The Chemistry of Powder and Explosives - Sciencemadness Dot Org

18 PROPERTIES OF EXPLOSIVES
stood between the ends of the cordeau; thence the velocity of
detonation in meters per second.
Velocities of detonation have recently been measured by highspeed
photography of the explosions through a slit, and by other
devices in which the elapsed times are measured by means of a
cathode-ray oscillograph.
The Munroe Effect
The mark which explosive waves, traveling toward each other
on the same piece of cordeau, make at the point where they meet
is evidently due to the fact that they spread out sideways at the
point of their encounter. Their combined forces produce an effect
greater than either alone could give. The behavior of jets of
water, shot against each other under high pressure, supplies a
very good qualitative picture of the impact of explosive waves.
If the waves meet at an angle, the resultant wave, stronger than
either, goes off in a direction which could be predicted from a
consideration of the parallelogram of forces. This is the explanation
of the Munroe effect.
Charles Edward Munroe, 6 while working at the Naval Torpedo
Station at Newport, discovered in 1888 that if a block of guncotton
with letters countersunk into its surface is detonated with
its lettered surface against a steel plate, the letters are indented
into the surface of the steel. Similarly, if the letters are raised
above the surface of the guncotton, by the detonation they are
reproduced in relief on the steel plate, embossed and raised above
the neighboring surface. In short, the greatest effects are produced
on the steel plate at the points where the explosive material
stands away from it, at the points precisely where explosive
waves from different directions meet and reinforce each other.
Munroe found that by increasing the depth of the concavity in
the explosive he was able to produce greater and greater effects
on the plate, until finally, with a charge which was pierced completely-
through, he was able to puncture a hole through it. 7 By
introducing lace, ferns, coins, etc., between the flat surface of a
6
For biographical notice by C. A. Browne, see /. Am. Chem. Soc, 61,
731 (1939).
7
Cf. article by Marshall, "The Detonation of Hollow Charges," /. Soc.
Chem. Ind., 29, 35 (1920).