184 GLUCOSIDES 



single saponin, namely, Solanin, has basic properties; this 

 substance, which occurs in Solanum nigrum, S. dulcamara and 

 in the fruit of potatoes, owes its basic property to the presence 

 of a nitrogen atom (see Nitrogen Bases, p. 261), and appears 

 to form a connecting link between the saponins and the 

 alkaloids. 



The neutral saponins are precipitated from solution by 

 basic lead acetate, while acid saponins are precipitated by lead 

 acetate. Similarly, barium hydroxide precipitates neutral 

 saponins in the form of their barium compounds (see below). 



On hydrolysis with dilute mineral acids* the saponins 

 yield sugars such as glucose, galactose, arabinose, and rham- 

 nose, together with other substances termed sapogenins, the 

 constitution of which is unknown. 



The nature of the sapogenin obtained from any particular 

 saponin varies with the conditions of the hydrolysis ; in some 

 cases careful hydrolysis may yield a primary sapogenin and a 

 sugar, while more complete hydrolysis gives rise to an end 

 sapogenin together with more sugar. 



The hydrolysis of Digitonin, the saponin contained in 

 Digitalis purpurea, may, according to Kiliani, be represented 

 by the equation : 



Digitonin Digitogenin Glucose Galactose 



On mixing together alcoholic solutions of a saponin and of 

 cholesterol a precipitate of the cholesterol compound is at 

 once formed (p. 17). These cholesterol compounds are, as a 

 rule, easily decomposed ; in most cases, prolonged extraction 

 with ether will remove the cholesterol, and the saponin is re- 

 covered unchanged and possesses its original physiological 

 action. 



The saponins are reducing agents, and will reduce am- 

 moniacal silver nitrate to metallic silver; similarly, prolonged 

 boiling with mercuric chloride reduces this substance to 

 calomel ; saponins also blue a solution of potassium ferri- 

 cyanide containing ferric chloride, by reducing the ferric salt 



* Hydrolysis can, in some cases, be effected by bacteria, and Quillaia 

 saponin is even said to be hydrolysed by emulsin (see Gonnermann: " Pfliiger's 

 Archiv," 1906, 113, 185). 



