ABSTRACT
This chapter gives the results of a detailed investigation of the radioactivity of thorium compounds which has thrown light on the questions connected with the source and maintenance of the energy dissipated by radioactive substances. During an investigation of the emanating power of thorium compounds, to be described later, evidence was obtained of the separation of an intensely radioactive constituent by chemical methods. Two methods are used for the measurement of radioactivity, the electrical and the photographic. The examples of radium in pitchblende and of the thorium-excited radioactivity make it certain that comparatively large ionization effects are produced by quantities of matter beyond the range of the balance or spectroscope. The curves of the recovery and decay of the activities of thorium and ThX with time suggested the explanation that the radioactivity of thorium was being maintained by the production of ThX at a constant rate.
