After the refilling of the cells, a few minutes should be allowed for the battery to recover its powers, and another attempt may be made to obtain a spark. If this is still unsuccessful, the zincs may be lifted out of the cells and examined.

They dissolve slowly, and the immersed portion of one or more may be found to have disappeared, of course suspending the action of the battery.

Replacing the zincs which are nearly or quite past their usefulness by new ones, a supply of which may with advantage be procured at any electrical goods store and kept on hand, the wires should next be inspected. It is very possible that they may be found wrongly connected, or hooked loosely over the binding-screws, instead of being firmly held under them so as to make good electrical contact; or a wire may have been corroded through and separated by contact with sal-ammoniac solution, and the continuity of the current thereby broken; or the wires connecting the battery with the spark-coil, or the spark-coil with the house system, may be broken, or corroded, or loosely connected, or short-circuited, either with each other or with some extraneous conductor, often the gas-fixture itself.

If the battery has enough energy left in it to give a small spark, although not a sufficiently vigorous one for lighting gas, it may be used to test the house wires for short-circuits by disconnecting the main wire from the carbon end of the battery, and attaching to the carbon a short piece of wire for use in testing. All the house wires that are accessible may then be touched with the end of this testing wire, and the appearance of a spark will show a short-circuit in the wire touched. The reason of this is that all the wires in the house system are interrupted at some point, the pressure of a button, or pulling of a chain, being necessary to close the connection; and if a current from the battery can pass through any one of them without the pressing of a button or pulling of a chain, the circuit of which that wire forms a part must be improperly closed at some point of its course, so that the current passes without the interposition of the button or chain. The effect would of course be the same without disconnecting the house wires, but it would be invisible, and the object of making the disconnection and using the testing wire is simply to reveal the passage of the current by a spark.

Testing for short-circuits.

If, as is the practice of the best contractors, every house wire is furnished with a tag, near the battery, showing to what circuit it belongs, the detection of the one requiring attention will be easy; and, even if there are no such tags, the test will furnish useful indications as to what further steps may be necessary.

If no short-circuit is revealed by the test, the house wires may be connected again, and the buttons which control the automatic burners examined, by unscrewing and taking off the plate. The contact springs, which are pressed by the button to make connection, sometimes break, or fall out of place, either short-circuiting the wire, or making the button useless; and the wires sometimes slip out from under the binding-screws.

If everything is found in order here, the trouble is probably due to the polarization of the battery, which, as a matter of fact, is a very common accident with electric gas-lighting batteries.

Polarization of battery.

These batteries, like those used for operating electrical bells and burglar alarms, are always of the "open-circuit" type, in which the chemical action which generates the electricity is suspended except when the electrical current is actually passing; so that, until the circuit in any wire connected with it is completed by making contact between the separated portions, either by pressing a contact spring with a button, or by making the platinum wires of a pendant burner meet by pulling the chain, the battery remains quiescent, no chemical change taking place in it. This property of open-circuit batteries particularly adapts them to house work, where they are called upon only occasionally for currents; but it is accompanied with the inconvenience that, being suited only to momentary currents, they deteriorate rapidly if the duration of the current is prolonged, the carbons of the cells becoming saturated with bubbles of hydrogen, which prevent further chemical action. This effect is called polarization, and any short-circuiting or crossing of the wires, by permitting the passage of a continuous current, soon polarizes the battery and makes it inert. If the current passes only for a few hours, the hydrogen bubbles which fill the pores of the carbons may be slowly absorbed, so that, after it has been allowed to recuperate for several days, the battery may regain its powers; but a current continued for several days polarizes the carbons so effectually that they can be restored only with difficulty.

In pendant burners, where the current passes, in the form of a spark, when a light platinum wire, arranged with a spring, is drawn past a short fixed wire, attached to the burner in such a position that the spark will be in the stream of gas, the spring wire should be drawn, by means of the chain, entirely past the fixed wire, so that, after making contact, it will pass beyond, opening the circuit again; and, when the chain is released, the wire, which is drawn back by a spring, should brush past the fixed wire, making a second contact, accompanied by a second spark, and continue its course, again opening the circuit. As there is a certain amount of friction between the two wires, as one brushes past the other, the force of the spring is sometimes barely sufficient to overcome this friction; and, if the chain is released slowly, the wires may be left in contact. This, of course, permits a continuous current to flow, so long as they remain in contact, and the battery, in consequence, immediately begins to lose its efficiency by polarization; so that, a few hours later, it will give only a feeble spark, or none at all, at any of the burners.

As soon as this phenomenon is observed, all the pull burners should be immediately examined, to see if the platinum wires have been left in contact; and if any are found in that condition, they should at once be separated. The apparatus must then be left to itself for three or four days, or even for a week, and at the end of that time the power of the battery may be found fully restored. If, however, this should be insufficient to depolarize it, new carbons may be put in; or the old ones may be lifted out of the cell and soaked for an hour or two in hot water, or moderately heated in an oven, to drive the hydrogen bubbles out of the pores, and then replaced.

The battery used for operating electric bells is similar to that for electric gas-lighting, but smaller, two or three cells being sufficient; and no spark coil is interposed in the circuit. It is liable to polarization in the same way, if the wires are crossed without insulation, or are otherwise short-circuited; and the contact springs, under the buttons, not infrequently break, making the button inoperative. These troubles, however, are easily remedied, and the battery cells, if not polarized, may at any time be restored to efficiency by new zincs, and fresh charges of ammonium chloride; so that very little skill is required to keep a bell battery permanently in good condition.

Burglar-alarms are operated in the same way as other electric bells, and by a battery of the same sort. As, however, the bells are rung by means of contact springs brought into action by raising a window, or opening a door, or stepping on a door-mat, and as contact springs in the frame of a window or door are very liable to deterioration by weather or by accident, the system should be tested at regular intervals, and any defects corrected, if it is to' be kept in efficient condition. The wires of burglar-alarms also, particularly if they are put in by irresponsible travelling electricians, are often very carelessly run, over floors, or on walls, so that they soon become damaged.

Electric bells.

Burglar-alarms.

The householder of a scientific turn of mind will find interest, as well as economy, in caring for the electrical appliances connected with his dwelling; and, with a little insulated wire, a battery cell or two, and a few switches or buttons, he can often arrange very convenient temporary call-bells or burglar-alarms for himself.