devine@asgb.UUCP (Robert J. Devine) (05/22/85)
I hope this ends this discussion whether hot water freezes faster
than colder. My posting of a week or so ago told of the real story
of a chem TA winning a bet from a professor on this.
Here is the truth. The following is from Jearl Walker's book
"The Flying Circus of Physics" (he is now a columnist for Scientific
American magazine).
"In cold regions like Canada or Iceland, it is common
knowledge that water left outside will freeze faster
if it is originally hot. While this may seem completely
wrong to you, it is not just an old wives' tale, for
even Francis Bacon noticed it."
"The critical feature is the increased evaporation from
the initially warmer water. If equal masses of warmer
and cooler water are set outside in freezing weather and
in open-topped containers, the evaporation from the
warmer water will reduce the mass remaining in that
container. With less mass to cool, the water in that
container can overtake the cooling of the initally
cooler water and reach the freezing point sooner. The
actual cooling rate can depend somewhat on the composition
of the containers, the circulation above the containers
and the circulation in the water. Although Bacon
commented on the effect and although the result is wll
known in Canada, people in warmer countries find it
mysterious."
Bob Devine