# Is my CO2 in liquid form in a mixed gas cylinder?

I recently acquired a 5-liter mixed gas cylinder that has 70% nitrogen and 30% carbon dioxide, used for dispensing beer. The cylinder pressure is 200 bar (2900 PSI) and my room temperature is around 20C to 22C (68F to 72F).

I've started to wonder whether the gas ratio can be disturbed by the CO2 changing its thermodynamic state due to room temperature fluctuations. Given the parameters, should I expect the CO2 to be in gaseous or liquid form?

• To a first approximation, it seems the carbon dioxide is near its liquid/gas equilibrium curve, though it's hard to be precise because the ideal gas approximation probably isn't very good in these conditions. If any of it is liquid, then yeah the ratio is going to be affected. If you gently swirl/rock the cylinder, can you detect any sloshing? Commented Oct 27, 2023 at 10:54
• Without particular gas data it is hard to say the gas condition. For illustration: Nitrous gas N2O has comparable critical temperature as CO2. While it is liquid at room T at 100 bar, the mixture 1:1 (V/V) with oxygen is at 200 bar gaseous. Commented Oct 27, 2023 at 11:29
• I can only assume that the store that sold you the tank knows what they are doing and that it will work for the intended purpose. So use it and don't worry.
– MaxW
Commented Oct 27, 2023 at 12:26