rapidly takes up the potential of the air surrounding the active substance. In this respect it is more convenient and rapid in its action than the ordinary taper or water dropper, but on account of the disturbance of the electric field by the strong ionization produced, it is probably not so accurate a method as that of the water dropper.
120. Effect on liquid and solid dielectrics. P. Curie22 made the very important observation that liquid dielectrics became partial conductors under the influence of radium rays. In these experiments the radium, contained in a glass tube, was placed in an inner thin cylinder of copper. This was surrounded by a concentric copper cylinder, and the liquid to be examined filled the space between. A strong electric field was applied, and the current through the liquid measured by means of an electrometer.
The following numbers illustrate the results obtained:
| Substance | Conductivity in megohms per 1 cm. 3 |
|---|---|
| Carbon bisulphide | 20 × 10 -14 |
| Petroleum ether | 15 „ |
| Amyline | 14 „ |
| Carbon chloride | 8 „ |
| Benzene | 4 „ |
| Liquid air | 1·3 „ |
| Vaseline oil | 1·6 „ |
Liquid air, vaseline oil, petroleum ether, amyline, are normally nearly perfect insulators. The conductivity of amyline and petroleum ether due to the rays at -17° C. was only ⅒ of its value at 0° C. There is thus a marked action of temperature on the conductivity. For very active material the current was proportional to the voltage. With material of only ¹⁄₅₀₀ of the activity, it was found that Ohm’s law was not obeyed.
The following numbers were obtained:
| Volts | Current |
|---|---|
| 50 | 109 |
| 100 | 185 |
| 200 | 255 |
| 400 | 335 |
For an increase of voltage of 8 times, the current only increases about 3 times. The current in the liquid thus tends to become “saturated” as does the ordinary ionization current through a gas. These results have an important bearing on the ionization theory, and show that the radiation probably produces ions in the liquid as well as in the gas. It was also found that X rays increased the conductivity to about the same extent as the radium rays.
Becquerel23 has recently shown that solid paraffin exposed to the β and γ rays of radium acquires the property of conducting electricity to a slight extent. After removal of the radium the conductivity diminishes with time according to the same law as for an ionized gas. These results show that a solid as well as a liquid and gaseous dielectric is ionized under the influence of radium rays.