Ian Stirling wrote in message ...
N. Thornton wrote:

CO2 is almost as good (or slightly better, I can't remember) than Argon.

Heat conduction in a gas is dependant on the molecular weight.
N2 is 18, O2 is 16, and CO2 is 48.
I think Ar is 45, though I'm pulling that from dodgy memory.

I suspect argon is used instead of CO2, as CO2 may react slowly with
the aluminium along with trace moisture.

Butane would be even better, with a molecular weight of 58, but has
some obvious problems

You could fairly easily get the air dry enough.
Take a large block of ice, thread some tubing through it, put it in
the freezer, then blow air (slowly) through the tubing.
Most of the moisture will freeze out on the walls.
Good enough for double glazing anyway.

interesting. Butane sounds good too, theres no mechanism to spark it
inside dg, and if it leaks the concentration and amount are going to
be non problems.


NT