Conventionally, the first biosensor was one of these devices invented by Leland Clark to measure dissolved oxygen. Three of these devices are used to detect trace heavy metals in an experiment that sweeps (20[1])between plating and stripping them. Concentrated potassium chloride is used to store a glass pen-shaped type of these devices that is used to measure pH. Chemists today prefer silver-silver chloride to mercury as the standard (*) reference for these devices. In shorthand notation, double pipes separate the solid components of these devices from their dissolved ions. Half-reactions occur at the surface of these devices. For 10 points, name these devices found in the reservoirs of a galvanic cell or at the ends of a battery, which can be anodes or cathodes. ■END■