42 ANATOMY AND PHYSIOLOGY 



13. If preferred, de-chlorophyllized leaves may be cut 

 into small pieces, boiled in water in a test-tube over 

 a Bunsen flame, and the water then tested for the 

 presence of starch. 

 B. Test for Sugar: 



1. We have seen that starch is a practically insoluble 

 carbohydrate. We also know that sugar is a read- 

 ily soluble carbohydrate. The chemical formula for 

 a molecule of starch is CeHioOs. If we combine 

 with this molecule one molecule of water (H^O) we 

 have a molecule whose composition is represented 

 by the formula C 6 Hi 2 O 6 L(C 6 Hio0 5 )n + H 2 = 

 CeHijOj. This is grape sugar. Sugar, then, differs 

 from starch in possessing relatively more hydrogen 

 and oxygen in its molecule. The process of con- 

 verting starch into sugar is termed hydrolysis, and 

 since it converts an insoluble substance into a 

 solubile one, it is a kind of digestion. 



2. The sugar ordinarily used for culinary purposes is 

 cane sugar. Its formula is C^H^On. Explain 

 how cane sugar differs from starch chemically. 



Experiment 22. To demonstrate a test for the presence 

 of grape sugar (C 6 Hi 2 O 6 ). 



3. The reagent commonly used for this test is called 

 Fehling's solution, from the name of the scientist 

 who first employed it. The solution is prepared 

 by mixing one volume of each of the following stock 

 solutions with two volumes of distilled water (e.g., 

 10 c.c. of each, and 20 c.c. of distilled water). 



(1) 17.5 grams of copper sulphate dissolved in 500 c.c. 

 of distilled water. 



(2) 86.5 grams of sodium-potassium- tartrate (Ro- 

 chelle salts) in 500 c.c. of distilled water. 



