New Scientist Premium- Why water freezes faster after heating - News: "A common chemical process may explain a bizarre property of water that has been a mystery since the time of Aristotle
A common chemical process may explain a bizarre property of water that has been a mystery since the time of Aristotle - how hot water can freeze more quickly than cold.
This strange and counter-intuitive effect was first observed by the ancient Greek philosopher and was made famous in recent times by a Tanzanian school student called Erasto Mpemba. He noticed that the sugared milk he was using to make ice cream froze more quickly if it started out hot. But what is behind the so-called 'Mpemba effect'?
According to Jonathan Katz of the Washington University in St Louis, it's all to do with solutes. 'You have to ask yourself: what does heating do to water that makes it easier to freeze?' he says. 'The answer is that it precipitates out solutes.'