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Re: independence of gasses in solution

On Fri, 14 Jan 2000, Peter Aitken wrote:

> > C'mon, man, it's a scientific fact that O2 and CO2 are independent.
> > Chuck Gadd's experiment demonstrated this. You are wrong. Period.
> > Adding CO2 does NOT reduce O2.
> I am afraid it is you who are wrong. Gasses in solution are not independent
> of each other. Adding CO2 (or any other gas) to a tank will in fact reduce
> O2.

I disagree with Mr. Aitken.

> This is expressed by Henry's law which states that the volume of a gas
> dissolved is proportional to its partial pressure. Chuck's experiments must
> have overlooked something, or more likely the changes were not detectable by
> his measurement methods. Gasses in solution are measured in terms of their
> partial pressure, and at equilibirium the partial pressure of the dissolved
> gasses will equal the pressure of the gas.


Mr. Aitken's arguments describe a system of mixed gases held at one
atmosphere pressure in equilibrium with water.  I think the arguments are
right for that system, but that has nothing to do with aquariums.  We (and
the fish and the plants and etc.) add and remove gasses from the water and
the water is never at equilibrium with the air.

The actual gas concentrations in aquarium water always differ from the
equilibrium concentrations.  Comparing the actual concentrations in water
to the concentrations at equilibrium with air tells us which direction the
gases diffuse across the surface of the water, but that's about all the
equilibrium values are good for.

Roger Miller