The teacher would assign some of the better students (I was a weird kid; I got good grades in sciences, I was also a jock (a rather good wrestler), and I also ran with an outlaw motorcycle club. Hard to classify) demonstrations to set up and run for the class. My project was a chlorine generator to be run under the suction hood. I played with the reagents they gave me, and increased the amount of chemicals I was using until I got a gas clearly visible from across the room. No problem except I ran out of reagents. The father of a friend of mine was a chem professor at Case (local to me) and got me in to appropriate some replacement supplies. They were apparently more concentrated or more pure, because when I ran the demo, the huge clout escaped the hood and they evacuated the entire science wing of the school. Fortunately there were no injuries or repercussions.