This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Balsam of Tolu is a balsam obtained by making incisions in the trunk of Myroxylon Toluifera, Humboldt, Bonpland, and Kunth (N.O. Leguminosoe).
The tree is a native of Colombia, and occurs plentifully in the forests near the river Magdalena and its tributary the Cauca. The balsam, which receives its name of Tolu from a small town near Cartagena, on the northern coast of Colombia, is collected by cutting a V-shaped notch in the bark, and fixing below it a gourd into which the balsam flows. Many such incisions at varying heights may be made on the same tree, which, however, is much exhausted by the tapping. The contents of these gourds are emptied into skin bags and conveyed to the coast, where the balsam is transferred to tins for exportation. It is shipped chiefly from Savanilla and Cartagena.
Although the twigs of the tree contain schizogenous secretion ducts, these are soon thrown off and no new ones are formed. The bark of the trunk, from which the balsam is obtained, contains no secretory tissue, and the balsam is probably secreted in ducts formed in the new wood, a change induced by the incisions made in the tree (compare the production of colophony).
Balsam of Tolu when freshly imported is a soft, tenacious, yellowish brown, resinous mass, not soft enough to flow, but taking the form of the vessel in which it is kept. By keeping, it gradually hardens to a brownish, and, especially in cold weather, brittle and easily powdered mass which, however, readily softens when warmed. It has an agreeable, fragrant, though not powerful odour, an acidulous balsamic taste, and adheres to the teeth when chewed. A small piece warmed and pressed into a thin film between two glass slides exhibits, when examined by the microscope, colourless crystals embedded in a transparent mass and accompanied by a little vegetable debris.
It is easily soluble in alcohol, acetone, and chloroform, but only partially soluble in carbon disulphide, yielding to the latter principally cinnamic acid. The solution obtained by gently warming the balsam with carbon disulphide leaves when evaporated about 25 per cent, of crystalline residue consisting chiefly of cinnamic and benzoic acids. The British Pharmacopoeia requires that the balsam should contain at least 25 per cent, of free aromatic acids, but it has been shown that 20 per cent would be a more reasonable requirement. Cocking and Kettle (1918) found an average of about 36 per cent, of total aromatic acids, free and combined, of which about 8 per cent, was free benzoic and 12.8 free cinnamic acid, 7 per cent, combined benzoic, and 8 per cent, combined cinnamic acid.
Tolu balsam was examined by Oberlander (1894), who found it to contain the following constituents: about 7.5 per cent, of an oily liquid (consisting of benzyl benzoate with a little benzyl cinnamate), traces of vanillin, free aromatic acids, principally cinnamic, and resin. The resin, amounting to about 80 per cent, of the drug, yielded by saponification an alcohol (toluresinotannol), and cinnamic acid, with which was associated a little benzoic acid.
Distilled with water good fresh balsam of Tolu yields from 1.5 to 3.0 per cent, of a very aromatic volatile oil containing tolene, styrol, and free benzoic and cinnamic acids.
Tolu balsam is used chiefly as a pleasant ingredient in cough mixtures. It possesses antiseptic properties due to the cinnamic and benzoic acids contained in it.
The chief adulterants of balsam of Tolu are colophony and balsam that has previously been used in making syrup of Tolu and hence deprived of most of its free cinnamic acid and aromatic constituents.
The acid value of genuine balsam ranges from 107.4 to 147.2, and the saponification value from 170 to 202.
Colophony may be detected by exhausting the balsam with carbon disulphide and evaporating the filtered solution. Pure balsam gives about 25 per cent, of crystalline residue; if colophony is present the residue is resinous and gives with concentrated sulphuric acid a green colour; a petroleum spirit extract of the residue shaken with an equal volume of a 0.1 per cent, solution of cupric acetate assumes a bright green colour if colophony is present. -
Exhausted balsam may be detected by the deficient amount of substances soluble in carbon disulphide and of aromatic acids.