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.

Canada balsam, also called Canada turpentine or balsam of fir, is a turpentine which is made from the resin of the balsam fir (Abies balsamea).

It is the fir's resin, dissolved in essential oils, and is a viscous, sticky, colourless (sometimes yellowish) liquid, that turns to a transparent yellowish mass when the essential oils have been allowed to evaporate.

Due to its high optical quality, its refractive index (n = 1.55, very close to that of glass), and its purity it is mainly used in optics as an invisible-when-dry glue for glass. It is soluble in xylene, amorphous when dried, and it does not crystallize with age, so its optical properties do not deteriorate.

Some uses include:

• in biology to conserve microscopic samples. The sample is sandwiched between the microscope slide (a glass plate) and the cover plate (a small thin glass plate) and Canada balsam is used to glue the arrangement together and enclose the sample to conserve it;
• in optical technology to glue together optical elements such as two prisms to form a beam splitter, or two lenses;
• to fix scratches in glass (car glass for instance) as invisibly as possible.
• in oil painting to achieve glow and facilitate fusion.

Canada balsam is sometimes incorrectly called Balm of Gilead. The true balsam is a fir tree; Balm of Gilead is a type of poplar.

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