| Product. | T | Radiations. | |
| Radium, | α rays. | ||
| Emanation, | 4 | days, | α rays. |
| Radium A, | 3 | mins., | α rays. |
| Radium B, | 21 | mins., | no rays. |
| Rαdium C, | 28 | mins., | α, β and γ rays. |
When the emanation has been left in a closed vessel for several hours, the emanation and its successive products reach a stage of approximate radioactive equilibrium, and the heating effect is then a maximum. If the emanation is suddenly removed from the tube by a current of air, the heating effect is then due to radium A, B and C together. On account, however, of the rapidity of the change of radium A (half value in three minutes) it is experimentally very difficult to distinguish between the heating effect of the emanation and that of radium A. The curve of variation with time of the heating effect of the tube after removal of the emanation is very nearly the same as the corresponding curve for the activity measured by the a rays. These results show that each of the products of radium supplies an amount of heat roughly proportional to its a ray activity. Each product loses its heating effect at the same rate as it loses its activity, showing that the mission of heat is directly connected with the radioactive changes. The results indicated that the product, radium B, which does not emit rays, does not supply an amount of heat comparable with the other products. This point is important and requires more direct verification.
Since the heat emission is in all cases nearly proportional to the number of a particles expelled, the question arises whether the bombardment of these particles is sufficient to account for the heating effects observed. The kinetic energy of the α particle can be at once determined, since e/m and v are known.
The following table shows the kinetic energy of the a particle deduced from the measurements of Eutherford and Des Coudres. The third column shows the number of a particles expelled from 1 gram of radium per second on the assumption that the heating effect of radium (100 gram calories per gram per hour) is entirely due to the energy given out by the expelled α particles.
| Observer. | Kinetic. | Number of Particles expelled per Second from 1 Gram of Radium. |
| Rutherford | ergs | |
| Des Coudres | ergs |
This hypothesis that the heating effect of radium is due to bombardment of the α particle can be indirectly put to the test in the following way. It seems probable that each atom of radium in breaking up emits one α particle. On the disintegration theory, the residue
