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The convection currents in the warm water help in the rapid heat exchange which is why warm water is used.
(I don't have a citation other than a colleague who showed me the explanation online yesterday)
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
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Ah! An interesting new angle...
Regards,
Rob Philpott.
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Not quite - boiled water has dissolved gasses removed, and will freeze faster.
When you heat water on a stove to boiling point, you will see bubbles form for some time before the water reaches the boiling point. This is dissolved gases coming out of solution, and if you capture the bubbles, you will see that their content is not H2O. Once the water reaches boiling point ("rolling boil"), then the water is changing phase and the content of gas emitted is water vapor (H2O).
Water (even boiling water) that has the dissolved gases removed will freeze faster than warm or even cold water.
Never moon a werewolf.
- Harvey
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Thanks - (in danger of being a complete pain in the arse) has this theory been peer reviewed scientifically?
I ask this as having just done a quickish google there do appear to be a few theories none of which have been conclusively proven correct.
e.g. Mpemba theory[^]
“That which can be asserted without evidence, can be dismissed without evidence.”
― Christopher Hitchens
modified 8-Jan-14 9:45am.
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When taking engineering courses it was explained by the fact the hot water is losing energy already where as cold water has to start losing heat(energy). Poor man's explanation after 30 plus years of forgetting. At the time we calculated the "proof".
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That is saying that energy loss has momentum. I don't think that is true, and it should be relatively easy to prove in a lab. [Haven't done it myself...]
Never moon a werewolf.
- Harvey
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As I say I do not remember exactly what the science was but I remember doing the calculations.
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Not saying that energy loss has momentum, but technically, fluid temperature is very closely related to the average momentum of the water molecules - if I recall correctly, temperature (being a measure of internal water energy) is proportional to the average kinetic energy of the water molecules (or something along those lines), which in turn is proportional to the average of the square of the molecules' momentum.
So I would say that heated water, having a higher average molecular kinetic energy, exchanges higher amounts of energy with its environment, therefore in turn loses more energy to it (and cools faster).
Then again, I may be wrong in that. I seem to have forgotten most of the thermodynamics I've been taught.
Φευ! Εδόμεθα υπό ρηννοσχήμων λύκων!
(Alas! We're devoured by lamb-guised wolves!)
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H.Brydon wrote: Not quite
"the Mpemba effect" 
Bastard Programmer from Hell 
If you can't read my code, try converting it here[^]
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Was gonna post this, but I was beaten to it. Good link. 
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it is actually so that hot water freezes more quickly than cold water, although it is not yet known why.
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V. wrote: ...although it is not yet known why.
Yes it is ... see my previous reply in this thread.
Never moon a werewolf.
- Harvey
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Boiling water to snow[/\]chemistry.about wrote: This science trick is as easy as throwing boiling water into the air and watching it instantly change into snow.
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That is freaky! I think I prefer the regular quakes we have here in Southern California. 
Soren Madsen
"When you don't know what you're doing it's best to do it quickly" - Jase #DuckDynasty
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yes, it's real. and my FB feed is currently full of people demonstrating that it works in their back yards.
cold air, pot full of hot water => snow
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More to the point: given the amount of snow they already have, why are they adding any blooming more? 
Never underestimate the power of stupid things in large numbers
--- Serious Sam
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Don't forget we use Fahrenheit so -15 here is a lot colder than -15 there : )
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Yeah. Imagine if it was -40! How much colder would that be?
Never moon a werewolf.
- Harvey
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It works - really! A couple of points, though... The liquid immediately separates into droplets, vastly increasing the surface area exposed to the cold, plus it is moving, effectively the same as a stiff breeze. Both factors contribute to the rapid freezing. Besides, it's been really, really cold. It was so cold, in fact, that Miley Cyrus stuck to her wrecking ball, and a Liberal in D.C. was spotted with his hands in his own pockets!
Will Rogers never met me.
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