CARBOHYDRATES 99 



lytic and inverting enzymes, the poly-saccharides are, as a rule, hy- 

 drolyzed into the simple carbohydrates. The reaction may be indicated 



(C 6 H 10 5 ) n + nH 2 . : nC 6 H 12 6 

 Poly-saccharide Water Mono-saccharide 



Simple poly-saccharides, and di-saccharides are formed as intermediate 

 products in the cleavage and in turn these are further hydrolyzed. 



C 12 H 22 U + H 2 , 2 C 6 H 12 6 



Di-saccharide Water Mono-saccharide 



The color reactions with iodine, fermentation with yeast and bacteria, 

 the formation of characteristic crystalline osazones with phenylhydrazine 

 and the reducing of alkaline solutions of the oxides of metals like copper, 

 bismuth, mercury, and ammoniacal silver solutions, are the most widely 

 used reactions for testing and differentiating the carbohydrates. The 

 reduction of alkaline solutions of the metallic oxides is due to the easily 

 oxidized aldehyde and ketone structure of the sugar. 



The more common carbohydrates may be listed as follo\vs: 



1. Mono-saccharides. 



Hexoses, C 6 H 12 O 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 



