I got a torch set from Craigslist for pretty cheap money. It came with a cart and a bottle of gas. The guy is real sure it's O2, but the label had CO2 and Argon, with the percentages faded totally away. And the fitting is not the "normal" O2 fitting, but seems to match that of CO2 bottles.
The gas itself has no smell at all. And I held a lit match in front while I just let a little gas squirt out. I would have expected O2 to have fired that match right up, but it just put it out.
I was hoping it was O2, as that would have saved me from buying a bottle. But even without it, the cart, regulators, hose, torch, and tools is worth what I paid.
So is there any way to tell what's in there? I'd like to sell it, but I think "mystery gas" wouldn't get a lot of takers.