RAFFINOSE 89 



fineries, however, contain from 2-3 per cent of raffinose (hence 

 the name) and form the chief commercial source of this sugar. 



As the concentration of the raffinose increases it tends to 

 crystallize out together with the cane sugar in the form of 

 mixed crystals having a peculiar and characteristic pointed 

 appearance quite different from ordinary cane sugar. 



Numerous methods * have been described for preparing 

 pure raffinose from molasses, but as they are mostly rather 

 tedious they will not be detailed here. 



According to Bau,f raffinose may be extracted from cotton 

 seeds by the following simple process. The powdered seeds, 

 after being freed from fat by means of ether, are extracted 

 with hot 70 per cent alcohol and the extract is heated with 

 animal charcoal, filtered, and evaporated ; on cooling raffinose 

 crystallizes out and may be further purified by recrystalliza- 

 tion from alcohol. 



Raffinose crystallizes with 5 molecules of water in clusters 

 of slender glistening needles or prisms whose composition is 

 expressed by the formula C 18 H 32 O 16 . 5H 2 O. It dissolves in 

 water and in methyl alcohol, in which latter solvent cane sugar 

 is only sparingly soluble, but is hardly soluble in ethyl alcohol, 

 whereas cane sugar is appreciably soluble. 



It is strongly dextro-rotatory, ao= + 104-4, in 10 per cent 

 solution, and consequently cane sugar in which raffinose occurs 

 as an impurity appears to contain more than 100 per cent of 

 sucrose when estimated polari metrically ; hence raffinose is 

 sometimes known as " plus sugar ". 



It does not reduce Fehling's solution, nor does it react with 

 phenylhydrazine. 



On careful hydrolysis raffinose breaks up at first into levu- 

 lose and a disaccharide melibiose. 



C 18 H 32 16 + H 2 = C 6 H 12 6 



Raffinose Levulose Melibiose 



On heating further the melibiose itself is broken up as 

 follows : 



C ia H 22 O u + H 2 = C 6 H 12 6 + C 6 H 12 6 

 Melibiose Dextrose Galactose 



* v. Lippmann : " Die Chemie d. Zuckerarten," 3rd ed., Braunschweig, Vol. 

 II., p. 1628. 



fBau: "Chem. Zeit.," 1894, 18, 1796. 



