66 



PLANT COMPOUNDS 



rotatory, and will not reduce Fehling's solution. Its most 

 characteristic reaction is to turn blue in the cold with a 

 solution of iodine (in alcohol or potassium iodide). The 

 compound formed is supposed to be (C24H 4 o02oI)4.HI, which 

 breaks up on heating, but which reforms again when the 

 solution is cooled down. 



Fig. 19. — Rice starch. 

 Figs. 15 to 19. — Starch grains. Bureau of Chemistry, United States 



Department of Agriculture. 



Under the action of enzymes, diastase for example, 

 starch hydrolyzes to maltose (Section 55), thus: 



2(C 6 Hio0 5 )n + nH 2 = nCi 2 H 2 20n. 



In so doing, however, it passes through a series of hydro- 

 lytic compounds, named successively: Amylodextrin, colored 

 blue by iodine; erythrodextrin, colored red by iodine; achro- 

 odextrin, not colored by iodine; maltodextrin, not colored 

 by iodine; maltose, not colored by iodine. These various 

 dextrins differ from starch in containing a smaller number of 

 CeHioOs groups in their molecules. They are colorless, 



