1. US Patent No. 2 511 952.
2. US Patent No. 3 079 310.
3. US Patent No. 4 431 496.
4. N. Furuya and S. Motoo,J. Electroanal. Chem. 179 (1984) 297.
5. I. Iliev, S. Gamburtsev, A. Kaisheva, E. Vakanova, I. Mukhovski and E. Budevski,Dept. Chem., Bulg. Acad. Sci. 7 (1974) 223.