The ventilation should be free, not only to insure dryness, but to prevent chance of an explosion, as the gases given off during charge form an explosive mixture if confined. For this reason never bring an exposed flame near the battery when it is gassing. Direct sunlight should not fall on the cells. The trays, the benches on which the cells rest, and all metal work (iron and copper) should be painted with asphaltum varnish. =Assembling and placing cells in position.=—Place the jars, after they have been cleaned, in position on the stands, which should be provided for the purpose and which should be so situated in the room that each cell will be easily accessible. The jars are set in the trays, which previously should be filled with fine dry sand even with the top, the trays resting on the glass insulators. Place the elements as they come from the packing cases on a convenient stand or table (the elements are packed positive and negative plates together; the positive has plates of a brownish color, the negative of a light gray—the negative always has one more plate than the positive), cut the strings that bind them together, and carefully pull the positive and negative groups apart, throwing the packing aside. After carefully looking over both groups and removing any dirt or other foreign matter, assemble them, with separators between each positive and negative plate. When putting into the jars be careful that the direction of the lugs is relatively the same in each case, thus causing a positive lug of one cell always to connect with a negative of the adjoining one, and vice versa. This insures the proper polarity throughout the battery, bringing a positive lug at one free end and a negative at the other. Before bolting or clamping the lugs together, they should be well scraped at the point of contact to insure good conductivity and low resistance of the circuit; this should be done before the elements are taken apart and directly after unpacking, if the battery is to be set up at once. The connections should be gone over and tightened several times after the lugs are first fastened together to insure good contact. =Connecting up the charging circuit.=—Before putting the electrolyte into the cells, the circuits connecting the battery with the charging source must be complete, care being taken to have the positive pole of the charging source connected with the positive end of the battery. =Electrolyte.=—The electrolyte is dilute sulphuric acid of a specific gravity of 1.210 or 25° Baumé, as shown on the hydrometer at temperature of 70° F. The electrolyte should cover the top of the plates by one-half inch to three-fourths inch, and must be cool when poured into the cells. The jars should be numbered with asphaltum varnish and a line made with the same material to indicate the height at which the electrolyte should be kept.