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Re: Gas solubility

	The equilibrium concentration of a gas dissolved in water is 
dependent on _two_ things - the partial pressure of that gas in contact
with the water and the Henry's law constant for that gas in water.
The constant for CO2 is a lot higher than that for oxygen, so for
the same partial pressure, there would be a lot more CO2 than there
would be oxygen.

	We make some very complicated systems, with plants, fish, CO2
systems as well as the air all in contact with the water.  An overall
equilibrium will be set up as far as gas concentrations in the water
are concerned, but _none_ of the individual interfaces with the water
may be at equilibrium.  Transport of gases between the media is 

	It is not difficult to get a situation where _both_ CO2 and O2
concentrations are well above the equilibrium concentrations with the
atmosphere, simply because we inject CO2 into the system and the plants 
add O2.  If the fish don't use all the O2, then the aquarium will lose
both gases to the atmosphere at its surface.  Any other gases will maintain
their own equilibria at the surface, and these will not be affected by
our interference unless we add so much stuff that the gas at the suface
of the water is no longer of normal atmospheric composition.

	The other thing to consider is the concentration of a gas in the
water that corresponds to a partial pressure of one atmosphere of that gas.
If the concentration of the gas in the water goes above _that_ then
bubbles of the _pure_ gas can and will form.  I think that happens in
aquaria, with oxygen.  This still doesn't affect the amounts of other
gases there, unless the transport of the gas in question is so enormous
as to "sweep" others away.

	Ideally, if you want to understand this, a good physical chemistry
textbook is invaluable.

	Remember, we are _not_ talking about simple gas/liquid equilibrium.

Paul Sears        Ottawa, Canada