Canada balsam

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Canada balsam, also called Canada turpentine or balsam of fir, is a turpentine which is made from the resin of the balsam fir tree (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.^{[citation needed]}

Some uses include:

• in biology to conserve microscopic samples. The sample is sandwiched between a microscope slide and a coverslip 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.