That was the perfect opportunity to teach the first step of The Scientific Method. The next step was the Hypothesis - what do you think will happen, based on the scientific knowledge you already have?

Then you have to Plan The Experiment, which in this case, would probably really energize the students' brain power. They'll LOVE figuring out this experiment. I would bet that EVERY student would be engaged in this one.

It's the Doing The Experiment that might be problematic, and end up with the teacher explaining themselves to the School Board: "All I can say is, it seemed like a good idea at the time. I guess you had to be there."