a pure resin which exudes from the Rhus copallinum, a tree which is a native of Mexico; and also from the Eleocharpus copalifer, an East Indian tree, as well as from some unascertained trees on the Guinea coast. Copal occurs in lumps of various sizes, and it has different shades of colour and degrees of transparency, from the palest and most transparent greenish-yellow hue, to a dark and somewhat opaque brown. It is too hard to be scratched by the nail, and hence the durability of the varnish prepared from it. It breaks with a conchoidal fracture, and possesses neither sensible taste nor odour. Copal forms one of the most valuable varnishes we possess, but it is extremely insoluble in the various menstrua while in its ordinary state. It is soluble in ether, and the solution may be mixed with alcohol without precipitating it. It is insoluble in boiling alcohol of the strength 0·825, but one and a half parts of anhydrous alcohol digested for 24 hours with one part of copal dissolves it completely; that portion of the copal which is insoluble in alcohol being soluble in a saturated solution of that portion which is soluble in the anhydrous alcohol. Camphor, however, possesses the peculiar property of enabling alcohol to dissolve copal in the cold. Pure coutehoucine acts very feebly on copal even at the boiling temperature; but equal parts of this fluid and of alcohol of 0·825 strength, according to Dr Ure, readily dissolve copal without the aid of heat, forming a perfectly liquid varnish. Fresh rectified oil of rosemary dissolves the East Indian copal in any proportion; but it will not dissolve the West Indian, or more properly the Mexican, copal. Spirit of turpentine only dissolves from one to two per cent. of raw copal. When copal is melted by means of heat its solvent properties are greatly altered, and it then dissolves freely. in alcohol and in turpentine—a property that is turned to account in the preparation of most of the varnishes made with this resin. See Varnish.