III. On the refractive indices of gaseous potassium, zinc, cadmium, mercury, arsenic, selenium and tellurium

Abstract

We have continued, with more perfect apparatus, the enquiry recorded in a previous paper on the refractive indices of the vapours of elements which are not gaseous at ordinary temperatures. The instrument employed was the refractometer of Jamin, and the arrangement of the apparatus has been fully described in the paper just cited, so that it requires only a brief recapitulation here. Two similar exhausted tubes are placed in the paths of the rays of monochromatic light between the mirrors, and a known weight of the element is vaporised in one of them, of which the volume is known. The tubes are heated by means of a simple form of electric furnace, consisting of two coils of nickel wire embedded in asbestos.