386 



MR. J. E. PETAVEL ON THE PRESSURE OF EXPLOSIONS. 



take into account the cohesion of the gas, or allow for the possible variation of the 

 value b with temperature and density. 



Taking these circumstances into account, the agreement between the theoretical 

 and experimental values may be considered satisfactory. 



Distribution of the Explosive. 



In a long narrow vessel a certain amount of vibration almost invariably occurs 

 during the combustion of the explosives. If the explosive is concentrated in one part 

 only of the enclosure, the effect is increased and the pressure rises by sharp steps, as 

 shown in fig. 18. With some powders the sudden increments of pressure become 



T~/ME v 



Fig. 18. Diagram showing the type of vibration set up at the commencement of an explosion when the 

 charge placed in a long enclosure is not uniformly distributed. The successive sharp increments of 

 pressure correspond with successive impacts of the wave. 



dangerously large and an abnormally high maximum is reached in one or two steps. 

 This phenomenon seems to be the transition between an explosion and a detonation. 



That it is difficult, in fact almost impossible, to detonate cordite has long been 

 recognised as one of its principal advantages. Nevertheless, signs of abnormal 

 explosion were visible whenever the charge was crowded together in one part of the 

 enclosure. A fairly typical case is shown in fig. 4, Plate 21, a similar effect being 

 recorded in many other cases, notably F 68, F 69, and F 70 (Tables XL, XII., XIII.). 



The experiments in this direction had to be confined to pressures of about 

 1000 atmospheres. From these tests it seems probable that by working under similar 

 conditions, but with a higher gravimetric density, cordite would give results not 

 unlike those obtained by VIEILLE* in the case of " B.F." and other powders. 



* See "Etude des Pressions Ondulatoires," 'Annales des Poudres et Salpetres,' vol. III., pp. 177-236. 

 VIEILLE, in the course of this work, obtained instantaneous pressures amounting to three times the normal 

 value. Using a method of calculation similar to that given below, he showed that the speed of propagation 

 of the smaller disturbance is in fair agreement with the speed of sound in the same medium. 



