Zone melting is a method of removing impurities from solid materials that are used in industry and in research. Germanium metal was the first material to be refined commercially using this procedure. Germanium can be purified by zone melting until it contains only 1 atom of an impurity in every 10 billion atoms. If a boxcar of sugar were this pure, it would contain only one grain of impurity. Extremely pure germanium and other substances are used in making semiconductor electronic devices, such as transistors and integrated circuits.