electrochemically by oxidising the silver at an anode in a chloride solution. A porous (or fibrous) filter located at/near the tip of the reference electrode allows to establishing a liquid contact between the solution to be measured and the electrolyte solution in equilibrium with the silver chloride (AgCl) coating the Ag(s) surface. An insulated electrical wire connects the silver rod with the measuring instrument. The voltmeter negative terminal is connected to the test wire. The electrode body contains potassium chloride to stabilize the silver chloride concentration. When working in seawater, this body can be removed and the chloride concentration is fixed by the stable salinity of seawater. The potential of a silver:silver chloride reference electrode with respect to the standard hydrogen electrode depends on the composition of the electrolyte solution and on temperature. Notes to this table:(1) The table data source is NACE International (National Association of Corrosion Engineers), except where a separate reference is given. (2) Elj is the liquid junction potential between the given electrolyte and a reference electrolyte with a molal activity of chloride of 1 mol/kg. The electrode has many features making it suitable for use in the field: Stable potential Non-toxic components Simple construction Inexpensive to manufacture They are usually manufactured with saturated potassium chloride electrolyte, but can be used with lower concentrations such as 1 mol/kg potassium chloride. As noted above, changing the electrolyte concentration changes the electrode potential. Thus care should be taken to either use silver chloride reference electrodes in a frit-sealed chamber of saturated potassium chloride (see picture above), or for the quasi-reference electrode configuration (silver wire coated in silver chloride with no frit or potassium chloride reservoir), ensure the local chloride concentration is both constant and sufficiently high to maintain a stable potential and stable silver chloride layer. Silver chloride is slightly soluble in strong potassium chloride solutions, so it is sometimes recommended the potassium chloride be saturated with silver chloride to avoid stripping the silver chloride off the silver wire. Biological electrode systems Silver chloride electrodes are also used by many applications of biological electrode systems such as biomonitoring sensors as part of electrocardiography (ECG) and electroencephalography (EEG), and in transcutaneous electrical nerve stimulation (TENS) to deliver current. Historically, the electrodes were fabricated from pure silver, or from metals such as tin, nickel, or brass (an alloy of copper and zinc) coated with a thin film of silver. In