CARBOHYDRATES. 311 



Groups of carbohydrates. 



Glucoses. Saccharoses. Amyloses. 



C 6 Hi 2 O 6 . C, 2 H 22 O n . C 6 H 10 O 5 . 



Grape-sugar. Cane-sugar. Starch. 



, -rr Fruit-sugar. Melitose. Dextrine. 



. ( Vegetable. - 

 .= I Mannitose. Maltose. Gums. 



Cellulose. 



I A 1 ( 



Animal. J l nos ite. Milk-sugar. Glycogen. 



Grape-sugar, C 6 H 12 6 (Ordinary glucose, Dextrose}. This sub- 

 stance is very abundantly diffused throughout the vegetable 

 kingdom, and is often accompanied by fruit-sugar. It is con- 

 tained in large quantity in the juice of many fruits; the per- 

 centage of grape-sugar in the dried fig is about 65, in grape 

 10-20, in cherry 11, in mulberry 9, in strawberry 6, etc. 



Grape-sugar is also found in honey and in minute quantities 

 in the normal blood (0.1 per cent, or less), and traces occur, 

 perhaps, in normal urine, the quantity in both liquids rising, 

 however, during certain diseases as high as 5 per cent. 



Grape-sugar is produced in the plant from starch by the 

 action of the vegetable acids present ; it may be obtained arti- 

 ficially from starch (or from many other carbohydrates) by 

 heating with diluted mineral (sulphuric) acids. Starch is also 

 converted into glucose by the action of diastase, a substance 

 formed during the fermentation of various seeds (grain, etc.) ; 

 it is for this reason that grain, used for alcoholic liquids, is 

 allowed to germinate, during which process diastase is formed, 

 which, acting upon the starch, converts it into fermentable 

 glucose. 



Glucose is generally met with as a thick syrup which crystal- 

 lizes with difficulty, combining during crystallization with one 

 molecule of water. Glucose is very soluble in water and less 

 sweet than cane-sugar; when heated to 170 it loses water, and 

 is converted into glucosan, C 6 H 10 O 5 ; by stronger heating it loses 

 more water and forms caramel, a mixture of various substances. 



Grape-sugar combines with various metallic oxides (alkalies, 

 alkaline earths, etc.), and also with organic acids, forming a 

 series of compounds known as glucosides. 



Grape-sugar may be recognized analytically : 



1. By causing a bright red precipitate of cuprous oxide when 



