Subject: Electrolysis results

We are homeschoolers who tried to do an experiement 
to make hydrogen and oxygen out of water. We didn't 
have any gold nibs, so we just used copper wire 
attached to the battery. We also added salt to the 
water.  We got some hydrogen, but no oxygen.  The 
next day, the wire on the oxygen end was broken and 
there was a blue-green precipitate in the water.
What is it?
Thanks for your help.

Re: Electrolysis results