1. Asperen, K. van, and Oppenoorth, F. J., Chemisch Weekblad (in the press, 1954) (Dutch text only; publication in English will follow in due course).
2. Reith, J. F., Chemisch Weekblad, 49, 691 (1953). (Dutch text only).
3. Schechter, M. S., and Hornstein, I., Anal. Chem., 24, 544 (1952).