Heh heh. The great thing about it is that although there's some danger of fire the powder burns so quickly that it's unlikely to catch anything else on fire. It used to be the standard theatrical fireball medium for appearances of genies, disappearances of wizards, etc.
Of course, I wouldn't be able to say from personal experience that a vegetable duster full blown across an alcohol lamp gives a MUCH more impressive fireball.
Of course not. (Of course it was cheaper then and you could buy it in 3 pound bags instead of those dinky little half pint bottles . . . )
Thats what I liked about NI3. Plenty of concussion, but no flames. Besides, if you're caught with it, the average middle school history teacher wouldn't have the slightest idea that some nasty looking purple goop in a jar could cause any mayhem....until it dries.