CO₂ for welding? But it doesn't burn. Actually that's the point, it's used to shield the arc from the oxygen in the air. The best gas to use is a mixture of Argon and CO2 but its really expensive compared to CO₂ which works fine. A 1 litre bottle of Argon mix at 60 x atmospheric pressure is equivalent to 60 litres when released. You work that out using the ideal gas equation which applies since the Argon doesn't liquify at that pressure, CO₂ does so you have to do a different calculation. One mole of gas occupies about 22 litres at atmospheric pressure and the molar mass of CO₂ is 44. The 5 kg contained in my tank contains about 114 moles which is about 2500 litres, 42 times more gas for twice as much money. The recommended flow rate is 10 litres per minute so that´s over 4 hours of continuous welding. Did someone mention greenhouse gas?