The man who used letters to make explosions more destructive

You can etch words into metal with an explosion, and those words reveal a startling thing about how explosives work. It's called The Munroe Effect, named for a guy who helped make explosions more damaging than ever.

Charles Munroe was not a sailor, but he spent the latter part of the 1800s working with them at a United States naval torpedo station. As part of his duties as chemist, he worked with guncotton. A worryingly unstable mixture of plant pulp and nitric acid, guncotton was used as an explosive in weapons. Munroe tested guncotton from a manufacturer that sent the navy wads of the stuff with the company name stamped into one side. The letters were slightly indented on the guncotton. After Munroe had set the guncotton off, he noticed that those same letters slightly indented on nearby metal. When, on the other hand, he made guncotton into packages with raised lettering, the letters were slightly raised on nearby metal after the explosion. Indenting the letters on the explosive made the explosion, in that area, more powerful. Raising them made it less so.

More experiments showed this to be true in almost all cases when a hollow was carved into the explosive. Although the overall power of the explosion wasn’t different, the penetrating power in that area of the explosion was greatly increased. To understand why, think about the dynamics of an explosion. If a mound of explosive is formed, and material all goes off at once, the sides of the mound fly out sideways and give little force to the "top" of the explosion. If there’s a hollow made in the explosive, the explosion blows the sides of the hollow inwards, towards each other. This creates a huge amount of force that can go nowhere but up. The top of the explosion is much more powerful.

The idea of using this particular indentation to direct and increase the power of an explosion was called the Munroe Effect, after its discoverer. It allows explosives to be more focused and powerful using less overall explosive material. And it lets us carve our names into metal plates.

Top Image: Jon Sullivan

Via Proceedings of the Newport Natural History Society and Wisegeek.