Poplar buds. Populus nigra, Populus balsamifera. Balsam poplar buds, Balm of Gilead buds.
Poplar Buds. N. F. IV. Populi Gemmae. Balsam Poplar Buds. Balm of Gilead Buds.—"The air-dried, closed winter leaf-buds of Populus nigra Linné or Populus balsamifera Linné (Fam. Salicaceae), collected early in the spring. Preserve the buds in tightly-closed containers of glass or tin." N.F.
In most trees of the genus Populus, the leaf-buds are covered with a resinous exudation, which has a peculiar, agreeable, balsamic odor, and a bitterish, balsamic, somewhat pungent taste. It is abundant in the buds of Populus nigra L., or the black poplar of Europe, which are official in some parts of that continent. They contain resin and a peculiar volatile oil. The buds of P. balsamifera L., the Balsam Poplar or Tacamahac, growing in the northern parts of North America and Siberia, are also highly balsamic; and a resin is said to be furnished by the tree. The buds are obtained from P. candicans Ait. and are often called Balm of Gilead buds. Poplar buds are described in the N. F. IV as "conical, pointed, up to 2 cm. in length and from 2 to 5 mm. in thickness, consisting of closely imbricated scales, externally brown and glossy, glutinous with fragrant resin. Odor pleasant, balsamic; taste aromatic and bitter." The virtues of the poplar buds are probably analogous to those of the turpentines and balsams. They have been used in pectoral, nephritic, and rheumatic complaints, in the form of a tincture, and a liniment, made by macerating them in oil, has been applied externally in local rheumatism. The unguentum populeum, Pommade de Bourgeons de Peuplier, is made, according to the directions of the French Codex, from 100 Gm. each of the dried contused leaves of white poppy, belladonna, henbane, and black nightshade, and 800 Gm. of dried poplar buds. The leaves are moistened with 400 Gm. of alcohol and allowed to stand twenty-four hours in a closed vessel; 4000 Gm. of lard is now added and the mixture heated gently during three hours, stirring frequently, the crushed poplar buds are then added and allowed to digest for ten hours at a gentle heat, and the whole strained and cooled slowly. This is an anodyne ointment, employed in Europe in painful local affections. It has been ascertained that poplar buds are capable of imparting a principle to ointments which obviates their tendency to rancidity. Poplar buds are an ingredient of Syrupus Pini Strobi Compositus, N. F. and of Syrupus Pini Strobi Compositus cum Morphina, N. F.
The bark of P. tremuloides Michx., or American aspen, and of P. tremula L., or European aspen, is possessed of tonic properties, and has been used in intermittent fever. In the bark of the latter Braconnot found salicin, C13H18O7, and another crystallizable principle which he named populin, C20H22O8 + 2H2O. It is in these, probably, that the febrifuge properties of the bark reside. They may be obtained by precipitating a saturated decoction of the bark with solution of lead subacetate, filtering, precipitating the excess of lead by sulphuric acid, again filtering, evaporating, adding animal charcoal towards the end of the evaporation, and filtering the liquor while hot. Salicin gradually separates, upon the cooling of the liquor, in the form of crystals. If, when this principle has ceased to crystallize, the excess of sulphuric acid in the liquid be saturated by a concentrated solution of potassium carbonate, the populin will be precipitated. If this be pressed between folds of blotting paper, and redissolved in boiling water, it will be deposited, upon the cooling of the liquid, in the crystalline state. The leaves of P. tremula are also said to yield more populin than does the bark. It is probable that both principles exist in the bark of P. tremuloides and other species. Schaak (A. J. P., 1892, 226) found a bitter principle in the bark of P. alba L., which was most likely populin. Populin is very light and white, of a bitter, sweetish taste, analogous to that of licorice. It is soluble in 1896 parts of cold and about 70 parts of boiling water, and is more soluble in boiling alcohol. It loses its two molecules of water of crystallization at 100° C. (212° F.), and at 180° C. (356° F.) it fuses to a colorless liquid, from which at a higher temperature benzoic acid may be sublimed. Acetic acid and the diluted mineral acids dissolve it, and, upon the addition of an alkali, let it fall unchanged. Piria first showed it to be benzoyl salicin, C13H17(C7H5O)O7 + 2H2O. He then decomposed it and prepared salicin from it. Populin has been prepared synthetically by Schiff and by Dobbin and White. (P. J., 73, p. 233.) When populin is boiled with baryta water or milk of lime, the benzoic acid precipitated by ferric chloride, the excess of iron removed by lime, and the excess of lime by carbon dioxide, the remaining liquid yields salicin on evaporation. The same conversion may be effected by heating populin with an alcoholic solution of ammonia to 100° C. (212° F.). Piria obtained from populin 28.9 per cent. of benzoic acid. (P. J., xv, 378.) T. L. Phipson, basing his experiments upon the results of Piria, has succeeded in preparing populin artificially by combining salicin and benzoic acid. Nothing more is necessary than to dissolve the two substances in alcohol, and to concentrate the solution. Crystals are formed having all the characters of populin, and consisting of salicin and benzoic acid combined in the proportion of their equivalents. (Chem. News, Dec. 6, 1862, 278.) Dobbin and White make populin from salicin and benzoyl chloride. (Y. B. P., 1904, 506.) The flower-buds of P. tremuloides yielded a bitter resin to R. Glenk. It was of yellowish-brown color, strong, hop-like odor, and had a melting point of 51° C. (123.8° F.). (A. J. P., 1889, 240.)