ance of TNT may be improved. A further discussion of these and 

 other explosives is ruled out either by security requirements or by the 

 fact that little is known about their properties as underwater explosives. 



F. Initiating niaterials. Many varieties and combinations of es- 

 pecially sensitive explosives are used as the primary material in setting 

 off explosives. The exact composition and weight of such materials in 

 detonation caps are trade secrets, but the various possible materials in- 

 clude lead azide, mercury fulminate, PETN, and tetryl. The per- 

 formance of a detonation cap is rated in terms of exceeding various 

 arbitrary tests and it is not to be expected that similarly rated de- 

 tonators from different manufacturers will produce the same results in. 

 underwater measurements. Any classification of detonator caps as to 

 function is beyond the scope of this discussion, but seismographic caps, 

 which detonate in a much smaller and more reproducible time interval 

 after applying a firing current, should be mentioned. 



