ELECTRIC RESISTANCE.

Resistance is offered by all substances to the electric current, and varies with the nature of the substance.

Most metals are good conductors; wood and stone offer considerable resistance, and silk, glass and ebonite are practical non-conductors; but remember if a non-conductor is wet or even damp it becomes a good conductor, moisture or water being a first-class conductor. On the other hand, conductivity is diminished by an increase of temperature—otherwise dryness. The following table will give a good idea of the conductivity of metals:

That of silver being100
That of copper is97
That of gold is74
That of platinum is17
That of iron is16
That of lead is8
That of German silver is7.5
That of mercury is1.6

Therefore, generally, good conductors are all the metals, carbon, water, aqueous solutions, moist bodies besides wood, cotton, hemp, etc. Good insulators or non-conductors are paraffine, solid or liquid, turpentine, silk, sealing wax, india rubber, dry glass or porcelain. The best electrical conductors are the best thermal conductors, and a “red hot” temperature converts insulators into fairly good conductors.