Giant salt granules......I should have read the description

I picked up a great tip years ago, either on here or "ahem" another technicians forum. For the diffusion demo, forget crystals - just use a small bit of blue tack to pick up some of the powder & drop that into the flask. I also gave up on feeding the pot.permang down a tube at the same time - just drop it straight into the flask - the few little streamers that it leaves as it sinks are nothing compared to the real convection streams.
I like it! You could put that on Top Tips!
we use potassium permanganate coarse crystals for the cannon fire demo (ethanol, H2O2, coarse KMnO4).
Getting to the end of the supply and I have been looking for similar but seeing nothing.
Haven't tried it with powder so I don't know what difference it makes when it presumably runs faster.
Guess I have to stop looking and make some crystals!

Does your school have detention, with pupils sitting in silence doing work? A bit of rock pounding might be a good deterrent and get rid of some of that excess energy that makes them cause trouble!