CARBOHYDRATES 99 



The more common carbohydrates may be listed as follows: 



1. Mono-saccharides. 



Hexoses, C 6 H 12 O 6 dextrose, levulose, galactose. 



Pentoses, C 5 H 10 O 5 arabinose, xylose, rhamnose (methylpentose, 



C 6 H 12 5 ). 



2. Di-saccharides, C 12 H 22 O n , 



Maltose, saccharose (cane-sugar), lactose. 



3. Poly-saccharides, (C 6 H 10 O 5 ) n . 



Dextrin group dextrins. 



Starch group starch, inulin, lichenin, glycogen. 



Cellulose group cellulose. 



Dextrose (glucose, grape-sugar) is an aldose found in honey and 

 in many fruit juices where it is usually associated with levulose. It is 

 present in the blood in small amounts, o.i to 0.15 per cent., in normal 

 urine in minute traces, and in diabetic urine. It is not as sweet as cane- 

 sugar. Glucose is produced on boiling starch with dilute acids. It is very 

 soluble in water and is slightly soluble in alcohol. It crystallizes from 

 water in leaves or plates and from alcohol in anhydrous needles. Dextrose 

 rotates the plane of polarized light to the right its specific rotation is given 

 by the expression [a] d = +52.5. It forms a characteristic glucosazone 

 when boiled with phenylhydrazine in the presence of acetic acid; the osazone 

 crystallizes from the hot solution. Glucose reduces metallic oxides in 

 alkaline solution. It undergoes alcoholic fermentation with yeast and acid 

 fermentation with certain bacteria. 



CH 2 OH CH 2 OH 



CHOH CHOH 



CHOH CHOH 



CHOH CHOH 



CHOH CO 



CHO CH 2 OH 



Dextrose. Levulose. 



Levulose (fructose) is a ketose and is found associated with dextrose 

 in many fruits, the mixture probably being produced by the hydrolysis of, or 

 preceding the synthesis of, cane-sugar. It may be prepared by the hydrolysis 

 of inulin and, along with dextrose, by the inversion of cane-sugar on boiling 

 with dilute mineral acids or through the action of specific enzymes. It is 



