Ancient Exploding Cannonballs

Planetes writes "There is a story on MSNBC about some surprise archaeology. Apparently, cannonballs from shipwrecks are "exploding" (more like heating up and cracking open) when they are exposed to air. At least one reacted so violently it reached several hundred degrees. Talk about a booby trap. I'd never have seen this one coming." Heat from oxidation (that's "rusting", if you haven't taken chemistry) has started many fires in cargo ships carrying iron.

Comments

Great Balls of Fire!!

[savage_panda]

This information is great to know if ever your stranded on a desert island with a coral reef around it, which has caused some shipwrecks of vintage warships with cannonballs. It would be a way to cook coconuts, a way to heat your hut at night, and start fires without matches, not to mention the other basic uses of a cannonball like lawn bowling and basketball.

definition of ancient?

[tps12]

When I read "ancient," I was thinking Greeks, Romans, or Moslems. I was all, "whoa, they had cannon, that's tight." But it looks like they are actually considerably more recent.

:(

Cross your legs

[hij]

The combination of oxygen and sea salt caused rapid oxidation resulting in the balls? ?exploding? open and crumbling into bits.

This is why I don't like to pull them out into the open air.

Rust at work

[R2.0]

There's a road in the northwest that was closed because it was effecively on fire. The state specified ground-up tires be used in the fill under the road in an eco-friendly gesture. Groundwater started the steel belts in the fill rusting, the heat started the rubber burning, and now smoke is coming out of the ground.

Re:Rust at work

[R2.0]

Here ya go smartass: http://www.metrokc.gov/procure/green/rubber.htm

Like in KSR's Mars trilogy

[MagikSlinger]

One of the theories I've always heard is that if Martian soil was ever exposed to signficant water (i.e., enough to thoroughly wet it), the soil of Mars could start reacting violently because it's mostly iron that hasn't had the advantage of water to ensure the iron is fully rusted.

KSR has some fun with this when he described a flood released onto pristine Martian soil. Snap, crackle, pop, kids.

Re:Like in KSR's Mars trilogy

[TwP]

Isn't the soil on Mars already rusted, hence the red color?

Re:Like in KSR's Mars trilogy

[ObviousGuy]

Yes. Take your tetanus shots before going.

Re:Like in KSR's Mars trilogy

[MagikSlinger]

Isn't the soil on Mars already rusted, hence the red color?

I forgot to mention that in my original post. From what I gather, only a small precentage of it is rusted (almost entirely on the surface of the rock or grain). Deep inside, there is iron just waiting for water to react with. As another poster mentioned, the Viking landers discovered "novel" chemistry when it was exposed to water. I don't know if it exploded, but it certainly did chemically react with the water.

Re:Basic chem

[PD]

We, the chemist (I am a chemist), tell you there is such a thing in the college freshman chemistry classes (and anything below that level), but in reality, carbon dioxide really disolves in water, not forming carbonic acid.

Do you lie to students in order to make them better chemists?

Frankly, I'm a little disturbed by this. I recall that my teachers and professors did NOT lie to us about carbolic acid. And nothing bad happened to me. So why exactly do you do this?

Re:Basic chem

[PD]

Crap. CARBONIC. I typed carbolic by accident. Carbolic acid is different.

Contains oxygen: handle with care.

[Observer]

Arthur C Clarke wrote a short piece about conditions on Earth as deduced from observations by astronomers of the long-extinct Martian civilisation (obtained by archeological investigations undertaken by early scientific expeditions from Earth in the early 21st century, IIRC - one of his early pieces). The Martian scientific consensus was that intelligent life could not possibly evolve on Earth, because 20% of its atmosphere was made up of the dangerously reactive element oxygen. Any life that did exist would have to be heavily armoured and shielded from exposure to such a corosive substance, and even then, there was evidence of sporadic large-scale chemical reactions on the surface of the planet, a terrifying natural phenomenon for which the scientists had invented the technical term "fire". Clearly, no life at all could possibly survive such events....

ACC was quietly ignoring the question of what was maintaining the level of such a reactive substance in the atmosphere in the first place, but he was also making a good point: most people do underestimate how reactive oxygen can be outside the everyday circumstances that we're familiar with. Wood burns, but we can make stoves out of iron, so iron doesn't burn easily, right? Wrong. Stuff an iron pipe with iron rods, blow pure oxygen down it and heat the open end for a while with an oxy-acetylene torch and you get one of the more powerful cheap cutting flames around. The cannon-balls had apparently had lots of fine channels corroded into them by years of exposure to sea-water so there was a large surface area unprotected by a covering of rust: in the cases where the iron combusted sufficient area of unprotected iron became exposed as or after the water evaporated which was enough to get the reaction started.

And Primo Levy commented in one of his books (Periodic Table, perhaps? I don't have it to hand to check) about how treacherously ready sawdust could be to spontaniously combust. A more obviously flammable example than iron, but a similar situation: with more surface area and less nearby mass to absorb heat from any reaction that does start, sawdust is that much more liable to behave dangerously that timber in bulk.

Ancient explosive ordinance

[j_w_d]

The older explosive ordinance was packed with black powder and fused so that it would ignite when fired from a gun. The problem with black powder is that while wet, it is perfectly safe. When it dries out it is unstable. I have participated in archaeological monitoring where the UEO guys were working to locate and safe ammunition ranging in age from Viet Nam War back to the Civil War. That ammunition occasionally still contained black powder that WOULD detonate (actually deflagrate I suppose) when dry. "Ancient exploding cannon balls" could very well ruin your whole day if not treated with some real respect.

Steel wool

[t]

I'm suprised no one has mentioned steel wool. If you've never played with some, it is incredibly flammable.

t.