In reply to Ridge:
> I thought that theory had been disproved?
The generalisation that people make from it, that hot water will always freeze faster than cold water is definitely wrong. I don't believe for a moment that hot water in a sealed nalgene bottle will freeze sooner than cold water would in the same bottle under the same circumstances, not on your nelly.
That said though, I occasionally work in ice rinks and know a few people whose job it is to look after the ice there. I couldn't guarantee that there isn't confirmation bias or somesuch going on, but they definitely believe in the Mpemba Effect. Albeit in very different circumstances.
The Zamboni smooths out the ice by planing its surface and then adding a thin layer of fresh water behind it as it goes. It generally cuts off more ice than it replaces, so the ice also has to regularly be built up again by 'flooding' the rink when there is time for fresh water to freeze. Sometimes time is tight, especially in arenas like Sheffield and Nottingham where the ice is boarded over for concerts and then has to be uncovered, cleaned up, flooded and cut several times to be ready for an ice hockey match the following day.
When 'flooding' the ice, it's standard practice for the hose to go on the hot tap rather than the cold. The people who do the job are convinced it freezes faster that way and unlike plumbers they do actually watch it freeze, sometimes whilst anxiously checking their watch because they're working to a deadline.
V different circumstances though obviously, because the hot water is being spread out into a huge flat puddle (60x30m and only a few mm deep) with existing ice underneath at about -10°C and dry air above for some of the hot water to evaporate into.
Post edited at 12:07