GLUCOSIDES 43 



takes place to glucose and saligenin (^^-hydroxy- 

 benzyl alcohol) : 



XH2OH 



The following tests should be performed with the 

 solution to demonstrate the presence of the products 

 of hydrolysis : — 



(i.) The hydrolysed solution is rendered alkaline 

 with caustic soda, Fehling's solution added, and the 

 mixture boiled. The characteristic red precipitate 

 of cuprous oxide shows the presence of glucose. 



(ii.) A small quantity of strong K^Cvfi^ solution is 

 added to the hydrolysed solution, which is then boiled 

 with I or 2 c.c. of concentrated sulphuric acid. 

 The saligenin is oxidised to salicylic aldehyde, which 

 is recognised by its characteristic smell, somewhat 

 resembling that of benzaldehyde. 



25. Hydrolysis of Amygdalin. (Cyanogenesis.) 



About 20 grams of almonds are ground up, soaked 

 in water, and allowed to stand for half an hour. 



The enzyme emulsin hydrolyses the amygdalin in 

 the presence of water, with production of glucose, 

 benzaldehyde (oil of bitter almonds), and hydrocyanic 

 acid, thus : — 



C2oH27NOii + 2H20 = C6H6CHO + HCN + 2C6Hi206. 



The benzaldehyde is recognised by reason of its smell, 

 while the presence of hydrocyanic acid can be demon- 

 strated as follows : — 



The liquid is transferred to a distillation flask, and 

 about 20 c.c. distilled over into a receiver through a 

 suitable condenser. 



