Experiments were also made with the dregs left after liquefied
air had nearly entirely evaporated, and again with the same
result; no increase in discharging power is produced by
concentration of a possible radioactive constituent of the
atmosphere. We have since found that the radium emanation
withstands prolonged sparking with oxygen over alkali, and also,
during several hours, the action of a heated mixture of
magnesium powder and lime. The discharging power was maintained
unaltered after this treatment, and inasmuch as a considerable
amount of radium was employed it was possible to use the self-
luminosity of the gas as an optical demonstration of its
persistence. In an experiment in which the emanation mixed with
oxygen had been sparked for several hours over alkali, a minute
fraction of the total mixture was found to discharge an
electroscope almost instantly. From the main quantity of the gas
the oxygen was withdrawn by ignited phosphorus, and no visible
residue was left. When, however, another gas was