Fig. 25.—Preparation for experiment in electrotyping.
Fig. 26.—Sealing-wax mold suspended in solution of saturated copper sulphate, near to sheet of copper or coil of wire.
So long as the current continues flowing a reddish deposit will form on the blacklead surface, and if the action be allowed to continue until a fair thickness of metal is secured, the wax may be carefully melted off, leaving an exact relief of a fifty-cent piece’s reverse side in a copper. Any medal or seal may be used in place of the silver piece to obtain a first mold, but the coin has been mentioned as being probably the most suitable article near at hand.
With this example of electrotyping, our series of descriptions must terminate. But the embryo scientist, who has traveled thus far, need not cast his apparatus to the winds and henceforward forsake electrical matters. He may arrange various combinations of wines and liquids—such, for example, as passing the current through water to his motor, and noting the decrease in speed, or insert various lengths of iron wire in the circuit. Possibly the batteries will betray exhaustion, and they may then be reinstated by discarding the old salt solution, rinsing and replenishing the granulated zinc, and washing the flannel bags in permanganate of potash solution. These batteries are, in fact, a real asset, as they can be used—three or four together—in setting up an electric-bell installation, and are easily replenishable, when at length their life begins to ebb.
An endless fund of amusement—less expensive and more instructive than many—awaits those who explore the realms of the pygmy lightning spark.