Microscope Mounting Medium: Canada Balsam Dissolved in Benzene

Canada balsam is the oleoresin of the balsam fir, collected by breaking the blisters on its bark into a bottle (US Dispensatory, 1907). Dried, it is clear and glassy, with a refractive index close to crown glass, so it was long the standard medium for permanent microscope slides, dissolved in a solvent (Wikipedia). Here it is thickened and dissolved in benzene, which the Dispensatory names as dissolving it completely. Proportions are ours. The picture: our drawing.