TRISACCHARIDES 91 



* 



MELECITOSE. C 18 H 32 O 16 , 2H 2 O. 



This is a sugar which occurs in the sap of Larix europaea 

 and in Persian manna ; it crystallizes with two molecules of 

 water in rhombic prisms, and is dextro-rotatory (<Z D = +83). 

 It does not reduce Fehling's solution, and on hydrolysis yields 

 first a molecule of glucose and a disaccharide turanose, 

 C 12 H 22 O n which subsequently itself breaks up into one mole- 

 cule of glucose and one of fructose. 



STACHYOSE. C 24 H 42 O 21 , 4 H 2 O. 



This substance occurs in the tubers of S tacky s tuberifera 

 and in a large number of leguminous seeds.* It forms plate- 

 like crystals, which dissolve readily in water to give a faintly 

 sweet solution, which is dextro-rotatory (a D = + 148). It does 

 not reduce Fehling's solution. When boiled with dilute mineral 

 acid it yields one molecule each of glucose and levulose, and 

 two molecules of galactose.f 



GENTIANOSE. C 18 H 32 O 16 . 



This trisaccharide occurs in the roots of Gentiana lutea. 

 On hydrolysis by mineral acids it is converted into two 

 molecules of glucose and one of fructose. Hydrolysis by 

 means of dilute acids breaks it up into one molecule of 

 fructose and one of gentiobiose (see p. 87), while Aspergillus 

 niger resolves it into one molecule of glucose and one of 

 sucrose. Gentian ose does not reduce Fehling's solution. 



SUGARS OF UNKNOWN MOLECULAR WEIGHT OR SUGAR-LIKE 

 POLYSACCHARIDES. 



Of these sugars lupeose and agavose are examples. The 

 former, which occurs in lupin seeds, does not reduce Fehling's 

 solution, and on hydrolysis yields galactose, fructose and 

 glucose. It is supposed to be a tetrasaccharide.J 



Agavose, obtained from Agave americona, is an optically 

 inactive sugar of unknown constitution which reduces Fehling's 

 solution. 



*Tanret; " Compt. rend.," 1912, 155, 1526. 



f Planta and Schulze: " Ber. deut. chem. Gesells," 1891, 24, 2705. 



% Schulze : id., 1910, 43, 2233. 



Michaud and Tristan : " Araer. Chem. J.," 1892, 14, 548. 



