DISACCHARIDES 77 



of this sugar, while one of the most important sources of sugar is the 

 root of the sugar-beet, a variety which has originated by selection from 

 the common beet (Beta maratima). Cane-sugar was not known in 

 Europe until its introduction from the tropical parts of Asia where the 

 sugar-cane has been grown from time immemorial. The possibility 

 of extracting cane-sugar from beets was not realized until it was pointed 

 out by the German chemist Marggraff in 1760. Hence the large con- 

 sumption of sugar now obtaining among European peoples is a recently 

 acquired habit. It is, of course, of enormous nutritive importance as 

 it results in reducing by an equivalent amount the requirement of 

 starch and other polysaccharides. It also enables us, when sugar from 

 the cane is used, to utilize tropical areas for the production of carbo- 

 hydrate foodstuffs and set free greater areas of the temperate regions 

 for the cultivation of polysaccharides and proteins (grains, meat and 

 dairy products) for which the tropical areas of the world are not suit- 

 able. The consumption of sugar from the cane is therefore economically 

 preferable to the consumption of sugar from the beet. 



Cane-sugar does not reduce Fehling's solution nor does it exhibit 

 mutarotation. It is neither potentially nor actually an aldehyde or a 

 ketone. It is very readily hydrolyzed by acids, therein differing 

 markedly from other disaccharides, and it yields on hydrolysis, one 

 molecule of d-Glucose and one of d-Fructose (levulose). It will be 

 recollected that d-fructose is levorotatory, and the levorotatory power 

 of d-fructose being greater than the dextrorotatory power of d-glucose, 

 the mixed products of cane-sugar hydrolysis are levorotatory. Cane- 

 sugar, on the contrary, is dextrorotatory, so that hydrolysis of cane- 

 sugar in solution leads to a change of optical rotation from right to 

 left. Hence the process of the hydrolysis of cane-sugar is frequently 

 termed Inversion. 



Cane-sugar is built up by the union of a molecule of d-glucose with 

 one of d-fructose. The question arises, however, from which of the two 

 d-glucoses is cane-sugar derived; the a-d-glucose or the /3-d -glucose? 

 This question is answerable in a very simple way. It is possible to 

 hydrolyse cane-sugar very much more rapidly than a-d-glucose can 

 undergo transformation into /3-d-glucose or vice versa. It will be 

 recollected that a-d-glucose possesses a much higher dextrorotatory 

 power than /3-d-glucose. Now we find that the glucose produced in the 

 hydrolysis of cane-sugar possesses, initially, a high rotatory power. 

 On adding ammonia, which accelerates the transformation of a- into 

 0-glucose, the rotation due to glucose falls. Hence the glucose set 

 free in the hydrolysis of cane-sugar is a-glucose, and cane-sugar is 

 therefore to be regarded as a derivation of a-d-glucose. 



Cane-sugar does not react with phenylhydrazine. It contains 

 eight hydroxyl groups, for it forms an octa-acetate, in which these 

 groups have been replaced by acetyl groups. Apart from this it has 

 not proved possible to ascribe any satisfactory constitutional formula 

 to cane-sugar. The synthesis of cane-sugar has, however, been accom- 



