the amount of radium present. For example, the activity only increased 24 times for a millionfold increase of the radium present, from 10-9 mgrs. to 10-3 mgrs.
These results, however, have not been confirmed by later experiments made by Eve. He found that, over the range examined, the activity was directly proportional to the amount of radium present, within the limits of experimental error. The following table illustrates the results obtained. The radium was evaporated down in platinum vessels 4·9 sq. cms. in area.
| Weight of radium in milligrams | Activity in arbitrary units |
|---|---|
| 10 -4 | 1000 |
| 10 -5 | 106 |
| 10 -6 | 11·8 |
| 10 -7 | 1·25 |
For an increase of one-thousandfold of the quantity of radium, the activity increased 800 times, while Voller states that the activity, in his experiments, only increased 3 to 4 times.
In the experiments of Eve, the activity was measured by observing the increased rate of discharge of a gold-leaf electroscope when the platinum vessel containing the active deposit was placed inside the electroscope. The activity of 10-8 mgrs. was too small to be measured with accuracy in the electroscope employed, while 10-3 mgrs. gave too rapid a rate of discharge. On the other hand, the method of measurement employed by Voller was unsuitable for the measurement of very weak radio-activity.
Eve also found that a small quantity of radium kept in a closed vessel did not lose its activity with time. A silvered glass vessel contained a gold-leaf system, such as is shown in Fig. 12. A solution containing 10-6 mgrs. of radium bromide was evaporated over the bottom of the vessel of area 76 sq. cms. The activity, after reaching a maximum, has remained constant over the 100 days during which observations have so far been made.
These experiments of Eve, as far as they go, show that the activity of radium is proportional to the amount of radium present, and that radium,