The Becquerel rays and the properties of radium / by R.J. Strutt.

  • Rayleigh, Robert John Strutt, Baron, 1875-1947.
Date:
1906
Catalogue details

Licence: Public Domain Mark

Credit: The Becquerel rays and the properties of radium / by R.J. Strutt. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    The position of the end of the thread can be read on the scale, just as in reading a thermometer. To prevent the ice between the walls of the vessel getting melted by the heat of the room, the whole instrument is packed in ice. The narrow graduated tube, and the mouth of the vessel, alone project. If now a little radium is introduced inside the vessel, it is found that the end of the mercury thread begins to recede. The contents of the vessel are contracting, or, in other words, the ice between the walls is melting; and this goes on indefinitely. As soon as the radium is withdrawn, the end of the mercury thread remains steady. When the radium is again introduced, the mercury thread begins to recede steadily, and continues to do so, so long as the radium is left inside. We saw above (see p. 32) that it had been sug- gested that radio-active bodies drew their supplies of energy from the surrounding air. If this were so, the molecules of the surrounding air would lose energy, and its temperature would fall. The experi- ment we have just described conclusively proves that this is not the case. For, if the heat emitted by the radium were drawn from the surrounding air, there should be no heating effect on the whole from the air and the radium taken together. But the air was included with the radium inside the calorimeter, and the heating effect is observed none the less. It is evident, therefore, that radium does not draw its energy from this source. Let us return now to consider more quantitatively the experiment with Bunsen's calorimeter. If we know the size of the graduated tube, and if we found the rate at which the mercury moves, it is easy to find the change of volume in an hour, and to calculate the amount of ice which has been melted in