74 THE CARBOHYDRATES 



LACTOSE OR MILK SUGAR. 



This disaccharide, though of considerable importance in 

 the animal kingdom, is never found in plants and need not 

 therefore be considered here. 



TRISACCHARIDES. 



RAFFINOSE. 



This sugar occurs in cotton seeds, barley, eucalyptus, 

 manna and also in the beetroot ; the juice of this latter contains 

 on an average about 1 5 per cent of cane sugar but only 0-02 per 

 cent* of raffinose. The molasses from beet sugar refineries, 

 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 f 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,J 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^gHg^O^g. 5H2O. 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, ar>= + 104 "4°, in 10 percent 



*Strohmer : " Oest. Ung. Z. f. Zuckerind. u. Landw.," igio, 39, 649. 

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

 IL p. 1628. 



X Bau : *'Chem. Zeit," 1894, 18, 1796. 



