Recently, I posted about having received Gever Tulley's book Fifty Dangerous Things (You Should Let Your Children Do) as a gift from Max, and mentioned the plan to spend our summer session giving as many of those things a go as feasible in preschool.
At the end of the day, we still had a half gallon of vinegar remaining, along with quite a bit of baking soda, so yesterday I turned the materials over to Dennis, Vivian, and George's dad Terry, along with one-gallon zip-lock bags. I wasn't a witness, but I heard from across the outdoor classroom, first the squeals of anticipation then the cheering, with each giant explosion.
We threw spears, we tried licking 9-volt batteries, we broke glass, set out to master the perfect somersault, hammered nails, and threw rocks. This time we made a bomb in a bag.
Now, with all due respect to Mr. Tulley, the children of Woodland Park feel that they have devised a superior "bomb in a bag" technique, one that perhaps does not create as large an explosion, but really delivers when it comes to building suspense.
The basic idea of both types of bag-bombs is to combine baking soda and vinegar in a zip-lock style plastic bag, then let the pressure that builds from the chemical reaction burst the bag open with an explosive Pop!. Since the baking soda and vinegar react with one another instantly, the challenge is getting the bag sealed before the reaction loses too much of its energy. The book's version of the experiment involves wrapping the baking soda in a square of paper towel, adding the vinegar to the bag, then keeping the two compounds segregated while closing the bag. I've tried it. It does buy you time to get the bag sealed and makes for a wonderful explosion.
Our version was the kind of happy accident that comes from letting kids mess around with various liquids and powders. If you want to read the full story of our how we learned to make a bomb in a bag last summer, click here, but in a nutshell we combined baking soda with dish soap, then added vinegar. The soap, we found, replaces the paper towel, acting as a retardant, slowing down the chemical reaction enough that one can get the bag sealed in time. In this kind of bag-bomb the pressure builds more slowly as does our anticipation as we stand around in a semi-circle giggling in suspense.
Sealing a zip-lock baggie isn't a skill many preschoolers have mastered even under the most sedate of circumstances, so that was a job left to me, which explains why I don't have any photos from this year's efforts -- my hands were too busy. The ones you see here are from last summer.
We started by carefully placing our bombs on the ground, tables, or other surfaces, but as we became more comfortable with them, many of the kids opted to hold their bombs, feeling with their hands as the pressure first builds, then releases with the explosion.
After a couple dozen explosions, Thomas had the idea to try burying one in the sand pit. It was a memory, I think, from last summer when we tried the same thing to little effect. We dug a hole, created a bomb on the spot, then quickly buried it. I hadn't expected much, but the sudsy liquid spouted through the sand a good 8-inches into the air, "like a volcano."
(In all honesty, I'm not sure that our version of the bag-bomb is objectively superior in any way, other than having been invented by us. But then again, that's everything, right?)