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>Posted on 21 Jun 1995 at 15:01:53 by AHDNN1A.DDRAKE01@ed*.co* I am really answering here because I just wanted to tell David above that I got his mail but have been unable to get my replies past the mailer program running at "eds". >My understanding is that the helium is such a small and energetic >gas that is will work through many materials, especially the rubber >orings that are in manifolds and seal the tank valve to the neck of >the tank. Strictly speaking, it is the *temperature* alone that determines the amount of energy packed into the motion of a gas molecule. This kinetic energy as it is called must equate 1/2 m v v, m being the mass of the molecule in question and v the speed. For a given temperature it follows that the lightweight He atom moves much faster and "probes" the boundary more often (and more thourough) than say a huge fat O2 molecule. Not only that, the absolute miniscule size of the He atom allows it to work it's way through many materiels normally thought of as having a "sealing" property. Lastly, the He atom doesn't waste time talking to the locals either as it makes it's way through say an o-ring because He is very inert. Hydrogen is even more "energetic" but is a bit bigger I think and also diffuses slower through most solids because it will form chemical bonds to the locals (even to metals). Someone said that He would make it through a plastic soda bottle. I've also read that many (large?) aromatic molecules (whatever that is) travels through plastic too. (This reminds me of the lie written on the synthetic thermal underwear I have: "Guranteed not to retain odor"). john cc015012@br*.br*.ed*
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