On Tue, 13 Mar 2007 03:14:42 +0100, wrote:

The meter works by hydrogen ions passing through
the humid air until they are balanced.

There is no such animal as "hydrogen ions passing through the humid
air". What can be exchanged is pure water (think in terms of
distillation - evaporation/condensation) and carbon dioxide (plus
other gases, which won't change solution pH). Relying on CO2
equilibrium for pH measurements doesn't look like a reliable idea to
me - it may work only as long as CO2 is the only reason for pH
changes.

I studied Chemical Engineering and have some understanding of what you
are saying. What I do know is that the pHs in the two bodies of water
seem to reach equilibrium. My pH meter seems to work. I was just
speculating about the actual mechanism. Perhaps it is the CO2 gas.

Assuming CO2 equilibrium is responsible for the pH equilibrium there are
at least two possible problems. First, such equilibrium needs hours to be
established, so your pH meter has a very long response time. Second, it
can work only as long as both solutions are identical - so any acids/bases
added with food, medicines, fertilizers and so on will break the 'device'.

While it can be an interesting experiment I would be reluctant to rely on
its indications.

Borek
--
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