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Treebeard's Stumper Answer
18 Oct 96

Here's another question about heat that came up in science class this week when we mixed salt and ice as part of showing that fire produces water vapor. In cold climates, we use salt to melt ice from walkways and roads. But we also use salt to freeze ice cream the old fashioned way. How can this be?

(Hint: think about fans!)


How can we use salt to melt ice and also to freeze ice cream? Ice melts in both cases, but as it melts, it draws heat from its surroundings. This cools the ice cream in the same way that moisture evaporating from our skin cools us when we sit before a fan. Refrigerators use the same principle, though I used to have a propane refrigerator that cooled my food with a flame. Now there's a real stumper!

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Marc Kummel / mkummel@rain.org