116 



THE CARBOHYDRATES. 



[CH. V. 



Sucrose (cane sugar) is widely distributed in the 

 vegetable kingdom, where it functions as a reserve material. 

 It crystallises well, is very soluble in water, and has a much 

 sweeter taste than glucose. 



It does not reduce Fehling's solution, does not form an 

 osazone, and does not behave as an aldehyde or ketone. 

 It is hydrolysed very readily by boiling acids to a mixture 

 of glucose and fructose. Cane sugar is dextrorotatory, 

 but since fructose is more laevorotatory than glucose is 

 dextrorotatory, a mixture of the two in equal parts is 

 laevorotatory. So the sign of rotation being inverted by 

 hydrolysis, the process is known as inversion, and the 

 product as " invert sugar." This hydrolysis is also effected 

 by the enzyme invertase (sucrase), which is found in the 

 small intestine and in certain yeasts. 



The constitution of cane-sugar is not yet definitely 

 established, but in all probability it is formed by the 

 condensation of glucose and fructose in such a way as to 

 destroy both the aldehyde and the ketone groups. 



H.C 



CH 2 OH 



CH 2 OH 



Glucose portion. 



CH 8 OH 



Fructose portion. 



Use a freshly prepared i per cent, solution of pure white crystalline cane 

 sugar (" coffee sugar ") for the following reactions. 



129. Repeat Exs. 95 and 97. Sucrose is not affected by alkali, 

 and does not reduce alkaline copper solutions. 



