104 PLANT COMPOUNDS 



an aldehyde or ketone group. Carbohydrates are divided 

 into two classes, the Sugars and the Non-sugars. 



The principal sugars contain either one unit group of six 

 carbon atoms, called monosaccharides, like dextrose and 

 levulose, or two unit groups, called disaccharides, like sucrose 

 and maltose. The sugars are soluble crystalline compounds, 

 of sweet taste. Dextrose is dextrorotatory; that is, it turns 

 the plane of polarized light to the right. It reduces Fehling's 

 solution and forms glucosides which are condensation pro- 

 ducts of dextrose with an alcohol, aldehyde, or ketone. 

 Levulose is levorotatory; that is, it turns the plane of polar- 

 ized light to the left. It also reduces Fehling's solution. 

 Sucrose is dextrorotatory and does not reduce Fehling's 

 solution. It is hydrolyzed by an enzyme called invertase, 

 or by dilute mineral acids, to equal quantities of dextrose 

 and levulose. This mixture of sugars is called invert sugar, 

 because its rotation is to the left, or is inverted from that 

 of sucrose. This is due to the fact that the levorotation of 

 levulose is stronger than the dextrorotation of dextrose. 

 Maltose is dextrorotatory and reduces Fehling's solution. 

 It is hydrolyzed by an enzyme called maltase, or by dilute 

 mineral acids, to dextrose, one molecule of maltose changing 

 to two molecules of dextrose. The hydrolysis of sucrose 

 and maltose shows the glucoside-like character of these 

 disaccharides. 



The non-sugars, or polysaccharides, contain an unknown 

 number of unit groups of the monosaccharides. They are 

 non-crystalline, tasteless, and insoluble in cold water. 

 Starch is composed of cellulose-covered grains which split 

 in hot water and form a semisolution called starch paste. 

 It turns blue with iodine, does not reduce Fehling's solution, 

 and hydrolyzes with diastase to maltose, and with dilute 

 mineral acids to dextrose. Cellulose is much more complex 

 in structure than starch. It unites with alkalies like sodium 

 hydroxide, and with acids like nitric and acetic. The soda 

 cellulose treated with carbon disulphide is soluble in water 

 from which the cellulose is regenerated in different physical 

 form by spontaneous decomposition. The resultant material 

 can be used for a variety of purposes on account of its 



