1. C. P. Stewart andA. Stolman, ?Toxicology, Mechanism and Analytical Methods? (Academic Press, New York, 1960) p. 202.
2. Satya Prakash, ?Advanced Chemistry of Rare Elements? (S. Chand & Co Ltd, Delhi, 1975) pp. 565.
3. Madhu Phull andP. C. Nigam,Ind. J. Chem. Ed. 8 (1981) 22.
4. W. F. Neuman andM. W. Neuman,Chem. Rev. 53 (1953) 1.
5. A. S. Posner, ?Phosphorus and its Compounds?, Vol. II, edited by J. R. van Wazer, (Interscience, New York, 1961) pp. 1429?59.