is best fitted, the one serving as a check on the other. Voltage has the great disadvantage in that it is dependent upon the rate of current flowing. Open circuit readings are of no value, as a cell reads almost the same discharged as it does charged. On the other hand, a voltmeter is a very easy instrument to read and may be located wherever desirable. Specific gravity readings are almost independent of the current flowing, but the hydrometer is difficult to read, not very sensitive and the readings must be taken directly at the cells.

Charging the Storage Battery.-Great care should be used in charging and the charging rates given by the various manufacturers should be followed whenever possible. It is essential that the positive wire carrying the charging current be connected with the positive plates of the battery. The positive pole of a cell is usually indicated by a plus sign or by the letter "P." In case of doubt always ascertain the proper polarity of the terminals before charging. This is done by immersing the ends in acidulated water, about an inch apart. The one around which the more bubbles collect is the negative, and should be connected with negative pole of the battery. If a cell is not connected properly it will be ruined. A battery always should be charged, if possible, at a low charging rate, because it will overheat if energized too rapidly. The normal temperature is between 70 and 90 degrees Fahrerheit. When the battery is fully charged the solution assumes a milky white appearance and bubbles of gas are seen rising to the surface of the electrolyte. All foreign matter should be kept out of the batteries as any metallic substance finding its way into the cell or between the terminals will short circuit the cell and perhaps ruin it before its presence is known. The terminals, the outside of the cell and all connections, should be kept free from acid or moisture. A neglect of these essentials means corrosion and loss of capacity by leakage. There is one point in connection with the charge which should be especially emphasized, namely, that the final voltage corresponding to a full charge is not a fixed figure, but varies widely, depending upon the charging rate, the temperature, the strength of the electrolyte, and age of the battery. For this reason, charging to a fixed volt

Fig. 74.-Appliances for Charging and Testing Storage Batteries.

age is unreliable and likely to result disastrously. The charge should be continued until the voltage or gravity ceases rising, no matter what actual figures are reached. Old cells at high tempera

tures may not go above 2.4 volts per cell, whereas if very cold, they have been known to run up to three volts.

The points to be especially emphasized in connection with the charge are:

First-On regular charges keep the rates as low as practical and cut off the current promptly. It is preferable to cut off a

little too soon rather than to run too long where there is any question.

Second-Overcharges must be given at stated intervals and continued to a complete maximum. They should be cut off at the proper point, but when in doubt it is safer to run too long, rather than to cut off too soon.

Third-Do not limit the charge by fixed voltage.

Fourth-Keep the temperature within safe limits.

Fifth-Keep naked flames away from cells while charging as the gas given off is inflammable. Always see that gas vents are clear before charging.

The following table will undoubtedly be of value as a guide to the proper charging rates of batteries of various ampere hour capacities, the assumption being that these are all 3 cell batteries that will show between 6.5 and 7.5 volts when fully charged. While most manufacturers of batteries furnish instruction books, these may be lost, so some compact reference is needed. The overall dimensions of the batteries are given so the capacity may be determined even if the marks of identification on the name plate are obliterated

A battery may be charged from any source of direct current. Garages, central stations, lighting plants, etc., can do the work, and in many instances where direct current is used for power

purposes, a simple charging outfit is operated from the dynamo. Where alternating current only is available, a rectifier which changes alternating current to direct current may be installed and the battery charged with no inconvenience and at comparatively small cost. All of these methods will be considered in proper sequence and typical charging outfits described.

Remedies for Loss of Battery Capacity.-When a battery gives indication of lessened capacity it should be taken apart and the trouble located. If the cell is full of electrolyte it may be of too low specific gravity. The plates may be sulphated, due to lack of proper charge or too long discharge. The cells may need cleaning, a condition indicated by short capacity and a tendency to overheat when charging. Sometimes a deposit of sediment on the bottom of the cell will short circuit the plates. If the specific gravity is low and the plates have a whitish appearance, there being little sediment in the cells, it is safe to assume that the plates are sulphated. Sediment should be removed from the cells and the plates rinsed in rain or distilled water to remove particles of dirt or other adhering matter.

The rate at which the sediment collects, depends largely upon the way a battery is handled and it is, therefore, necessary to determine this rate for each individual case. A cell should be cut out after say fifty charges, the depth of sediment measured and the rate so obtained, used to determine the time when the battery will need cleaning. As there is apt to be some variation in the amount of sediment in different cells, and as the sediment is thrown down more rapidly during the latter part of a period than at the beginning, it is always advisable to allow at least onefourth inch clearance. If the ribs in the bottom of the jars are 134 inches high, figure on cleaning when the sediment reaches a depth of 11⁄2 inches. Before dismantling a battery for "washing," if practical, have it fully charged. Otherwise, if the plates are badly sulphated, they are likely to throw down considerable sediment on the charge after the cleaning is completed

There have been many complaints of lack of capacity from batteries after washing. Almost without exception this is found. to be due to lack of a complete charge following the cleaning.