(Science: microscopy) a resin from the balsam fir abies balsamea. Dissolved in xylene, toluene, or benzene it is used as a mountant for permanent microscopical preparations. Its refractive index may vary from 1.530 to l.545 and its softening point from room temperature to 100deg.C, these properties varying with age and solvent content. If impure it discolours with age.
See: lens, Bertrand.