Substitutes—A great number of trees are capable of affording gums more or less similar to gum arabic. There is to be mentioned for instance Prosopis glandulosa Torrey, a tree growing from 30 to 40 feet in height, occurring very abundantly in Texas, and extending as far west as the Colorado and the gulf of California. It is universally known by its Mexican name Mesquite. It belongs to the same suborder of the Mimosæ like the Acaciæ tribe of the Adenanthereæ. Mesquite gum agrees not with the fine description, but with the inferior sorts of gum arabic, and is sometimes used in America,[921] since 1854, in the manufacture of confectionery and the arts.
Feronia Gum, or Wood Apple Gum. This is the produce of Feronia Elephantum Correa, a spiny tree, 50 to 60 feet high, of the order of Aurantiaceæ, common throughout India from the hot valleys of the Himalaya to Ceylon, and also found in Java. There exudes from its bark abundance of gum, which appears not to be collected for exportation per se, but rather to be mixed indiscriminately with other gum, as that of Acacia.
Feronia gum sometimes forms small roundish transparent, almost colourless tears, more frequently stalactitic or knobby masses, of a brownish or reddish colour, more or less deep. In an authentic sample, for which we are indebted to Dr. Thwaites of Ceylon, horn-shaped pieces about ½ an inch thick and two inches long also occur.
Dissolved in two parts of water, it affords an almost tasteless mucilage, of much greater viscosity than that of gum arabic made in the same proportions. The solution reddens litmus, and is precipitated like gum arabic by alcohol, oxalate of ammonium, alkaline silicates, perchloride of iron, but not by borax. Moreover, the solution of Feronia gum is precipitated by neutral acetate of lead or caustic baryta, but not by potash. If the solution is completely precipitated by neutral acetate of lead, the residual liquid will be found to contain a small quantity of a different gum, identical apparently with gum arabic, inasmuch as it is not thrown down by acetate of lead. If the lime is precipitated from the Feronia mucilage by oxalate of potassium, the gum partially loses its solubility and forms a turbid liquid.
From the preceding experiments, it follows that a larger portion of Feronia gum is by no means identical with gum arabic. The former, when examined in a column of 50 mm. length, deviates the rays of polarized light 0°·4 to the right,—not to the left as gum arabic. This was, we believe, the first instance of a dextrogyre gum;[922] Scheibler has afterwards shown (1873) that there are also dextrogyre varieties among the African gum from Sennar. Gum arabic may be combined with oxide of lead; the compound (arabate of lead) contains 30·6 per cent. of oxide of lead, whereas the plumbic compound of Feronia gum, dried at 110° C., yielded us only 14·76 per cent. of PbO. The formula (C₁₂H₂₁O₁₁)₂Pb + 2(C₁₂H₂₂O₁₁) supposes 14·2 per cent. of oxide of lead.
Feronia gum repeatedly treated with fuming nitric acid produces abundant crystals of mucic acid. We found our sample of the gum to yield 17 per cent. of water, when dried at 110° C. It left 3·55 per cent. of ash.
CATECHU.
Catechu nigrum; Black Catechu, Pegu Catechu, Cutch, Terra Japonica; F. Cachou, Cachou brun ou noir; G. Catechu.
Botanical Origin—The trees from which this drug is manufactured are of two species, namely:—
1. Acacia Catechu Willd. (Mimosa Catechu L. fil., M. Sundra Roxb.[923]), a tree 30 to 40 feet high, with a short, not very straight trunk4 to 6 feet in girth, straggling thorny branches, light feathery foliage, and dark grey or brown bark, reddish and fibrous internally.