Karen, years ago, I bought a little bottle of silver testing
solution (JSP; #gt41) which is handy for identifying base metals. You
clean the metal first, then put a drop on it -- base metal will
produce a greenish foam, silver a creamy white. I assume that gold
might give results similar to silver. The solution seems to be some
sort of nasty acid -- don't get it on anything else. Another part of
the problem is that the wire might be gold-filled, in which case
filing a groove into the center of it would be good.
Another test method might be to rub a bit of wire known to be brass
on a matte black stone, then rub a streak of the unknown wire on the
same stone. Put a little dilute nitric acid on each one and compare
the rate of disappearance of the two streaks.
But probably others will have simpler ways of doing this!
All the best,