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



actual maximum is probably of the order of 40 tons per square inch. At a point on 

 the surface the maximum pressure is at least twice as great, 80 tons per square inch.* 



The arrangements are shown in fig. 12. 



The gun-cotton cylinder A is fixed by short splints of wood opposite the end of the 

 shaft B, which is of mild steel l inches diameter and from 15 to 30 inches long. This 

 shaft is suspended as a ballistic pendulum with a pencil and paper for recording its 



movement. The end piece C, from |- to 6 inches long, is held on by magnetic 

 attraction. The faces of the joint are a scraped fit. In line with the shaft is the box 

 D, which is also suspended as a pendulum and provided with a recording pencil. Some 

 part of the momentum given to the box is due to the blast from the gun-cotton ; this 



* The pressure developed by the explosion of gun-cotton in a vessel which it completely fills does not 

 appear to have been measured. From measurements made with changes of lower density Sir ANDREW 

 NOBLE estimates that it would be about 120 tons per square inch ('Artillery and Explosives,' p. 345). 

 Allowing for the partial expansion during the process of detonation, this agrees fairly well with the 

 pressure here determined. 



t In these cases the air space between the gun-cotton and the end of the shaft was 1 inch. In all the 

 others it was f inch. 



