>Lee Bell wrote:
>Since we're divers, the
>correct question for us might be, "what is the effect on buoyancy, in
water,
>of a cubic foot of gas compressed to X psi/bar/whatever."  In case this is
>the real question, I'll give an approximate answer . . . very approximate.
>Note, this is not the only answer.  I usually figure my buoyancy changes
by
>about 5 lbs as my 80 cubic foot tank empties.  That's for a dive in salt
>water.  Mine buoyancy never actually changes by this much since my tank is
>never allowed to be completely empty.  Assuming, however, that 5lbs is
about
>right, then a cubic foot of gas, at 3,300 psi, is approximately 5/80 or
>about .06 lbs . . . I hope.

Or just check the specs of your tank if you dive something different than a
Alum 80.
The bouyancy difference from empty to full is the weight(mass) of the air
it takes to fill the tank. For obvious reasons you won't be going from full
to empty on a dive(I hope) but it still should give you an idea.

I like your point that "A cubic foot of air, at one ata, in air also at 1
ata "weighs" . . . nothing.  It's dead, absolute and comletely neutral.
The same cubic foot of air, at one ata, in water, weighs less than
nothing."