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RE: temperature dependence of oxygen solubility

> On Wed, 24 Sep 1997 15:42:38 -0400 "Murphy, Kevin E." wrote:
> 	Correct me if I am mistaken, but doesn't warm water hold MORE oxygen
> than cold water?

I am behind on my APD reading, and I know that this statement has 
already been corrected, but as this one comes up so often I thought I'd 
add a little more to the previous replies. It is a general rule of 
thumb that the solubility of most solids increases with temperature, 
whereas the solubility of gases decreases. The solubility of a gas is 
proportional to the inverse of an empirically measured constant 
(Henry's-law constant, kB).  For oxygen in water, some specific values 
of kB given in a textbook are, when pressure is in mmHg:

             kB     inverse kB    relative
                      (1/kB)      solubility
20 deg C    2.95      0.3390        1.64
40          4.14      0.2415        1.17
60          4.84      0.2066        1.0

You can see that the effect exists, but it is not as large as is often 
made out. In the context of tanks containing plants and/or fish, we are 
normally talking about temperature changes of only 2-5 deg C, and the 
drop in O2 capacity is negligible compared with other factors which are 
more temperature sensitive, such as the metabolic rate of the plants 
and fish, the generation time of bacteria and protozoa, etc.

Ross Drewe
Note: correct address is rdrewe at melbpc_org.au