ration: FIG. 205.--The heating element in the electric stove.]

291. Blasting. Until recently, dynamiting was attended with serious
danger, owing to the fact that the person who applied the torch to the
fuse could not make a safe retreat before the explosion. Now a fine
wire is inserted in the fuse, and when everything is in readiness,
the ends of the wire are attached to the poles of a distant battery
and the heat developed in the wire ignites the fuse.

[Illustration: FIG. 206.--An electric pad serves the same purpose as a
hot water bag.]

292. Welding of Metals. Metals are fused and welded by the use of
the electric current. The metal pieces which are to be welded are
pressed together and a powerful current is passed through their
junction. So great is the heat developed that the metals melt and
fuse, and on cooling show perfect union.

293. Chemical Effects. _The Plating of Gold, Silver, and Other
Metals._ If strips of lead or rods of carbon are connected to the
terminals of an electric cell, as in Figure 208, and are then dipped
into a solution of copper sulphate, the strip in connection with the
negative terminal of the cell soon becomes thinly plated with a
coating of copper. If a solution of silver nitrate is used in place of
the copper sulphate, the coating formed will be of silver instead of
copper. So long as the current flows and there is any metal present in
the solution, the coating continues to form on the negative electrode,
and becomes thicker and thicker.

[Illustration: FIG. 207.--An incandescent electric bulb.]

The process by which metal is taken out of solution, as silver out of
silver nitrate and copper out of copper sulphate, and is in turn
deposited as a coating on another substance, is called electroplating.
An electric current can separate a liquid into some of its various
constituents and to deposit one of the metal constituents on the
negative electrode.

[Illustration: FIG. 208.--Carbon rods in a solution of copper
sulphate.]

Since copper is constantly taken out of the solution of copper
sulphate for deposit upon the negative electrode, the amount of copper
remaining in the solution steadily decreases, and finally there is
none of it left for deposit. In order to overcome this, the positive
electrode should be made of the same metal as that which is to be
deposited. The positive metal electrode gradually dissolves and
replaces the metal lost from the solution by deposit and
elec