1. J. Valentin and G. Wagner, Pharm. Zentralhalle,91, 291 (1952).
2. B. Kakac and I. Vejdelek, in: Handbook of Colorimetry [in German], Vol. 1, Jena (1962), p. 354.
3. G. Nöll, Pharmazie,10, 609 (1955).
4. G. M. J. Barton and A. F. Gardner, Anal. Chem.,30, 279 (1958).
5. W. Olechnowicz-Stepien, Acta Polon. Pharm.,14, 33.