HYDROLYSIS OF STARCH 119 



12 per cent commercial hydrochloric acid for twenty-four 

 hours, Brown and Morris found that granules, while retaining 

 their external features, had acquired the power of dissolving in 

 hot water without the formation of paste. The addition of 

 alcohol to such a solution caused the immediate precipitation 

 of a white substance known as soluble starch, which is turned 

 blue by iodine, is strongly dextro-rotatory, [a] D = 202, and 

 does not reduce Fehling's solution. On the other hand, if 

 starch is boiled for some time with dilute hydrochloric acid, 

 it is converted into glucose, a fact which is made use of in 

 estimating starch. 



That maltose is also produced as an intermediate product 

 of the acid hydrolysis of starch has been shown by Fernbach 

 and Schoen,* and also by Weber and Macpherson,f who have 

 proved it to be present in commercial glucose (see p. 73). Ac- 

 companying the conversion of starch into glucose there is, 

 however, the formation of varying quantities of gummy sub- 

 stances known as dextrins (q.v.) ; it is, however, not known for 

 certain whether these dextrins are formed directly by the action 

 of the acid on the starch, or whether they are produced by the 

 condensing action of the acid on the glucose already formed ; 

 there is moreover great difference of opinion with regard to 

 the nature and number of these substances which are formed. 



Action of Malt or Diastase on Starch. 



The action of malt extract or diastase (see p. 371), like 

 that of mineral acids, is primarily a hydrolytic one in which 

 the starch is converted into a sugar ; but the diastase does not 

 carry the hydrolysis so far as the acid, the sugar produced 

 being a disaccharide, maltose, and not a monosaccharide. At 

 the same time some dextrin is also formed. Although the 

 mechanism of this reaction is very complex and has led to a 

 great deal of discussion, the ultimate change may be con- 

 veniently represented by the following formulae : 



(C 6 H 10 5 ) n + H 2 -> C 12 H 22 O n + (C 6 H 10 5 ) X 

 Starch Maltose Dextrin 



* Fernbach and Schoen : "Bull. Soc. Chim.," 1912, [iv.], n, 303. 

 f Weber and Macplierson : " J. Amer. Chem. Soc.," 1895^ 17, 312. 



