Published online by Cambridge University Press: 14 March 2018
The method described is one that can be used to measure the refractive indices of minerals when no refractometer is available. The readings are consistent to ±0·002 and are in reasonable agreement with those obtained using a refractometer.
The principle of the method is to mix two liquids with different refractive indices. One of these is a typical immersion liquid with a very low volatility. It must have a refractive index greater than that of the mineral under investigation. The other, more volatile liquid has a refractive index less than that of the mineral. The two liquids selected must be miscible in all proportions, but must not react together. The mineral is completely immersed in a mixture of the two liquids.