CHEMISTRY OF SAPONINS 183 



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 : — 



CsjHgaO,^ + 2H2O = C;,oH4806 + ■zQ^^VivP^ + "^^^^vP^ 

 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. 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. 



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 

 to the ferrous condition, and so giving rise to the formation 

 of Turnbull's blue. 



If boiled with acetic anhydride, alone or in presence of 

 sodium acetate or zinc chloride, the saponins are converted 

 into acetyl derivatives which are no longer toxic. On boiling 

 the acetyl derivatives with alcoholic potash the acetyl groups 

 are removed, but the resulting compound is not identical with 

 the original saponin. 



When treated with a hot saturated solution of baryta a 



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

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

 Archiv," 1906, 113, 185). 



