The circuit is completed by the wire, but also by a salt bridge, which is also a U-shaped tube that contains a salt solution that allows the metal ions to go from the anode to the cathode.

电路由电线完成， 但也由盐桥完成，盐桥也是一个 U 形管， 内含盐溶液，可让金属离子从阳极流向阴极。