I've got some of the stuff Pete's talking about.
Around ten years ago a magician came to Edinburgh for the Fringe, and he was using this as a crowd stopper for his street show. He gave me a supply in return for teaching him the muscle pass - he told me to store it in two separate film cannisters and keep them apart.
The idea is to take a _very_ small amount of each powder and mix them _very_ carefully on a flat surface. Dab your fingertip in the powder, and if you snap your fingers there is a large bang, a puff of smoke and, depending on how much you had on your finger, a degree of pain and first degree burning. Also, it discolours your finger and thumb tips with a lovely purple stain.
One day I met up with him and he told me that he had dropped his briefcase and it exploded - the outside of the case survived but the insides, and most of his props, were purple toast.
I haven't tried the stuff for about nine years now - the cannisters are in my box - and I'm not sure how stable they are. Perhaps I'll mix up a bit and drop a stone of it to test...
Take care, Ian