ABSTRACT
This chapter investigates the property possessed by the compounds of thorium of giving a radioactive emanation, and also into the nature of the emanation itself. It shows that the compounds of thorium, besides being radioactive in the same sense as the uranium compounds, also continuously emit into the surrounding atmosphere, under ordinary conditions behaves in all respects like a radioactive gas. This emanation will darken a photographic plate, and will render a gas capable of conducting an electric current. A small current is able to pass through a gas exposed to the radiations, even with a very weak electric field and the measurement of this current by means of the electrometer affords a means of comparing the intensities of radiation. Frederick Soddy's result shows that within the limit of accuracy desired we may take the amount of emanation as directly proportional to the weight of the substance.
