194 THE CONSTITUENTS OF PLANTS. IX. 



sulphuric acid. So obtained it is used in brewing and in the 

 manufacture of jams and sweetmeats. 



It crystallizes with difficulty and is much less sweet than 

 cane sugar. It reduces copper solutions and easily undergoes 

 fermentation. 



Its compounds with lime and baryta, C G H 12 G .CaO and 

 C 6 H 12 O 6 .BaO, are insoluble in alcohol. 



Gulose, Galactose, Talose, and Idose are isomeric sugars. 

 All these bodies are, like mannose and glucose, aldohexoses, 



I 

 i.e., contain the group HCO. 



Fructose, C H U O 6 - CH,OH.(CHOH) 3 .CO.CH 2 OH, also 

 called levulose and fruit sifgar, occurs in most sweet fruits. It 

 is produced, together with an equal amount of glucose, by the 

 hydrolysis of cane sugar 



cj^Ou+HaO = c 6 H M o,,+c fl H M o fl 



Dextrose. Levulose. 



Since cane sugar is dextro-rotatory and levulose more levo- 

 rotatory than dextrose is dextro-rotatory, the mixture resulting 

 from the hydrolysis of cane sugar rotates the plane of polarisa- 

 tion to the left. Hence the name invert sugar given to the 

 mixture. Fructose also is formed by the action of hot water 

 upon inulin. 



An inactive form of fructose has been formed artificially by 

 the action of lime or magnesia upon formaldehyde, COH 2 , or 

 of soda upon glycerose, i.e., glyceryl aldehyde, C 3 H 6 ;S . The 

 main product of this reaction has been called Formose (i-fruc- 

 tose) ; in addition a-Acrose (methose) is produced. 



Sorbinose or Sorbose occurs in the berries of the mountain 

 ash, probably as sorbitol, C 6 H 14 6 . It is a crystalline, very 

 sweet substance, turned yellow by alkalies, and capable of re- 

 ducing copper solutions. It is not fermentable by yeast. 



(b) The Saccharobioses, Dioses, or Di-saccharides. 



These sugars consist of two molecules of hexoses or monoses 

 united together with the elimination of a molecule of water. 

 They, therefore, possess the composition C IZ H. W O U . They are 



