

168 



REACTION-INTENSITIES OF STARCHES. 



(6) Another form is an inversion of the latter, gela- 

 tinization proceeding very slowly at first and then in- 

 creasing with additional increments of time. Such 

 curves are illustrated in the reactions of Brunsdonna 

 sanderce alba with uranium nitrate (Chart D 15), of 

 Hippeastrum pyrrha with nitric acid (Chart D46), of 

 Crinum kircape with strontium nitrate (Chart D 163), 

 and of Nerine sarniensis var. corusca major and N. 

 giantess with potassium sulphocyanate (Chart D219). 

 In this form there is a tendency to a continuously in- 

 creasing increment of starch gelatinized with increasing 

 increments of time. 



(c) A third form, and one that is frequently ob- 

 served, shows reactions that begin relatively or absolutely 

 slowly, followed by progressively increasing reaction, and 

 this in turn by progressively decreasing reaction, with 

 additional increments of time, thus giving a curve that 

 approximates the form of the letter /. Such a curve is 

 typified in the reactions of all f our starches of the Amaryl- 

 lis-Brunsvigia-Brunsdonna group with chloral hydrate 

 (Chart D 1), and in one or more of these starches with 

 chromic acid, pyrogallic acid, potassium iodide, calcium 

 nitrate, and copper nitrate (Charts D 2, D 8, I) 14, and 

 D 18). This curve is a modification of the first form 

 of the circumlinear type, the modification being brought 

 about chiefly by a relatively marked early resistance of 

 the grains to the reagent. The duration of the period 

 and the degree of resistance are very variable. In some 

 instances there is merely a suggestion of resistance ; and 

 in others resistance is very marked in both degree and 

 duration ; and in others various intermediate gradations 

 and variations. Thus, in the reactions of Amaryllis 

 belladonna and Brunsvigia Josephines with cobalt nitrate 

 (Chart D 17) there is only slight evidence of this early 

 resistance, while in the Brunsdonna sanderce alba and 

 B. sanderce reactions the resistance is very marked (Chart 

 D 2), in the latter instance there being only 3 and 1 per 

 cent respectively of the total starch gelatinized in 5 min- 

 utes; while 77 and 79 per cent, respectively, was gela- 

 tinized during the succeeding 10 minutes. In the 

 chromic-acid reactions of the Nerine crispa-elegans- 

 dainty maid-queen of roses group this period lasts in all 

 four starches for 15 minutes, followed by a rapid gela- 

 tinization, giving a well-marked / form of curve. While 

 all four starches may show this resistance with one rea- 

 gent, one or all may not with others, and the degree and 

 duration of the resistance may either or both be quite 

 variable. Thus, in the chloral-hydrate reactions, two of 

 the starches show slight early resistance, and two not any 

 (Chart D 190) ; in the potassium-sulphocyanate reactions 

 all four show a resistant period, two for 5 minutes, and so 

 on. The inclination of this form of curve is very varia- 

 ble, in some instances, being less than 30 (Chart D 2) ; 

 in others, about 50 (Chart D 1), in others about 80 

 (Chart D 18) ; and in others, between or beyond these 

 extremes, the less the angle the less rapid, as a whole, is 

 the process of gelatinization. 



Curves are not infrequently found which do not pur- 

 sue a uniform rectilinear or curvilinear course, so that 

 they are not classifiable among the forms stated. In 

 other words, they appear to be at times erratic in their 

 courses. For instance, in the reactions of Brunsdonna 

 sanderce with sodium sulphide (Chart D 12) the curve 



during the first 15 minutes appears like a segment of the 

 / form, but between the 15-minute and 45-minute inter- 

 vals the curve drops instead of rises. In the sodium- 

 hydroxide reactions with Brunsdonna sanderce alba 

 (Chart D 11), it seems from the courses of the curves of 

 the other starches shown in the chart that the curve 

 should have risen decidedly more by the end of the 15- 

 minute interval, impinging at perhaps the 30 per cent ab- 

 scissa instead of at the 16. In some instances these seem- 

 ing or actual aberrations in the progress of gelatinization 

 may be due to errors of experiment that are attributable 

 to errors of estimation or to variations in attendant con- 

 ditions ; but in most and probably in nearly all instances 

 they are owing to peculiarities, molecular or physical, of 

 the starch grains, as is indicated by the occurrence of 

 identical or practically identical records when experi- 

 ments have been repeated, even under varying incidental 

 conditions. 



The curves of gelatinization of the starches consti- 

 tuting a parental-hybrid group tend usually to divergence 

 in their courses during the early part of the reactions, 

 and when a definite position-relationship (highest, inter- 

 mediate, same or lowest) is once established it is com- 

 monly retained throughout the courses of the curves, but 

 the degree of separation may be very variable, usually in- 

 creasing for a variable period and then decreasing or 

 increasing, more frequently decreasing. In some in- 

 stances there is little or no difference between two or 

 more of the curves of the group during an early period of 

 the experiment, the length of which period being varia- 

 ble, this period being followed by variable degree of 

 divergence ; and in other instances, while divergence may 

 be marked during the early and mid-periods of experi- 

 ment, there may be sameness during the final period, and 

 so on. 'Crossing of curves is occasionally observed, but 

 recrossing is very rare. Such peculiarities as are here 

 indicated are illustrated in large part by the Amaryllis- 

 Brunsvigia-Brunsdonna reactions (Charts D 1 to D 21). 

 In most of these charts (excepting those in which gela- 

 tinization is very rapid or very slow) there occurs pri- 

 marily divergence and secondarily convergence. In 

 Chart D 21 there is practically divergence from begin- 

 ning to end of reaction. Charts belonging to the diver- 

 gent type are common, for instance, among the Crinum 

 zeylanicum-longifolium-kircape group (Charts D 148 to 

 D168). 



Different starches may exhibit with a given reagent 

 the same or different curves. Thus the chloral-hydrate 

 reactions with different starches show varying differences 

 in regard to both type and form of type and in the de- 

 gree of inclination of the curves. This feature is shown 

 by both the individuals of the groups of parental and 

 hybrid starches and by the different generic groups, as 

 seen, for instance, by an examination of the reactions 

 of the four starches as presented in Chart D 1. and by 

 the reactions of various generic representatives shown in 

 Charts D 22, D 85, D 127, D 190, D 265, D 361, D 379, 

 D 463, D 484, D 505, D 545, D 574, D 595, D 616, and 

 D 619. Similar variations will be found in the reactions 

 of other reagents, these differences being usually more 

 conspicuous in the case of reagents that act usually with 

 moderate activity than with those which act commonly 

 with either much or little intensity. 



