174 



DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



Potato. 



The boliavior of potato starch 

 toward these reagents may be briefly 

 summarized as follows: The first 

 effect of chromic acid and other 

 swelling reagents is to make the 

 lamellEE more distinct; this is fol- 

 lowed by the development of the 

 crystalloidal character of the lamellae, 

 which is most jironounced in those 

 colored blue with iodine; this is fol- 

 lowed by the production of small 

 tracts or channels connecting the 

 contiguous lamella;, particularly in 

 the middle of the grain; succeeding 

 this there is the formation of chan- 

 nels which are larger and plume-like 

 in appearance, the grain meanwhile 

 swelling quite perceptibly, the mid- 

 dle portion becoming clearer antl 

 assuming a zigzag outline, between 

 which and the periphery of the grain 

 a nvmiber of crystalloidal lamelkc 

 arise; the grain now becomes spheri- 

 cal and marked by a number of con- 

 centric lamellre near the periphery; 

 the latter finally ruptiu-es and then 

 follows a gi-adual solution of the 

 gram, the jjeripheral layer sometimes 

 recurving like the cutin layer of an 

 epiilermal cell on treatment with 

 sulphuric acid. 



Wheat. 



In wheat starch the develoiiment 

 of the crystalloidal character of the 

 lamella; is followed by the formation 

 of narrow, interrujited or continu- 

 ous, radial channels near the peri- 

 phery of the grain, which are some- 

 times connected with lamelte occur- 

 ring near the midfUe of the grain; 

 the grain meanwhile swells quite 

 perceptibly, the center becomes 

 clearer, the contents are crowded 

 into crescent-shaped halves, wliich 

 are still connected at the poles; the 

 contents of each of the halves of the 

 grain consist of crystalloidal lamella; 

 in which are then produced small 

 tracts or channels connecting the 

 continuous lamellse; the halves in 

 some instances finally separating and 

 slowly dissolving. In some cases, on 

 the other hand, there is a corrosion 

 of the grain at the periphery, fol- 

 lowed by gradual disintegration 

 without the separation into halves. 



Corn. 



The first effect of reagents upon 

 the corn starch-grain is to bring 

 out the point of origin of growth; 

 the latter becomes larger and in 

 some cases more or less zigzag in 

 outUne; between this and the peri- 

 phery of the grain arise more or 

 less interrupted or continuous radial 

 channels (usually the latter); the 

 crystalloidal structure of this grain 

 develops slowly and is most i)ro- 

 nounced when the grain has swollen 

 to two or three times its normal 

 size; at tMs stage we find that the 

 center of the grain ha.s become 

 clear and the point of origin of 

 growth has become obliterated in 

 some cases, and between it and the 

 periphery occur numerous crystal- 

 loidal lamell similar to those ob- 

 served in the potato starch; finally 

 the peripheral layer ruptures and 

 there is a gradual disintegration of 

 the grain. Sometimes the grain 

 appears to separate into as many 

 parts as there were arms to the 

 point of origin of growth, particu- 

 larly when acted upon by saliva or 

 diastase. 



The behavior of starch towards chromic acid was studied by Harz (Beiheft. z. bot. 

 Centralbl; Woch. f. Brau., 1905, xxii, 721), who found that with chromic acid alone 

 colors are obtained, varying from a yell o wish-grayish-green to an oUve-gi'een, and 

 finally a golden-yellow, accorchng to the concentration of the solution. With a 

 mixture of cliromic and sulphuric acids the colors were shades of green. The different 

 kinds of starch, and also different grains of the same starch, varied greatly in their 

 behavior, so much so that starch can not be regarded as a physically uniform sub- 

 stance, the grains differing from one another according to the den,ser or looser constitu- 

 tion of their ultimate complexes. 



Sodium salicylate has been reported by Lenz (Seventh Inter. Congress Appl. Chem., 

 London, 1909; Jour. Soc. Chem. Ind., 1909, xxviii, 731) as a reagent to be employed in 

 the niicrochemical differentiation of starches of different kinds. He states that if a trace 

 of rye starch, in a hanging drop of a solution of 1 part of sodium salicylate in 11 parts of 

 water, is examined under a magnification of 200, at the ordinary temperature, it will be 

 found that after the lapse of an hour (more distinctly after 24 hours), most of the large 

 granules have swollen ; only a small part resists the action of the salicylate and still shows 

 the polarization cross between crossed nicols. In the case of wheat starch, only a few of the 

 large granules become swollen; after 1 to 24 hours the outline of the unswollen wheat 

 starch-gi'anules is sharply defined, and the granules, unlike those of rye starch, do not 

 become flattened (starch of any kind which has been altered by storage in a moist condi- 

 tion swells on treatment with the salicylate solution). Barley and millet starches swell 

 to a small extent only. But few of the grains of oats, maize, rice, potato, bean, pea, lentil, 

 and arrowroot starches become swollen. 



TEMPERATURES OF SWELLING AND GELATINIZAIION. 



When starch-grains are heated in water they begin to swell at temperatures usually 

 between 45 and 55, sometimes higher and sometimes lower, according to the source of 

 the starch. As the temperature increases the grains lose their form and become gelatinous. 



