Use a graphite pencil to write a letter (or other small figure) on one side of a sugar cube.
Place the sugar cube into a glass of water. (A white cup works best for visibility. Or you could use a clear glass and place it on a piece of white paper).
Wait and watch.
The sugar will dissolve in the water, but the graphite from the pencil will not. As the sugar dissolves out from underneath the graphite, the graphite will float the top of the water.
If you're lucky (and I'm usually not) the graphite will stay together and you'll have your letter floating on the surface of the water. If it doesn't stay together, you'll just have small gray flecks floating on the surface (as seen above).