1. F. Feigl, ?Qualitative Analysis by Spot Tests?, Elsevier Publishing Co. New York. 1946. p. 19.
2. Ibid., p. 18.
3. Ibid., p. 165.
4. Ibid., p. 134.
5. F. Feigl, ?Specific, Selective, and Sensitive Reactions?, Academic Press New York. 1949. p. 570.