Buignet has first shown (1861) that copaiba varies in its optical power. A sample from Trinidad examined by one of us was strongly dextrogyre, and also several samples imported in 1877 from Maturin (near Aragua, Venezuela), and Maracaibo into Hamburg, whereas we found Pará balsam to be levogyre.[895]
The Pará and Maranham balsams are regarded in wholesale trade as distinct sorts, and experienced druggists are able to distinguish them apart by odour and appearance, and especially by the greater consistence of the Maranham drug. Maracaibo balsam is reckoned as another variety, but is now rarely seen in the English market. West Indian copaiba is usually said to be of inferior quality, but except that it is generally opalescent, we know not on what precise grounds.
Chemical Composition—The balsam is a solution of resin in volatile oil; the latter constitutes about 40 to 60 per cent. of the balsam,[896] according to the age of the latter and its botanical origin. The oil has the composition C₁₅H₂₄; its boiling point is 245° C. or even higher. It smells and tastes like the balsam, and dissolves in from 8 to 30 parts of alcohol 0·830 sp. gr. The oil exhibits several modifications differing in optical as well as in other physical properties, but numerous samples of the drug, either dextrogyre or levogyre, invariably afforded us essential oils deviating to the left; their sp. gr. varies from about 0·88 to 0·91.
After the oil of copaiba has been removed by distillation, there remains a brittle amorphous resin of an acid character soluble both in benzol and amylic alcohol, and yielding only amorphous salts. Sometimes copaiba contains a small amount of crystallizable resin-acid, as first pointed out in 1829 by Schweitzer. By exposing a mixture of 9 parts of copaiba and two parts of aqueous ammonia (sp. gr. 0·95) to a temperature of-10° C., Schweitzer obtained crystals of the acid resin termed Copaivic Acid. They were analysed in 1834 by H. Rose, and exactly measured and figured by G. Rose. Hess (1839) showed that Rose’s and his own analyses assign to copaivic acid the formula C₂₀H₃₂O₂. It agrees with Maly’s abietic acid from colophony in composition, but not in any other way. Copaivic acid is readily soluble in alcohol, and especially in warmed copaiba itself; much less in ether. We have before us crystals, no doubt of copaivic acid, which have been spontaneously deposited in an authentic specimen of the oleo-resin of Copaifera officinalis from Trinidad, which we have kept for many years. The crystals may be easily dissolved by warming the balsam; on cooling the liquid, they again make their appearance after the lapse of some weeks. After recrystallization from alcohol they fuse at 116-117 C°., forming an amorphous transparent mass which quickly crystallizes if touched with alcohol.
An analogous substance, Oxycopaivic Acid, C₂₀H₂₈O₃, was examined in 1841 by H. von Fehling, who met with it as a deposit in Pará Copaiba. And lastly Strauss (1865) extracted Metacopaivic Acid, C₂₂H₃₄O₄, from the balsam imported from Maracaibo. He boiled the latter with soda-lye, which separated the oil; the heavier adjacent liquid was then mixed with chloride of ammonium, which threw down the salts of the amorphous resin-acid, leaving in solution those of the metacopaivic acid. The latter acid was separated by hydrochloric acid and recrystallization from alcohol. We succeeded in obtaining metacopaivic acid by washing the balsam with a dilute solution of carbonate of ammonium, and precipitating by hydrochloric acid. The precipitate dissolved in dilute alcohol yields the acid in small crystals, but to the amount of only about one per cent.
These resin-acids have a bitterish taste and an acid reaction; their salts of lead and silver are crystalline but insoluble; metacopaivate of sodium may be crystallized from its watery solution.
Commerce—The balsam is imported in barrels direct from Pará and Maranham, sometimes from Rio de Janeiro, and less often from Demerara, Angostura, Trinidad, Maracaibo, Savanilla, and Cartagena. It often reaches England by way of Havre and New York. In 1875 there were exported 10,150 kilogrammes from Savanilla, 99,800 lb. from Ciudad Bolivar (Angostura), and 65,243 kilos. from Pará.
Uses—Copaiba is employed in medicine on account of its stimulant action on the mucous membranes, more especially those of the urino-genital organs.
Adulteration—Copaiba is not unfrequently fraudulently tampered with before it reaches the pharmaceutist; and owing to its naturally variable composition, arising in part from its diverse botanical origin, its purity is not always easily ascertained.
The oleo-resin usually dissolves in a small proportion of absolute alcohol: should it refuse to do so, the presence of some fatty oil other than castor oil may be surmised. To detect an admixture of this latter, one part of the balsam should be heated with four of spirit of wine (sp. gr. 0·838). On cooling, the mixture separates into two portions, the upper of which will contain any castor oil present, dissolved in alcohol and the essential oil. On evaporation of this upper layer, castor oil may be recognized by its odour; but still more positively by heating it with caustic soda and lime, when œnanthol will be formed, the presence of which may be ascertained by its peculiar smell. By the latter test an admixture of even one per cent. of castor oil can be proved.