GUARANA′. Syn. Paullinia, Brazilian cocoa. An alimentary and medicinal substance prepared from the seeds of Paullinia sorbilis, a Brazilian tree. The dried seeds, deprived of their aril, are pounded and kneaded into a mass, which is afterwards made into oblong or rounded cakes (GUARANA BREAD). These cakes are used as we use chocolate—mixed with water and sugar, and drank as a beverage. In Brazil this beverage is largely consumed, both on account of its nutritive qualities, and for its stomachic, febrifugal, and aphrodisiac effects. See Chocolate, &c., also below.
GUARANINE′. A crystalline substance discovered by M. Martius in guarana. It appears to be identical with caffeine, the active principle of coffee and tea.
GUD′GEON. The Cyprinus gobeo (Linn.), a small fresh-water fish, common almost everywhere. The white is considered the best. It was formerly used in medicine.
GUM. Syn. Gummi, L. The general term for an important class of vegetable products. Gums are more or less soluble in cold water, but insoluble in alcohol, ether, and oils. They are obtained from certain plants in amorphous masses; most of them exude spontaneously, or on puncturing the bark. The most perfect type of this class is the substance called GUM ARABIC, or GUM ACACIA. The gums are employed as demulcents in medicines, and are used as cements, and for giving stiffness and gloss to textile fabrics. Among the vulgar the term is often incorrectly applied to the resins and gum resins.
Gum Acacia. Syn. Gum Arabic; Acaciæ gummi (B. P.); G. arabicum, G. acacia, Acacia (Ph. L.), L. “From various species” (of Acacia) “yielding gum” (Ph. L. & E.), chiefly Acacia arabica and A. vera. “Whitish or yellowish, transparent or cracked on the surface, and opaque; brittle; it dissolves freely in water.” (Ph. L.) It is scentless, and may be bleached by exposure to the sun and air, at the temperature of boiling water. Sp. gr. 1·355. (Ure.) The pure soluble principle of gum Arabic is termed ARABIN (which see). Barbary or Morocco gum, Gum Senegal, and East India gum, are inferior commercial varieties of the same substance from other species of Acacia (see below).
Powdered gum Arabic (PULVIS ACACIÆ) is frequently adulterated with flour or farina, or with Senegal or other inferior gums. The first may be detected by agitating a little of the powder with cold water; the pure gum dissolves rapidly, whilst the starch or flour falls to the bottom of the vessel. Or, a little of the powder may be mixed with boiling water, and when cold, tested with tincture of iodine; if it contains starch or flour, the paste will assume a blue colour. If it contains cherry-tree gum or tragacanth, it will be only partly soluble in cold water, and the paste will be partly coloured, and more or less interspersed with gelatinous clots.
For the detection of dextrin in gum Arabic Hager finds that when some of the adulterated article is placed in a glass dish, with vertical sides, and a solution of ferric chloride, density 1·48, diluted with an equal volume of water, is poured over it until the grains are just covered, in the course of a minute or so that particles of gum Arabic will adhere to the bottom of the vessel, whilst the grains of dextrin do not.
Much of the white gum Arabic of the shops is formed by bleaching gum Senegal, by what is called ‘Picciotto’s process.’ The gum is dissolved in water, and sulphurous acid gas passed through the solution. The liquid is afterwards boiled to expel the sulphurous acid, a little of which, however, still remains behind. To obtain the gum in a still whiter state, carbonate of baryta is added, and after agitation the mixture is filtered; it is afterwards shaken with gelatinous alumina, again filtered, and evaporated. The product (BLEACHED GUM) is very white, but lacks the peculiar toughness and adhesiveness of the best gum acacia.
Gum, Barbary. Syn. Morocco gum. An inferior product, consisting of a mixture of several Acacia gums. It is exported from Mogador.
Gum, Bassora. A solution of yellowish gum brought from the neighbourhood of Bassora. It differs from most gums in being nearly insoluble in water. The plant yielding it is believed to be a species of Mimosa. It contains the principle BASSORIN, which also exists in gum tragacanth.