Studies on the Starch-iodine Reaction

The usefulness of the radiomicrometer in the study of reactions involving a marked color change was indicated in a previous paper (1). It was there shown that the starch-iodine reaction could be investigated in this way. The present paper reports further observations on the reaction, which bear upon the problem of the chemical specificity of some starches and upon the nature of starch-iodide. There exists a very extensive literature on the specificity of starches, much of which is noted in the exhaustive monograph of Reichert (2). The histological findings indicate that starch grains of any given plant have certain common characteristics, more or less distinctive of the family, genus, species, etc. With regard to chemical specificity, matters are more unsettled. Differences in staining behavior, viscosity or plasticity, temperature range of gelatinization, etc., may be due to dissimilar physical states rather than to variations in chemical constitution. Elementary analysis has not evidenced differences between starches (2). Further, Ling and Nanji (3) have shown that the amylose : amylopectin ratio is practically constant in starches which do not contain hemicelluloses (4), while when hemicelluloses do occur, the hemicellulose content is much affected by the history of the preparation (5). The starch-iodine reaction affords still another means of approach to the problem of the chemical specificity of starches. Since its discovery by Colin and de Claubry (6) in the laboratory of Gay-Lussac, this reaction has been the subject of numerous investigations. The blue color was regarded as specific from the time of Stromeyer (7), until Claude Bernard showed that an abnormal glycogen may be formed in paralyzed muscles which will