A re-examination of the light scattered by gases in respect of polarisation. II.— Experiments on helium and argon

Abstract

This gas, owing to its small refractivity, scatters so little light that purity becomes of the first importance. As is well known, the best method of purification is by cooled charcoal, according to the method of Dewar. To use it to the best advantage, a convective circulation was maintained which delivered a stream of freshly purified gas into the region where the primary beam traversed it. A charcoal vessel was used about 2 inches diameter and 8 inches long, containing 100 grm. of coarsely granulated charcoal, a perforated zinc fitting, as shown, prevented the charcoal from dropping out at the bottom. The connections were as shown in the figure and fitted on to the brass cones of the vessel, fig. 6 of previous paper. The liquid air was contained in a special vacuum vessel, which had an exit at the bottom as shown. The vessel was made of silica, as a glass vessel of this shape could hardly be expected to stand the strains which would result from cooling. The rubber cork at Z was in two halves to make assemblage easier, and a layer of vaseline, melted and poured on the top of it, held the liquid air satisfactorily. The weight of the vacuum vessel with the liquid air contained, was taken on the rubber cork, which kept it well pressed home. As to the remaining supports of the vacuum vessel and the rubber cork, it will suffice to mention that they were carefully arranged to avoid unnecessary constraints.