You have to buy or rent a bottle and the gas itself isn't exactly cheap. CO2 fire extinguishers
however can be had for next to nothing at a junk yard. Just make sure there's still some
in it. You will now be MAG welding which works fine for regular steels, but not for
aluminium. You will need to make some slight modification to the connection of your
gauge to get it to thread on to the CO2 extinguisher.
