1. D. I. Mendeleev. Fundamentals of Chemistry. State Chem. Press, 1947. p. 484. E. V. Britske and N. E. Pestev, Thermal Preparation of Phosphoric Acid and Concentrated Phosphates, Trans, Fertilizer Research Inst. No. 59. 1929.
2. V. I. Ipatyev and V. I. Nikokev, Ber., 61, 630 (1928);V. I. Ipatyev. A. A. Vvedensky. and A. V; Frost, - I- Gen. Chem. 632 (1931).
3. J. Berthaud, Comptes rend., 143, 1166 (1906).
4. J. B. Senderens, Bull., [4], 1, 687 (1907).