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Fig. 86—How Exide Stand-by Battery Helped to Handle Unexpected Lighting Load.

The tank linings are of pure sheet lead, the lap seams being burned with the hydrogen flame. The upper edges of the lining extend over the edges of the tank and down outside clear of the tank faces. Drip points are provided, so spaced that they come between the tank supports. Good insulation of the cells is an essential. The Exide insulator consists of a glass body surrounded by an inverted petticoat, this forming an annular trough partly

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Fig. 87.–Battery-Room of Calumet River Draw-bridge of Calumet &

Western Indiana Railroad.

filled with oil, the whole being covered with a lead cap extending down around the sides but out of contact therewith. Each oil insulator rests on a truncated cone or pedestal of earthenware or a composition not affected by acid. Each cell is covered with a plate of heavy glass, which serves to condense the acid spray. All conductors are of specially heavy section lead-coated copper bars, firmly bolted together. The plates of each cell, joined together

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to form an element or plate group, are lead-burned to soft-lead busbars.

The total number of cells required is determined by the maximum busbar voltage permissible at the end of a high-discharge rate. For example, if a battery is installed of capacity enough to carry a maximum peak load for ten minutes a voltage of 100 each side of a three-wire system might be considered satisfactory. This would call for 75 cells each side. If at any time during the day it is necessary to float the battery at a voltage as low as 115 volts, the main battery would consist of 55 cells each side, leaving an auxiliary battery of 20 end-cells on each side. These end-cells are brought into action as needed by special switches.

In arranging a battery-room for such a large battery, special attention is given the floor construction, because drainage is important. Ventilation must be exceptionally good, and all exposed metal work should be protected by acid-proof paint. Concrete has been used for battery-room floors, and is satisfactory if care is taken to flush it with water frequently to wash away any electrolyte that may have accumulated. Hard-burned tile or vitrified brick is much more suitable. The floor should be laid on a concrete foundation, of sufficient strength to carry the weight. The slope should be such as to allow for positive drainage, and the floor covered with asphaltum felt. Spaces of 14 inch are left between the bricks or tiles, these spaces being grouted with asphalt compound. An exhaust ventilating system is almost an essential if the battery is used much. The fan parts should be of bronze, and air from the room should be filtered through an air-box having perforated lead screen to eliminate acid spread. It is said that air in a battery-room should be changed completely four times an hour during the gassing period of the charge.

Storage Batteries for Draw-Bridge Operation. An unfailing source of power is an absolute necessity where draw-bridges are operated by electric motors, as most of them are. This applies especially to railway bridges, where any failure of the power supply would seriously interrupt travel on either the waterway or railway. Vessels have been badly injured dụe to failure to open a draw. Bridges may be operated by separate power plants, consist

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Fig. 88.—Calumet & Western Indiana Railroad Bridge in Open and Closed Positions.

ing of dynamos driven by internal-combustion engines, or they may take their power from a trolley or lighting system. In either case, an auxiliary storage-battery installation insures absolutely reliable service, even in event of failure of the main source of current. This is of special value where a bridge is over a widely used stream. The main principles of operation and the requirements are practically the same as obtain when storage batteries are used for stand-by service. A typical installation, where the movable span of the bascule pattern is 186 feet long and weighs 1,100,100 pounds itself, in addition to a 3,000,000-pound concrete counterbalance, consists of two batteries, one to furnish power for the bridge motors, the other for signals and lighting. The larger battery consists of 120 type F11 "Chloride Accumulator" elements in lead-lined wooden tanks. Each element has a normal capacity of 400 ampere-hours at 240 volts. The general arrangement of the tanks in the battery-room is shown at Fig. 87. The views at Fig. 88 show the bridge in open and closed positions.

Edison Storage-Battery Mine Lamp.—The greatest danger in mines to-day is from the use of unprotected flames wherever the deadly fire damp is likely to be encountered. Artificial light is an essential which formerly could not be obtained with safety unless provided in such minute quantity as to seriously curtail production. The Davy safety oil lamp is well known and has been widely used, but electric lighting gives much superior results. Much ingenuity has been shown in trying to adapt portable electric lamps to this work, but the stumbling-block always has been the production of current for their operation. The only practical source of energy is naturally some sort of battery, and many attempts have been made to modify the old types of cells so that they would serve the purpose satisfactorily. The advocates of the primary battery soon found that the inherent defects of this type were greatly magnified when an endeavor was made to produce a portable form of small size and weight with sufficient capacity to keep an electric lamp burning any considerable time. Aside from this, the electrical energy is produced in a primary battery by the consumption of the zinc plates, so that there was constant expense and trouble for their renewal. The primary cell was early elimi

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