Re: Reprocessing Air In Submarines

Dear Andrew,

Sorry about how long this reply has taken.

First of all, a little background.
Air is composed of 78% Nitrogen, 21% Oxygen, 1% Argon, 0.3% CO2 and
the rest is in trace amounts.  
see: Air

Our bodies need Oxygen to "burn" the food that we eat to survive.
We give off CO2 as a waste product.  The major component of the
atmosphere, Nitrogen, is breathed in and out without any change.

The answer to your question is that the air in submarines is processed
to remove the CO2 by a strong base.  The chemical reactions are:
CO2  +  H2O  ==> H2CO3 (carbonic acid)
H2CO3 + Ca(OH)2  ==>  CaCO3 (Limestone) + 2 H2O

The limestone is not very soluble in strongly basic solution and
precipitates.  
see: soda-lime

The Oxygen that gets used up is replenished by an electrolysis cell to
decomposed water into Hydrogen and Oxygen.  The Hydrogen is collected
in metal sponges which adsorb quite a lot for their weight (metal
"hydrides")
The Oxygen is collected, compressed, and bled into the submarines atmosphere
as needed to keep the % of Oxygen steady at about 21%.  
see: 
MAD archive about electrolysis

Good question!

Mike Gallagher