224 THE CARBOHYDRATES. 



hydrolytic cleavage of complex carbohydrates. Isomaltose is also obtained 

 from glucose by reversion (see page 225). 



The disaccharides or hexobioses are to be considered as glucosides, 

 each of which is derived from two monosaccharides with the exit of 1 

 molecule of water. Corresponding to this, their general formula is 

 Ci2H220n. On hydrolytic cleavage and the addition of water they 

 yield 2 molecules of hexoses, either 2 molecules of the same hexose or 

 one each of two different hexoses. Thus 



Saccharose +H20 = glucose + fructose; 

 Maltose + H2O = glucose -f glucose ; 

 Lactose -f-H^O = glucose +galactose. 



The configuration of the disaccharides has not been positively determined. 



The fructose turns the polarized ray more to the left than the glucose 

 does to the right; hence the mixture of hexoses obtained on the cleavage 

 of saccharose has an opposite rotation to the saccharose itself. On 

 this account the mixture is called INVERT-SUGAR, and the hydrolytic 

 splitting is designated as inversion. This term, "inversion," is not only 

 used for the splitting of saccharose, but is also used for the hydrolytic 

 cleavage of compound sugars into monosaccharides. The reverse reaction, 

 whereby monosaccharides are condensed into complex carbohydrates, is 

 called reversion. 



We subdivide the disaccharides into two groups, first, the group to 

 which saccharose belongs, where the members do not have the property 

 of reducing certain metallic oxides; and the second group, to which the 

 two maltoses and lactose belong, the members acting like monosaccharides 

 in regard to the ordinary reduction tests. The members of the latter 

 group have the character of aldehyde alcohols, and in milk-sugar the 

 aldehyde characteristics are connected with the glucose fraction. 



Saccharose, or CANE-SUGAR, occurs extensively distributed in the 

 plant kingdom. It occurs to the greatest extent in the stalk of the sugar- 

 millet and sugar-cane, the roots of the sugar-beet, the trunks of certain 

 varieties of palms and maples, in carrots, etc. Cane-sugar is of extraor- 

 dinary great importance as a food and condiment. 



Saccharose forms large, colorless monoclinic crystals. On heating it 

 melts in the neighborhood of 160 C., and on heating more strongly it 

 turns brown, forming so-called caramel. It dissolves very readily in 

 water, and- according to HERZFELD, 1 100 parts of saturated saccharose 

 solution contain 67 parts of sugar at 20 C. It dissolves with difficulty 

 in strong alcohol. Cane-sugar is strongly dextrorotatory. The specific 

 rotation is only slightly modified by concentration, but is markedly 



1 See Tollens' Handbuch der Kohlehydrate, 2. Aufl. 1, 154. 



