Resins

Resins are a class of substances which are of vegetable origin, being usually obtained (1) as exudations from the bark or incisions of certain trees, (2) by extraction from plants by means of alcohol or other solvent, or (3) as solidified masses or fossil resins in certain geological formations, e.y. the coal measures. They are usually translucent, yellowish, amorphous bodies, with a peculiar odour. They are insoluble in water, but soluble in many organic liquids, e.g. benzine, turpentine. They melt if heated, and are combustible, giving a smoky and luminous flame. In composition they appear to consist chiefly of a mixture of different acids closely allied to bodies of the terpene class, and probably derived from them by oxidation. They verge into the balsams and the soft oleo-resins, there being no essential or fixed difference. Many are used for the preparation of varnishes, as copal, dammar, etc. Others find application in medicine, e.g. guaiacnm, copaiba, etc., while others are put to varied uses in the arts, as ordinary pine-resin, colophony, amber, frankincense, Canada-balsam, benzoin, etc. [Balsams.]