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From: mickey@illogica.UUCP (Michael Thompson)
Newsgroups: net.cooks
Subject: Re: freezing hot water
Message-ID: <115@illogica.UUCP>
Date: Sun, 19-May-85 21:47:19 EDT
Article-I.D.: illogica.115
Posted: Sun May 19 21:47:19 1985
Date-Received: Fri, 24-May-85 21:30:45 EDT
References: <188@sdcarl.UUCP> <10500002@haddock.UUCP>
Organization: Illogica Systems, Hayward, CA
Lines: 44

> 
> /* Written  8:47 pm  May 12, 1985 by rusty@sdcarl in haddock:net.cooks */
> /* ---------- "freezing hot water" ---------- */
> well, now that we've beaten the boiling water issue to death;
> one thing that i've always had trouble believing is the common
> belief that if you use hot water for making ice cubes that they
> will freeze faster.  does anybody have any idea why they should
> do that?
> -- 
> 	rusty c. wright
> 	{ucbvax,ihnp4,akgua,hplabs,sdcsvax}!sdcarl!rusty
> /* End of text from haddock:net.cooks */
> 
> Is this true or just creative b.s. ?

It's true. It does take less time for hot water to freeze than an
equal volume of cold water.

The rate at which a liquid approaches temperature equilibrium with
it's environment is related to the difference in temperature between
the liquid and it's environment.

(Which do you think will have the most rapid temperature change? 
	a) An ice cube thrust in a glass of cold water.
	b) A glowing, white-hot steel rod thrust in a glass of cold
	water.
)

So, hot water cools ~faster~ than an equal volume of cold water
because the temperature difference between it and it's environment
is greater.

"But... But... wait!", you exclaim. "There exists a point at which
the ~hot~ water will be the same temperature as the cold! After that
point the temperature difference will be equal and they should cool
at the same rate."

Yes, but the volume of the hot water will be ~less~ because some of
the hot water will have evaporated by that time. Since there is less
water to freeze, it freezes faster.


		    -Michael B. Thompson
		    {decvax,ucbvax}!dual!vecpyr!altos86!illogica!mickey