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Re: Silicone tubing and CO2

Wayne writes:

> I have heard this repeated before but I don't buy it at all. Silicone
tubing
>  does harden a little bit over time but it lasts many years. I have tested
>  the tubing by placing my yeast sugar system under water and clamping off
the
>  end of the silicone tubing line. There were no detectable leaks at all
let
>  alone a loss of 30% of the gas. In my test situation the silicone line
was
>  under considerable pressure too. In actual practice the pressure in the
CO2
>  line is vanishingly small or even negative. Perhaps silicone tubing leaks
if
>  it is under 40 psi pressure but it sure doesn't seem to at low
presssures.

Bob Dixon wrote:

The way that gas passes through a membrane, it would come out the other side
a single molecule at a time.  There would be no bubbles.... hey!! maybe this
would make for a good diffuser if you stuck , like 20 feet of it in the
substrate and just let it seep up into the water column.

I reply:

Point taken. I did another experiment that I figure wasn't very accurate but
I still did not measure any loss of CO2. I put the CO2 line in the output
side of the filter pump any measured the bubble rate through a bubble
counter. I then put the CO2 line in the intake side of the pump and allowed
a few hours for the CO2 output to stabilize and I did not measure any
difference in the bubble count. If there was a significant amount of CO2
loss or if a significant amount of air was difusing through the tubing I
think there would be a difference. I did this a few times because the yeast
sugar generator does not produce gas at a really stable rate but I couldn't
detect any difference.

Now since Paul says that it is the difference in partial pressure that
matters, does that mean that the oxygen and nitrogen would enter the tubing
at the same rate in either case but the CO2 should be leaving the tubing at
a lower rate in the lower pressure situation? I guess the difference
wouldn't be that big and any difference I did measure would not be telling
the whole story. Sounds like that experiment is crap too :-(

Wayne