THE FOOD OF THE PLANT 61 



Inferences. — The starch formed in the leaf is con- 

 verted into sugar, a soluble substance; and in this 

 form it travels about the plant. 



The change by which starch is converted into sugar 

 is one of hydrolysis (page 60), similar to that by which 

 cane-sugar is converted into grape-sugar. 



It may be represented as a chemical equation. Thus : 



{C,R,fi,)x+x{B.,0} = a;(CeHj A) 

 Starch. Grape-sugar. 



The exact value of x is not known. 



It has already been shown that, when cane-sugar is 

 boiled with a mineral acid, it is converted into grape- 

 sugar. 



In the following experiment it will be shown that the 

 process whereby starch is converted into sugar is similar 

 to that by which grape-sugar is formed from cane- 



EXPERIMENT 40 



Aim. — To find out what happens to starch when it is 

 boiled with a mineral acid. 



Method. — Small pieces of potato, or powdered starch, 

 can be used in this experiment. To this, water and a 

 few drops of hydrochloric acid are added. The whole is 

 then boiled. At intervals of two or three minutes a 

 little of the liquid is removed and treated with iodine 

 in order to test for starch. 



When the iodine solution no longer gives any starch 

 reaction the remaining liquid is tested for sugar. 



Observations. — Each time the iodine test is applied 

 the amount of starch is found to decrease. Finally no 

 starch is left. The remaining liquid shows the presence 

 of a reducing sugar. 



Inference. — Starch is converted into sugar when 

 boiled with a mineral acid. 



