Dissolve a few turnings of your alloy in HNO3 (or KNO3 + hot 50% H2SO4 if no HNO3 is available), dilute with dH2O, filter from the undissolved SnO2
and add dilute H2SO4 (or another solution containing sulfate ions) to the filtrate. Lead produces a white precipitate.
If quite a lot of lead is present, it will also make a precipitate of PbCl2 with chloride solution. |