Spark Photography as a Means of Measuring Rate of Explosion

Abstract

The explosive was placed in a long cartridge having excess charges in small equally spaced side openings which were set off in succession as the explosive reached them so that each became the center of a spherical sound wave. An instantaneous photograph of shadows of these sound waves was obtained by means of a spark which occurred automatically when the explosion reached a certain opening and closed an electrical circuit. From the radii of the spherical waves and the distance between the openings the rate of explosion was determined. Rates for various charges were found as follows: lead styphnate.11×.15×10.0 cm, 369 meters per second; loosely packed mercury fulminate.15×.25×14.0 cm, 1205 meters per second; well packed gunpowder.45 cm in diameter and 12 cm in length, 261 meters per second.