Terebinthina Canadensis, B.P. Canada Turpentine.
Canada turpentine, or balsam of fir, is an oleoresin obtained from the balsam fir, Abies balsamea, Mill. (N.O. Coniferae), a tree indigenous to the United States and Canada. The oleoresin is secreted in schizogenous ducts in the bark, and collects in cavities, which form blisters; the latter are punctured and the oleoresin collected. It is also official in the U.S.P. Canada turpentine forms a pale yellow, viscid liquid, often exhibiting a slight greenish fluorescence. It has an agreeable, terebinthinate odour, and bitter, acrid taste. It becomes more viscid on keeping, and dries to a hard, transparent varnish that shows no disposition to crystallise. It solidifies when mixed with about one-sixth of its weight of magnesia and a little water.
Soluble in all proportions of benzene, chloroform, or ether freely soluble in oil of turpentine or alcohol.
Constituents.—Canada turpentine contains a bitter principle which is soluble in water, but consists essentially of a mixture of 70 to 80 per cent. of resin, with 16 to 24 per cent. of volatile oil, which consists chiefly of laevo-pinene. The resin contains about 20 per cent. of an indifferent resene (canado-resene), 20 per cent. of amorphous canadinic acid, and 60 per cent. of amorphous α- and β-canadolinic acids, with is associated a trace of crystalline canadolic acid. The specific gravity of the turpentine is about 0.987 to 0.994; optical rotation, +1° to +4°; refractive index, 1.518 to 1.521; acid value, 84 to 87.
Action and Uses.—Canada turpentine is not given internally, but is occasionally employed as a pill excipient with such deliquescent salts as calcium iodide and chloride. It is used in the preparation of flexile collodion, and in microscopy as a mounting medium. For the latter purpose, the balsam is warmed in an open dish until a portion of the mass transferred to a slab sets to a brittle solid. It is then dissolved in an equal quantity of xylol or other suitable solvent. Such a solution forms a non-crystallising mounting medium, having a refractive index approximating to that of ordinary glass, and therefore involving a minimum dispersion of light. For microscopic use, it should be as nearly neutral as possible; it, however, gradually undergoes oxidation, becomes acid, and slowly bleaches aniline colours.