Saponin

Saponin is a vegetable principle contained in various plants, including the Saponaria officinalis, or Soap-wort, the Polygala senega, several varieties of Lychnis, the fruit of the horse-chestnut, and in Quillia bark. It is readily extracted from the root of soap-wort by means of boiling alcohol, which, as it cools, deposits the saponin as an amorphous sediment. It derives its name from its behaviour with water, in which it is soluble in all proportions, yielding an opalescent fluid which froths when shaken like a solution of soap, if even $\backslash frac\{1\}\{100\}$th part of saponin be present. Its solution, or an infusion of soap-wort, is sometimes employed in place of a solution of an alkaline soap for cleansing the finer varieties of wool from grease. The various preparations for cleaning kid gloves, &c., which are sold under fancy names at every exhibition, owe their virtues to saponin. It is also employed by aerated water makers to give apparent body to their lemonade, &c., the public regarding a persistent head or froth as a guarantee of excellence.