1. British Standarts Test Institution, 1904–1952, Brit. Standart Specification.
2. GOST 6651-59 USSR Committee of Standards.
3. British Standart Specification B.S. 1904–1964.
4. Gmelins Handbuch, Verlag Chemie, Weinheim 1957.
5. Černý M., Měrová technika 4 (1956), 37 (in Czech).