REACTION-INTENSITIES WITH EACH AGENT AND REAGENT. 



147 



of two different kinds of groups. The starch molecule 

 behaves as an amphoteric electrolyte, acting as an acid 

 or base in relation to the components of the reagents 

 to form different salts, the reactions being attended by 

 the splitting off of hydrogen or hydroxyl ions. All of 

 the reagents used in this research to gelatinize starch 

 are aqueous solutions of electrolytes or imperfect electro- 

 lytes, and hence each is partially ionized, the degree of 

 ionization varying with the different reagents ; more- 

 over, there is a variety of elements and molecules, acid 

 and base, that may enter into chemical combination with 

 the starch molecules. Hence it follows that each solu- 

 tion is a complex that consists of molecules of water and 

 solute, and of ions of water and of solute. Having now 

 a starch molecule that may assume either acid or basic 

 properties, and reagents that contain both water and 

 various kinds of elements and molecules that may enter 

 into chemical combination with the starch to form salts, 

 it is obvious that the phenomena of gelatinization or 

 swelling, quantitatively and qualitatively, may vary more 

 or less markedly in accordance with the chemical reac- 

 tions that occur coincidently with the adsorption of 

 water. An examination of the list of reagents used in 

 this research will show that there are well-defined classi- 

 fications or groupings in accordance with peculiarities 

 of the substances entering into the reagents as the 

 solutes, as, for instance, organic acid, inorganic acids, 

 potassium salts, sodium salts, hydroxides, sulphides, ni- 

 trates, chlorides, etc. Not only are variations to be 

 expected in the reactions because of differences in the 

 composition of these reagents, but also because of differ- 

 ences in the molecular arrangements of the starch mole- 

 cules. If the starches from different plant soiirces exist 

 in different stereoisomeric forms, it seems upon the basis 

 of our knowledge of the peculiarities of stereoisomcrs 

 in general that variations in the reactions that are due 

 to this peculiarity may be as great or even greater than 

 those due to differences in the reagents that is, that 

 variations in the reactions of different starches with a 

 given reagent may be as marked or more marked than 

 those in the case of a single starch with different rpa- 

 gents. This has been found to be a fact by the results 

 of this research. 



In the study of the phenomena of gelatinization that 

 are definitely associated with peculiariti^ of the rea- 

 gents the object has been to demonstrate differences in 

 the behavior of different reagents without reference to 

 the cause of these differences, except as they go to prove 

 the existence of starch in stereoisomeric forms that are 

 modified in specific relationship to the plant source. 

 Obviously, there would be many advantages in a com- 

 bined study of both gross phenomena of gelatinization 

 and reactions that occur during and subsequent to gela- 

 tinization, and much is to be gained by the use of reagents 

 in equimolecular solutions; but certain unavoidable con- 

 ditions attending this research made it necessary to 

 pursue the studies of the actions of reagents with refer- 

 ence to effect and without more than incidental reference 

 to cause. 



It will be recognized, from what has been stated, that 

 the reactions are conditioned by both starch and rea- 

 gent. Having a number of starches of presumably dif- 

 ferent stereoisomeric forms, there remained the selection 



of the kind and concentration of reagents that would 

 elicit such differences in the reactions as would demon- 

 strate clearly not only isomerism but an isomerism that 

 is specific in relation to genera, species, varieties and 

 hybrids. It was found advantageous, in formulating 

 these solutions, to disregard entirely concentrations upon 

 the gram-molecular basis and to determine experimen- 

 tally the strengths of solution that seemed best adapted 

 to give wide ranges of reaction with different starches 

 under the same conditions of experiment. The marked 

 variations in the behavior of different starches with a 

 given reagent, and of different reagents with a given 

 starch, are presented in striking form in Charts A 1 

 to A 26 ; but these features are brought out even better 

 in certain respects in Charts E 1 to E 46, and very much 

 better in most respects in Charts B 1 to B 42. The first 

 group of charts has been considered in a previous sub- 

 section of this chapter ; the second group will be taken 

 up in a subsequent subsection; and the third group will 

 here be studied in only sufficient detail to meet 

 requirements. 



In the construction of the group of charts designated 

 B 1 to B 42 the main purpose was to bring out certain 

 extraordinary peculiarities in the reactions of selected 

 pairs (occasionally more) of reagents with a number 

 of starches which are taken tentatively to be representa- 

 tive of genera and of subgeneric divisions. In the selec- 

 tion of the reagents for comparison it seemed that 

 characteristics peculiar to each of the several reagents 

 could be presented particularly well if in one group of 

 this series of charts the reactions of a given reagent are 

 taken as the standard of comparison with the reactions 

 of each of the other 25 agents and reagents ; and if in 

 a second group we compare the reactions of certain two 

 or more agents or reagents, selected because of certain 

 peculiarities, such as similarity or dissimilarity of agent 

 and reagent, this plan was carried out. In th<^ first 

 series the reactions of nitric acid are taken as the stand- 

 ard ; and in the second series the reactions of anilines, 

 inorganic acids, hydroxides, sulphides, etc., various com- 

 binations of two or more agents and reagents were made. 



To reiterate, there is in the polarization reaction? 

 no molecular alteration of the starch molecule ; color 

 reactions are present with gentian violet and safranin 

 which are attributable to adsorption without detectable 

 attendant molecular disorganization ; in the iodine reac- 

 tions there is in all probability a union of iodine and 

 starch to form an unstable iodide of starch, but no 

 intermolecular breaking down ; in the temperature reac- 

 tions intermolecular disorganization is associated with 

 the adsorption of water, but without the loss of properties 

 that characterize the starch molecule ; and in the chemi- 

 cal-reagent reactions not only intermolecular disorgan- 

 ization occurs, but various associated reactions that 

 depend upon the acid or base character and particular 

 elements and molecules of the reagents. From this it 

 would follow that these reactions fall into well-defined 

 groups: the polarization, aniline, iodine, temperature, 

 and chemical-reagent reactions, respectively. 



When the reaction-intensities with polarization, gen- 

 tian violet, safranin, iodine, and temperature are plotted 

 out in curves, as in Chart B 1, and the chemical -reagent 

 reaction-intensities are plotted out, as in Charts B 2 to 



