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Fig. 43.-Devices Used in Charging and Caring for Storage Batteries.

of the rubber tube an ordinary chemist's clip, which controls the flow of liquid, is placed. In order to start a flow of liquid it is necessary to blow into a bent glass vent tube, which is also inserted into the stopper. Once the rubber tube has become filled

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Fig. 44.—Outlining Positions of Hydrometer in Electrolyte When

Cell is Discharged at A and When Cell is Charged at B. Method of Determining Electrolyte Level at C. How to Take Specific Gravity Reading Shown at B.

with liquid, merely opening the clip will allow the liquid to flow into the battery as desired.

In most communities the incandescent lighting circuit is used for charging batteries on account of the voltage of the power circuits being too high. The incandescent lighting circuit may be

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Fig. 45.-Simple Stand for Carrying Electrolyte or Distilled Water

Bottle at A. Method of Using Rollinson Electrolyte Rectifier
Shown at B.

any one of six forms. A direct current of either 110 or 220 volts used over short distances, either 220 or 410 volts on three-wire circuits over long distances, alternating current at a constant potential, usually 110 volts and in various polyphase systems. It might be stated that in the majority of instances house and garage ughting circuits furnish direct current of 110 volts. We will consider 12 devices used with the alternating form, one of which is

shown at Fig. 45 B. This is known as the Rollinson electrolytic rectifier, which is based upon the following principles: When an element of aluminum and a corresponding element or plate of iron are submerged in a solution of certain salts, using these elements as negative and positive terminals, respectively, the passage of an

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Fig. 46.—Mercury Rectifier Bulbs and Methods of Wiring to Charge

Storage Battery From Alternating-Current Mains.

electric current through the solution produces a chemical action which forms hydroxide of aluminum. A film of hydroxide thus formed on the aluminum element repels the current. The arrangement of the cell will then permit current to pass through it in one direction only, the film of chemical preventing it from passing in the opposite direction. The result is that if an alternating current is supplied to the cell a direct pulsating current can be obtained from it. The cutfits usually include a transformer for reducing the line voltage to the lower voltages needed for batterycharging purposes. Regulation of the current is effected in the simplest type by immersing the elements more or less in the solution in the jar. As complete instructions are furnished by the manufacturers, it will not be necessary to consider this form of rectifier in detail.

One of the most commonly used rectifying means is the mercury are bulb. This device is a large glass tube of peculiar shape, as shown at Fig. 46, which contains a quantity of mercury in the base. On either side of this lower portion two arms of the glass bulbs extend outwardly, these being formed at their extremities into graphite terminals or anodes, indicated as A and A-1 in the diagram at Fig. 47. The current from the auto transformer is then attached one to each side. The base forms the cathode or mercury terminal for the negative wires. The theory of this action is somewhat complicated, but may be explained simply without going too much into detail. The interior of the tube is in a condition of partial vacuum, and while the mercury is in a state of excitation a vapor is supplied. This condition can be kept up only as long as there is a current flowing toward the negative. If the direction of the current be reversed so that the formerly negative pole becomes a positive the current ceases to flow, as in order to pass in the opposite direction it would require the formation of a new cathode element. Therefore the flow is always toward one electrode, which is kept excited by it. A tube of this nature would cease to operate on alternating-current voltage after half a cycle if some means were not provided to maintain a flow continuously toward the negative electrode. In the General Electric rectifier tube there are two anodes and one

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