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Re: Using a CO2 "bell jar"

David Jones wrote Sat, May 3:  (parts snipped)

>I was upset at wasting all the bubbles so used a pyrex jug to trap the bubbles
>under the water, allowing them additional time to dissolve into the water.
>This provides a comprehensible visual display of the rate that the CO2
>dissolves. After the jug became filled up and attempted to break out of the
>aquarium a few times, I finally found a rock big enough to encourage the
>jug to remain  submerged.

This "bell jar" approach is a good way to get most of the CO2 produced to
dissolve in the water, but gas that is not CO2 will accumulate  and will
have to be emptied from time to time.  In the first place the yeast
generator will not put out 100% CO2 because what is being produced is
mixing with the air that was in the bottle when it was set up.  In the
second place, even if you were bubbling 100% CO2 into the bell jar, before
all the CO2 could diffuse into the water of your tank, dissolved gasses in
the water of your tank will diffuse out of the water into the bubble of
CO2.  Your tank water is in pretty good equilibrium with the atmosphere,
which is 79% N2 and 21% O2.  The bubble of CO2 in the bell jar starts out
with no N2 and O2, and, therefore, N2 and O2 will diffuse out of the water
into it.  As CO2 goes out of the bubble, N2 and O2 enter it.  The bubble
will get smaller only because CO2 diffuses out faster than the N2 and O2
diffuse in, but there will always be some bubble left.  It is no big deal
to empty the jar, and the main reason I am writing this is so that you
won't worry that what you are emptying out is CO2 that hasn't dissolved in
the water for some reason.

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174