EXPERIMENTS ON SOLID AND GASEOUS EXPLOSIVES. 387 



Unfortunately, for this very reason, the experiments could not be carried out in a 

 laboratory. 



The sharp steps which go to make up these records may be accounted for in the 

 following manner : When the explosive, which is packed closely at one end of the 

 chamber, bursts into flame, a pressure wave is sent out which travels to the end of the 

 cylinder and is then reflected back. When this wave, on its return journey, reaches 

 the explosive, the combustion, which in the meantime had been proceeding uniformly, 

 is accelerated in proportion to the increased pressure. The case is one of rmitual 

 reaction between the two phenomena. Any irregularity in the combustion tends to 

 start a pressure wave which in turn enhances this irregularity. The process is 

 cumulative in its effects, and with the high gravimetric densities used in ballistic 

 work it may, and doubtless occasionally does, cause disastrous results.* 



Incidentally the present work confirms ViEiLLE'st views as to the discontinuity of 

 pressure set up by wave actions, the successive steps of the curve rising abruptly, if 

 not instantaneously. 



The velocity of propagation of the wave is measured directly by the time elapsing 

 between the successive sharp increments of pressure which are recorded. 



When a wave is set up at the commencement of the explosion, the impacts on the 

 recording gauge succeed each other at intervals of 0'00125 or 0'00121 second when 

 the charge in the cylinder is at gravimetric densities of O'lO or 0*15 respectively. 

 The path traversed, i.e., the double length of the enclosure, is 139'3 centime, and the 

 corresponding velocities 1114, 1150 metres per second. \ 



Occasionally, when cordite of the smallest diameter is used, the wave motion is still 

 sharply defined at the maximum pressure. The time interval is then O'OOHO second 

 for a gravimetric density of 0*1 and the speed 1266 metres per second. 



From the general formula for the velocity of sound we can calculate the theoretical 

 speed under these circumstances, 



V= A/ 

 P 



These factors, with the exception of y, are well known, 



When the combustion is complete, the density, p, of the resulting gases is equal to 

 the gravimetric density of the charge. 



The elasticity, E, is measured by the rate of change of pressure with density. 



* See CORNISH, 'Proc. Inst. Civ. Eng.,' vol. 144, p. 241, 1901. 

 t 'Memorial des Poudres et Salpetres,' vol. 10, pp. 177-260, 1899-1900. 



| Theoretically the speed should be the same in either case ; the thermal loss, which is relatively less 

 at higher gravimetric densities, probably accounts for the difference. 



3 D 2 



