Chemistry teacher Neil Dixon showed that science in classroom doesn't have to be boring:
In the experiment illustrated below, pupils at South Bromsgrove Community High School, Worcestershire are shown how the reactivity of a substance is related to its surface area. A material in powder form exposes much more of its surface to the air; as a result, normally inert substances can become highly reactive. Milk is scarcely combustible when it comes out of a cow, but if dried and powdered it becomes highly inflammable - as the images show.
'It is an intriguing experiment,' says Dixon. 'You have a flame near the ground. Then you sprinkle the powdered milk over it. Then the milk ignites. You can create a fireball several metres high. The point is to show that storing powdered materials on a large scale, or letting dust build up in a storage facility, can be risky.
--TwoDragons