1. Z. G. Fratkin and N. G. Polivanova, Methods of Analysis of Chemical Reagents and Preparations [in Russian], Moscow (1966).
2. V. L. Ginzburg, N. P. Glukhovetskaya, and N. N. Danilov, Zh. Analit. Khim.,17, 1096 (1962)
3. E. V. Schreiber, Fres. Z. Anal. Chem.,210, 93 (1965).
4. M. Myunks, Zav. Lab.,34, 165 (1968).
5. Eug. Cruseanu, V. Bartos, and Gh. Mozes, VII Sesiune comun. tehnstiint. Sec. 4, Bucuresti (1970), p. 1.