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Your ice cubes have been sublimating. . |
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Sublimation is no mean feat. It requires that a substance take a leap of faith, changing from a solid directly to a gas -- do not pass
go, do not turn to a liquid first. It's not exactly against the laws of chemistry, but it's not the normal progression. Set an ice cube on the counter and you'll see how an obedient substance warms up. As the outer molecules of H20 pick up energy from the warm air, they move faster and unlock from each other. Gravity drags the loosened molecules into a pool around the ice. If you watch long enough you'll see the pool of liquid begin to shrink: The molecules, getting warmer still, speed up enough to break free and disperse in the air. They're gassified. |
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What could possibly inspire an ice cube to skip right over the liquid stage? . |
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"In any mass, like an ice cube, you'll always have molecules that are frozen solid, and liquidy molecules, and gassy ones hovering
around the area," explains Bob Chartuk, an answer man with the National Weather Service. "When you add wind, that allows more of the
gaseous molecules to leave the mother ship." In your freezer, the extra wind is a rather recent innovation designed to combat normal household humidity. Bits of water vapor are always invading iceboxes. Each time you open the door, damp air rushes in. Between the time you remove and replace a package of coffee beans, it accumulates a skin of moisture that condenses from the warm kitchen air. In old-fashioned fridges, all this moisture used to form crystals. These slowly transformed the freezer box into a wondrous winter scene that could engulf an entire turkey. Vigorous application of a spatula or butter knife was a regular maintenance requirement. |
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The frost-free fridge is a marvelous labor-saver, but its secret appetite for ice is less enchanting. . |
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Under normal circumstances, the outer molecules of an ice cube are already itching to hop off and populate the air inside the freezer --
it's the nature of any gas to spread uniformly through its environment. As the molecules struggle to lift off in a frost-free fridge,
however, a stream of air sucks them away. This prevents the ice-cube molecules from founding a crystal colony on the Cool Whip. But the
fake wind also excites the next layer of molecules on the ice cube, so they get up and hover, too. The wind, just as it does on a snow
bank, speeds up the process of sublimation. And where do the ice cubes end up? They condense and freeze in a layer on the evaporator coil inside the freezer wall. Periodically, the coil heats up to shed this ice, and your ex-cubes, liquid at last, trickle into a pan under the fridge, where heat from the motor causes them to gassify once again. (Their vaporous wraiths could theoretically reenter your freezer when you open the door.) You pay for all this labor-saving service in higher electric bills -- and with guests who try not to stare as you root around under the fridge for the ice cubes that got away. |
 Vocabulary Sublime, adj. In Latin, this means "up to the lintel," a lintel being the top of a doorway. To sublimate a thing is to raise it to a high and exalted position, on a par with, say, water vapor.
Check out more of "The Skinny On ..." stories:
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Hannah Holmes routinely runs to the convenience store for ice from her home in Portland, Maine. In addition to her numerous
contributions to Discovery Online, she writes for Escape, Outside, Sierra, Backpacker, Eco Traveler and Women's Sports and
Fitness. Write her at skinny@online.discovery.com.
Main WebLinks Picture: Brian Frick | Copyright © 1997 Discovery Communications, Inc. |