166 GLUCOSIDES [ch. 



Aesculin is characterized by giving in water solution a blue fluor- 

 escence which can be detected even in great dilution. The fluorescence 

 is increased in alkaline, and decreased in acid, solution. 



Expt. 155. DemoTistration of the presence of aesculin in Aesculus hark. Strip off 

 the bark from some young twigs of Aesculus and boil in a little water in an evaporating 

 dish. Filter and pour the filtrate into excess of water in ^a large vessel. A blue 

 fluorescent solution will be formed. 



Glucosides of Flavone, Flavonol and Anthocyan Pigments. 



These substances have already been considered in Chapter viii. 



Glucosides of vakious Composition, 



Coniferin. This glucoside (see also p. 104) occurs in various members 

 of the Coniferae and also in Asparagus. On hydrolysis with mineral acids 

 or emulsin, it breaks up as: 



/X 



Coniferin 



OH 



Coniferyl alcohol 



Arbutin. This glucoside is found in the leaves of the Bearberry 

 (Arctostaphylos Uva-ursi), Pyrola, Vaccinium, and other Ericaceae and 

 also of the Pear (Pyrus communis). 



On hydrolysis with acids arbutin yields quinol and glucose: 



C12H16O7 + HaO;^ CfiHeOa + CeHjoOe 



The same hydrolysis is brought about by the enzyme emulsin. 



It has been suggested that the darkening of leaves of the Pear 

 (Bourquelot and Fichtenholz, 11, 12, 13) either on autolysis or injury, or 

 at the fall of the leaf, is due to the hydrolysis of the arbutin by a gluco- 

 side-splitting enzyme in the leaf, and subsequent oxidation of the 

 hydroquinone so formed by an oxidase. 



Expt. 156. Extraction of arhutin from leaves of the Pear (Pyrus communis). 

 Weigh out 100 gms. of fresh leaves (without petioles). Tear the leaves into small 

 pieces and drop them as quickly as possible into about 500 c.c. of boiling 96-98 0/ 

 alcohol in a flask. Boil for about 20 mins., adding more alcohol if necessary. Then 

 filter off the alcohol and pound up the leaf residue in a mortar and extract again with 

 boiling alcohol. Filter and distil off the alcohol from the extract in vacuo. Extract 

 the residue with 100-200 c.c. of hot water and filter. Warm the filtrate and precipitate 

 with lead acetate solution until no more precipitate is formed. This removes flavones» 



