rROJECTTLES CONTAINING EXPLOSIVES A. R. 139 



gravity of the explosive by 8, that the pressure in kilograms per 

 square centimeter exerted by the charge on the base of the projectile 

 20X^X20,000 



is equal to which is 4005. Taking § as equal to 1.5. it 



1,000 

 results that the effort tending to crush the column of explosive as the 

 projectile starts from rest proceeds in increasing progression from 

 the point toward the base where in contact with the latter it amounts 

 to 600 kilograms per square centimeter. 



On the other hand, under the influence of the rifling the projectile 

 acquires a motion of rotation whose maximum velocity at the instant 

 of leaving the bore is about 300 revolutions per second, and this angu- 

 lar velocity corresponds to a circumferential velocity of the inside 

 walls of about 50 meters per second. 



These figures show the magnitude of the forces to which the ex- 

 plosive material of the charge is subjected depending on the duration 

 of the blow from the cannon. It by this becomes obvious that a 

 powerful explosive which has been used on a large scale in the mining 

 industry and in rock work is nevertheless unfit for use in charging 

 projectiles. However, we now know the precise conditions that an 

 artillery explosive must satisf3^ 



Eegarding these characteristics, the most important is that the 

 force and rate of detonation shall be as large as possible. It has 

 been observed that this last requirement implies the use of crystalline 

 substances, but it should be stated that the realization of this de- 

 sideratum is, notwithstanding, secondary, since experience has shown 

 that a satisfactory detonation can be obtained with plastic substances 

 if a detonator capable of imparting a sufficiently high velocity is 

 used. 



In order to insure safety in firing, the explosive should be capable 

 of resisting the effects of inertia which are developed in the chamber 

 of the piece. If it be a solid — and this is generally the case — it should 

 be absolutely compact in structure and should adhere strongly to the 

 walls of the shell. 



The meeting of this last condition is necessar}^ in order to prevent 

 the friction of the charge resulting from a difference in speed of 

 rotation between the shell and its explosive due to the inertia of the 

 latter. The compactness of loading tends to prevent compression 

 and shock on the interior of the explosive mass following the travel 

 of the projectile through the bore. The adhesion of the explosive to 

 the walls of the shell can be determined at the outset by following the 

 method used in loading cartridges in which the explosive, instead of 

 being placed directly in the cavity in the shell, is first enveloped in 

 thin sheet -metal or cardboard and, thus surrounded, is introduced 

 into the chamber of the shell after the walls have been coated with 



