RESINS are proximate principles found in most vegetables, and in almost every part of them; but the only resins which merit a particular description, are those which occur naturally in such quantities as to be easily collected or ex tracted. They are obtained chiefly in two ways, either by spontaneous exuda tion from the plants, or by extraction by heat and alcohol. In the first case, the discharge of resin in the liquid state is sometimes promoted by artificial inci sions made in summer through the bark into the wood of the tree.
Resins possess the following general properties :—They are soluble in alcohol, insoluble in water, and melt by the ap plication of heat, but do not volatilize without partial decomposition. They have rarely a crystalline structure, but, like gams, they have no particular form. They ignite readily, burn with a bright light, and give much smoke. They are quite insoluble in water, but dissolve readily in cola and hot alcohol, from which they are precipitated by water. Resins dissolve in ether and volatile oils, and by heat combine with fat oils. They mix with sulphur and phosphorus. Car buret of sulphur dissolves them, chlorine bleaches them, and nitric acid converts them into artificial tan. Every natural resin is a compound of two or three pure resins, as is the case with oils. Some are soluble in hot or cold alcohol—ether, naptha, and turpentine. Resins which contain essential oil are called balsams ; a few contain benzoin acids. The solid resins are amber, anime, benzoin, colo phony copal, copal, danunara, dragon's blood, elm', guise, lac, julep resin, ladanum, mastic, sandarach, storax, taca mahac.
An ingenious memoir upon the resins of dammar, copal, and anime, has lately been published. by M. Guibourt, an emi nent French from which the following extract may he found interest ing.
The hard copal of India and Africa, especially Madagascar, is the product ot• the hymenam verrueosa ; it is transparent and vitreous within, whatever may he its appearance outside ; nearly colorless, or of a tawny yellow ; without taste or smell in the cold, and almost as hard as amber, which it much resembles, but from which it may be distinguished, 1st, by its smelting and kindling at a candle-flame, and running down in drops, while amber burns and swells up with out flowing ; 2dly, this hard copal or anime, when blown out and still hot, exhales a smell like balsam eopaiva or capivi: while amber exhales an unplea sant bituminous odor ; Idly, when moist ened by alcohol of 85 per cent., copal becomes sticky, and shows after drying a glazed opaque surface, while amber is not affected by alcohol ; 4thly, the copal affords no suceinie acid, as amber does, on distillation.
When the pulverized copal is digested in cold alcohol of 0.830, it leaves a con siderable residuum, at first pulverulent, but which swells afterward, and forms a slightly coherent mass. When this pow der is treated with boiling alcohol, it assumes the consistence of a thick gluten, like crumbs of bread, but which does not stick to the fingers.