probable, from analogy, that an intermediate product, corresponding to Th X in thorium, would be found in actinium[1]. Recent work has verified this supposition. Giesel[2] and Godlewski[3] independently observed that a very active substance could be separated from "emanium," very similar in chemical and physical properties to Th X in thorium. This product will, from analogy, be called "actinium X." The same method, which was used by Rutherford and Soddy to separate Th X from thorium, is also effective in separating actinium X from actinium. After precipitation of the active solution with ammonia, actinium X is left behind in the filtrate. After evaporation and ignition, a very active residue remains. At the same time, the precipitated actinium loses a large proportion of its activity.
Giesel observed the separation of an active product, using a fluorescent screen to detect the radiations. A very complete examination of the product actinium X has been made by Godlewski in the laboratory of the writer.
After separation of actinium X, the activity, whether measured by the α or β rays, increases about 15 per cent. during the first day, and afterwards decays exponentially with the time, falling to half value in 10·2 days. The activity of the separated actinium was small at first but steadily increased with the time, reaching a practical maximum after an interval of sixty days. After the first day, the decay and recovery curves of activity are complementary to one another. The curves of rise and decay are shown graphically in Fig. 82, curves I and II respectively.
Godlewski observed that a solution of actinium, freed from actinium X, gave out very little emanation, while a solution of actinium X gave off the emanation in large quantity. The amount of emanation from the solution was measured by observing the activity produced in a testing vessel, similar to that shown in Fig. 51, when a constant current of air was passed through the solution. The emanating power of actinium X decreased exponentially with the time at the same rate as that at which the actinium X lost its activity. At the same time the actinium solution increased
