Germanium is a shiny grey-white solid. It has a density of 5.323 g/cm and is hard and brittle. It is mostly unreactive at room temperature but is slowly attacked by hot concentrated sulfuric or nitric acid. Germanium also reacts with molten caustic soda to yield sodium germanate Na 2 GeO 3 and hydrogen gas. It melts at 938 °C. Germanium is a semiconductor with an electrical conductivity of around 2 × 10 S•cm and a band gap of 0.67 eV. Liquid germanium is a metallic conductor, with an electrical conductivity similar to that of liquid mercury.