These images show the world’s smallest test tubes, each .00004 inch long, .0000002 inch in diameter, and filled with silver particles. About five years ago, chemists discovered that sheets of carbon molecules can curl up on themselves and form tubes. Walter de Heer, a physicist at the Georgia Institute of Technology, packed some of these tubes with silver nitrate. He then bombarded them with electrons. The heat generated caused the silver to separate from the nitrate; some of the nitrate then escaped the tubes as gas. This is the first time such carbon tubes have been used to carry out a chemical reaction. Although there is no immediate practical application, De Heer says the tubes might one day provide an easy way to make atomic-scale wires for use in micromachines.