THE INTERACTION OF IODINE AND STARCH. PART I

Titrations of solutions of amylase, potato starch and shoti starch with iodine have been carried out using a potentiometer and a photo-electric colorimeter respectively, for measuring the iodine activities and the intensities of colour, at different concentrations of starch and iodine and in the presence of diff­erent concentrations of potassium iodide. It has been shown that the photo-colorimetric titration can be used as a method for estimating the amylose contents of starches. The shapes of these titration curves are altered by changes in the concentrations of the reactants and of potassium iodide,

The iodine-complexes of starch and amylase have been precipitated from solution in the presence of different concentrations of iodine, potassium iodide and sodium chloride, washed with solutions of sodium chloride and sodium sulphate, and finally analysed for determining the starch-iodine ratio. This ratio has been found to remain practically unchanged in all these oases, the actual values ranging between 3.6 and 4.0 glucose units per atom of iodine. The significance of the results has been discussed and the formation of a chemical compound of starch and iodine in the precipitated complex has been suggested.