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From: gv@hou2e.UUCP (A.VANNUCCI)
Newsgroups: net.physics
Subject: Re: A thought experiment on freezing water
Message-ID: <597@hou2e.UUCP>
Date: Fri, 31-May-85 14:42:27 EDT
Article-I.D.: hou2e.597
Posted: Fri May 31 14:42:27 1985
Date-Received: Sat, 1-Jun-85 03:17:40 EDT
References: <765@oddjob.UUCP>
Organization: AT&T Bell Labs, Holmdel NJ
Lines: 40

>>There has been a discussion in net.cooks (of all places) of whether
>>or not it is possible to freeze hot water faster than cold water, all else
>>being equal.
>>
>>There have been several explanations as to why it might happen. ....
>
>(This is an excelent argument for increased funding of science
>instruction at the elementary school level.)
>
>Assumption:  The temperature of an object never takes a sudden jump,
>it varies continuously, although in some cases the change is rapid.
>
>Then consider two samples of water, one hot and one cold.
>At some time the hot sample will cool down to the initial
>temperature of the cold water.  How will it then freeze 
>faster than the cold water?  You might argue that some of
>the hot water will have evaporated and that under some con-
>ditions the initially hot water could then freeze faster
>due to its lesser volume, but then I will say that "a given
>size ice cube can never be formed more quickly from hot
>water than from cold."

  A few years ago the Scientific American column "The Amateur Scientist"
discussed the issue of whether hot water freezes sooner than cold water
under certain conditions (e.g. when washing your car in subfreezing
temperatures). The conclusion was the following: Obviously, if you
use distilled, de-gassed water in a sealed container, the cold water
will reach freezing point and start freezing before the hot water.
However, "real-world" water (the stuff that comes out of you bathroom
faucet) contains plenty of dissolved gases and other assorted dissolved
junk. Water that has been heated has lost much of the dissolved gases
and other stuff, so that if evaporation is the primary cooling mechanism
(such as when you are washing your car) those few extra cal's may not
be sufficient to counteract the faster evaporation rate and hot water
will indeed freeze faster than cold water.

		Giovanni Vannucci
		AT&T Bell Laboratories      HOH R-207
		Holmdel, NJ 07733
		hou2e!gv