the final number when radio-active equilibrium is reached, then (section 133),
Since the activity of the emanation falls to half value in 1 minute
and N₀ = 87q₀, or the number of emanation particles present when a steady state is reached is 87 times the number produced per second.
Radium Emanation.
144. Discovery of the emanation. Shortly after the discovery of the thorium emanation, Dorn6 repeated the results, and, in addition, showed that radium compounds also gave off radio-active emanations, and that the amount given off was much increased by heating the compound. The radium emanation differs from the thorium emanation in the rate at which it loses its activity. It decays far more slowly, but in other respects the emanations of thorium and radium have much the same properties. Both emanations ionize the gas with which they are mixed, and affect a photographic plate. Both diffuse readily through porous substances but are unable to pass through a thin plate of mica; both behave like a temporarily radio-active gas, mixed in minute quantity with the air or other gas in which they are conveyed.
145. Decay of activity of the emanation. Very little emanation escapes from radium chloride in the solid state, but the amount is largely increased by heating, or by dissolving the compound in water. By bubbling air through a radium chloride solution, or passing air over a heated radium compound,