The Glass Electrode

A diagram of the simple glass electrode is shown in figure 12. It consists of a glass tube on the end of which is sealed a glass bulb that is porous to ions but impedes all liquid flow. The glass used for this purpose is specially treated glass and the walls of the bulb must be very thin. This makes the bulb very fragile and, thus, care has to be taken in its design and manufacture to protect it appropriately and, when used, needs careful handling. In the centre is a platinum rod that makes electrical connection to the electrolyte in the bulb. There are a number of different salts that can be used for the electrolyte and the choice will depend on the type of measurement.

A diagram of a glass electrode is shown in figure 12. The electrode can be used singly in conjunction with another reference electrode, both electrodes being placed in the test solution or, alternatively, both the glass electrode and the reference electrode can be combined in one housing producing a single unit that can be placed in the liquid under test. In either case the same type of high input impedance voltmeter would be used to measure the net potential across the two half-cells.

Figure 12. The Simple Glass Electrode