well smeared with vaseline after tightening. Bolt a spring terminal clip to each end lug and mark the positive and negative ends for identification; a daub of red paint on the positive terminal is the usual method. The cut-away illustration of the completed storage battery, on page 122, shows the plates clearing the bottom of the jars; this is necessary to provide sediment space. The electrolyte for filling the cells is made by mixing chemically pure concentrated sulphuric acid with chemically pure water. The full-strength acid is mixed with the water to obtain the suitable specific gravity necessary for the battery; the usual proportion is 20% acid by volume. When mixing the acid, never add the water to the acid; pour the correct amount of water in a bottle, pitcher or jar and then add the acid to the water very slowly. Ready-prepared electrolyte can be obtained from the local battery-service station, saving much time and trouble, and the maker is advised to buy his electrolyte rather than make it. Fill each cell so that the electrolyte will come about 14 in. above the tops of the plates; any space between the jars and the case should be filled with corrugated board or similar material, to hold the jars rigid.
The storage battery completed, we are now ready for the rectifier, or charger as it is commonly known; this is made from a single quart-size fruit jar. An electrode support is made for the top of this jar from a strip of hardwood, ½ in. wide, boiled in paraffin; the aluminum electrode is cut from a sheet of heavy aluminum, the thickness of which is not important, but the heavier the better, and it should be as pure as possible to obtain. The lead electrode is cut from heavy sheet lead; both electrodes are 7 in. long by 14 in. wide; drill three holes in one end of each electrode and fasten to the wood top as shown in the insert on this page, with brass wood screws, the center screw holding a spring-clip connector. Fill the jar with either a saturated solution of borax; a rather dilute solution of sodium bicarbonate, or, better still, a solution of monobasic ammonium phosphate in the proportion of one pound to the gallon of distilled water. In either case, distilled water must be used in making the solution; fill the jar to within about one inch of the top and pour a thin layer of transformer oil or other heat-resisting oil to prevent evaporation or creeping. Set the rectifier jar in a small tub of water that is provided with an inlet and an outlet to keep the water level below the top of the jar by at least 2 in. This is easily done by means of two short lengths of rubber tubing connected to a faucet and drain, the outfit, of course, being placed near the water supply. This cooling tub need not be equipped for water circulation, but this method is advised for best results. The hookup shown in sketch above is self-explanatory and needs little
