1. J. Timmermann andF. Burriel, Chim. Ind., 25 (1931) 196.
2. L. Kofler, Mikrochem., 15 (1934) 242.
3. B. Oehrner, Pharm. Ztg., 108 (1963) 374.
4. H.Bervenmark, N. A.Diding and B.Oehrner, Bericht WHO, Pharm., 391.
5. V. G. Colarusso andM. A. Semon, Anal. Chem., 40 (1968) 1521.