due to the time taken for the emanation to be carried into the testing vessel, gave the temperature at which some of the emanation commenced to volatilize. The ionization current in the testing vessel rose rapidly to a maximum value, showing that, for a small increase of temperature, the whole of the radium emanation was volatilized. The following table gives an illustration of the results obtained for a current of hydrogen of 1·38 cubic centimetres per second.
| Temperature | Divisions per second of the electrometer |
|---|---|
| -160° | 0 |
| -156° | 0 |
| -154°·3 | 1 |
| -153°·8 | 21 |
| -152°·5 | 24 |
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