Other tomes: Sayre
Copal.—The copals are a class of hard resins used principally in varnish manufacture. They are of various origins, both geographically and botanically. Their principal characteristics are their hardness, high melting point and comparative insolubility unless subjected to destructive distillation. There are three chief varieties: (1) Fossil copal, found in the ground in localities where the trees yielding it have entirely disappeared. (2) Semi-fossil copal, collected from the ground in the neighborhood of living copal trees. (3) Fresh copal, found on living trees, either as the result of natural exudation or from artificial incisions. The fresh copal is of least value and the fossil copal is most highly prized.
East African copals, known in commerce as Ammi gum or resin, are fossil varieties coming from Zanzibar, Madagascar and along the East African Coast. American copals are collected in South America and probably originated from trees related to those which produced the East African copals, although the product is softer. Kauri or cowrie copal or Kauri gum, as it is often called, is found in New Zealand exclusively. M. Kahan has investigated Acera copal and Benin copal (Arch. d. Pharm., 1910, ccxiviii, p. 443) and gives the percentages of the various constituents found.
A study of South American varieties of copal has been made by S. Machenbaum (Arch. d. Pharm; 250, Nos. 1-6 and 13), in which the constituents are stated to be copalic acid, copalolic acid, copalo-resene, copalmic acid, volatile oil and ash.
Fossil copal from Guiana has been studied by J. C. Essner (Annal. Chim. Anal., xvii, p. 166), who gives the following constants: Sp. gr. 1.089; colorless portion, acid value 118, saponification value 127, iodine value 84.3; yellow portion, acid value 125, saponification value 151, iodine value 81.5.
Zanzibar copal is obtained from several species of Trachylobium. The trunk and limbs are covered with a clear resinous exudation, portions of which, after solidifying, drop to the ground and are collected, while other portions are broken from the tree. This kind of resin is always smooth, and is exported to India. Another variety, with an indented, goose-flesh surface, known in the English market as anime, is dug from the earth, and though the product of forests now extinct, originated probably from the same tree. (P. J., 1869, p. 54.) It is in roundish, irregular, or flatfish pieces, sometimes several pounds in weight, often rough over the surface, probably from the impression of sand in its soft state, colorless, or brownish-yellow, more or less transparent, very hard, with a shining, conchoidal fracture, inodorous and tasteless. By heat it melts and emits gases, loses from 15 to 20 per cent. of weight, and is altered so as to become more soluble in ether, alcohol, or oil of turpentine, and in this way copal varnishes are usually made. It is not a proximate principle, but consists of various resins united in different proportions. According to Unverdorben and Filhol, some five different resins can be obtained by the successive action of solvents. Sierra Leone copal comes from Western Africa. According to Daniell (P. J., xvi, p. 369), this is derived from the Copaifera Guibourtiana Benth., a large tree growing preferably in mountainous regions. The drug is mostly collected, not from the tree itself, but from the beds and borders of streams, into which it is washed down, during the rains, from the hillsides, in the soil of which it had been deposited.
The Sierra Leone copal is described by Daniell as occurring "in small round tears, or irregular conical and smooth nodulated masses, seldom exceeding in size an ordinary duck egg. They are covered, to a greater or less extent, by a peculiar white efflorescence, which increases by age. Their color graduates from a pale green to a lemon or dull yellow."
Inhambane copal has been shown to be the product of Copaifera Gorskiana Benth. and seeds sent to Kew Gardens in 1886 germinated, and the plant has been widely introduced into both the East and West Indies, and into Australia. (P. J., xix, 508.)
A variety of copal comes from the East Indies. This has been ascribed to Vateria acuminata Hayne (Fam. Dipterocarpaceae), but is probably the product of a Trachylobium; at least a specimen of this resin was collected by Perottet from the Trachylobium Hornemannianum Hayne, which he found growing in the Isle of Bourbon. This tree is a native of Madagascar, and probably of the neighboring parts of Africa, and Perottet was informed that the copal of India is taken thither by the Arabs of Muscat, who obtain it from the east coast of Africa. (J. P. C., 3e ser., i, 406.) It is described by Schindler as of a globular form, softer and more transparent than the other varieties, with a surface always clear, and having an agreeable odor when heated. It is readily and freely dissolved by the oils of turpentine and rosemary when pure, but not by these fluids when rendered resinous by age. It is more readily fusible than the others, and makes the best varnish.
The West India copal is in flat pieces, seldom weighing more than three ounces, rarely containing insects, very hard, of a rough appearance, of a yellowish color, and without odor or taste. It is much less readily dissolved by oil of turpentine than the East India variety, swells but does not dissolve in oil of rosemary and is slightly soluble in absolute alcohol. Another kind, probably also American, is in convex or concave pieces, about a pound in weight, often containing insects and other impurities. In solubility it resembles the last mentioned variety, in fusibility is intermediate between it and the East Indian, and is altogether inferior. (P. J., 1850.) For an account of the present views on the nature of copal resins, see Tschirch, Die Harze und die Harzbehälter, Leipzig, 1900.
For descriptions of the so-called Manila copal and Kauri copal which are derived from the conifers, see p. 1417.
Copal lotion.—Under the trade name Adhaesol there appears on the market a lotion containing: Copal, 350 parts; benzoin, 30 parts; tolu, 30 parts; ol. thyme, 20 parts; alpha-naphthol, 3 parts; ether, q. s., 1000 parts. It is used as an antiseptic varnish in diphtheritic affections of the throat.