A New Indicator for lodometric Analysis

Abstract

IT is well known to analysts that starch is very far from being an ideal indicator for iodine, and the disadvantages from which it suffers are not all avoided by the use of an acid-solubilized starch. It will be agreed that the chief disadvantages attending the use of starch are : (1) the insolubility of starch in cold water ; (ii) the instability of starch dispersions in water, in consequence of which a stock solution soon deposits a flocculent precipitate of retrograded starch ; (iii) that starch gives with iodine a water-insoluble complex, the formation of which precludes the addition of the indicator early in the titration ; and (iv) the “drift” of end-point which is particularly marked when the solutions used are dilute.