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Jan24-08, 06:10 AM
P: 80
From what I can remember of this phenomenon people have done experiments where dissolved constituents were carefully controlled and everything was done to make the hot and cold sample of water identical and still they found that in some cases the hot water froze first.This is why I proposed some form of adsorption process on the walls of the container.Dissolved substances in water can lower its freezing point and perhaps in the hot water sample the substances are being adsorbed by or driven into the container wall lowering the concentration of dissolved substances and raising the freezing point.
There is also the idea that hot water in cold air sets up stress and strain in a metal pipe and that this is why a hot pipe bursts - a bit like metal fatigue!
I also think that in examples I've heard of where people pour hot water into a frozen bowl outdoors and it freezes much quicker than expected that what could be going on here is that there is lots of hot water vapour evaporating into the air which then cools rapidly and forms ice crystals that fall back into the bowl and provide nuclei for other crystals to form.