Secretion of the Balsam—No observations have yet been made as to the secretion of the balsam in the wood, or the part that is played by the operation of scorching the bark. Neither the unscorched bark nor the wood, as we have received them, possess any aromatic odour.
The old accounts speak of a very fragrant resin, far more valuable than the ordinary balsam, obtained by incisions. We have made many inquiries for it, but without the least success. Such a resin is easily obtainable from the trunk of M. Toluifera.
Description—Balsam of Peru is a liquid having the appearance of molasses, but rather less viscid. In bulk it appears black, but when examined in a thin layer, it is seen to be of a deep orange-brown and perfectly transparent. It has a balsamic, rather smoky odour, which is fragrant and agreeable when the liquid is smeared on paper and warmed. It does not much affect the palate, but leaves a disagreeable burning sensation in the fauces.
The balsam has a sp. gr. of 1·15 to 1·16. It may be exposed to the air for years without undergoing alteration or depositing crystals. It is not soluble in water, but yields to it a little cinnamic and traces of benzoic acid; from 6 to 8 parts of crystallized carbonate of sodium are required to neutralize 100 parts of the balsam. It is but partially and to a small extent dissolved by dilute alcohol, benzol, ether or essential or fatty oils, not at all by petroleum ether. The balsam mixes readily with glacial acetic acid, anhydrous acetone, absolute alcohol or chloroform. Its rotatory power is very insignificant.
Chemical Composition—The peculiar process by which balsam of Peru is obtained, causes it to contain a variety of substances not found in the more natural resin of Myroxylon Toluifera; hence the two drugs, though derived from plants most closely allied, possess very different properties.
Three parts of the balsam mix readily with one part of bisulphide of carbon, yet a further addition of the latter will cause the separation of a brown flocculent resin. If the balsam be mixed with thrice its weight of bisulphide, a coherent mass of dark resin, sometimes amounting to about 38 per cent. of the balsam, is precipitated. The bisulphide of carbon forms then a perfectly transparent brown liquid. If this solution is shaken with water, the latter removes Cinnamic and Benzoic acids. To separate them, ammonia is cautiously added, yet not in excess.[807] The solution of cinnamate and benzoate thus obtained and duly concentrated, yields both these acids in white crystals on addition of acetic or hydrochloric acid.
The resin separated by means of bisulphide of carbon as above stated, is a black brittle amorphous mass, having no longer the specific odour of the balsam. It is soluble in caustic alkalis, also in alcohol; the solution in the latter which may be considerably purified by charcoal, reddens litmus, and is abundantly precipitated by an alcoholic solution of neutral acetate of lead. Kachler (1869) by melting this resin with potash obtained about ⅔ of its weight of protocatechuic acid.[808] By destructive distillation, it furnishes benzoic acid, styrol,C₈H₈, and toluol, C₇H₈.
As to the solution obtained with bisulphide of carbon, it forms, after the bisulphide has evaporated, a brownish aromatic liquid of about 1·1 sp. gr., termed Cinnameïn. This substance may also be obtained by distillation, yet less easily, on account of its very high boiling point, about 300° C.
Cinnameïn, C₁₆H₁₄O₂, is resolved by concentrated caustic lye into benzylic alcohol, C₇H₁₄O₂, and cinnamic acid, C₉H₈O₂, whence it follows that cinnameïn is Benzylic Cinnamate. This is, according to Kraut (1858, 1869, 1870) and to Kachler (1869, 1870), the chief constituent of the balsam. The former chemist obtained from it nearly 60 per cent. cinnameïn. Kachler assigns to the balsam the following composition: 46 per cent. of cinnamic acid, 32 of resin, 20 of benzylic alcohol. These latter figures however are not quite consistent: 46 parts of cinnamic acid (molecular weight = 148) would answer to 73 parts of benzylic cinnamate; and 20 parts of benzylic alcohol require on the other hand only (mol. weight = 108) 27·4 parts of cinnamic acid in order to form benzylic cinnamate (mol. = 238).
Benzylic cinnamate, prepared as above stated, is a thick liquid, miscible both with ether or alcohol, not concreting at -12° C., boiling at 305° C., yet under ordinary circumstances not without decomposition. By exposure to air, it slowly acquires an acid reaction; by prolonged action of potash, especially in an alcoholic solution, toluol is also formed. In this process, cinnamate of potassium finally forms a crystalline mass, while an oily mixture of benzylic alcohol and toluol, the so-called “Peruvin” constitutes the liquid part of the whole.