THE CARBOHYDRATES 21 



into two molecules of hexose, is easily effected by acid 

 hydrolysis (boiling with dilute acids). 



C^H^On + H 2 -> 2C 6 H 12 O 6 



The bihexoses do not undergo direct alcoholic fermentation, 

 but they are easily hydrolysed by a variety of enzymes, and 

 it is probable that this is a condition precedent to all or 

 nearly all the fermentative changes to which they are subject. 



Sucrose, saccharose, or saccharobiose is the ordinary house- 

 hold sugar. It is commonly called cane sugar because it 

 was formerly obtained almost exclusively from sugar cane 

 (saccharum officinarum). Large quantities are now obtained 

 from beetroots (Beta maritima) and from certain varieties of 

 maple. 



Sugar canes and beetroots, of course, require very different 

 treatment for the extraction of the sugar, but in principle 

 the methods are much alike. Briefly, in both cases, the 

 material is reduced to pulp by machinery, and the juiceTwhich 

 contains from 10 to 20 per cent, of sugar is separated by 

 diffusion. Lime is then added to neutralise the acids and 

 precipitate proteins. The solution is filtered through animal 

 charcoal to decolorise it, and concentrated by evaporation 

 in vacuum pans to a thick syrup from which the sugar 

 crystallises on cooling. The product so obtained is called 

 " raw sugar," and the mother liquor containing uncrystallisable 

 sugar is called molasses or treacle. 



Pure cane sugar is a very stable compound. It melts 

 without decomposition at 160 C. and resolidifies on cooling. 

 It does not reduce Fehling's solution. It is dextrorotatory in 

 its action on polarised light, [a] D = + 66*5. On hydrolysis 

 it is split up into equal molecules of dextrose (^/-glucose) and 

 Isevulose (^-fructose), and as the specific rotatory power of the 

 latter exceeds that of the former (p. 20) the optical activity 

 is reversed or "inverted," i.e. the mixture is laevorotatory, 

 [a] D = 1 8*8. This mixture is therefore often called 

 "invert sugar" and the process of hydrolysis is described as 

 " inversion." 



Taking all the facts into consideration Fischer has proposed 



