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November 8, 2010
Volume 88, Number 45
p. 72

Chemical-free Salt, Exploding Cannonballs, Wet-dog Shake

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Scott Denmark
40 lb of nothing: Salt with no chemicals.

The last thing Scott Denmark expected to find during a visit to his local hardware superstore was an outbreak of IRRATIONAL CHEMOPHOBIA. Yet there he was, leaving the store, when he came upon a bag of Morton solar salt crystals, emblazoned with the statement “No chemicals or additives.”

“I could not believe my eyes,” says Denmark, a chemistry professor at the University of Illinois, Urbana-Champaign. Why would Morton Salt—a company that’s been selling its iconic ionics since 1848—suddenly forget that salt is, in fact, a chemical?

“The intention of the statement on our package was to help consumers understand that Morton Salt Solar Salt is pure solar salt without additives,” a public relations flack responded to a query from Newscripts. “There are solar salt products on the market that contain additives for water softening.”

Morton, in the future, please keep our salt chock-full of chemicals.

Speaking of salt, it turns out that sea salt—and not Blackbeard’s ghost—plays a part in booby-trapping cast-iron cannonballs in the deep. Such plunder has a TENDENCY TO EXPLODE upon its return to dry land, according to the folks at the io9 blog (io9.com) and the Big Site of Amazing Facts (bigsiteofamazingfacts.com). That’s something to keep in mind on your next hunt for sunken treasure.

It seems that the cast iron that makes up cannonballs is riddled with tiny cavities. As the sea salt electrolytically eats away at the iron, hydrogen and other gases collect in these pockets. Because they’re at the bottom of the ocean, the gases are under a tremendous amount of pressure. Raising the cannonballs from the seabed causes that gas to expand. If it expands too quickly: BLAM!

It’s not just gas that gathers in cannonballs’ nooks and crannies. Sulfate-reducing bacteria can colonize cracks and crevices in the iron, where they denude sulfates of their oxygen, spitting out reduced sulfur compounds. Such sulfur species react with the cannonballs to form iron sulfide.

Although such compounds are thermodynamically stable on the seafloor, they oxidize when brought to the surface. This exothermic reaction produces acid and can make cannonballs expand with explosive results.

For engineering’s sake: It’s the wet-dog shake.

Finally, any salty dog who’s ever been boat-bound with a genuine canine knows that there’s an inevitable explosion when the water-logged pooch returns to the ship after a swim: The WET-DOG SHAKE.

Now, Andrew Dickerson, a mechanical engineering graduate student at Georgia Institute of Technology, and coworkers have used high-speed video and fur-particle tracking to try to understand how fast a dog needs to shake in order to dry off (arxiv.org/abs/1010.3279).

Dickerson and colleagues filmed different dogs shaking and used the video to measure their periods of oscillation. A Labrador retriever, for example, shakes at 4.3 Hz. The researchers created a mathematical model based on the assumption that the centripetal forces to remove the water have to exceed the surface tension between the water and the hair.

They predicted that a mammal’s shaking frequency should scale to r–0.5, where r is the animal’s radius. So, smaller animals need to shake faster to dry themselves. As it turns out, mice shake at 27 Hz, cats at 6 Hz, and grizzly bears at 4 Hz.

But doggone it all, those experimentally determined shaking frequencies actually scale to r–0.75. Dickerson has some ideas as to why his model doesn’t quite match, but what the Newscripts gang really wants to know is where he dug up the funding for this study.

Bethany Halford wrote this week's column. Please send comments and suggestions to newscripts@acs.org.

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2011 American Chemical Society
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