SAPONINS 263 



treated with lead acetate which precipitates the acid saponins, 

 while the neutral saponins are only precipitated by basic 

 lead acetate. The resulting lead salts of the saponins are 

 best decomposed by treatment with dilute sulphuric acid. 

 Alternatively, saponins may in many cases be precipitated 

 from their aqueous solutions by saturated baryta, and in some 

 cases they may be salted out by the saturation of their solu- 

 tions by ammonium sulphate. 



From their solutions in alcohol they are precipitated by 

 alcoholic solutions of cholesterol or phytosterol with the 

 formation of cholesterides, a property of digitonin which is 

 utilized for estimating sterols (see p. 50). These cholesterol 

 compounds are, as a rule, easily decomposed ; in most cases, 

 prolonged extraction with ether will remove the cholesterol, 

 and the saponin is recovered unchanged and possesses its 

 original physiological action (see below). 



Constitution. 



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 other 

 sapogenin together with more sugar. 



The hydrolysis of digitonin, the saponin contained in 

 Digitalis purpurea, may, according to Kiliani, be represented 

 by the equation — 



C,,U,,0,^ + 2H2O = CjoH^sOe + 2C6Hi,06 + 2CeHi,Oe 

 Digitonin Digitogenin Glucose Galactose 



Reactions. 



The following reactions are made use of in demonstrating 

 the presence of a saponin : — 



* 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). 



