I want to qualitatively test for the presence of oxygen within argon gas. I would like the test to be positive if approx $1\%$ or more is oxygen, but definitely negative if less than $0.1\%$. Anywhere in between is fine—A quantitative test is a bonus. I was thinking of heating iron filings in the gas to deduce it. I'm not sure what apparatus and setup I would need since heating gas expands, I would like to use ultra low tech equipment. I'm thinking of using water or cooking oil displacement to hold the extra gas, but I don't know if argon would dissolve, or how much oxygen would dissolve. Preferably a nonflammable, certainly nontoxic liquids (or tests).
This should do it