THE VOLATILE PART OF PLANTS. 63 



The experiments of Grouven show that gum arable is 

 digestible by domestic animals. There is little reason to 

 doubt that all the gums are digestible and serviceable as 

 ingredients of the food of animals. 



#. The Glucoses, C 6 Hi 2 6 (or C 5 H 10 5 ), are a class of 

 sugars having similar or identical composition, but dif- 

 fering from each other in solubility, sweetness, melting 

 point, crystal-form and action on polarized light. 



The glucoses, with one exception, contain in 100 parts : 



Carbon ........................... 40.00 



Hydrogen ........................ 6.67 



Oxygen ........................... 53.33 



100.00 



Levulose, or Fruit Sugar (Fructose), CHi 2 0, 

 exists mixed with other sugars in sweet fruits, honey and 

 molasses. Inulin and levulin are converted into this 

 sugar by long boiling with dilute acids, or with water 

 alone. When pure, it forms colorless crystals, which 

 melt at 203, but is usually obtained as a syrup. Its 

 sweetness is equal to that of saccharose. 



Dextrose or Grape Sugar, C 6 H 12 6 , naturally oc- 

 curs associated with levulose in the juices of plants and 

 in honey. Granules of dextrose separate from the juice 

 of the grape on drying, as may be seen in old " candied " 

 raisins. Honey often granulates, or candies, on long 

 keeping, from the crystallization of its dextrose. 



Dextrose is formed from starch and dextrin by the ac- 

 tion of hot dilute acids, in the same way that levulose is 

 produced from inulin. In the pure state it exists as 

 minute, colorless crystals, and is, weight for weight, but 

 two-thirds as sweet as saccharose or cane-sugar. It fuses 

 at 295. 



Dextrose unites chemically to water. Hydrated glucose, Cs 

 occurs in commerce in an impure state as a crystalline mass, which 

 becomes doughy at a slightly elevated temperature. This hydrate 

 loses its crystal-water at 212. 



Dissolved in water, dextrose yields a syrup, which is 



