It will be noticed that the ionization from potassium and rubidium is very large compared with that from the other metals. It was found that the penetrating power of the potassium and rubidium radiations was also quite large. A given sample of a potassium salt gave the following results:
Sheets of Foil
It will be seen that the rays are very heterogeneous and vary in penetration from that of the very penetrating β rays of uranium downward. Sodium, lithium and ammonium salts showed no more activity than zinc. The rays from rubidium were found less penetrating than those from potassium. The activity of uranium is about a thousand times that of potassium. Photographs were also taken by making use of the rays from potassium and rubidium.
Campbell's results are in consonance with the experiments made some time ago by J. J. Thomson. Thomson showed that rubidium and potassium emit negatively charged particles which were deflected by an electrostatic field in the same way as the ordinary corpuscles.
In summing up we find that:
1. Some of the elements, as radium and thorium, are intensely radioactive.
2. Radium is very widely distributed through the rocks of the earth, and in radioactive minerals is found to exist in a constant proportion with uranium.
3. Radium and its products are also to be found in the air and play an important rôle in atmospheric phenomena.
4. The ordinary metals are slightly radioactive, emitting radiations that seem very much like the α radiation from the radio-elements.
5. Potassium and rubidium emit radiations similar to the β rays.