The sugar cube page
The burning sugar cube trick
Place a sugar cube on a fireproof surface (an ashtray, for example). Challenge your mark to set it on fire using a match. They won't be able to do it. When they give up in frustration, rub some fine ash onto the cube, then set it on fire. It will burn with a nice blue flame. Your mark may object, and say that it is the ash burning. You reply that it is indeed the sugar burning; the ash acts as a catalyst and is not burned.
Fasten a sugar cube in a wire loop, which serves as a handle. Apply ash to one corner. Hold the corner in a candle flame until it starts to burn, then remove it. The cube will drip a sticky black liquid containing carbon (make sure you have a dish for this to drip on to), and at the same time will shoot out tiny rings of smoke.
The floating sugar cube trick
You can make a "trick" sugar cube that will sink in a cup of hot liquid, then float without dissolving. You will need some collodion, which, conveniently enough, is the main ingredient of New Skin, which is used to cover blisters. Pour some New Skin in a small cup. Dunk the sugar cube in the New Skin, making certain that it is completely immersed, and hold it there for 20-30 seconds. It is easiest to do this using tweezers. Remove it and set it aside to dry for one full day.
The collodion has covered all of the sugar crystals. When the cube is dropped into hot water (or tea), eventually the sugar melts, leaving the collodion "skeleton" behind, which floats. Do not, of course, eat the collodion treated cube.