Page:Radio-activity.djvu/304

 The following table shows the results obtained for different currents of hydrogen and oxygen.

+++-+-+ +++-+-+ +++-+-+
 * | Current of Gas  |T_{1}|T_{2}|
 * Hydrogen| ·25 c.c. per sec.|-151·3 |-150  |
 * "   | ·32     "     "  |-153·7 |-151   |
 * "   | ·92     "     "  |-152   |-151   |
 * "   |1·38     "     "  |-154   |-153   |
 * "   |2·3      "     "  |-162·5 |-162   |
 * Oxygen | ·34     "     "  |-152·5 |-151·5 |
 * "   | ·58     "     "  |-155   |-153   |

The temperature T_{1} in the above table gives the temperature of initial volatilization, T_{2} the temperature for which half of the condensed emanation had been released. For slow currents of hydrogen and oxygen, the values of T_{1} and T_{2} are in good agreement. For a stream of gas as rapid as 2·3 cubic centimetres per second the value of T_{1} is much lower. Such a result is to be expected; for, in too rapid a stream, the gas is not cooled to the temperature of the spiral, and, in consequence, the inside surface of the spiral is above the mean temperature, and some of the emanation escapes at a temperature apparently much lower. In the case of oxygen, this effect appears for a gas stream of 0·58 cubic centimetres per second.

In the experiments on the thorium emanation, on account of the rapid loss of activity, a slightly different method was necessary. The steady stream of gas was passed over the thorium compound, and the temperature was observed at the instant when an appreciable movement of the electrometer appeared. This gave the temperature at which a small fraction of the thorium emanation escaped condensation, and not the value T_{1} observed for the radium emanation, which gave the temperature for which a small fraction of the previously condensed emanation was volatilized.

The following table illustrates the results obtained.

+++-+ +++-+ +++-+
 * | Current of Gas  |Temperature|
 * Hydrogen| ·71 c.c. per sec.| -155° C. |
 * "   |1·38  "      "    | -159° C.  |
 * Oxygen | ·58  "      "    | -155° C.  |