GUMS AND RESINS
The true gums are formed as the result of the disintegration of internal tissues, for the most part from the decomposition of cellulose, through a process known as gummosis. Gums contain a large amount of sugar and are closely allied to the pectins. They are colloidal in nature and soluble in water, either dissolving completely or swelling, but are insoluble in alcohol and ether. They exude naturally from the stems, or in response to wounding. The commercial gums reach the market in the form of dried exudations. Gums are especially common in plants of dry regions. They find their greatest use as adhesives, and are also used in printing and finishing textiles, as a sizing for paper, in the paint and candy industries, and as drugs. The three most, important commercial gums are gum arabic, gum tragacanth, and karaya gum.
Gum Arabic . This is a dried gummy exudation obtained from Acacia Senegal and related species, small native trees of arid Northern Africa. They are extensively cultivated in the Sudan. The trees are tapped between February and May, when the fruits are ripe. Transverse incisions are made with a small ax (Fig. 77) and thin strips of the outer bark are torn off. The gum slowly exudes as a viscous liquid, collects in a drop, and hardens. After three to eight weeks these "tears" are collected. They are bleached by the sun, and the impurities are removed before shipping. Gum arabic was used by the Egyptians as early as 2000 B.C. Sudan gum has been an article of commerce since A.D. 100. Several kinds reach the world's markets. Kordofan or hashab gum is exported from the region around Cairo and Port Sudan, while Senegal gum comes from north of the Senegal River. Gum arabic is slowly and completely soluble in cold water and has it high degree of adhesiveness and viscosity. Most of it is used in the textile, mucilage, paste, polish, and confectionery industries, and as a glaze in painting. In medicine it is used as an emulsifying agent and as a demulcent.
Gum Tragacanth . This gum forms as a result of the transformation of the pith and medullary-ray cells into a mucilaginous substance that exudes naturally or after the bark has been punctured or excised. It comes from Astragalus gummifer and other species of the genus, thorny shrubs of the and regions of Western Asia and Southeastern Europe.