SPECTROPHOTOMETRIC STUDIES ON FERROUS COMPLEXES OF QUINOLINE- AND PYRIDINE-CARBOXYLIC ACIDS. PART II. FERROUS PICOLINATE SYSTEM

The strongly coloured, highly soluble ferrous complex with picolinic acid forms the subject matter of the present investigation in respect of its usefulness for the estimation of iron. The coloured complex has been found to develop its maximum colour intensity between pa 5.2 and 9. The presence of KCN, so also of pyridine to some extent, increases this colour intensity with an absorption maximum lying at about 440 mμ. The coloured system, with or without KCN, obeys Beer's law. The composition of the coloured complex is given by I FeII; 3 acid, with an instability constant 5.07 x 10-12 The complex thus acquires the character of a univalent anion