154 THE CARBOHYDRATES 



Amylase forms 66 per cent of the granule ; it is a poly- 

 merized a-hexa-amylose ; is soluble in water and gives a 

 clear bright blue colour with iodine ; it is converted by barley 

 or malt diastase completely into maltose at 50° C. 



Amylopectin forms 33 per cent of the granule ; it is a 

 polymerized phosphoric acid ester of aj3-hexa-amylose ; when 

 made into a paste with hot water, it gives a bluish-black 

 coloration and precipitate with iodine (amylopectin extracted 

 with alkali gives a violet coloration with iodine) ; it is de- 

 phosphated and depolymerized by barley diastase at 50°, 

 yielding a/3-hexa-amylose. 



Amylohemicellulose is the name given by Ling and Nanji 

 to a substance associated with and, in the case of the cereal 

 starches, apparently forming an integral part of the granule. 

 Starches of the potato and arrowroot, on the other hand, 

 contain hardly any of this material, although the tuber of the 

 potato actually contains a considerable quantity which, in- 

 stead of forming part of the starch granule, remains attached 

 to the cell wall. 



Amylohemicellulose contains from I-2-I-3 per cent of 

 ash and is regarded by Ling and Nanji as a calcium, mag- 

 nesium, and iron salt of a silicic and phosphoric ester of a- 

 amylose ; it is converted by malt diastase quantitatively into 

 maltose but, unlike amylose, it is unacted upon by barley 

 diastase. On the other hand, like amylose it gives a blue 

 colour with iodine, and being associated in some cases with the 

 cell wall it is liable, when occurring in wood, to be mistaken 

 there for starch.* 



Action of Acids on Starch. 



The action of acids on starch varies according to the 

 strength of the acid, the duration of the action, and the tem- 

 perature of the experiment. To complicate matters, there are 

 considerable divergences in regard to the interpretation of the 

 results obtained by the different workers. As an illustration 

 of the very different effects which may be produced under 

 different conditions, the following experiments may be 



quoted. 



* Ling and Nanji : " J. Chem. Soc," 1925, 127, 652. 



