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/ Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=5083