A HANDY LIGHT.
Figure 188 shows a simple and handy form of light which utilizes the current from a home made primary cell. It consists of a glass fruit jar, fitted with a tight wooden top. A miniature porcelain socket and a 1.5 volt tungsten lamp are mounted on top.
The battery is arranged so that the zinc element can be drawn up out of the solution when the light is not in use and any waste thereby prevented. The zinc electrode consists of a strip of that metal fastened onto the lower end of a brass rod by means of two threaded nuts. The upper end of the rod passes through a small metal collar on the top of the cover, provided with a thumb-screw so that when the electrode is lifted up out of the solution it may be clamped firmly in that position.
The zinc strip should not be so long that it will not clear the solution when raised up if the jar is about half filled.
[Illustration: FIG. 188.—A Handy Light.]
The positive electrode is a battery carbon mounted on the lower end of a brass rod. The brass rod in this case is not movable because the carbon can remain in the solution indefinitely without any waste.
The joint between the brass rods and the electrode should be coated with paraffine so that the chemicals in the solution will not cause any corrosion. The rods should be connected to the lamp socket. When the zinc is lowered into the solution, the lamp will be lighted by the current generated.
The electrolyte should be that described as the "bichromate" solution on page 34 of Vol. I of this book.