1. D. A. Detmar and W. Van der Velde, Analyt. China. Acta15, 173 (1956).
2. I. Bozsai, Acta Chim. Acad. Sci. Hung.9, 159 (1956).
3. B. Cristau, Ann. pharm. France16, 26 (1958).
4. J. Zyka and A. Berka, Microchem. J., Symp. Ser.2, 789 (1962).
5. N. H. Furman (ed.), Standard Methods of Chemical Analysis, 6th Ed., Vol. I., New York: Van Nostrand. 1961. p. 96.