Magic Disappearing Ink - How could we NOT include this classic in the Pocket Money Section? I remember playing this joke on my mum when I was a (very annoying) wee nipper - she didn't find it funny (and I missed out on my post-tea Trio biscuit that day), but it still tickles me when I think of it.
Here's how it works: pour a little of the ink onto white fabric, a shirt or a tablecloth. A good one is dad's shirt just before he goes to work (!). After a short while it will miraculously disappear! A great way to wreak havoc on a dull Monday morning!
(WARNING! Alkaline substance. Use only as directed. Keep away from children. Do not put in eyes or mouth. Do not drink.)
Water, Thymolphthalein, Sodium Hydroxide .