CANADA BALSAM, an exudation of the North American balsam fir, called also Canada turpentine and balsam of fir. It is strictly speaking a turpentine (q.v.) and not a balsam (q.v.), and at ordinary temperature is a yellow solid. It belongs to the class of oleo-resins which are natural products consisting of resin (q.v.) dissolved in a volatile oil. It is of importance in optics on account of its refractive index, which is 1.53 for the sodium D lines, being close to that of glass.
(See also BINOCULAR INSTRU MENT; COLOUR; FIR; OPTICS, GEOMETRICAL ; LENS.)