Section 3.3.4. Media for organic substances

Organic substances are usually soluble in organic liquids, but not usually in aqueous solutions. The saturated solutions listed in Table 3.3.4.1 (Jelley, 1934, p. 245) are generally satisfactory. For substances of low solubility, the organic liquids listed in Table 3.3.4.2 may be useful; the refractive index of diluted aqueous solutions changes with time because of evaporation.

Table 3.3.4.1| top | pdf | Aqueous solutions for use as immersion media for organic crystals Salt of saturated solution Lithium iodide 1.490 Sodium iodide 1.496 Potassium iodide 1.456 Barium iodide 1.528 Tetrasodium dioxypentathiostannate 1.615

Table 3.3.4.2| top | pdf | Organic immersion media for use with organic crystals of low solubility Compound Diethyl oxalate 1.41 Di-n-butyl carbonate 1.41 Triethyl citrate 1.44 Tri-n-butyl citrate 1.44 n-Butyl phthalate 1.49 α-Bromonaphthalene 1.66 α-Iodonaphthalene 1.70 Methylene iodide 1.74

If the index of refraction is greater than about 1.7, the media at the end of Table 3.3.2.1 have to be used. These usually dissolve organic crystals, so that the immersion liquid becomes saturated with the compound. The refractive index of the saturated medium is then measured with a microrefractometer (Jelley, 1934, pp. 236–240).