1. Welcher, F. J., Organic Analytical Reagents, 4, 159 (D. Van Nostrand, New York, 1948).
2. Fiegl, F., and Caldas, A., Anal. Chem., 23, 8 (1951).
3. The Analysis of Titanium and its Alloys, 47 (Imperial Chemical Industries, Ltd., London, 1959).
4. Swank, H. W., and Mellon, M. G., Indust. Eng. Chem., Anal. Ed., 10, 7 (1938).
5. Sandell, E. B., Colorimetric Determination of Traces of Metals, second ed., 364 (Interscience, 1950).