184 PENTOSES 



The methyl pentoses, C 6 H 19 5 , Rhamnose, Chinovose and Fucose. 



Erythritol, C 4 H 10 O 4 . 



Adonitol, C 5 H 10 O 5 . 



Mannitol, Dulcitol and Sorbitol, C 6 H 8 (OH) . 



Perseitol, C 7 H 9 (OH) 7 . 



The Furfuroids. 



Lignone or Lignose. 



Pectin substances. 



The Glucosides and similar bodies. 



The monosaccharoses 



1. The pentoses, C 5 H 10 O 5 . The most important are Z-arabinose 

 and Z-xylose. 



Arabinose. This rarely, if ever, occurs free in plants but is easily 

 obtained by the hydrolysis of araban, which is one of the gum-like 

 constituents of many vegetable tissues. 



It is a crystalline solid with intensely sweet taste, very soluble in 

 hot, but much less soluble in cold, water and insoluble in alcohol. Its 

 constitution is represented by the formula : 



HC( 



HCO 



30H 

 HOCH 

 HOCH 

 H 2 COH 



It is therefore /-arabinose though it is strongly, dextro-rotatory. 

 The dextro-form has been obtained artificially. 



Xylose. This, too, does not occur ready formed in plants but 

 results from the hydrolysis of xylan, the main constituent of wood 

 gum. It resembles arabinose in properties but dissolves in hot 

 alcohol. 



Like arabinose it is an aldose and reduces copper salts. Eibose is 

 another isomeric pentose obtained artificially. Xylose and ribose 

 have the following constitutional formulae : 



HCO HCO 



HCOH HOCH 



HOCH HOCH 



HCOH HOCH 



H 2 COH H,COH 



Z-xylose. Z-ribose. 



