Figure 84 comprises two schematic drawings labelled 'a' and 'b'. Drawing 'a' depicts a horizontal rectangular metal block with a wire soldered to each end. The left hand face of the block is labelled '-' and the right hand face is labelled '+'. There are arrows superimposed on the block pointing from left to right. In the midst of these arrows the label 'electrons' is written on the side of the block.

Drawing 'b' is directly below drawing 'a' and shows two vertical plates facing each other with electrolyte between them. The distance between the plates is the same as the length of the block in drawing 'a'. The left hand plate is labelled '-' and the right hand plate is labelled '+'. There is a wire attached to each plate. An arrow next to the left hand wire indicates that electrons are flowing along the wire into the left hand plate. There are black arrows in the electrolyte, labelled 'negative ions', pointing from left to right. An arrow next to the right hand wire indicates that electrons are flowing along the wire out of the right hand plate. There are white arrows in the electrolyte, labelled 'positive ions', pointing from right to left.

5.4 Batteries, chemistry and corrosion