In article ,
(Graham Ramsay) wrote:

Can anybody help my comprehension with this please?
Many web sites (and a few answers in newsgroups) say
that using an airstone will break the surface tension
(which it surely will) and thus increase the exchange of
gas. Almost as if the surface tension was preventing
the gas from moving between water and atmosphere.
In a forum I'm in I received this response when I claimed
that a circular water current and surface agitation,
not the breaking of surface tension or the increased
contact area due to air bubbles, was the main purpose
of using an airstone:

Quote:
"Surface tension is needed to stop complete gaseous escape
from a body of water. breaking up the surface tension promotes
far greater gaseous exchange"
Unquote:

Now I left school some time ago and never went to
college but it strikes me that if that were true then, by
the simple act of adding a drop of detergent to the water
surface, all the gas in the water would now escape into
the atmosphere.
How does surface tension, on its own, prevent the exchange
of gas between a body of water and the atmosphere?

This is rubbish. Bubble do not break the surface tension, bubbles are
little balls of surface tension. It sounds like someone has taken a quite
long explanation of why the gaseous exchange takes place, and simplified
it to the point where it is no longer true. The truth is all about rates
of delusion and fluid dynamics, which are far too complicated to go into
here - and anyway I'd have to go and look them up.

Roger Sleet
Roger's Aquatic Pages http://www.sleet.plus.com