George E. Cawthon wrote:
No it isn't. The volume of the cylinder is about
0.5 cubic foot, so the amount of gas that it
contains is ALWAYS 0.5 cubic foot; it doesn't make
any difference what the pressure is.

Within the cylinder, yes. But cylinders aren't sold according to their empty
volume; they're sold and rated according to the volume of gas they can hold at
their rated pressure.



Your 4th
sentence is also incorrect. At some pressure and
temperature you get liquid air which fills the
cylinder and at that point you can't put any more
air into cylinder since a liquid is only slightly
compressible.


OK, I'll give you that point. My bad. But I'll bet the tank will blow long
before the air liquifies. 3000 psi scuba cylinders will blow the safety disk at
around 4000 psi; get hydrotested at 5000 psi, and will catastrophically fail at
around 7500 psi. Will air liquify at 500 ATM? What gases would? I pulled out
my trusty old CRC Handbook of Chemistry and Physics but couldn't find the
information.


Your last point is also incorrect;
there was is no assumption about the pressure, and
it still matters not a whit since the cylinder
volume is 0.5 cubic feet so that is all the air it
can hold no matter what the pressure is as long as
it is gas.


But it can certainly be pressurized to hold much more gas than .5 cubic feet.
Otherwise there's no way in hell it can hold more than it holds at one
atmosphere.



--
Mortimer Schnerd, RN

VE