ABSTRACT
A specimen of very radioactive radium was placed in a glass vessel connected with a mercury pump. On exhausting to a low vacuum and allowing the apparatus to stand, the pressure steadily increased. When the very small volume of gas thus collected flowed along the glass tubes, it rendered them phosphorescent, and if left in for some time, rapidly blackened them. The gas itself was powerfully radioactive, i.e. it continuously gave out a type of Roentgen rays, which made gases partial conductors of electricity and rapidly acted on a photographic plate. The emanation, obtained by passing a slow current of air over heated radium, was found to preserve its radioactive powers for weeks, when kept in a closed metal vessel. By determining the rate of diffusion of the emanation into air or other gases, using the electrical method, it is possible to obtain an approximate estimate of its molecular weight.
