X-Message-Number: 5083
Date: Tue, 31 Oct 1995 20:45:08 -0500
From: "Keith F. Lynch" <>
Subject: Re: CRYONICS: flash freeze

I don't think we have to put CRYONICS in the subject line any more.

In #5076, Mike Darwin <> writes:
> I have always wanted to try the REVERSE of what Bob suggests: cool
> to near 0 C and then PULL A VACUUM.  Will that cause the liquid to
> freeze instantly at a higher point?

No.  In a vacuum, pure water freezes at 0.01 C instead of 0 C.  Not
much difference.  And, as Brian mentioned would happen when a high
pressure is released, the freezing of water always gives off heat, and
this heat would prevent any but a small amount of water from freezing.

The only way to freeze anything suddenly is to find a way to remove a
lot of heat in a hurry.  I can't think of any way to do that with a
brain, unless you can thread heat-superconductors all through it.
Unfortunately, the only known heat superconductor is liquid helium,
which only works if what you're trying to cool is already far below
liquid nitrogen temperature (4 K instead of 77 K).  (Superconductors
of electricity are not superconductors of heat, contrary to common
belief.)  Another approach would be to cut the brain into thin slices,
and freeze them individually.  But that's almost certainly a cure
that's worse than the disease.

The boiling point of water varies with pressure far faster than the
freezing point does.  At a pressure below about 1/100 atmosphere,
the boiling point is lower than the freezing point, and water has
no liquid state at all, similarly to the way dry ice (frozen CO2)
works at ordinary pressures.  The resulting rapid evaporation does cause
lots of cooling, but only down to about 0 C, not significantly below it.
And it strongly dehydrates the tissues, and may cause damaging pressure
differentials if cold steam bubbles get trapped and need to push
something (like brain tissue) aside to escape.

So unless you want freeze-dried patients, I think vacuum is probably
best avoided.
--
Keith Lynch, 
http://www.access.digex.net/~kfl/


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