Cooling foods when there's not a socket around

Thanks to the second law of thermodynamics, Mohammed Bah Abba has developed a refrigerator that doesn't need electricity. What's more, it costs 30 cents to make.

The elegant design consists of an eathenware pot nestled inside a larger pot, packed with a layer of damp sand. When the "Pot-in-Pot" system is stored in a very dry, well-ventilated place, the water held in the pots' clay walls and sand evaporates, carrying heat with it. The inner pot therefore cools down- and makes a useful refrigerator in the northern deserts of Nigeria, where Abba lives and works. Abba says his trials showed that tomatoes would last several weeks instead of several days and that African spinach (amaranth), which normally wilts within hours of harvest, can last up to 12 days. (He's never measured, though, just how many degrees cooler the inner pot becomes).

Abba's fridge provides an alternative for desert cultures, which generally dry their foods to preserve them. Drying doesn't diminish protein or calorie content much, notes William r. leonard, a biological anthropologist at Northwestern University who has worked in the high desert of the peruvian altiplano. "But things like vitamin C are likely to be in shorter supply" in the dried foods, Leonard says. In addition, some foods, such as spinach and onions, cannot be dried, remarks Abba, a lecturer at Jigawa State Polytechnic in dutse, Nigeria. The Pot-in-Pot may have great social impact, too: Abba says that young girsl who used it would not have to sell their families' freshly picked foods right away and thus would have time to go to school.

For his work, Abba received one of five biennial Rolex Awards for Enterprise on September 27. The others were Elizabeth Nicholls, a Canadian paleontologist who unearthed an ichthyosaur in British Columbia; Maria Eliza Manteca Onate, an Ecuadorian environmentalist promoting sustainable farming in the Andes; Laurent Pordie, a French ethnopharmacologist who is preserving traditional Tibetan healing methods in northern India; and David Schweidenback, an American recovering used bicycles in the U.S. for shipment to developing countries. (see http://www.rolexawards.com)

Updated: Thursday, September 6, 2007.