FIG. 16.—EXPERIMENT SHOWING THE CURRENT.
MICROPHONE AND TELEPHONE.
Take two small carbon rods, p p, if procurable, if not, use two ordinary nails, and connect them up in the circuit of the battery; lay them upon a thin box so that the rods or nails cross each other, as in Fig. 17; insert the electromagnet in the circuit; move the coils out a little beyond the ends of the cores, lay a thin iron plate over the ends of the coils, then jar the box upon which the bars, p p, are laid, or drop a pin upon it, or scratch it with a piece of paper, and the sound will be heard by placing the ear against the iron plate resting upon the coils of the magnet.
FIG. 17.—MICROPHONE AND TELEPHONE.
ELECTRO METALLURGY.
Dissolve an ounce of sulphate of copper in a half pint of water; add a few drops of sulphuric acid; connect with the zinc pole of the battery the object to be coppered. To the wire connected with the carbon attach a small plate of copper. Hang the object and the copper plate in the solution a short distance apart. A deposit of copper will be quickly formed.
THE HEATING EFFECT OF THE CURRENT.
With a piece of very fine platinum wire (No. 36 or 40), placed in the circuit of the battery, the heating effect of the current may be shown. A half inch of No. 36 platinum wire will serve for the experiment. If the battery is in good condition it will heat from 1/8 to 1/4 inch of the wire red hot. This is sufficient to light gas or an alcohol lamp, also to ignite powder or gun cotton.