ARTIFICIAL graphite for use in graphite-moderated nuclear reactors, as anodes for mercury vapour rectifiers, and crucibles for vacuum fusion work should contain little gas. Otherwise, when the graphite is heated to operating temperatures, the gas is desorbed, resulting in adverse effects. For example, in the graphite-moderated nuclear reactor, hydrogen and carbon monoxide released from the graphite can interact with the fuel-cladding material (usually zirconium or stainless steel), resulting in hardening and embrittlement of the metal. Released carbon monoxide can disproportionate on cooler metal heat-exchanger surfaces depositing carbon, resulting in an adverse effect on the heat-transfer and flow properties of the system.