TheApple

For Halloween at school, I carefully carve a pumpkin with basic shapes for a face and set the pieces back in and the top on.  I then make a hole in the back and leave it where the students can not see it.  When the students are in their seats I dim the lights and tell them I am experimenting with a new carving technique.  I get the pumpkin and place it on my demo table or on a back lab bench.  It is important that no one is directly in front of it.  Hopefully they can't see it is precarved.  I often take out my "sheild of science", which is just 3 large pieces of clear plexiglass connected with piano hinges to stand and block any spatter.  Other supplies I have handy:  Tesla coil (for spark), calcium carbide (CaC2), and a tuna can with water in it.  With the students watching I tell the history of miners lamps and how CaC2 in water makes acetylene gas, the same gas used for welding, and at the same time I place the tuna can inside the pumpkin, drop in a 5 or 6 chips of CaC2, replace the lid.  It takes about 30 seconds to a minute to get the right air:gas ratio so I chat for a bit, keeping an eye on the clock.  I might explain how the Tesla coil makes a spark.  When I judge it is time I make sure I have their attention and I touch off the gas through the hole in the back.

What happens next is a wonderfully loud boom and a nice flash of light with all the pumpkin pieces flying out!  They love it!

sanmccarron says ...

For Halloween at school, I carefully carve a pumpkin with basic shapes for a face and set the pieces back in and the top on.  I then make a hole in the back and leave it where the students can not see it.  When the students are in their seats I dim the lights and tell them I am experimenting with a new carving technique.  I get the pumpkin and place it on my demo table or on a back lab bench.  It is important that no one is directly in front of it.  Hopefully they can't see it is precarved.  I often take out my "sheild of science", which is just 3 large pieces of clear plexiglass connected with piano hinges to stand and block any spatter.  Other supplies I have handy:  Tesla coil (for spark), calcium carbide (CaC2), and a tuna can with water in it.  With the students watching I tell the history of miners lamps and how CaC2 in water makes acetylene gas, the same gas used for welding, and at the same time I place the tuna can inside the pumpkin, drop in a 5 or 6 chips of CaC2, replace the lid.  It takes about 30 seconds to a minute to get the right air:gas ratio so I chat for a bit, keeping an eye on the clock.  I might explain how the Tesla coil makes a spark.  When I judge it is time I make sure I have their attention and I touch off the gas through the hole in the back.

What happens next is a wonderfully loud boom and a nice flash of light with all the pumpkin pieces flying out!  They love it!

It was a day of pumpkin "carvings"!  I am exhausted.  Watch for pictures to come. :) 

I also faked cutting myself- which I thought was pretty morbid but the students enjoyed:  I rubbed some ferric chloride on my arm ahead of time (with the lights out they don't notice the yellow tint), and dissolved some ammonium thiosulfate in a beaker of water.  In front of the students I dipped a dull knife in the water "to sterilize it" and dragged it across my arm.  A blood red color emerges.  LOL!