450 MR. B. HOPKINSON ON MEASURING THE PRESSURE PRODUCED IN THE 



that which became the convex face (lower face in fig. 9). Fig. 10 is a view of the 

 broken edge of one of the two fragments. The plate shown in fig. 1 1 was a flat piece 

 of boiler plate l inch thick. A slab of 1 Ib. of gun-cotton was detonated against 

 that which is the under side in the figure and the two pieces subsequently fitted 

 together again and photographed. Thinner plates e.g., I inch thick are usually 



B 



A I \B 



i \ 



Fig. 8. 



Fig. 9. 



Fig. 10. 



Fig. 11. 



cracked in two places, one at each edge of the gun-cotton slab, and the portion 

 covered by the slab is blown out of the plate, sometimes whole and sometimes 

 shattered into pieces. The fact that no tamping is necessaiy suggests that the 

 duration of the process of detonation is of the same order as the time taken by sound 

 to travel an inch or less in air, so that during the conversion of the cotton into gas 

 there is not time for much expansion.* If this be so, the maximum pressure 



h The velocity of detonation of long trains of gun-cotton has often been measured and is variously 

 estimated at 18,000 to 20,000 feet per second. If the same velocity obtained in the small primers they 

 would be completely converted into gas in about 2 x 1Q~ 6 sees, 



