Powdered sulfur and iron filings are mixed together. What physical property could you use to separate them?

Magnetism - the filing would be attracted to a magnet, the sulfur would not.

You could also use melting point. Sulfur will melt at 115.21 °C, (239.38 °F) while iron won't melt until 1538 °C (​2800 °F). Of course once it melts you wouldn't have powdered sulfur any more - you'd have liquid sulfur.