160 



REACTION-INTENSITIES OF STARCHES. 



that almost any kind of reagent in aqueous solution 

 may react with starch in this way. lu fact, however, it 

 is rather surprising to find how few reagents outside 

 of certain well-defined groups are effective. It is also 

 to be noted that there are various substances which while 

 in any concentration in aqueous solution may be prac- 

 tically or absolutely inactive as a gelatinizing agent at 

 room temperature may aid or hinder the gelatinizing 

 effect of heat, as is evident by their property of lower- 

 ing or raising the temperature of gelatinization (page 

 146). As a corollary, there may be found two reagents, 

 each of which when alone is active, that may be inactive 

 when associated in solution, as, for instance, solutions 

 of potassium hydroxide and nitric acid, both of which 

 are active when in separate solution, but inactive in the 

 form of potassium nitrate; and that a gelatinizing rea- 

 gent may be rendered less active or even inert by the 

 presence of another reagent, as, for instance, the presence 

 of alcohol, glycerine, or sodium chloride in concentration. 



In the selection of the reagents used in this research 

 a very large number of most varied kinds, electrolytes and 

 non-electrolytes, and in various concentrations, were 

 tried, the number aggregating probably 200 ; but un- 

 fortunately only a partial list was preserved. One of the 

 difficulties met with in making this selection and in 

 determining the concentration was in the wide differ- 

 ences in the behavior of different starches that could 

 not be foretold excepting to a very limited degree. That 

 is, if a given reagent in any concentration was found 

 to be useless when tested with a given starch it could 

 not be set aside because it might be found to be not only 

 active but even extremely active with another starch. 

 It was also found that there are certain starches that have 

 a high to very high reactivity; others low to very low 

 reactivity, and others high to moderate reactivity with a 

 given reagent in given concentration. Thus, with a 

 given reagent while the starches of Lilium tend to high 

 to very high reactivity, those of Hippeastrum and 

 Hcemanthus tend mostly to low or very low reactivity, 

 and those of the Irids mostly to intermediate gradation 

 or moderate reactivities. It was also found that certain 

 reagents are with all starches very strong gelatinizers, 

 while others, in any concentration, tend to be relatively 

 feeble; and still others that represent intermediate gra- 

 dations. The reactions with sulphuric acid and sodium 

 salicylate are mostly high to very high ; those of chromic 

 acid mostly moderate to high; those of barium chloride 

 mostly low to very low; those of pyrogallic and nitric 

 acids widely variable with different starches, etc. 



It is obvious, in so far as values of individual rea- 

 gents are concerned, that it must be recognized that 

 the most useful in the differentiation starches are those 

 whose activities show the most marked differences with 

 different starches or, in other words, which show the 

 widest and most numerous fluctuations of the reaction- 

 intensity curves, as is instanced in the records of pyro- 

 gallic acid and nitric acid; that the fast-reacting 

 ivnu'cnts are of especial value in the differentiation of 

 the slow to very slow reacting starches ; and that the 

 slow-reacting reagents are similarly valuable in relation 

 to the rapidly reacting starches. A selection of the rea- 

 gents on this basis is manifestly necessary where starches 

 of diverse character are to be studied. In the testing of 



the various reagents to determine their values it was 

 found in practice desirable to make at the outstart very 

 concentrated solutions, using in the case of acids and 

 bases generally approximately 50 per, cent solutions, and 

 of salts approximately saturated solutions, and then 

 modify the concentrations in the direction the intensity 

 of the reaction indicates. It was also found of advan- 

 tage to use for the first test a form of starch that is 

 classed among the readily gelatinized and readily ob- 

 tainable, such as that of Lilium candidum, and then make 

 the final tests with this starch and with others which 

 are classed among those having mostly a high, moderate, 

 low, and very low reactivity, respectively. In this way 

 reagents were selected which in kind and concentration 

 have served admirably, although by no means perfectly, 

 in eliciting peculiarities of the various starches here 

 studied. 



The following very incomplete list of the reagents and 

 their effects shown by the starch of Lilium candidum, 

 may be of advantage to subsequent investigators : 



