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Canada balsam, yellow, oily, resinous exudation obtained from the balsam fir. It is an oleoresin (see resin) with a pleasant odor but a biting taste. It is a turpentine rather than a true balsam. On standing, the essential oil in Canada balsam evaporates, leaving behind the resin as a hard, transparent varnish. Canada balsam is valued as an optical mounting cement, e.g., for lenses and microscope slides, since it yields, when dissolved in an equal volume of xylene, a noncrystallizing cement with a refractive index nearly equal to that of ordinary glass. It is used also in paints and polishes.
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