SECTION IV. 



GLUCOSIDES. 



A GLUCOSiDE may be defined as a substance which on hydrolysis 

 yields a reducing sugar, wherefore, strictly speaking, di-, tri- 

 and poly-saccharides would be included. Custom, however, 

 restricts the term to those compounds which in addition to 

 reducing sugars also yield one or more other substances which, 

 not infrequently, are of an aromatic nature. The non-sugar 

 constituent, which is sometimes termed an aglucan, may belong 

 to various chemical classes as is seen in the following selected 

 examples : — 



Glucoside. Aglucan. 



Salicin. The alcohol saligenin. 



Coniferin. Coniferyl alcohol. 



Amygdalin. Benzaldehyde and hydrocyanic acid. 



Monotropitin. Methyl salicylate. 



Phaseolunatin. Acetone and hydrocyanic acid. 



Arbutin. The phenol hydroquinone. 



Indigo. Indoxyl. 



Sinigrin. AUyl isothiocyanate. 



Anthocyanin. Anthocyanidin. 



Quercitrin. Flavonol. 



The tannins, fiavones, and anthocyans, owing to their special 

 botanical significance, will be dealt with in subsequent sections. 



The carbohydrate constituent of the glucoside molecule 

 is commonly glucose, but many other sugars may occur in 

 place of the glucose ; galactose and mannose amongst the 

 hexoses ; rhamnose and other pentoses ; gentiobiose, C12H22OH, 

 the disaccharide of amygdahn ; and primeverose, CnHagOio, 

 the disaccharide of monotropitin. 



The glucosides are generally soluble in water or dilute 

 alcohol which solvents may be used for their extraction from 

 plant tissues. Owing to the fact that glucosides are not pre- 

 cipitated by lead acetate, their solutions may be purified by 



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