GUITAR. This musical instrument, in various shapes, may be traced to the remotest periods of antiquity. It was often called Citlern and Gillern by the old English poets. The English and French guitar of the last century was wide and thin in body, short in the neck, and strung with wire. The modern guitar, which is of the Spanish kind, and dif fering little from the lute, consists of a body from seventeen to eighteen inches in length, four in depth, and of a neck of about sixteen inches, the latter carrying a finger-board divided by seventeen frets. It has six strings, three being of silk covered with silvered wire, and three of catgut. Tho compass of this elegant instrument is from E below the base staff to A above the treble staff, including all the intermediate tones and semitones. The best and cheapest guitars are made in Ger many.
GUM. This vegetable juice is of more universal occurrence than any other secretion by plants. It is the material generally pre pared by them for their own nourishment, and is at first in a state of solution ; but when it escapes to the exterior of the bark it frequently becomes thickened, and even solid and pulverisable. The purest gum (arabic) consists of a principle termed arabin, and is soluble in water, forming with it a mucilage. Other gums contain bassorine, either alone or with arabin and other matters. The term gum is sometimes erroneously applied to gum resins, such as assafwtida, &c.
Most of the commercial gums are obtained by incisions made in the bark of soveral species of acacia growing in Arabia, India, Upper Egypt, Senegal, &c. The specimens differ considerably in colour, even when ob tained from the same species. Genuine gum
arable occurs in pieces from the size of a pea to that of a walnut, or larger, which are irre gular in shape, or roundish or angular ; either white, yellowish, or dark wine-yellow ; scarcely any odour; taste mawkish, glutinous. Gum, when in powder, is often adulterated. with starch, the presence of which is detected by tincture of iodine ; or, when cold water is used for the solution of the gum, the starch will remain undissolved. The mucilage made with cold water is not only purer, but keeps better, and for all purposes for which it can be used is preferable to that made with warm water, which is the common method.
Gum is highly nutritive, six ounces in twenty-four hours being deemed sufficient to sustain the life of an adult ; yet it is not very easily digested when taken alone. Gum will often pass through the stomach nearly un• changed, if not associated with some bitter or astringent principle. This property how ever renders it demulcent in affections both of the throat and also of the intestines, by sheathing the membrane from air or the irritation of acrid secretions. Hence allowing a portion to dissolve is also used to suspend many insoluble matters in water. Its agglu tinating properties render it valuable in many of the arts.
Of four kinds of gum which are enumerated in the Board of Trade tables, the quantities imported in 1848 were Cwts.
Gum-arabic .. 21,022 Gum-Senegal .. 7,404 Gum-copal 2,058 Gum-tragacanth.. .. 234