Connect the wire leading from the plates to a voltmeter and you will notice that the pointer will not move away from zero.
Disconnect the wires and mark one plate as the *positive*, by means of a little cross; mark the other plate *negative*, with a straight line.
Connect two good bichromate cells in series and lead the positive terminal to the lead plate marked with a cross. Connect the negative pole of the battery to the other lead plate. Bubbles of gas will immediately begin to arise from the lead plates. Let the batteries remain connected for about five minutes and then remove them. If you then connect the two lead plates to the voltmeter again you will find that the needle now swings nearly to two volts.
You will also find that your storage cell, for the two lead plates are now a storage cell, will also ring a bell or run a small motor for a few seconds.
The two lead plates became *charged* when the current from the bichromate cells was passed through them. This little experiment illustrates the principle of the storage cell very well.
A storage cell made of lead plates in the manner just described would not possess sufficient capacity to make it worth while as a practical cell. It has been found that if instead of a solid flat plate, a framework or grid is used, consisting of a set of bars crossing one another at right angles, leaving spaces between, which are filled with a paste made of lead oxides, there will be a considerable gain in the capacity of the cell.
A Homemade Storage Cell.
The storage cell illustrated in the accompanying illustrations is very simple to make and a battery of them capable of delivering six or eight volts will prove a very convenient source of current for performing all sorts of electrical experiments.
[Illustration: FIG. 39.—Showing how the Plates for a Storage Cell may be made from Sheet Lead by boring it full of holes and filling with paste.]
The plates are cut from sheet lead from one-quarter to five-sixteenths of an inch thick. The height and width will depend upon the size of the jars used. There are several sizes of rectangular glass storage cell jars on the market, and if the plates are made about three inches wide and three and one-half inches high, they will fit the smallest size of jar. A lug about one inch and one-half long and three-quarters of an inch wide is left projecting at the top.