The plant, it will be remembered, was originally extracted with ether in which rhamnose is practically insoluble.
The exception referred to is the occurrence of a free sugar, supposed to be rhamnose, in a certain palm-wine.
Fustin, on heating with dilute sulphuric acid, gave fisetin and a sugar supposed to be rhamnose.
It is composed of one molecule of glucose united to two molecules of rhamnose (methyl pentose, C6H12O5).
By warming with alkalies or barium hydroxide, rhamnose is colored yellow.
Glucosides which are derivatives of rhamnose require a special enzyme, known as rhamnase, for their hydrolysis.
The solution then gave the above mentioned characteristic tests for rhamnose.