Page:Incandescent electric lighting- A practical description of the Edison system.djvu/91

 the space below the partition. The zinc plates are kept a proper distance apart by hard rubber fittings, which are also arranged to keep the plates from resting upon the bottom of the bottle.

The small wires before mentioned as passing from the clips above the bottles to the lower space of the meter box lead the current to the zinc plates in such a manner that it must pass from one plate to the other through the zinc solution. In doing this the current detaches particles of zinc from one of the plates and transfers them to the other, thus decreasing the weight of the first plate. One ampere, acting for one hour, will deposit a known amount of zinc upon the negative plate in the bottle; and it is by removing and weighing the plates that the amount of current which has passed through the meter is ascertained.

The bottles are arranged in the meters in pairs, two pairs being used in the large sizes of three-wire meter to insure by comparison greater accuracy in