122 THE CARBOHYDRATES 



obtained from Geum urbanum, and is found to be composed 

 of one molecule of glucose and one of arabinose.* 



STROPHANTHOBIOSE. Ci^H.^Oio. 



This disacchaiide likewise occurs in a glucoside, stro- 

 phanthin. On hydrolysis it yields mannose and rhamnose 

 (CeHi^OJ.t 



TRISACCHARIDES. 



RAFFINOSE. C,oH,,0 



18^-^32^ia- 



This sugar occurs in cotton seeds, barley, eucalyptus, 

 lotus, $ and also in the beetroot ; the juice of this latter con- 

 tains on an average about 15 per cent of cane sugar but only 

 0-02 per cent § of raffinose. The molasses from beet sugar re- 

 fineries, however, contain from 2-3 per cent of raffmose (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 raffi.nose from molasses, but they are mostly rather 

 tedious and a more convenient source for its preparation is 

 cotton-seed meal ^ 



Raffinose crystallizes with five molecules of water in clusters 

 of slender glistening needles or prisms whose composition is 

 expressed by the formula CigHggOie . 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. 



* Bertrand and Weisweiller: " Compt. rend.," 1908, 146, 1413. 

 Herissey and Cheymol : id., 1925, 180, 384 ; and 181, 565. 



f Feist : " Ber. deut. chem. Gesells.," 1900, 33, 2091. 



X Hemmi : " J. Coll. Agr. Imp. Univ. Sapporo," 1921, 9, 249. 



§ Strohmer : " Oest. Ung. Z. f. Zuckerind u. Landw.," 1910, 39, 649. 



II V. Lippmann : " Die Chemie d. Zuckerarten," 3rd ed., Braunschweig, 

 Vol. II., p. 1628. 



^ Englis, Decker, and Adams : " J. Amer. Chem. Soc," 1925, 47, 2724. 

 Harding : " Sugar," 1922, 240. 



