Question

What chemical test do you use to distinguish between iron and iron sulphide (axcept using a magnet)?

Answer 1

One of the standard tests for arsenic in water is to apply ferric sulfide, if arsenic is there in any form, a reaction between arsenic and the sulfide will yield a bright yellow arsenic sulfide compound. So you could do the opposite, try to react an arsenic compound (aresnate will do) with the iron or iron sulphide. If the sulfide is present, you will get a bright yellow compound.
Magnets are easier.