part 24

(1872), 255.

This oleo-resin, which has the smell and taste of copaiba, but a much darker colour, was first examined by one of us in 1865, having been sent from the India Museum as a sample of Wood Oil; it was subsequently forwarded to us in more ample quantity by Dr. Bidie of Madras. It is a thick, viscid fluid, which, owing to its intense tint, looks black when seen in bulk by reflected light; yet it is perfectly transparent. Viewed in a thin layer by transmitted light, it is light _yellowish-green_, in a thick layer _vinous-red_,—hence is dichromic. It is not fluorescent, nor is it gelatinized or rendered turbid by being heated to 130° C., thus differing from Wood Oil.[898] Broughton[899] obtained by prolonged distillation with water an essential oil to the extent of 25 per cent. from an old specimen, and of more than 40 per cent. from one recently collected. The oil was found to have the same composition as that of copaiba, to boil at 225° C., and to rotate the plane of polarization to the left. The resin[900] is probably of two kinds, of which one at least possesses acid properties. Broughton made many attempts, but without success, to obtain from the resin crystals of copaivic acid.

The balsam of _Hardwickia_ has been used in India for gonorrhœa, and with as much success as copaiba.

GUMMI ACACIÆ.

_Gummi Arabicum_; _Gum Arabic_; F. _Gomme Arabique_; G. _Arabisches Gummi_, _Acacien-Gummi_, _Kordofan-Gummi_.

=Botanical Origin=—Among the plants abounding in mucilage, numerous Acaciæ of various countries are in the first line. The species

## particularly known for affording the largest quantities of the finest

gum arabic is _Acacia Senegal_[901] Willdenow (syn. _Mimosa Senegal_ L., _A. Verek_ Guillemin et Perrottet), a small tree not higher than 20 feet, growing abundantly on sandy soils in Western Africa, chiefly north of the river Senegal, where it constitutes extensive forests. It is called by the negroes _Verek_. The same tree is likewise found in Southern Nubia, Kordofan, and in the region of the Atbara in Eastern Africa, where it is known as _Hashab_. It has a greyish bark, the inner layers of which are strongly fibrous, small yellowish flowers densely arranged in spikes 2 to 3 inches long, and exceeding the bipinnate leaves, and a broad legume 3 to 4 inches in length containing 5 to 6 seeds.

[898] It may be further distinguished from Wood Oil as well as from copaiba, if tested in the following simple manner:—Put into a tube 19 drops of bisulphide of carbon and one drop of the oleo-resin, and shake them together. Then add one drop of a mixture of equal parts of strong sulphuric and nitric (1·42) acids. After a little agitation the appearance of the respective mixtures will be as follows:—

_Copaiba_—Colour faint reddish-brown, with deposit of resin on sides of tube.

_Wood Oil_—Colour intense purplish-red, becoming violet after some minutes.

_Oleo-resin of Hardwickia_—No perceptible alteration; the mixture pale greenish yellow.

By this test the presence in copaiba of one-eighth of its volume of Wood Oil may be easily shown.

[899] Beddome, _op. cit._

[900] See also Hazlett, _Madras Monthly Journ. of Med. Science_, June 1872.

[901] Figures in Guillemin and Perrottet _Floræ Senegamb. tent._ 1830, p. 246, tab. 56; also Bentley and Trimen, _Med. Plants_,