Fig. 34.
| Specific Inductive Capacity. | |
|---|---|
| Dry air | 1.000 |
| Sulphur | 2.590 |
| Hard rubber | 2.290 |
| Paraffin | 1.996 |
| Shellac | 2.750 |
| Kerosene | 2.225 |
| Paraffin oil | 2.710 |
| Castor oil | 4.962 |
| Olive oil | 3.575 |
Condensers made with dielectric of high inductive capacity (insulation being equal) will retain greater charge than those made with dielectrics of low inductive capacity. Thus, one made with shellac would be nearly half as great again as with paraffin.
Capacity of a condenser increases with area of foil surface, with diminished distance between foil plates and with increase of insulation.
CHAPTER V.
EXPERIMENTS.
The luminous effects that can be obtained by means of a Ruhmkorff coil are exceedingly beautiful and instructive. The simplest experiment of this nature is the production of the spark consequent on the approximation of the electrodes attached to the secondary coil. This spark can be varied in both length, intensity, or shape by the form and nature of the substances between which it is permitted to pass. Attach to each end of the discharger a fine steel needle, and bring them together until the spark jumps from one to the other. A long thin snapping spark will pass, which, however, appears to be trying to take any but a straight path across the air gap. The peculiar crookedness of this, as in a lightning flash, is credited to the fact of particles of matter floating in the air conducting the current better than the pure air. The curious odor noticed in these discharges, as, in fact, in the working of all high-tension apparatus, is ozone—O3, triatomic oxygen. This gas, so noticeable after a thunderstorm, has a powerful effect on the mucous membranes of the throat and nasal passages, and must be inhaled with caution. It is being used by the medical profession for the destruction of germs and for general therapeutic service.
Substitute pieces of fine iron wire for the needles, and bring the ends together about one quarter the distance through which the normal spark will pass. The spark will be found to have changed its appearance, now being thick and redder, or, rather, of a deep yellow, and to possess vast heating qualities.
The iron wire will melt at one electrode, and if the other be examined it will be perceived that it has not even become warm. The cold wire will be the one connected to the positive pole of the coil.