Filling a tube with methane (and other gases)

[Beni]

For my EE in physics, I need to fill a 1 meter tube of diameter 10cm with air, CO2 and methane, and then hermetically seal it.

The tube will have glass on either end for light to pass through.

The first two gases are relatively easy to handle. For air I just close the open end (the other side is already sealed tight) and for CO2 I lower a tube to the bottom, open the gas valve and continue letting it flow until the match (which I place at the opening) is extinguished and then another 1 second for good measure. (By the way, can someone tell me if this method results in a mixture of air and CO2 in tube or just CO2)

For these two the only small problem I have is that I don't exactly know the amount or pressure of the gas inside the tube. I've so far assumed it to be the same.

Methane, however, is turning out to be much more complicated due to its explosive nature Additionally, I cannot rely on the same property I used with CO2 since CH4 is lighter.

The only method I have thought of so far that might work is the water displacement method, whereby I fill the tube with water, turn it upside down into a tub of water and then let the gas flow in until it has pushed out the water completely. (Not sure if this works well on such a large tube :/ )

Thanks for any help

[Beni]

:Bump: I guess more people are back to school now

[Joe Boyle]

I'd go with water displacement personally, or you could fill it (upside down as the methane is less dense than air) until you can smell the methane at the opening, but that's not a very safe or accurate (or maybe it is?) method.