Here is a picture from an old copy of The Science and Practice of Welding by Davies.
Might give you some ideas of a propane bottle conversion.
Durham is far enough away from Cheshire I wont hear the banghttp://www.mig-welding.co.uk/forum/images/icons/icon10.gif
I seem to remember that the by-product is an 'orrible black sludge that has to be cleaned out and disposed of as well. Used to get it from the headlamps on my first car!!W/A