gum

gum term commonly applied to any of a wide variety of colloidal substances somewhat similar in appearance and general characteristics, exuded by or extracted from plants. In this classification, however, many substances that are not true gums are included, among them many resins , so-called gum resins, and such substances as frankincense, myrrh, labdanum, copal, amber, chicle, and rubber (gum elastic, India rubber). True gums are complex organic substances mostly obtained from plants, some of which are soluble in water and others of which, although insoluble in water, swell up by absorbing large quantities of it. With water they form thick, gluey fluids. Their chemical nature is complex. In general, they contain in various proportions carbon, hydrogen, oxygen, and such metals as calcium, magnesium, and potassium in the form of salts of various organic acids. Gum arabic, or gum acacia, is a typical, water-soluble gum obtained from various plants of the genus Acacia, chiefly those found in Africa. A complex polysaccharide containing metal salts, gum arabic varies in color from white to red and is used extensively in making inks, adhesives, and confections; in the textile industry for filling fabrics; and in medicine as an emollient. Gum senegal is very similar. Among the gum resins (mixtures of gums and resins) are ammoniac , asafetida, bdellium , gamboge , and myrrh. See also tragacanth .

Bibliography: See C. L. Mantell et al., The Technology of Natural Resins (1942); C. L. Mantell, The Water-Soluble Gums (1947, repr. 1965); R. L. Davidson, Handbook of Water-Soluble Gums and Resins (1980).

gum Secretions of plants. Gums are chemically complex, consisting mainly of various saccharides bound to organic acids. Common examples are gum arabic (used as an adhesive on envelopes and postage stamps), agar and tragacanth. Chewing gum is derived from the sapodilla tree. See also eucalyptus; resins

gum. A sticky liquid exuded by certain trees and shrubs, various types of which have been used in making paints from ancient times. The most commonly used is gum arabic, obtained from a species of acacia, which is the normal binding agent for watercolours.