This experiments demonstrates the dangers of flammable substances that have heavier-that-air vapours like ethoxyethane (diethyl ether) or petrol.
A length of guttering has one end raised and a lit flame is placed at the bottom end.
A small amount of ethoxyethane is poured at the top. After a short delay, the vapour ignites, having flowed down the guttering, and the flame shoots up the gutter in a spectacular fashion.
