IN measuring the refractive index of precious stones, we have succeeded in extending the range of the total reflectometer type of instrument by the preparation and use of liquids of higher refractivity than the sulphur in methylene iodide solution (nD<1.79) which is usually employed to make optical contact between the stone and the glass hemisphere of the instrument. The various immersion media of high refractive index proposed by Merwin1 and Wright2 were found to be unsuitable. Of a number of compounds prepared the following are worthy of note.