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After reading Rick's posting about liquid air a moment ago and then
deleting it I realized that there is something wrong with the facts
as he reports them. 

If the volume of a liquid is 250 times that of a gas (at sea level I
assume) then 300 bar tanks should not be possible because at 250 bar
the gas will be compressed to a liquid form and thus no longer compressable.
Also, if that were the case then air compressed to 200 bar would not
have a weight of 1/2 time a liquid with the same volume but about
4/5 of that weight.

Just some nits.

All this being said, the idea of using cryogenics to extract CO2 is
a clever one. My question would be, how much liquid nitrogen is necessary
to scrub for an extended dive of say 10 hours? Another consideration is 
that when you run out of liquid nitrogen there is no gradual deteriation
of your breathing mix -- failure will be rapid from that point.

There is another angle to this thing that occured to me. Suppose that 
the system used liquid O2 for insertion into the breathing mix. Do you
suppose that as the liquid O2 is released into a gaseous form it would
absorbe enough energy to provide the low temperatures necessary for the
cryogenic scrubber? My guess is that it wouldn't, but if it would then
as long as there is liquid 02 in the system it would be functional.

Eric

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