CH. V.] STARCH. 117 



130. To 3 cc. of the solution add i drop of concentrated HC1- 

 Boil for a few seconds. Cool under the tap. Add about 10 drops of 

 20 per cent, copper sulphate, 3 drops of glycerol, and about- 3 cc. of 

 20 per cent, sodium hydroxide. Boil. A marked reduction is 

 obtained. 



NOTE. Sucrose is hydrolysed extremely rapidly by acids into glucose and 

 fructose. Though the polysaccharides yield reducing sugars by acid hydrolysis 

 the above procedure would have very little effect on them. 



131. Repeat Exs. 114 and 115. Sucrose behaves like fructose. 



C. Polysaccharides. 



These compounds are formed by the condensation of an 

 indefinite number of molecules of monosaccharides. 



The pentosans (C 5 H 8 O 4 )n yield pentoses on hydrolysis. 



The hexosans (C 6 H 10 O 5 )n yield hexoses, generally glu- 

 cose, on acid hydrolysis. The polysaccharides described 

 below are hexosans. 



Starch is widely distributed in the vegetable kingdom 

 as a reserve carbohydrate. It occurs in the form of grains 

 in many roots, tubers, seeds, and leaves. The size and 

 shape of the grains are peculiar to each botanical species. 



These grains probably consist of at least two substances. 



A. " Amylopectin," or " starch cellulose." 



B. " Amylose," or " granulose." 



Amylopectin forms about 60 per cent, of the grain. It 

 is a mucilaginous substance, which swells up without dis- 

 solving in boiling water or in cold sodium hydroxide. It is 

 hydrolysed by acids into glucose. By certain enzymes, 

 called amylases, found in malt, saliva, and the pancreas, it is 

 converted into a mixture of maltose and " stable dextrin," 

 that is only very slowly hydrolysed to maltose and glucose. 

 It does not seem to give a blue colour with iodine. 



Amylose is soluble in cold water. It is rapidly and 

 completely converted to maltose by the amylases without 

 leaving a residuum of dextrine. It gives a blue colour with 



