CONSTITUENTS OF PLANTS 



367 



action of dilute acids upon starch. The acid splits up the 

 starch, and causes it to unite with water 



(C 6 H 10 5 ) + X H 2 = C 6 H 12 6 - 

 Starch. Glucose. 



The thick syrup formed after the acid is neutralized and the solu- 

 tion evaporated is called glucose syrup or corn syrup. It does 

 not consist of pure glucose. If a solid mass is produced, it is 

 called grape sugar. 



Fructose, C 6 H 10 O 5 , accompanies glucose in most fruits and 

 vegetables. It is difficult to crystallize. It is obtained by hydrolysis 

 of inulin. So-called invert sugar is a mixture of equal quantities 

 glucose and fructose, and is formed by the hydrolysis of sucrose. 

 Honey is a natural invert sugar, dissolved in water, with small 

 quantities of impurities. While glucose may be separated from 

 invert sugar comparatively easily, it is not easy to separate 

 fructose on account of its difficult crystallizability. 



Mannose, C 6 H 10 O D , has not been found in nature. It has been 

 prepared by the hydrolysis of vegetable ivory, the seeds of palms 

 and lilies, coffee beans, and gum arabic, etc. 



Galactose, C 6 H 10 O 5 , has not been found as such in nature. It 

 is a product of the hydrolysis of milk sugar, and of carbohydrates 

 found in seeds of lupines, beans, soja beans, peas, vetch, cress, 

 young clover, lupine, and lucerne plants, in gum arabic, fruits of 

 pears, etc. Nitric acid oxidizes it to mucic acid, which is almost 

 insoluble in water. A method for its estimation is based upon 

 this fact. 



Compound Sugars. The most important compound sugars are 

 cane sugar, milk sugar, raffinose, maltose, and stachyose. They 

 are derived exclusively from hexoses. 



