138 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



absolutely free of reducing power, but the achroodextriu retained a slight reducing power, 

 even after many successive precipitations. Because of the absence of reducing power in 

 amylodextrin and erythrodextrin, Moreau believes that sugar does not constitute a part 

 of the dextrin molecule. 



Many investigators have referred to the existence of a dextrin residue that is not 

 converted into sugar, but Fernbach and Wolff (Compt. rend., 190G, cxlii, 121G") found 

 that if the residual dextrin is separated it may be saccharified by malt extract, and there- 

 fore that if any dextrin exists which is not convertible into maltose it must be but an 

 infinitesimal part of the original starch. 



The dextrinizing action of formaldehyde was referred to on page 109, in connection 

 with Syniewski's investigations, the results of which have received confirmation in the 

 investigations of Reichard (Zeit. ges. Brauw, 1908, xxxi, 161), who noted the succession 

 of different color reactions with iodine as the processes proceeded. Erytlu-odextrins were 

 prepared by Tam-et (Compt. rend., 1909, cxlviii, 1775) from a weak alcoholic solution 

 of the insoluble precipitate (reverted starch) that formed in soluble starch on cooling, the 

 quantity of erythrodextrins obtained representing about 8 per cent of the total matter 

 dissolved in alcohol. 



A colorimetric method for determining the molecular weights of starch and its decom- 

 position products and related carbohydrates was reported by Wacker (Ber. d. d. chem. 

 Gesellsch., 1908, xli, 266; 1909, xlii, 2675). From these observations both erythrodextrin 

 and achroodextriu have the values of 4 hexose groups. 



ISOMALTOSE, MALTOSE, GLUCOSE, SACCHAROSE, ETC. 



The discovery of sugar as a product of the activity of weak acids on starch was 

 made by Ivirchhoff in 1811 (Schweigger's Journal, 1815, xiv, 389), and 3 years later he 

 found that gluten and germinating barley also gave rise to sugar. He and his contem- 

 poraries referred to this sugar as glucose. Over 30 years later Dubrunfaut (Aim. de 

 chim. et phys., 1847, xxi, 178) isolated this body, and from a study of its properties he 

 showed that it is not identical with glucose. This discovery seems, however, to have 

 made no impression, since the literature of the subject shows that various investigators 

 up to 1872 refer to tliis sugar as glucose; and even Musculus based his theory of the 

 hydrolysis of starch into dextrin and sugar upon the assumption that he was dealing with 

 glucose. O'Sullivan (Jour. Chem. Soc, 1872, x, 579) rediscovered the sugar described by 

 Dubrunfaut, and found that it had only 65 per cent of the reducing power of glucose, and 

 named it maltose. Petit (Bull. d. 1. Soc. clum., 1875, xxiv, 519) records, after digesting 

 starch-paste with diastase, that the preparation contained 5 per cent of dextrin and 

 two kinds of sugar, one of which he states reduces an alkaline solution of copjier oxide, 

 while the other is without influence; the latter, after being boiled with 1 per cent sul- 

 phuric acid, is saccharified, the resulting sugar being composed of about three-fourths of 

 this non-reducing sugar. 



Sachsse (Sitzungsber. d. Naturf. Gesellsch., Leipzig, 1877; Jahr. ii. d. Fort. d. Tier- 

 chemie, 1877, vii, 60), in discussing the formula usually given for starch that was objected 

 to by W. Niigeli, who proposed for the accepted CgHiqOj the formula C3eH(;203i, states 

 that it is the same as 6 (CgHjoOj) -I-H2O, and that tliis shght alteration is of interest 

 analytically, as it takes into consideration the amount of starch in the relative determina- 

 tion in the conversion into sugar. If the formula read CgHjoOs (mol. weight 162), 180 

 molecules of dextrose would be derived from 162 of starch, or 100 : 90; but if it read accord- 

 ing to Niigeli, there would be 1,080 molecules of dextrose fi'om 990 of starch, or 108 : 99. 

 Correct results, Sachsse states, are obtained by changing the fornuila to C3gH^.203j, while 

 in using the other formula CgHjoOs there was always an inexi)licable difference of 1 to 2 

 per cent. 



