I work at a hospital and I noticed that the oxygen cylinders are labelled as containing 630 litres of oxygen. (Yes yes, suuuper busy day at work) Similarly the flow rate out of the cylinder is set in L/min. This piqued my interest as I know a litre is a set volume, yet clearly the cylinder was not that large. So what is a litre in this case? …and why is it this way?
In: Physics
A liter is a liter of gas as normal atmospheric conditions (I believe the exact definition varies depending on where you are).
Volume measurements are nice because they don’t really care about what the gas is.
If I have a size “300” gas cylinder (aka size “T”) I know that stores 300 “standard” cubic feet of gas. That gas could be oxygen, nitrogen, methane, ammonia, air, forming gas, whatever. If I had to label everything based on mass then I would run into issues based on the fact that those gasses are all different densities and so a “full” cylinder of each would be a different mass.
You do see containers that are labeled based on mass, but these tend to be containers that are storing petroleum gasses, which tend to turn into a liquid at low pressures. If you’re American the classic example of this is probably the “20 pound” propane tank that gets used on propane grills.
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