gum resembling it, but generally in larger pieces, which is quite worthless. The Feronia elephantum of 
Roxburgh also yields a valuable gum, similar to Gu»n Arabic, which is commonly used by all the practi- 
tioners of Lower India ; and, according to Dr. F. Hamilton, gum, simply so called, may be procured in the 
Mysore, from the Melia Azederach ; Chironia glabra ; Mangifera indica ; Cassia auriculata ; rEgle mar- 
melos ; Shorea robusta, and several other trees. 
Qualities and Chemical Properties. — Gum Arabic is usually met with in small pieces, like tears; 
moderately hard; somewhat brittle, and may be reduced to a fine white powder. When pure, it is colourless, 
but has commonly a yellow tinge, and is not destitute of lustre. It has no smell. Its taste is insipid. Its 
specific gravity varies from 1.3161 to 1.4317- Water may be said to dissolve it entirely. The solution is 
known by the name of mucilage; which is thick, and adhesive: it is often used as a paste, and to give stiff- 
ness and lustre to linen. When spread out thin, it soon dries, but readily attracts moisture, and becomes 
glutinous. When mucilage is evaporated, the gum is obtained unaltered. It may be kept for years, without 
undergoing putrefaction. When gum is exposed to heat, it softens and swells, but does not melt; it emits 
air bubbles, blackens, and at last, when nearly reduced to charcoal, emits a low blue flame. After the gum 
is consumed, there remains a small quantity of white ashes, composed chiefly of the carbonates of lime and 
potash. Vegetable acids dissolve gum without alteration: the strong acids decompose it. Chlorine converts 
gum into nitric acid, according to the experiments of Vauquelin. If nitric acid be slightly heated upon gum 
till it has dissolved it, and till a little nitrous gas is exhaled, the solution, on cooling, deposits saclactic acid. 
Malic acid is formed at the same time; and if the heat be continued, the gum is at last changed into oxalic 
acid. Thus, no less than three acids are developed by the action of nitric acid on gum. 
Gum is insoluble in alcohol and ether, and both precipitate mucilage. 
From the experiments of Vauquelin, it appears that gum contains traces of iron; and he conjectures, 
that the lime which it contains is usually combined with acetic or malic acid. Berzelius analysed it, by 
burning it along with chlorate of potash, and found it composed of. 
Oxygen 51.306 
Carbon 41.906 
Hydrogen 6.788 
100.000 
Medical Properties and Uses. — Gum arabic is extensively employed for a number of purposes, 
both in the arts and in medicine. It is frequently used either to suspend in water various substances, which 
could not otherwise be kept equally diffused in that liquid, or as a useful colourless cement. Gum Senegal 
resembles gum arabic so nearly, that it is employed instead of it for all purposes in Hindustan ; and in this 
country is used in very large quantities by the calico-printers to mix the colours and the mordaunts in block 
printing. Gum arabic forms the basis of crayons, and the cakes of water-colours ; and of several liquid 
colours, of which common writing ink is a familiar example. 
All the vegetable mucilages are considerably nutritious ; hence in the countries where the gum arabic 
and Senegal grow native, they form an important article of diet, either alone or mixed with milk, rice, and 
other substances. In Guzerat, especially in the wastes, where the Babul tree (Acacia arabica ) is very 
common, the poorer inhabitants use the gum for food. Haselquist informs us, that a caravan whose pro- 
visions were exhausted, preserved themselves from famine, by the gum arabic, which they were carrying as 
merchandise. During the whole time of the gum harvest, of the journey, and of the fair, the Moors of the 
desert live almost entirely upon it, and experience has proved that six ounces are sufficient for the support 
of an adult during twenty-four hours. 
In medicine, this gum is used either by itself, or as a vehicle for other substances. Taken internally, 
its principal use is as a demulcent ; to envelop acrid matter, and to cover the surfaces that are too sensible 
to external impressions. Hence it is sometimes allowed to dissolve gradually in the mouth, to allay irrita- 
tion of the fauces; and its mucilage, sweetened with syrup, forms a useful remedy for tickling coughs, 
hoarseness, and diarrhoeas ; as well as in cardialgia, arising from oily substances received into the stomach. 
In these cases, it is sometimes advantageously joined with opiates and aromatics.. Though its action has 
been supposed not to extend beyond the fauces and alimentary canal, it has been frequently recommended 
in a great variety of diseases. It is given, either in powder, or dissolved in almond milk, &c. one ounce 
being sufficient to render a pint of liquid tolerably viscid. 
In pharmacy, gum arabic is employed to render oils, balsams, and resins, miscible with aqueous 
liquids ; and to give tenacity to substances made into troches and pills. Even Mercury may be suspended 
in water, by being rubbed for a considerable time with gum arabic ; which preparation is called, from its 
inventor, PlanFs solution. 
The pharmaceutical preparations into which gum arabic enters as a principal ingredient, are the Muci- 
lago Acacice, a simple solution of one part of the gum in two of boiling water ; the Emulsio Acacice Arabica, 
Ph. Ed. which is gum arabic dissolved in almond milk ; the Trochisci gummosi, Ed., with equal parts of 
gum, starch, and sugar ; and the Pulvis Tragacanthce compositus, Ph. Lond., a powder made of tragacanth, 
gum arabic, starch, and sugar. It is also an ingredient in the Confectio amygdalarum, L. Mistura cretce, 
L. Mistura Moschi, L. Mistura Guaiaci, L. and the Pulvis cretce compositus, L. 
In flower language Acacia signifies Platonic love. 
