1. C.S. Smith, Trans. A.I.M.E. (Metal Division) 137 (1940) 236.
2. F.H. Hayes, UMIST, Manchester, UK, personal communication.
3. L. Erdey, F. Paulik and J. Paulik, Hungarian Patent No. 152197, registered 31 October 1962, published 1 December 1965.
4. J. Rouquerol, Thesis, Faculty of Sciences of Paris University, 19 November 1964 (Série A, No. 4348, No. d’ordre 5199).
5. J. Rouquerol, Bull. Soc. Chim. Fr. (1964) 31.