1. Mellor's Modern Inorganic Chemistry;PARKES,1941
2. Systematic Inorganic Chemistry;YOST,1946
3. DUECKER, W. W. and WEST, J. R., The Manufacture of Sulfuric Acid, Reinhold, A.C.S. Monograph No. 144, 1959.
4. Compagnie de Saint-Gobain, French Patent 1309232, 16 November, 1961.