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Let me clear up a few misconceptions in response to the first poster
below, John:

1) The effusion of a gas across a boundary is strictly dependent
on the inverse of the square root of its molecular (or atomic) mass,
and NOT upon it being monatomic or polyatomic.  As an example, argon
(mass 40, monatomic) will actually effuse at a LOWER rate than nitrogen
(mass 28, polyatomic).

2) The thermal conductivity is an intensive property which is species
dependent, and NOT associated with its being monatomic.  For example,
the thermal conductivity of helium (monatomic, mass 4) is about 10 times
that of Argon (monatomic, mass 40), yet 1/10th that of Krypton
(monatomic, mass 84).

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Original message:

From: John Poco
Subject: Noble gases
Date: Tue, 22 Aug 2000 08:13:38 -0700

>> Since I make a living doing things with chemicals I will shed some
>> light on the gas issue.  In reality if you wanted a more optimum fill
>> gas argon would actually be a better choice from the standpoint of
>> heat transfer (its heat transfer is at least twice that of nitrogen
>> or air)-hence its use in some of the newer double pane windows...
>> Unfortunately argon and its cousins are monatomic (one atom) and
>> their diffusion through membranes (tires, o-rings, etc.) is fairly
>> rapid, relatively speaking.  Its also a little more expensive and
>> harder to find.  Nitrogen is of course diatomic and a larger molecule
>> that behaves mostly like air except without the oxidative
>> qualities-causes other materials to decay faster..I hope this has put
>> to rest the gas issue...

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