58 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



plexity and density of internal structure, and tliat in examining the decomposition products 

 of starch it was not until the achroodextrin stage of the degradation of the starch molecule 

 was reached that the products exhibited an apparently uniform molecular condition. 



Aniline dyes were used by Gastine (Compt. rend., 1906, cxlii, 1207; Jour. Soc. Chem. 

 Ind., 1906, XXV, 655) for the detection of rice flour in wheat flour. A sample is treated on 

 an object glass with a solution of a suitable dyestuff, drying the preparation at about 

 30 C, and then completing the desiccation by heating for a few minutes at 110 to 130 

 C. The preparation, he states, should be mounted in cedar-wood oil or Canada balsam 

 and examined under the microscope. For staining, a solution of aniline blue or green may 

 by employed of a strength of 0.05 grm. in 100 c.c. of 33 per cent alcohol. 



This treatment has the effect of showing the hilum of the minute rice starch-grains, 

 while wheat starch rarely exhibits a visible hilum. In rice flour isolated starch-grains are 

 rare, the grains generally occurring in clusters in starch-bearing cells. These clusters, 

 according to the above method, have a very characteristic appearance, since the hilum 

 of each starch-granule appears as a reddish-colored point, these red points being grouped 

 quite uniformly in symmetrical arrangement resembling a mulberry under a high magnifi- 

 cation. Wheat and rice starches do not take up the dyestuff; only the nitrogeneous mat- 

 ters are dyed. The fragments of rice flour therefore appear colored; the medium-size and 

 large granules of wheat are practically uncolored, but the small granules of the wheat, in 

 which the interstitial nitrogeneous matter is more abundant, are distinctly colored. The 

 grains of corn and buckwheat starches behave like rice. Potato, arrowroot, and sweet 

 potato starches, unlike the cereal and leguminous starches, absorb the dyestuff directly. 



According to Maquenne and Roux (Compt. rend., 1905, cxl, 1303; 1906, cxliii, 124) 

 starch consists of about 90 per cent of amylocellulose and about 10 per cent of amylo- 

 pectin. The former they describe as being devoid of gelatinizing power, but the latter as 

 gelatinizable. (See Chapter III, page 112.) Day (U. S. Dept. Agriculture, Office Expt. 

 Sta. Bull. 202, 1908) records three substances in starch-grains, which are designated blue 

 amylose, red amylose, and rose amylose, in accordance with the color reaction with iodine. 

 (See Chapter IV, page 166.) 



Some extremely interesting and original views of the chemical nature, and also of 

 the cause of the peculiar structure, of the starch-grain were published by St. Jentys (Bull. 

 d. I'academie d. sc. d. Cracovie, 1907; Jalir. ti. d. Fort. d. Theirchemie, 1907, xxxvii, 

 99), who records that the presence of tannin in the cell-sap, and the fact that a solution 

 of starch yields with this substance a preparation which is insoluble in cold water, led 

 him to the supposition that tannins enter into the composition of the starch-grain. Doubts 

 as to the components of the starch-grain were first aroused in St. Jentys by the results 

 of a series of experiments in connection primarily with the peculiar reactions of the starch- 

 grain and starch-paste with iodine. St. Jentys observes that starch-grains, as is well 

 known, are rarely colored a pure blue with iodine, but usually violet, and sometimes even 

 black. A still greater variety in color may be observed in dried starch-grains and starch- 

 paste which have been treated with iodine, the violet parts gradually going over into a 

 cherry-red, copper-red, or orange, and finally into a brownish-yellow. These various 

 colorings (which Nageli had already noticed) are due, St. Jentys states, to the presence 

 in the starch-grain of substances which differ in their behavior toward iodine. For exam- 

 ple, the starch-grains of potato pulp, from which the tannin had been removed by means 

 of a methyl-blue solution instead of water, were colored an indigo-blue with iodine after 

 the removal of the methyl-blue; the outer surface of the intact grains was colored violet, 

 while the inner part became more of a blue color. Other reagents also acted differently on 

 the outer and the inner parts of the grains. 



St. Jentys could extract nothing by cold water from intact grains, but some particles 

 passed into solution from the pulverized grains. Boiling with water, he states, evidently 



