My 5th/6th year chemistry teacher used to be very useful - if he saw us doing something incorrectly he would always try and teach us how todo it properly.

So...trying to blow the doors off cupboards led to gas containment devices and fuses/igniters, a small experiment with sodium led to a demonstration of the reactive combination of potassium and sulphuric acid which demolished the safety glass which was supposed to protect the class.

I seem to remember him letting us play with Mercury as well - but this was the Eighties and they didn't seem to be too worried about us back then

Having relatives with easy access to industrial solvents and chemicals makes for good barbecue lighting, although I have yet to try the classic liquid oxygen method.