INVERSION OF CANE SUGAR 33 



Specific Rotations of different Sugars. 



Cane sugar (sucrose) +66' 5° 



Glucose +53°^ 



Fructose —71° 



Maltose +141° 



Lactose +52° 



The polarimeter method is employed very largely for the 

 estimation of (cane) sugar in solutions obtained during the manu- 

 facture of that substance from cane or beet. The method is 

 capable of great accuracy, and has the additional advantage of 

 being quickly performed. 



19. Inversion of Cane Sugar. 



The bioses, being produced from two monose molecules by 

 condensation with the loss of i molecule of water, are generally 

 readily convertible into monoses by hydrolysis with dilute acids. 



Cane sugar, for example, readily undergoes this change, giving 

 a mixture of equal molecules of glucose and fructose, known as 

 " invert " sugar. 



C12H22O11+ H2O = C6,Hi206+ CgHiaOg. 

 Cane sugar Glucose Fructose. 



The specific rotation of cane sugar is +66'5°, while that of 

 glucose is +53°, and that of fructose -71°. The specific rotation 

 of the solution of invert sugar is therefore negative, and con- 

 sequently the progress of the inversion can be followed directly 

 by means of the polarimeter. 



Twenty-five c.c. of the 20 per cent, sugar solution 

 are thoroughly mixed with an equal volume of normal 

 HCl or H2SO4, and the observation tube of the polar- 

 imeter filled as quickly as possible with the mixture. 



A reading of the rotation is taken at once and the 

 time of reading noted. As the angle alters quickly 

 during the first few minutes, readings should at first 



1 When freshly dissolved in cold water, glucose gives a much 

 greater rotation, owing to the existence of an unstable isomeride, 

 which passes into a stable equilibrium mixture, slowly in the cold, 

 quickly on heating, or in the presence of alkali. 



C 



