Copal, the resinous juice of the rhus copal-Una of Mexico and the elmocarpus copalifer of India. It is obtained by the natives by cutting a notch in the tree, in which it collects.
Copal (Rhus copallina).
Another variety of the copal tree is found on the coast of Guinea, where lumps of the resin are gathered from the sands by the negroes. Copal is of various colors, from a pale yellow-hue to a dark brown, and of different degrees of transparency. It often includes insects and animal remains. It is harder than other gums, breaks with a conchoidal fracture, and has neither odor nor taste. An excellent and durable varnish is prepared from it. It melts with the heat of a spirit lamp, giving out an oily substance, and becoming deeper in color until it is converted into charcoal. Copal is not easily soluble in alcohol, the greater part merely swelling up and softening; but pulverized and then dried at a moderate heat, it dissolves in alcohol of 96 per cent. Camphor first dissolved in the alcohol increases its power of taking up the copal. It is much more soluble in ether, and the solution may be diluted with alcohol without the copal precipitating. Different kinds of copal are differently affected by ether; some dissolve readily, others with great difficulty. Tarnishes of different qualities may be thus obtained by the same solvent. After ether, some of the volatile oils are the best solvents of copal, as the oils of rosemary, lavender, and spruce.
The oils of petroleum and turpentine have little action on crude copal. "When fused, it dissolves more easily, but produces inferior qualities of varnish. Its composition, according to Dr. Ure, is carbon 79.87, hydrogen 9, oxygen 11.1; being of hydrogen 7.6 in excess above the quantity necessary to form water with the oxygen. An excellent recipe for varnish is the following given by Bottger: 1 part of camphor is dissolved in 12 parts of ether; 4 of copal are then added, and allowed to swell in it, when 4 parts of anhydrous alcohol and 1/4 part of rectified oil of turpentine are added. It is stated by Dr. Wight that on the Malabar coast a variety of this resin, called piney dammar, is made into candles which diffuse an agreeable fragrance, give a clear light with little smoke, and consume the wick without requiring snuffing. - A fossil copal is described in the books of mineralogy, which resembles the resin in its hardness, color, lustre, transparency, and difficult solubility in alcohol. It is found in the blue clay near London, and is called Highgate resin; and also in flattened drops on calc spar on the walls of a trap dike at an old lead mine in Northumberland. A similar fossil has been also obtained in the East Indies. The composition of the mineral is carbon 85.41, hydrogen 11.78, oxygen 2.67, ashes 0.136.