Performer displays an empty tube the audience can see right through, and a clear glass, full of sugar. Explain that you have a glass of sugar which is easily made into candy by putting it in the dark for an instant. Cover glass with the tube for an instant, then lift it away, and glass appears full with candy.
The apparatus can also be used with liquids, or other items. You can show the glass full of milk then make the milk vanish, or change to sweets.
Or for a bar act, show the glass full of tobacco, look around and remark that nobody seems to have brought his pipe, so there is no use offering them loose tobacco. Being a magician you can fix that, whereby you cover the glass, then lift the tube, and you have a glass of cigarettes which are at once passed out.
A useful piece of apparatus, specially for the kid show performer, easy to do, and very reasonably priced.