science experiment ideas

Today, as I returned from morning carpool, I wondered what was in my hand warmers?  So, the boys of 8-1 and I cut it open to see.  We all took a hypothesis that it should be a mineral or rock - it certainly felt like one.  Then, we watched it create warm air to expand over the beaker.  When we guessed that it could be iron, we tested it with a magnet - knowing that iron is magnetic. 

What do you think is in a hand warmer?