170 



DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



noted tliat it has tho jiropcrty of absorbing neutral salines, etc. The asserted acid char- 

 acter of starch is in accord with the observation of Ford and Guthrie (Chem. Soc. Trans., 

 1906, Lxxxix, 76), who state that soluble starch freed from impurities possesses feebly 

 acid properties, as is shown by the fact that it is capable of combining with sodium hy- 

 droxide to such an extent that the molecular conductivity of the sodium hydroxide solution 

 is reduced very considerably upon the addition of soluble starch. 



Table 19. 



MISCELLANEOUS CHEMICAL UIFFEKENCES. 



The proportions of insoluble residues are variable in relation to different kinds of 

 starches, as will bo noted by table 13 on page 166. W. Niigeli (Die Starkegruppe, etc., 

 loc. cit.) states that potato starch lea\'es a larger quantity of insoluble residue than wheat 

 starch, which is the reverse of the figures in Konig's table. Parow and Neumann (Zeit. 

 Spiritsind., 1907, xxx, 561) worked out a simple method for the determination of the 

 quantity of starch in commercial products. One of the best-known methods is to digest 

 the starch with malt extract, finish saccharification by dilute hydrochloric acid, and deter- 

 mine the dextrose by Fehling's solution, using 

 the theoretical factor 0.9 for calculating the 

 dextrose into terms of starch. Parow and 

 Neumann not only found this factor too low 

 (0.95 being better), but also that the deter- 

 mination could be made by a much simpler 

 method by which dextrose can be deterinined 

 polariscopically. In these experiments they as- 

 certained that each of the starches examined 

 has a specific factor, the differences depending 

 upon degrees of saccharification, which of 



course are indexes of the quantities of undigested residue. The factors given in table 19 

 were recorded. 



Parow (Zeit. Spiritusind., 1908, xxxi, 286) states that corn starch contains 0.44 per 

 cent of protein, potato starch 0.26, and cassava starch 0.23. Little or no importance is 

 to be attached to such data beyond the fact that they indicate the degree of contamination 

 rather than specific differences in the composition of starches from different sources. 



Various laboratory procedures were pursued by Bloemendal (Pharmac. Weekbl., 

 1906, xLviii, 1249; Wochschr. f. Brau., 1909, xxxiii, 436; Chem. Ab. Amer. Chem. Soc, 

 1909, III, 1102). He studied the properties of potato, rice, wheat, and arrowroot starches 

 as regards chemical composition, content of pentosans, heat of combustion, and specific 

 gravit3^ The C and H contents of the four starches were remarkably constant, varying 

 from 44.03 to 44.54, and 6.02 and 6.45, respectively, these figures corresponding to the 

 familiar mean values, C44.4 H6.2 O49.4. The C and H values were the same in the small 

 grains as in the large. The furfurol contents in the form of phloroglucids obtained by 

 boiling with hydrochloric acid were 0.025 for arrowroot and 0.032 for rice for each 2.5 

 grams of starch. The quantity of pentosans was very small. Unimportant differences 

 were noted in specific gravity, water-content, and heat values. 



COLOR REACTIONS. 

 lOUINE. 



The use of iodine as a color-test for starch dates from the earlier observers, and the 

 blue reaction is regarded as being specific, although Claude Bernard showed that an ab- 

 normal glycogen may be formed in paralyzed muscles which may gi\'e the same reaction, 

 while others have reported that some forms of plant mucus and of cellulose also gave a 

 blue reaction. The rapidity and intensity of the reaction to starches from diiTerent sources 



