1. DIN 51719-A, Testing of solid fuels, determination of ash content (in German), 1978.
2. ASTM 271-68, Laboratory sampling and analysis of coal and coke, 1970.
3. ASTM D1857-68, Fusibility of coal and coke ash, 1970.
4. DIN 51730, Testing of solid fuels, determination of ash melting, 1984.
5. Fireside slagging, fouling, and high-temperature corrosion of heat-transfer surface due to impurities in steam-raising fuels