Start the generator and bring it up to speed. Connect some form of resistance in "series" with the mains. A lamp in an ordinary lamp socket will do very well for this resistance. Dip the two ends of the wire (one coming from the generator, the other through the lamp) into a cup of water, in which a pinch of salt is dissolved. Bring them almost together and hold them there. Almost instantly, one wire will begin to turn bright, and give off bubbles. The wire which turns bright and gives off bubbles is the negative wire. The other is the positive.
A rough-and-ready farm electric plant, supplying two farms with light, heat and power; and a Ward Leonard-type circuit-breaker for charging storage batteries
Care of Battery
Since specific directions are furnished with all storage batteries, it is not necessary to go into the details of their care here. Storage battery plants are usually shipped with all connections made, or plainly indicated. All that is necessary is to fill the batteries with the acid solution, according to directions, and start the engine. If the engine is fitted with a governor, and the switchboard is of the automatic type, all the care necessary in charging is to start the engine. In fact, many makes utilize the dynamo as a "self-starter" for the engine, so that all that is necessary to start charging is to throw a switch which starts the engine. When the battery is fully charged, the engine is stopped automatically.
The "electrolyte" or solution in which the plates of the lead battery are immersed, is sulphuric acid, diluted with water in the proportion of one part of acid to five of water, by volume.
The specific gravity of ordinary commercial sulphuric acid is 1.835. Since its strength is apt to vary, however, it is best to mix the electrolyte with the aid of the hydrometer furnished with the battery. The hydrometer is a sealed glass tube, with a graduated scale somewhat resembling a thermometer. The height at which it floats in any given solution depends on the density of the solution. It should indicate approximately 1.15 for a storage battery electrolyte before charging. It should not be over 1.15—or 1,150 if your hydrometer reads in thousandths.
Only pure water should be used. Distilled water is the best, but fresh clean rain water is permissible. Never under any circumstances use hydrant water, as it contains impurities which will injure the battery, probably put it out of commission before its first charge.