Method of Measuring Explosion Pressures. 



483 



in a house on shore. The pot was calibrated in situ by the 

 second method described above. A survey or the bottom was 

 made in order to obtain the depth of water in the neighbour- 

 hood of the explosion. 



The method of procedure in obtaining an explosion record 

 was to assemble the guncotton on the raft and hang it in the 

 water. The crystal vessel was then lowered into the water 

 at the desired distance from the charge and the insulation 

 of the system tested. If found satisfactory, the photographic 

 plate was lowered in the cathode ray tube, the magnetic 

 field turned on and the key depressed for an instant, and the 

 explosion resulted. The cathode potential was noted, and 

 then the plate was lowered to a new position and a zero line 

 taken by depressing the key. A potential difference of 

 17*5 volts was applied to the condenser plates and the key 

 again depressed for an instant, giving the displaced line. 

 This displacement was used as a check on the reading of the 

 electrostatic voltmeter. On developing the plate a record 

 of the explosion wave is obtained, which also shows a small 

 reflected wave from the bottom. 



Fie-. 8. 



-001 -002-003 -Oil -012 -013 -014 -015 



77/77 e . ($ecoftc/<s t 



.Time-Pressure Curve for Explosion of 2J lb. of Dry Guncotton. 

 One cm. displacement =650 lb./sq. inch. 



Figure 8 gives a typical form of wave from the detonation 

 of a small charge of guncotton. A is the direct wave and R 



