CARBOHYDRATES. 533 



Disaccharides. 



The general physical properties and the solubility of disaccharides 

 are identical with those of the monosaccharides. They differ from them 

 by not fermenting directly and by not forming osazones. The empiri- 

 cal formula is C 12 H 22 O U . By treatment with dilute mineral acids or 

 by the action of certain enzymes they undergo hydrolysis i. e., take 

 up a molecule of water and are resolved into two hexose molecules. 

 Thus, cane-sugar splits up into dextrose and levulose ; lactose into 

 dextrose and galactose ; maltose into two molecules of dextrose. 



Cane-sugar is dextrorotatory, but the mixture obtained by the hy- 

 drolysis of cane-sugar is laevorotatory, because levulose turns the 

 plane of polarization more to the left than dextrose does to the right. 

 For this reason the mixture is called inverted sugar and the hydrol- 

 ysis inversion. The term inversion is therefore used to designate the 

 splitting of disaccharides into simpler sugars. The building up of 

 complex sugars from simple sugars is called reversion. 



Lactose and maltose reduce alkaline copper solution ; cane-sugar 

 does not. 



Cane-sugar, Saccharum, C 12 H 22 O U = 339.6 (Saccharose, Com- 

 mon sugar, Beet-sugar}. Cane-sugar is found in the juices of 

 many plants, especially in that of the different grasses (sugar-cane), 

 and also in the sap of several forest trees (maple), in the roots, stems, 

 and other parts of various plants (sugar-beet), etc. Plants contain- 

 ing cane-sugar do not contain free organic acids, which latter would 

 convert it into grape-sugar. 



Cane-sugar is manufactured from various plants containing it by 

 crushing them between rollers, expressing the juice, heating and 

 adding to it milk of lime, which precipitates vegetable albuminous 

 matter. The clear liquid is evaporated to the consistency of a syrup, 

 which is further purified (refined) by filtering it through bone-black 

 and evaporating the solution in " vacuum pans" to the crystallizing- 

 point; the mother-liquors are further evaporated, and yield lower 

 grades of sugar; finally a syrup is left which is known as molasses. 



Cane-sugar forms white, hard, distinctly crystalline granules, but 

 may be obtained also in well-formed, large, monocliuic prisms. It 

 dissolves in 0.2 part of boiling, in 0.5 part of cold water, and in 175 

 parts of alcohol ; when heated to 160 C. (320 F.) it fuses, and the 

 liquid, on cooling, forms an amorphous, transparent mass, known as 

 barley sugar; at a higher temperature cane-sugar is decomposed, 

 water is evolved, and a brown, almost tasteless substance is formed, 

 which is known as caramel or burnt sugar. Oxidizing agents act 



