1. F. Kopfer, Z. analyt. Chern.17, 26 (1878).
2. A. Dombrowski, Mikrochem.28, 136 (1940).
3. S. J. Clark, Quantitative Methods of Organic Microanalysis. London: Butterworths. 1956. p. 73.
4. A. M. G. Macdonald, Ind. Chemist35, 193 (1959).
5. G. Pippel andS. Römer, Chem. Techn.15, 36 (1963).