Re: [APD] CO2 Experiment #2

[David Aiken <daiken at iprimus_com.au>]

On 09/11/2005, at 2:22 AM, Jerry Baker wrote:

> Stuart Halliday wrote:
>> Surely the inverted tube will never fill up with water? As the CO2  
>> dissolves the vacuum caused will pull O2 or other gases back out  
>> into the tube?
>
> It is true that the tube will not fill completely with water. The  
> O2 and N2 will try to equalize with their partial pressures in the  
> water. My intent was to overfill the tube and measure how long it  
> took to reach a certain point.
>
>> Won't the strong current also cause CO2 to be dissipated at the  
>> top water level of the tank?
>
> The current will be severely limited so that it is only "strong"  
> right at the mouth of the test tube. It shouldn't even cause a  
> ripple at the water surface.
>
>> Suction caps as used for holding a air line between the edges of  
>> the tank with strong thread between them?
>
> That will probably work. Duh on me for not thinking of that.


I think there's a nasty assumption going on. I know this experiment  
is really about speed of CO2 dissolution at different dissolved CO2  
levels but already you are assuming that we've got O2 and N2 gasses  
in the tube as well as CO2. At the moment there's nothing to show  
that what is being collected is any more than the CO2 that's being  
injected into the tank. The O2 and N are supposition only at this  
stage and while it's easy to imagine that there will be some O2 in  
there if the experiment  was performed in a real live planted tank  
where the water was supersaturated with oxygen and pearling is  
occurring, nitrogen is a much less likely component even in a real  
tank. In a sterile bucket such as that used in your experiment we  
don't have supersaturation with O2, and nitrogen is much more  
insoluble in water than either O2 or CO2 so what basis do you have  
for assuming that there's any nitrogen exchanging out? It seems to me  
that there's a lot of assumption going on here.

Is the next step going to be claims that the gas collected contained  
x,y & z, with no testing whatsoever to determine that is the case,  
simply because the assumptions have been repeated so often by then  
that everyone is starting to believe them?

You're collecting bubbles of unknown content, and you're bubbling in  
close to pure CO2. You have no evidence at this stage for what the  
collected gas contains. Let's try to keep it scientific and dispense  
with the assumptions. If you want to say what has been collected, get  
the gas analysed and tell us the results.

David Aiken
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