192 Biological Chemistry. 



THE SUGARS. 



The best known representative of this class is cane- 

 sugar or sucrose, the ordinary sweetening agent prepared 

 usually from the sugar-cane and the beet. This substance 

 has the formula C 12 H 22 O n , but on hydrolysis (with dilute 

 solutions of mineral acids and certain ferments) it undergoes 

 scission into a mixture of equal parts of two isomeric sugars 

 known as dextrose or glucose and laevulose or fructose 

 C 12 H 22 O n + H 2 = C 6 H ]2 6 + C 6 H 12 6 



Dextrose. Laevulose. 



Dextrose rotates the plane of polarization to the right 

 and laevulose to the left. As the laevulose has a greater 

 laevo rotation than dextrose has a dextro rotation, the mix- 

 ture of equimolecular proportions of the two sugars is 

 laevo-rotatory. As the original cane-sugar solution is dex- 

 tro-rotatory, the direction of rotation changes on hydrolysis. 

 The conversion by hydrolysis of the cane-sugar into dex- 

 trose and Isevulose is known, therefore, as inversion, and 

 the mixture of sugars is called " invert sugar," and is 

 extensively used for the manufacture of preserves and of 

 alcohol. The simpler sugars, dextrose and Isevulose, belong 

 to the sub-class of the moTiosaccharoses ; whilst cane-sugar, 

 which is degraded on hydrolysis into two molecules of 

 moTiosaccharoses, is known as a disaccharose. Other sugars 

 still more complex than cane-sugar are known, which on 

 hydrolysis undergo scission into three molecules of mono- 

 saccharoses. As an example of this class, the sugar melitose 

 or raffinose, which is found in sugar-beet in small quantities, 

 and in Australian manna in relatively large quantities, 

 may be cited. This sugar undergoes scission on hydrolysis 

 into a mixture of the isomeric sugars dextrose, laevulose, 

 and galactose 



C J8 H 32 16 + 2H 2 = C 6 H 12 G -f C 6 H 12 6 + C 6 H 12 O fl 



Dextrose. Laevulose. Galactose* 



