Figure 88 is a schematic drawing of two lengths of pipe with a connecting collar. Next to the pipe near the collar there is a short length of I-section beam, labelled 'scrap'. Further away there is also a battery, labelled 'd.c. supply'. A wire goes from the connecting collar to the negative connection on the battery. Another wire goes from the positive connection on the battery to the piece of scrap.

 5.4 Batteries, chemistry and corrosion