e anode, is then placed within the tank,
parallel with the surface to be plated, known as the cathode, and so
mounted that it may be adjusted to or from the iron surface, or cathode.
A direct current of electricity is then caused to flow through the
copper plate and into the iron plate or surface, and the plating
proceeded with until the iron surface has a thin film of copper
deposited thereon. This is a slow process with the cyanide solution, so
it is discontinued as soon as possible, after the iron surface has been
completely covered with copper. This copper surface is thoroughly
cleaned off to remove therefrom the saline or alkaline solution, and it
is then immersed within a bath, containing a solution of sulphate of
copper. The current is then thrown on and allowed so to remain until it
has deposited the proper thickness of copper.

DIRECTION OF CURRENT.--If a copper and an iron plate are put into a
copper solution and connected up in circuit with each other, a primary
battery is thereby formed, which will generate electricity. In this
case, the iron will be positive and the copper negative, so that the
current within such a cell would flow from the iron (in this instance,
the anode) to the negative, or cathode.

The action of electroplating reverses this process and causes the
current to flow from the copper to the iron (in this instance, the
cathode).

CHAPTER XIV

ELECTRIC HEATING, THERMO ELECTRICITY

GENERATING HEAT IN A WIRE.--When a current of electricity passes through
a conductor, like a wire, more or less heat is developed in the
conductor. This heat may be so small that it cannot be measured, but it
is, nevertheless, present in a greater or less degree. Conductors offer
a resistance to the passage of a current, just the same as water finds a
resistance in pipes through which it passes. This resistance is measured
in ohms, as explained in a preceding chapter, and it is this resistance
which is utilized for electric heating.

RESISTANCE OF SUBSTANCES.--Silver offers less resistance to the passage
of a current than any other metal, the next in order is copper, while
iron is, comparatively, a poor conductor.

The following is a partial list of metals, showing their relative
conductivity:

Silver 1.
Copper 1.04 to 1.09
Gold 1.38 to 1.41
Aluminum 1.64
Zinc 3.79
Nickel 4.69
Iron 6.56
Tin