Characteristic of the Sahara is the date-palm, which flourishes where other vegetation can scarcely maintain existence, while in the semi-desert regions the acacia (whence is obtained gum-arabic) is abundant.
The acacia tree is common, and from it gum-arabic of good quality is obtained.
His early work on the movements of gases led him to examine the spontaneous movements of liquids, and as a result of the experiments he divided bodies into two classes - crystalloids, such as common salt, and colloids, of which gum-arabic is a type - the former having high and the latter low diffusibility.
True gum-arabic is the product of Acacia Senegal, abundant in both east and west tropical Africa.
The fruits of Zizyphus do not enter into the composition of the lozenges now known as jujubes which are usually made of gum-arabic, gelatin, &c., and variously flavoured.
Long by 22 broad, produces gum-arabic, and is the seat of a lucrative turtle-fishery.